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Re: Calculating the proper distance with filters for a FF

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  • 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 1 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 2 of 11 , Dec 4, 2006
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        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 3 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 4 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 5 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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