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Re: Calculating the proper distance with filters for a FF

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  • Robert Anderson
    Hi Terry I received the measurements from FLI s designer and he did mention to make sure I added the distance for the two glass surfaces but I will email him
    Message 1 of 11 , Dec 4, 2006
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      Hi Terry

      I received the measurements from FLI's designer and he did mention to
      make sure I added the distance for the two glass surfaces but I will
      email him again to confirm.

      I spoke with Markus today and he was un-sure if one counted the cover
      glass and the filters as he felt that they would not effect the light.

      Based on the SBIG calculations shown on their site, and the comments
      from both this group and the FLI engineer, I am positive that one
      does indeed need to take into consideration, the 2 x 3mm thick glass.

      I will make sure the FF is designed to also substract the distance it
      should screw into the FLI filter wheel. Might as well try for
      perfection, eh!

      Thanks again.

      Bob

      --- In tmboptical@yahoogroups.com, "Terry Tuggle" <tlt284@...> wrote:
      >
      > Bob,
      >
      > Yes; I was confused a little. In effect you have to make the
      adapter
      > 2mm longer, so yes; subtracting it from the ccd/filter wheel
      distance is
      > what to do. One other thing to be sure of is; does the reported
      distance
      > include the cover glass offset already?
      >
      > Sorry for the confusion.
      >
      >
      >
      > Terry
      >
      > http://www.geocities.com/tlt284@.../terryshuntofthemonth/
      >
      > _____
      >
      > From: tmboptical@yahoogroups.com
      [mailto:tmboptical@yahoogroups.com] On
      > Behalf Of Robert Anderson
      > Sent: Monday, December 04, 2006 10:18 AM
      > To: tmboptical@yahoogroups.com
      > Subject: [tmboptical] Re: Calculating the proper distance with
      filters for a
      > FF
      >
      >
      >
      > Hi Tim and Terry
      >
      > Sorry to continue this thread but Markus and I spoke today on the
      > subject of needing to add additional distance to off-set the impact
      > of glass between the FF and the CCD.
      >
      > According to common wisdom and supported by the SBIG document, one
      > needs to subtract a percentage of the thickness of any filters or
      > cover glass from the distance from the CCD to the front of the
      camera
      > plus Filter Wheel.
      >
      > Thus, if the distance from the CCD to the front of the camera and
      > filter wheel is 44.514mm and you have a 3mm thick CCD cover glass
      and
      > a 3mm thick filter, you need to subtract approximately 2mm from the
      > distance of the CCD to the front of the filter wheel which now
      > becomes 42.514mm.
      >
      > This has the effect of lenghtening the needed adapter from the R4
      > lens to the camera/filter wheel.
      >
      > TMB 175mm FF needs a distance of 113mm from the R4 lens to the CCD.
      > Plugging in the new number of 42.514, the extension from the R4
      lens
      > to camera/filter wheel is now 70.486mm, (plus the distance that the
      > FF screws into the threads of the camera/filter wheel).
      >
      > I have done up a Viso file, (JPEG version on link), for what I have
      > calculated out. Can you take a look at it and let me know if I have
      > the data correct?
      >
      > http://www.tpo <http://www.tpo.ca/Images/FLI-Imaging-Train-4.jpg>
      > ca/Images/FLI-Imaging-Train-4.jpg
      >
      > Thanks in advance.
      >
      > Bob
      >
      > --- In tmboptical@yahoogro <mailto:tmboptical%40yahoogroups.com>
      ups.com,
      > "Tube Tim" <potentate@> wrote:
      > >
      > > >--- In tmboptical@yahoogro <mailto:tmboptical%40yahoogroups.com>
      ups.com,
      > "Terry Tuggle" <tlt284@> wrote:
      > > >
      > > > Hi Bob,
      > > >
      > > > It is my understanding that you add the 1mm to the distance
      > > > for each 3mm glass. The 113mm distance is from the center of the
      > > > R4 lens, so you must measure that distance to the top of the FF
      > > > housing,
      > >
      > > Correct, a very important point.
      > >
      > > > and then subtract any screw in distance to the mating flange
      that
      > > > will mate to the extension tube. You really do not consider the
      > > > screw in distance; you measure from the mating flanges. So you
      > > > start with the 44.514mm distance and add the 2mm which =
      46.514mm.
      > > > Once you know the distance from the center of the rear R4
      > > > lens to the mating flange of the housing, you would add that to
      > the
      > > > 46.514mm, then; subtract that from the 113mm. The result would
      be
      > > > the distance needed for the extension tube; flange to flange.
      > > >
      > > > Peter, Tim, please correct me if this does not sound right to
      you!
      > > >
      > >
      > > The 1/3 thickness rule is news to me. When setting up the STL-11K
      I
      > > used the SBIG diagram:
      > >
      > > http://www.sbig
      <http://www.sbig.com/pdffiles/2400_1001_BASIC_ASSY.pdf>
      > com/pdffiles/2400_1001_BASIC_ASSY.pdf
      > >
      > > and used the distance of 1.470". For a 3mm filter SBIG allowed
      > > 0.0390-inches or 0.991mm. I guess the rule of thumb works! It
      > looks
      > > to me like you (Terry) have the correct 'sign' by adding to the
      > length
      > > of the adapter.
      > >
      > > I would place the FF lenses in a 'cell' (*) or carrier that has
      male
      > > threads on the outside and have this screw into an extension tube
      at
      > > the back of the focuser. The cell could be moved back N forth +/-
      > > 10mm or more (via the threading) and held in the optimal position
      > > with a jam nut. The adapter from this extension tube to CCD would
      > > then be simplified. Converting to a new CCD would be simply a
      > matter
      > > of changing the cell distance and a new adapter.
      > >
      > >
      > > Tim
      > >
      > >
      > > (*) think of the cell as a 100mm diameter cylinder with all
      thread
      > on
      > > the outside and the glass on the inside.
      > >
      > > >
      > > >
      > > > Terry
      > > >
      > > > http://www.geocitie
      > <http://www.geocities.com/tlt284@/terryshuntofthemonth/>
      > s.com/tlt284@/terryshuntofthemonth/
      > > >
      > > > _____
      > > >
      > > > From: tmboptical@yahoogro <mailto:tmboptical%40yahoogroups.com>
      ups.com
      > [mailto:tmboptical@yahoogro <mailto:tmboptical%40yahoogroups.com>
      ups.com]
      > On
      > > > Behalf Of Robert Anderson
      > > > Sent: Tuesday, November 28, 2006 8:17 AM
      > > > To: tmboptical@yahoogro <mailto:tmboptical%40yahoogroups.com>
      ups.com
      > > > Subject: [tmboptical] Calculating the proper distance with
      filters
      > > for a FF
      > > >
      > > >
      > > >
      > > > Hi all
      > > >
      > > > Just want to make sure I am calculating the proper distance for
      > the
      > > > positioning of the TMB 175mm FF with a new camera/filter wheel,
      > (FLI
      > > > Proline with 7 position filter wheel), that Markus is building
      > for me.
      > > >
      > > > I have the distance from the CCD to where the FF screws into
      the
      > > > filter wheel of 44.514mm less the max distance to screw the FF
      > into
      > > > the filter wheel of 1.875mm
      > > >
      > > > In-between the FF and the CCD are two glass surfaces, (the 3mm
      > BK7
      > > > CCD cover glass and the 3mm thick AstroDon filters).
      > > >
      > > > Do I add 1/3rd of the thickness of the two glass surfaces or
      > subtract
      > > > them from the total distance from the CCD to the rear cell of
      the
      > FF?
      > > >
      > > > Proper distance from FF to CCD is 113mm. Extension from back of
      > FF to
      > > > Filter wheel would be 113mm less the 42.639mm, (distance from
      > front
      > > > of filter wheel to CCD taking out the 1.875mm screw in
      distance)
      > > > equals 70.361mm.
      > > >
      > > > Do I add an extra 1mm for each 3mm glass surface or subtract
      that
      > > > from the 70.361mm extension?
      > > >
      > > > Cheers
      > > >
      > > > Bob
      > > >
      > > >
      > > >
      > > >
      > > >
      > > > [Non-text portions of this message have been removed]
      > > >
      > >
      >
      >
      >
      >
      >
      > [Non-text portions of this message have been removed]
      >
    • Tube Tim
      ... Hi Bob, I d suggest making the FF so that the lenses inside can be moved +/- 5mm. It would not be hard to do. Will the CCD be at focus the way you have
      Message 2 of 11 , Dec 4, 2006
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        >--- In tmboptical@yahoogroups.com, "Robert Anderson" <bob@...> wrote:
        >

        Hi Bob,

        I'd suggest making the FF so that the lenses inside can be moved +/-
        5mm. It would not be hard to do.

        Will the CCD be at focus the way you have drawn it? For my TMB's I
        have to use the 4" extension on the back of the focuser.


        Tim


        > Hi Terry
        >
        > I received the measurements from FLI's designer and he did mention to
        > make sure I added the distance for the two glass surfaces but I will
        > email him again to confirm.
        >
        > I spoke with Markus today and he was un-sure if one counted the cover
        > glass and the filters as he felt that they would not effect the light.
        >
        > Based on the SBIG calculations shown on their site, and the comments
        > from both this group and the FLI engineer, I am positive that one
        > does indeed need to take into consideration, the 2 x 3mm thick glass.
        >
        > I will make sure the FF is designed to also substract the distance it
        > should screw into the FLI filter wheel. Might as well try for
        > perfection, eh!
        >
        > Thanks again.
        >
        > Bob
        >
        > --- In tmboptical@yahoogroups.com, "Terry Tuggle" <tlt284@> wrote:
        > >
        > > Bob,
        > >
        > > Yes; I was confused a little. In effect you have to make the
        > adapter
        > > 2mm longer, so yes; subtracting it from the ccd/filter wheel
        > distance is
        > > what to do. One other thing to be sure of is; does the reported
        > distance
        > > include the cover glass offset already?
        > >
        > > Sorry for the confusion.
        > >
        > >
        > >
        > > Terry
        > >
        > > http://www.geocities.com/tlt284@/terryshuntofthemonth/
        > >
        > > _____
        > >
        > > From: tmboptical@yahoogroups.com
        > [mailto:tmboptical@yahoogroups.com] On
        > > Behalf Of Robert Anderson
        > > Sent: Monday, December 04, 2006 10:18 AM
        > > To: tmboptical@yahoogroups.com
        > > Subject: [tmboptical] Re: Calculating the proper distance with
        > filters for a
        > > FF
        > >
        > >
        > >
        > > Hi Tim and Terry
        > >
        > > Sorry to continue this thread but Markus and I spoke today on the
        > > subject of needing to add additional distance to off-set the impact
        > > of glass between the FF and the CCD.
        > >
        > > According to common wisdom and supported by the SBIG document, one
        > > needs to subtract a percentage of the thickness of any filters or
        > > cover glass from the distance from the CCD to the front of the
        > camera
        > > plus Filter Wheel.
        > >
        > > Thus, if the distance from the CCD to the front of the camera and
        > > filter wheel is 44.514mm and you have a 3mm thick CCD cover glass
        > and
        > > a 3mm thick filter, you need to subtract approximately 2mm from the
        > > distance of the CCD to the front of the filter wheel which now
        > > becomes 42.514mm.
        > >
        > > This has the effect of lenghtening the needed adapter from the R4
        > > lens to the camera/filter wheel.
        > >
        > > TMB 175mm FF needs a distance of 113mm from the R4 lens to the CCD.
        > > Plugging in the new number of 42.514, the extension from the R4
        > lens
        > > to camera/filter wheel is now 70.486mm, (plus the distance that the
        > > FF screws into the threads of the camera/filter wheel).
        > >
        > > I have done up a Viso file, (JPEG version on link), for what I have
        > > calculated out. Can you take a look at it and let me know if I have
        > > the data correct?
        > >
        > > http://www.tpo <http://www.tpo.ca/Images/FLI-Imaging-Train-4.jpg>
        > > ca/Images/FLI-Imaging-Train-4.jpg
        > >
        > > Thanks in advance.
        > >
        > > Bob
        > >
        > > --- In tmboptical@yahoogro <mailto:tmboptical%40yahoogroups.com>
        > ups.com,
        > > "Tube Tim" <potentate@> wrote:
        > > >
        > > > >--- In tmboptical@yahoogro <mailto:tmboptical%40yahoogroups.com>
        > ups.com,
        > > "Terry Tuggle" <tlt284@> wrote:
        > > > >
        > > > > Hi Bob,
        > > > >
        > > > > It is my understanding that you add the 1mm to the distance
        > > > > for each 3mm glass. The 113mm distance is from the center of the
        > > > > R4 lens, so you must measure that distance to the top of the FF
        > > > > housing,
        > > >
        > > > Correct, a very important point.
        > > >
        > > > > and then subtract any screw in distance to the mating flange
        > that
        > > > > will mate to the extension tube. You really do not consider the
        > > > > screw in distance; you measure from the mating flanges. So you
        > > > > start with the 44.514mm distance and add the 2mm which =
        > 46.514mm.
        > > > > Once you know the distance from the center of the rear R4
        > > > > lens to the mating flange of the housing, you would add that to
        > > the
        > > > > 46.514mm, then; subtract that from the 113mm. The result would
        > be
        > > > > the distance needed for the extension tube; flange to flange.
        > > > >
        > > > > Peter, Tim, please correct me if this does not sound right to
        > you!
        > > > >
        > > >
        > > > The 1/3 thickness rule is news to me. When setting up the STL-11K
        > I
        > > > used the SBIG diagram:
        > > >
        > > > http://www.sbig
        > <http://www.sbig.com/pdffiles/2400_1001_BASIC_ASSY.pdf>
        > > com/pdffiles/2400_1001_BASIC_ASSY.pdf
        > > >
        > > > and used the distance of 1.470". For a 3mm filter SBIG allowed
        > > > 0.0390-inches or 0.991mm. I guess the rule of thumb works! It
        > > looks
        > > > to me like you (Terry) have the correct 'sign' by adding to the
        > > length
        > > > of the adapter.
        > > >
        > > > I would place the FF lenses in a 'cell' (*) or carrier that has
        > male
        > > > threads on the outside and have this screw into an extension tube
        > at
        > > > the back of the focuser. The cell could be moved back N forth +/-
        > > > 10mm or more (via the threading) and held in the optimal position
        > > > with a jam nut. The adapter from this extension tube to CCD would
        > > > then be simplified. Converting to a new CCD would be simply a
        > > matter
        > > > of changing the cell distance and a new adapter.
        > > >
        > > >
        > > > Tim
        > > >
        > > >
        > > > (*) think of the cell as a 100mm diameter cylinder with all
        > thread
        > > on
        > > > the outside and the glass on the inside.
        > > >
        > > > >
        > > > >
        > > > > Terry
        > > > >
        > > > > http://www.geocitie
        > > <http://www.geocities.com/tlt284@/terryshuntofthemonth/>
        > > s.com/tlt284@/terryshuntofthemonth/
        > > > >
        > > > > _____
        > > > >
        > > > > From: tmboptical@yahoogro <mailto:tmboptical%40yahoogroups.com>
        > ups.com
        > > [mailto:tmboptical@yahoogro <mailto:tmboptical%40yahoogroups.com>
        > ups.com]
        > > On
        > > > > Behalf Of Robert Anderson
        > > > > Sent: Tuesday, November 28, 2006 8:17 AM
        > > > > To: tmboptical@yahoogro <mailto:tmboptical%40yahoogroups.com>
        > ups.com
        > > > > Subject: [tmboptical] Calculating the proper distance with
        > filters
        > > > for a FF
        > > > >
        > > > >
        > > > >
        > > > > Hi all
        > > > >
        > > > > Just want to make sure I am calculating the proper distance for
        > > the
        > > > > positioning of the TMB 175mm FF with a new camera/filter wheel,
        > > (FLI
        > > > > Proline with 7 position filter wheel), that Markus is building
        > > for me.
        > > > >
        > > > > I have the distance from the CCD to where the FF screws into
        > the
        > > > > filter wheel of 44.514mm less the max distance to screw the FF
        > > into
        > > > > the filter wheel of 1.875mm
        > > > >
        > > > > In-between the FF and the CCD are two glass surfaces, (the 3mm
        > > BK7
        > > > > CCD cover glass and the 3mm thick AstroDon filters).
        > > > >
        > > > > Do I add 1/3rd of the thickness of the two glass surfaces or
        > > subtract
        > > > > them from the total distance from the CCD to the rear cell of
        > the
        > > FF?
        > > > >
        > > > > Proper distance from FF to CCD is 113mm. Extension from back of
        > > FF to
        > > > > Filter wheel would be 113mm less the 42.639mm, (distance from
        > > front
        > > > > of filter wheel to CCD taking out the 1.875mm screw in
        > distance)
        > > > > equals 70.361mm.
        > > > >
        > > > > Do I add an extra 1mm for each 3mm glass surface or subtract
        > that
        > > > > from the 70.361mm extension?
        > > > >
        > > > > Cheers
        > > > >
        > > > > Bob
        > > > >
        > > > >
        > > > >
        > > > >
        > > > >
        > > > > [Non-text portions of this message have been removed]
        > > > >
        > > >
        > >
        > >
        > >
        > >
        > >
        > > [Non-text portions of this message have been removed]
        > >
        >
      • erdmanpe
        The problem with these fixed corrections and any rule of thumb is that they depend upon various assumptions. First, the correction is required because any
        Message 3 of 11 , Dec 4, 2006
        • 0 Attachment
          The problem with these fixed corrections and any rule of thumb is that
          they depend upon various assumptions. First, the correction is
          required because any optical element (even a set of parallel planes)
          changes the optical path. That correction depends upon the optical
          system's f/#. SBIG has made an assumption (unknown to us) about the
          system f/# and given (in their data sheets) an "optical path" length
          based upon that assumption.

          For a different f/#, a different correction is necessary. At a "slow"
          f/# (e.g. f/9), the correction will be less than SBIG's given value,
          I'm sure.

          You can check the correction necessary for your system by focusing
          without any filter elements in place (no FF involved). Then focus
          with a filter of this approximate thickness in place. The difference
          in focal positions is the correction distance under discussion.

          Peter

          --- In tmboptical@yahoogroups.com, "Robert Anderson" <bob@...> wrote:
          >
          > Hi Terry
          >
          > I received the measurements from FLI's designer and he did mention to
          > make sure I added the distance for the two glass surfaces but I will
          > email him again to confirm.
          >
          > I spoke with Markus today and he was un-sure if one counted the cover
          > glass and the filters as he felt that they would not effect the light.
          >
          > Based on the SBIG calculations shown on their site, and the comments
          > from both this group and the FLI engineer, I am positive that one
          > does indeed need to take into consideration, the 2 x 3mm thick glass.
          >
          > I will make sure the FF is designed to also substract the distance it
          > should screw into the FLI filter wheel. Might as well try for
          > perfection, eh!
          >
          > Thanks again.
          >
          > Bob
          >
          > --- In tmboptical@yahoogroups.com, "Terry Tuggle" <tlt284@> wrote:
          > >
          > > Bob,
          > >
          > > Yes; I was confused a little. In effect you have to make the
          > adapter
          > > 2mm longer, so yes; subtracting it from the ccd/filter wheel
          > distance is
          > > what to do. One other thing to be sure of is; does the reported
          > distance
          > > include the cover glass offset already?
          > >
          > > Sorry for the confusion.
          > >
          > >
          > >
          > > Terry
          > >
          > > http://www.geocities.com/tlt284@/terryshuntofthemonth/
          > >
          > > _____
          > >
          > > From: tmboptical@yahoogroups.com
          > [mailto:tmboptical@yahoogroups.com] On
          > > Behalf Of Robert Anderson
          > > Sent: Monday, December 04, 2006 10:18 AM
          > > To: tmboptical@yahoogroups.com
          > > Subject: [tmboptical] Re: Calculating the proper distance with
          > filters for a
          > > FF
          > >
          > >
          > >
          > > Hi Tim and Terry
          > >
          > > Sorry to continue this thread but Markus and I spoke today on the
          > > subject of needing to add additional distance to off-set the impact
          > > of glass between the FF and the CCD.
          > >
          > > According to common wisdom and supported by the SBIG document, one
          > > needs to subtract a percentage of the thickness of any filters or
          > > cover glass from the distance from the CCD to the front of the
          > camera
          > > plus Filter Wheel.
          > >
          > > Thus, if the distance from the CCD to the front of the camera and
          > > filter wheel is 44.514mm and you have a 3mm thick CCD cover glass
          > and
          > > a 3mm thick filter, you need to subtract approximately 2mm from the
          > > distance of the CCD to the front of the filter wheel which now
          > > becomes 42.514mm.
          > >
          > > This has the effect of lenghtening the needed adapter from the R4
          > > lens to the camera/filter wheel.
          > >
          > > TMB 175mm FF needs a distance of 113mm from the R4 lens to the CCD.
          > > Plugging in the new number of 42.514, the extension from the R4
          > lens
          > > to camera/filter wheel is now 70.486mm, (plus the distance that the
          > > FF screws into the threads of the camera/filter wheel).
          > >
          > > I have done up a Viso file, (JPEG version on link), for what I have
          > > calculated out. Can you take a look at it and let me know if I have
          > > the data correct?
          > >
          > > http://www.tpo <http://www.tpo.ca/Images/FLI-Imaging-Train-4.jpg>
          > > ca/Images/FLI-Imaging-Train-4.jpg
          > >
          > > Thanks in advance.
          > >
          > > Bob
          > >
          > > --- In tmboptical@yahoogro <mailto:tmboptical%40yahoogroups.com>
          > ups.com,
          > > "Tube Tim" <potentate@> wrote:
          > > >
          > > > >--- In tmboptical@yahoogro <mailto:tmboptical%40yahoogroups.com>
          > ups.com,
          > > "Terry Tuggle" <tlt284@> wrote:
          > > > >
          > > > > Hi Bob,
          > > > >
          > > > > It is my understanding that you add the 1mm to the distance
          > > > > for each 3mm glass. The 113mm distance is from the center of the
          > > > > R4 lens, so you must measure that distance to the top of the FF
          > > > > housing,
          > > >
          > > > Correct, a very important point.
          > > >
          > > > > and then subtract any screw in distance to the mating flange
          > that
          > > > > will mate to the extension tube. You really do not consider the
          > > > > screw in distance; you measure from the mating flanges. So you
          > > > > start with the 44.514mm distance and add the 2mm which =
          > 46.514mm.
          > > > > Once you know the distance from the center of the rear R4
          > > > > lens to the mating flange of the housing, you would add that to
          > > the
          > > > > 46.514mm, then; subtract that from the 113mm. The result would
          > be
          > > > > the distance needed for the extension tube; flange to flange.
          > > > >
          > > > > Peter, Tim, please correct me if this does not sound right to
          > you!
          > > > >
          > > >
          > > > The 1/3 thickness rule is news to me. When setting up the STL-11K
          > I
          > > > used the SBIG diagram:
          > > >
          > > > http://www.sbig
          > <http://www.sbig.com/pdffiles/2400_1001_BASIC_ASSY.pdf>
          > > com/pdffiles/2400_1001_BASIC_ASSY.pdf
          > > >
          > > > and used the distance of 1.470". For a 3mm filter SBIG allowed
          > > > 0.0390-inches or 0.991mm. I guess the rule of thumb works! It
          > > looks
          > > > to me like you (Terry) have the correct 'sign' by adding to the
          > > length
          > > > of the adapter.
          > > >
          > > > I would place the FF lenses in a 'cell' (*) or carrier that has
          > male
          > > > threads on the outside and have this screw into an extension tube
          > at
          > > > the back of the focuser. The cell could be moved back N forth +/-
          > > > 10mm or more (via the threading) and held in the optimal position
          > > > with a jam nut. The adapter from this extension tube to CCD would
          > > > then be simplified. Converting to a new CCD would be simply a
          > > matter
          > > > of changing the cell distance and a new adapter.
          > > >
          > > >
          > > > Tim
          > > >
          > > >
          > > > (*) think of the cell as a 100mm diameter cylinder with all
          > thread
          > > on
          > > > the outside and the glass on the inside.
          > > >
          > > > >
          > > > >
          > > > > Terry
          > > > >
          > > > > http://www.geocitie
          > > <http://www.geocities.com/tlt284@/terryshuntofthemonth/>
          > > s.com/tlt284@/terryshuntofthemonth/
          > > > >
          > > > > _____
          > > > >
          > > > > From: tmboptical@yahoogro <mailto:tmboptical%40yahoogroups.com>
          > ups.com
          > > [mailto:tmboptical@yahoogro <mailto:tmboptical%40yahoogroups.com>
          > ups.com]
          > > On
          > > > > Behalf Of Robert Anderson
          > > > > Sent: Tuesday, November 28, 2006 8:17 AM
          > > > > To: tmboptical@yahoogro <mailto:tmboptical%40yahoogroups.com>
          > ups.com
          > > > > Subject: [tmboptical] Calculating the proper distance with
          > filters
          > > > for a FF
          > > > >
          > > > >
          > > > >
          > > > > Hi all
          > > > >
          > > > > Just want to make sure I am calculating the proper distance for
          > > the
          > > > > positioning of the TMB 175mm FF with a new camera/filter wheel,
          > > (FLI
          > > > > Proline with 7 position filter wheel), that Markus is building
          > > for me.
          > > > >
          > > > > I have the distance from the CCD to where the FF screws into
          > the
          > > > > filter wheel of 44.514mm less the max distance to screw the FF
          > > into
          > > > > the filter wheel of 1.875mm
          > > > >
          > > > > In-between the FF and the CCD are two glass surfaces, (the 3mm
          > > BK7
          > > > > CCD cover glass and the 3mm thick AstroDon filters).
          > > > >
          > > > > Do I add 1/3rd of the thickness of the two glass surfaces or
          > > subtract
          > > > > them from the total distance from the CCD to the rear cell of
          > the
          > > FF?
          > > > >
          > > > > Proper distance from FF to CCD is 113mm. Extension from back of
          > > FF to
          > > > > Filter wheel would be 113mm less the 42.639mm, (distance from
          > > front
          > > > > of filter wheel to CCD taking out the 1.875mm screw in
          > distance)
          > > > > equals 70.361mm.
          > > > >
          > > > > Do I add an extra 1mm for each 3mm glass surface or subtract
          > that
          > > > > from the 70.361mm extension?
          > > > >
          > > > > Cheers
          > > > >
          > > > > Bob
          > > > >
          > > > >
          > > > >
          > > > >
          > > > >
          > > > > [Non-text portions of this message have been removed]
          > > > >
          > > >
          > >
          > >
          > >
          > >
          > >
          > > [Non-text portions of this message have been removed]
          > >
          >
        • Robert Anderson
          Two good points Tim. I will speak with Markus about the ability to move te lenses. I do not know as yet, where the CCD will be when in focus but I am hoping it
          Message 4 of 11 , Dec 4, 2006
          • 0 Attachment
            Two good points Tim.

            I will speak with Markus about the ability to move te lenses.

            I do not know as yet, where the CCD will be when in focus but I am
            hoping it is the same as where the camera sits right now which is
            approximately at 78mm on the scale on the focuser.

            In front of the CCD currently is the Optec filter wheel and Optec
            focuser. The TMB flattener should take up the same distance as the
            Optec focuser and the current camera and Optec filter wheel is pretty
            close to what the Finger Lakes camera/fitler wheel is.

            I will re-check the measurements tomorrow with the current setup. I
            have about 1.5 inches left of out-travel on the Starlight focuser,
            (73mm to 120mm).

            Gee, I hope I don't need an adapter!

            Cheers

            Bob

            --- In tmboptical@yahoogroups.com, "Tube Tim" <potentate@...> wrote:
            >
            > >--- In tmboptical@yahoogroups.com, "Robert Anderson" <bob@> wrote:
            > >
            >
            > Hi Bob,
            >
            > I'd suggest making the FF so that the lenses inside can be moved +/-
            > 5mm. It would not be hard to do.
            >
            > Will the CCD be at focus the way you have drawn it? For my TMB's I
            > have to use the 4" extension on the back of the focuser.
            >
            >
            > Tim
            >
            >
            > > Hi Terry
            > >
            > > I received the measurements from FLI's designer and he did
            mention to
            > > make sure I added the distance for the two glass surfaces but I
            will
            > > email him again to confirm.
            > >
            > > I spoke with Markus today and he was un-sure if one counted the
            cover
            > > glass and the filters as he felt that they would not effect the
            light.
            > >
            > > Based on the SBIG calculations shown on their site, and the
            comments
            > > from both this group and the FLI engineer, I am positive that one
            > > does indeed need to take into consideration, the 2 x 3mm thick
            glass.
            > >
            > > I will make sure the FF is designed to also substract the
            distance it
            > > should screw into the FLI filter wheel. Might as well try for
            > > perfection, eh!
            > >
            > > Thanks again.
            > >
            > > Bob
            > >
            > > --- In tmboptical@yahoogroups.com, "Terry Tuggle" <tlt284@> wrote:
            > > >
            > > > Bob,
            > > >
            > > > Yes; I was confused a little. In effect you have to make
            the
            > > adapter
            > > > 2mm longer, so yes; subtracting it from the ccd/filter wheel
            > > distance is
            > > > what to do. One other thing to be sure of is; does the reported
            > > distance
            > > > include the cover glass offset already?
            > > >
            > > > Sorry for the confusion.
            > > >
            > > >
            > > >
            > > > Terry
            > > >
            > > > http://www.geocities.com/tlt284@/terryshuntofthemonth/
            > > >
            > > > _____
            > > >
            > > > From: tmboptical@yahoogroups.com
            > > [mailto:tmboptical@yahoogroups.com] On
            > > > Behalf Of Robert Anderson
            > > > Sent: Monday, December 04, 2006 10:18 AM
            > > > To: tmboptical@yahoogroups.com
            > > > Subject: [tmboptical] Re: Calculating the proper distance with
            > > filters for a
            > > > FF
            > > >
            > > >
            > > >
            > > > Hi Tim and Terry
            > > >
            > > > Sorry to continue this thread but Markus and I spoke today on
            the
            > > > subject of needing to add additional distance to off-set the
            impact
            > > > of glass between the FF and the CCD.
            > > >
            > > > According to common wisdom and supported by the SBIG document,
            one
            > > > needs to subtract a percentage of the thickness of any filters
            or
            > > > cover glass from the distance from the CCD to the front of the
            > > camera
            > > > plus Filter Wheel.
            > > >
            > > > Thus, if the distance from the CCD to the front of the camera
            and
            > > > filter wheel is 44.514mm and you have a 3mm thick CCD cover
            glass
            > > and
            > > > a 3mm thick filter, you need to subtract approximately 2mm from
            the
            > > > distance of the CCD to the front of the filter wheel which now
            > > > becomes 42.514mm.
            > > >
            > > > This has the effect of lenghtening the needed adapter from the
            R4
            > > > lens to the camera/filter wheel.
            > > >
            > > > TMB 175mm FF needs a distance of 113mm from the R4 lens to the
            CCD.
            > > > Plugging in the new number of 42.514, the extension from the R4
            > > lens
            > > > to camera/filter wheel is now 70.486mm, (plus the distance that
            the
            > > > FF screws into the threads of the camera/filter wheel).
            > > >
            > > > I have done up a Viso file, (JPEG version on link), for what I
            have
            > > > calculated out. Can you take a look at it and let me know if I
            have
            > > > the data correct?
            > > >
            > > > http://www.tpo <http://www.tpo.ca/Images/FLI-Imaging-Train-
            4.jpg>
            > > > ca/Images/FLI-Imaging-Train-4.jpg
            > > >
            > > > Thanks in advance.
            > > >
            > > > Bob
            > > >
            > > > --- In tmboptical@yahoogro <mailto:tmboptical%
            40yahoogroups.com>
            > > ups.com,
            > > > "Tube Tim" <potentate@> wrote:
            > > > >
            > > > > >--- In tmboptical@yahoogro <mailto:tmboptical%
            40yahoogroups.com>
            > > ups.com,
            > > > "Terry Tuggle" <tlt284@> wrote:
            > > > > >
            > > > > > Hi Bob,
            > > > > >
            > > > > > It is my understanding that you add the 1mm to the distance
            > > > > > for each 3mm glass. The 113mm distance is from the center
            of the
            > > > > > R4 lens, so you must measure that distance to the top of
            the FF
            > > > > > housing,
            > > > >
            > > > > Correct, a very important point.
            > > > >
            > > > > > and then subtract any screw in distance to the mating
            flange
            > > that
            > > > > > will mate to the extension tube. You really do not consider
            the
            > > > > > screw in distance; you measure from the mating flanges. So
            you
            > > > > > start with the 44.514mm distance and add the 2mm which =
            > > 46.514mm.
            > > > > > Once you know the distance from the center of the rear R4
            > > > > > lens to the mating flange of the housing, you would add
            that to
            > > > the
            > > > > > 46.514mm, then; subtract that from the 113mm. The result
            would
            > > be
            > > > > > the distance needed for the extension tube; flange to
            flange.
            > > > > >
            > > > > > Peter, Tim, please correct me if this does not sound right
            to
            > > you!
            > > > > >
            > > > >
            > > > > The 1/3 thickness rule is news to me. When setting up the STL-
            11K
            > > I
            > > > > used the SBIG diagram:
            > > > >
            > > > > http://www.sbig
            > > <http://www.sbig.com/pdffiles/2400_1001_BASIC_ASSY.pdf>
            > > > com/pdffiles/2400_1001_BASIC_ASSY.pdf
            > > > >
            > > > > and used the distance of 1.470". For a 3mm filter SBIG allowed
            > > > > 0.0390-inches or 0.991mm. I guess the rule of thumb works! It
            > > > looks
            > > > > to me like you (Terry) have the correct 'sign' by adding to
            the
            > > > length
            > > > > of the adapter.
            > > > >
            > > > > I would place the FF lenses in a 'cell' (*) or carrier that
            has
            > > male
            > > > > threads on the outside and have this screw into an extension
            tube
            > > at
            > > > > the back of the focuser. The cell could be moved back N forth
            +/-
            > > > > 10mm or more (via the threading) and held in the optimal
            position
            > > > > with a jam nut. The adapter from this extension tube to CCD
            would
            > > > > then be simplified. Converting to a new CCD would be simply a
            > > > matter
            > > > > of changing the cell distance and a new adapter.
            > > > >
            > > > >
            > > > > Tim
            > > > >
            > > > >
            > > > > (*) think of the cell as a 100mm diameter cylinder with all
            > > thread
            > > > on
            > > > > the outside and the glass on the inside.
            > > > >
            > > > > >
            > > > > >
            > > > > > Terry
            > > > > >
            > > > > > http://www.geocitie
            > > > <http://www.geocities.com/tlt284@/terryshuntofthemonth/>
            > > > s.com/tlt284@/terryshuntofthemonth/
            > > > > >
            > > > > > _____
            > > > > >
            > > > > > From: tmboptical@yahoogro <mailto:tmboptical%
            40yahoogroups.com>
            > > ups.com
            > > > [mailto:tmboptical@yahoogro <mailto:tmboptical%
            40yahoogroups.com>
            > > ups.com]
            > > > On
            > > > > > Behalf Of Robert Anderson
            > > > > > Sent: Tuesday, November 28, 2006 8:17 AM
            > > > > > To: tmboptical@yahoogro <mailto:tmboptical%
            40yahoogroups.com>
            > > ups.com
            > > > > > Subject: [tmboptical] Calculating the proper distance with
            > > filters
            > > > > for a FF
            > > > > >
            > > > > >
            > > > > >
            > > > > > Hi all
            > > > > >
            > > > > > Just want to make sure I am calculating the proper distance
            for
            > > > the
            > > > > > positioning of the TMB 175mm FF with a new camera/filter
            wheel,
            > > > (FLI
            > > > > > Proline with 7 position filter wheel), that Markus is
            building
            > > > for me.
            > > > > >
            > > > > > I have the distance from the CCD to where the FF screws
            into
            > > the
            > > > > > filter wheel of 44.514mm less the max distance to screw the
            FF
            > > > into
            > > > > > the filter wheel of 1.875mm
            > > > > >
            > > > > > In-between the FF and the CCD are two glass surfaces, (the
            3mm
            > > > BK7
            > > > > > CCD cover glass and the 3mm thick AstroDon filters).
            > > > > >
            > > > > > Do I add 1/3rd of the thickness of the two glass surfaces
            or
            > > > subtract
            > > > > > them from the total distance from the CCD to the rear cell
            of
            > > the
            > > > FF?
            > > > > >
            > > > > > Proper distance from FF to CCD is 113mm. Extension from
            back of
            > > > FF to
            > > > > > Filter wheel would be 113mm less the 42.639mm, (distance
            from
            > > > front
            > > > > > of filter wheel to CCD taking out the 1.875mm screw in
            > > distance)
            > > > > > equals 70.361mm.
            > > > > >
            > > > > > Do I add an extra 1mm for each 3mm glass surface or
            subtract
            > > that
            > > > > > from the 70.361mm extension?
            > > > > >
            > > > > > Cheers
            > > > > >
            > > > > > Bob
            > > > > >
            > > > > >
            > > > > >
            > > > > >
            > > > > >
            > > > > > [Non-text portions of this message have been removed]
            > > > > >
            > > > >
            > > >
            > > >
            > > >
            > > >
            > > >
            > > > [Non-text portions of this message have been removed]
            > > >
            > >
            >
          • Robert Anderson
            This is an easy method to check Peter, thanks ever so much. I still have the Optec focuser on the scope, (took out the filters as I have my ST 402 with filters
            Message 5 of 11 , Dec 4, 2006
            • 0 Attachment
              This is an easy method to check Peter, thanks ever so much.

              I still have the Optec focuser on the scope, (took out the filters as
              I have my ST 402 with filters mounted on while I await the new camera
              to come in).

              I can do some star tests with the Optec filter out and then put it in
              and see how much I need to adjust to get back into focus.

              Again, thanks for the tip. Now I just need some clear skies up here
              in Winterland.

              Cheers

              Bob

              --- In tmboptical@yahoogroups.com, "erdmanpe" <erdmanpe@...> wrote:
              >
              > The problem with these fixed corrections and any rule of thumb is
              that
              > they depend upon various assumptions. First, the correction is
              > required because any optical element (even a set of parallel planes)
              > changes the optical path. That correction depends upon the optical
              > system's f/#. SBIG has made an assumption (unknown to us) about the
              > system f/# and given (in their data sheets) an "optical path" length
              > based upon that assumption.
              >
              > For a different f/#, a different correction is necessary. At
              a "slow"
              > f/# (e.g. f/9), the correction will be less than SBIG's given value,
              > I'm sure.
              >
              > You can check the correction necessary for your system by focusing
              > without any filter elements in place (no FF involved). Then focus
              > with a filter of this approximate thickness in place. The
              difference
              > in focal positions is the correction distance under discussion.
              >
              > Peter
              >
              > --- In tmboptical@yahoogroups.com, "Robert Anderson" <bob@> wrote:
              > >
              > > Hi Terry
              > >
              > > I received the measurements from FLI's designer and he did
              mention to
              > > make sure I added the distance for the two glass surfaces but I
              will
              > > email him again to confirm.
              > >
              > > I spoke with Markus today and he was un-sure if one counted the
              cover
              > > glass and the filters as he felt that they would not effect the
              light.
              > >
              > > Based on the SBIG calculations shown on their site, and the
              comments
              > > from both this group and the FLI engineer, I am positive that one
              > > does indeed need to take into consideration, the 2 x 3mm thick
              glass.
              > >
              > > I will make sure the FF is designed to also substract the
              distance it
              > > should screw into the FLI filter wheel. Might as well try for
              > > perfection, eh!
              > >
              > > Thanks again.
              > >
              > > Bob
              > >
              > > --- In tmboptical@yahoogroups.com, "Terry Tuggle" <tlt284@> wrote:
              > > >
              > > > Bob,
              > > >
              > > > Yes; I was confused a little. In effect you have to make
              the
              > > adapter
              > > > 2mm longer, so yes; subtracting it from the ccd/filter wheel
              > > distance is
              > > > what to do. One other thing to be sure of is; does the reported
              > > distance
              > > > include the cover glass offset already?
              > > >
              > > > Sorry for the confusion.
              > > >
              > > >
              > > >
              > > > Terry
              > > >
              > > > http://www.geocities.com/tlt284@/terryshuntofthemonth/
              > > >
              > > > _____
              > > >
              > > > From: tmboptical@yahoogroups.com
              > > [mailto:tmboptical@yahoogroups.com] On
              > > > Behalf Of Robert Anderson
              > > > Sent: Monday, December 04, 2006 10:18 AM
              > > > To: tmboptical@yahoogroups.com
              > > > Subject: [tmboptical] Re: Calculating the proper distance with
              > > filters for a
              > > > FF
              > > >
              > > >
              > > >
              > > > Hi Tim and Terry
              > > >
              > > > Sorry to continue this thread but Markus and I spoke today on
              the
              > > > subject of needing to add additional distance to off-set the
              impact
              > > > of glass between the FF and the CCD.
              > > >
              > > > According to common wisdom and supported by the SBIG document,
              one
              > > > needs to subtract a percentage of the thickness of any filters
              or
              > > > cover glass from the distance from the CCD to the front of the
              > > camera
              > > > plus Filter Wheel.
              > > >
              > > > Thus, if the distance from the CCD to the front of the camera
              and
              > > > filter wheel is 44.514mm and you have a 3mm thick CCD cover
              glass
              > > and
              > > > a 3mm thick filter, you need to subtract approximately 2mm from
              the
              > > > distance of the CCD to the front of the filter wheel which now
              > > > becomes 42.514mm.
              > > >
              > > > This has the effect of lenghtening the needed adapter from the
              R4
              > > > lens to the camera/filter wheel.
              > > >
              > > > TMB 175mm FF needs a distance of 113mm from the R4 lens to the
              CCD.
              > > > Plugging in the new number of 42.514, the extension from the R4
              > > lens
              > > > to camera/filter wheel is now 70.486mm, (plus the distance that
              the
              > > > FF screws into the threads of the camera/filter wheel).
              > > >
              > > > I have done up a Viso file, (JPEG version on link), for what I
              have
              > > > calculated out. Can you take a look at it and let me know if I
              have
              > > > the data correct?
              > > >
              > > > http://www.tpo <http://www.tpo.ca/Images/FLI-Imaging-Train-
              4.jpg>
              > > > ca/Images/FLI-Imaging-Train-4.jpg
              > > >
              > > > Thanks in advance.
              > > >
              > > > Bob
              > > >
              > > > --- In tmboptical@yahoogro <mailto:tmboptical%
              40yahoogroups.com>
              > > ups.com,
              > > > "Tube Tim" <potentate@> wrote:
              > > > >
              > > > > >--- In tmboptical@yahoogro <mailto:tmboptical%
              40yahoogroups.com>
              > > ups.com,
              > > > "Terry Tuggle" <tlt284@> wrote:
              > > > > >
              > > > > > Hi Bob,
              > > > > >
              > > > > > It is my understanding that you add the 1mm to the distance
              > > > > > for each 3mm glass. The 113mm distance is from the center
              of the
              > > > > > R4 lens, so you must measure that distance to the top of
              the FF
              > > > > > housing,
              > > > >
              > > > > Correct, a very important point.
              > > > >
              > > > > > and then subtract any screw in distance to the mating
              flange
              > > that
              > > > > > will mate to the extension tube. You really do not consider
              the
              > > > > > screw in distance; you measure from the mating flanges. So
              you
              > > > > > start with the 44.514mm distance and add the 2mm which =
              > > 46.514mm.
              > > > > > Once you know the distance from the center of the rear R4
              > > > > > lens to the mating flange of the housing, you would add
              that to
              > > > the
              > > > > > 46.514mm, then; subtract that from the 113mm. The result
              would
              > > be
              > > > > > the distance needed for the extension tube; flange to
              flange.
              > > > > >
              > > > > > Peter, Tim, please correct me if this does not sound right
              to
              > > you!
              > > > > >
              > > > >
              > > > > The 1/3 thickness rule is news to me. When setting up the STL-
              11K
              > > I
              > > > > used the SBIG diagram:
              > > > >
              > > > > http://www.sbig
              > > <http://www.sbig.com/pdffiles/2400_1001_BASIC_ASSY.pdf>
              > > > com/pdffiles/2400_1001_BASIC_ASSY.pdf
              > > > >
              > > > > and used the distance of 1.470". For a 3mm filter SBIG allowed
              > > > > 0.0390-inches or 0.991mm. I guess the rule of thumb works! It
              > > > looks
              > > > > to me like you (Terry) have the correct 'sign' by adding to
              the
              > > > length
              > > > > of the adapter.
              > > > >
              > > > > I would place the FF lenses in a 'cell' (*) or carrier that
              has
              > > male
              > > > > threads on the outside and have this screw into an extension
              tube
              > > at
              > > > > the back of the focuser. The cell could be moved back N forth
              +/-
              > > > > 10mm or more (via the threading) and held in the optimal
              position
              > > > > with a jam nut. The adapter from this extension tube to CCD
              would
              > > > > then be simplified. Converting to a new CCD would be simply a
              > > > matter
              > > > > of changing the cell distance and a new adapter.
              > > > >
              > > > >
              > > > > Tim
              > > > >
              > > > >
              > > > > (*) think of the cell as a 100mm diameter cylinder with all
              > > thread
              > > > on
              > > > > the outside and the glass on the inside.
              > > > >
              > > > > >
              > > > > >
              > > > > > Terry
              > > > > >
              > > > > > http://www.geocitie
              > > > <http://www.geocities.com/tlt284@/terryshuntofthemonth/>
              > > > s.com/tlt284@/terryshuntofthemonth/
              > > > > >
              > > > > > _____
              > > > > >
              > > > > > From: tmboptical@yahoogro <mailto:tmboptical%
              40yahoogroups.com>
              > > ups.com
              > > > [mailto:tmboptical@yahoogro <mailto:tmboptical%
              40yahoogroups.com>
              > > ups.com]
              > > > On
              > > > > > Behalf Of Robert Anderson
              > > > > > Sent: Tuesday, November 28, 2006 8:17 AM
              > > > > > To: tmboptical@yahoogro <mailto:tmboptical%
              40yahoogroups.com>
              > > ups.com
              > > > > > Subject: [tmboptical] Calculating the proper distance with
              > > filters
              > > > > for a FF
              > > > > >
              > > > > >
              > > > > >
              > > > > > Hi all
              > > > > >
              > > > > > Just want to make sure I am calculating the proper distance
              for
              > > > the
              > > > > > positioning of the TMB 175mm FF with a new camera/filter
              wheel,
              > > > (FLI
              > > > > > Proline with 7 position filter wheel), that Markus is
              building
              > > > for me.
              > > > > >
              > > > > > I have the distance from the CCD to where the FF screws
              into
              > > the
              > > > > > filter wheel of 44.514mm less the max distance to screw the
              FF
              > > > into
              > > > > > the filter wheel of 1.875mm
              > > > > >
              > > > > > In-between the FF and the CCD are two glass surfaces, (the
              3mm
              > > > BK7
              > > > > > CCD cover glass and the 3mm thick AstroDon filters).
              > > > > >
              > > > > > Do I add 1/3rd of the thickness of the two glass surfaces
              or
              > > > subtract
              > > > > > them from the total distance from the CCD to the rear cell
              of
              > > the
              > > > FF?
              > > > > >
              > > > > > Proper distance from FF to CCD is 113mm. Extension from
              back of
              > > > FF to
              > > > > > Filter wheel would be 113mm less the 42.639mm, (distance
              from
              > > > front
              > > > > > of filter wheel to CCD taking out the 1.875mm screw in
              > > distance)
              > > > > > equals 70.361mm.
              > > > > >
              > > > > > Do I add an extra 1mm for each 3mm glass surface or
              subtract
              > > that
              > > > > > from the 70.361mm extension?
              > > > > >
              > > > > > Cheers
              > > > > >
              > > > > > Bob
              > > > > >
              > > > > >
              > > > > >
              > > > > >
              > > > > >
              > > > > > [Non-text portions of this message have been removed]
              > > > > >
              > > > >
              > > >
              > > >
              > > >
              > > >
              > > >
              > > > [Non-text portions of this message have been removed]
              > > >
              > >
              >
            • Tube Tim
              ... and if he can t do this my machinst can. His machine work and finish on black polish anodize is the best. He even has product on Mars. ... That s what
              Message 6 of 11 , Dec 5, 2006
              • 0 Attachment
                >--- In tmboptical@yahoogroups.com, "Robert Anderson" <bob@...> wrote:
                >
                > Two good points Tim.
                >
                > I will speak with Markus about the ability to move te lenses.

                and if he can't do this my machinst can. His machine work and finish
                on black polish anodize is the best. He even has product on Mars.


                > I will re-check the measurements tomorrow with the current setup. I
                > have about 1.5 inches left of out-travel on the Starlight focuser,
                > (73mm to 120mm).
                >
                > Gee, I hope I don't need an adapter!

                That's what you must avoid. When I converted a focal reducer adapter
                to work on the TMB 4" CNC focuser I had to make it 80mm in length to
                avoid the need for the standard 100mm extension tube.

                Good Luck,

                ___
                Tim
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