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Re: [ccd-newastro] Need focal reducer help!

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  • Jim Thibert
    I have found with all the ccd optical train, especially when using a c14and st7 that .63 is tough enough let alone 3.3 R/C For the .63, I went to a VSE focuser
    Message 1 of 9 , Dec 1, 2003
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      I have found with all the ccd optical train, especially when using a c14and
      st7 that .63 is tough enough let alone 3.3 R/C

      For the .63, I went to a VSE focuser where the R/C is zero offset because
      its inside



      Good skies-clear eyes

      JImmy
      http://www.forterieobservatory.com
      formerly, www.frenchriverobservatory.com

      W78-55-12 N42-54-25
      C-14@f5.1 (st7-i/cfw8)and TV101(st7-e) on ParamountME with VSE m-3Robo





      ----Original Message Follows----
      From: "uwpf23" <uwpf23@...>
      Reply-To: ccd-newastro@yahoogroups.com
      To: ccd-newastro@yahoogroups.com
      Subject: [ccd-newastro] Need focal reducer help!
      Date: Mon, 01 Dec 2003 04:29:25 -0000

      Hi,
      I cannot achieve focus with a Meade F/3.3 focal reducer used with
      the following:
      1) Celestron CGE-1400 OTA. 3910mm focal length @ F-11 when no focal
      reducer used.
      2) CCD setup is an ST-7/CFW-8/AO-7 all attached together.
      3) JMI SmartFocus elecric micro-focuser.

      I've tried the following already:
      1) Mounted the reducer directly onto the visual back of the OTA first,
      then attached the JMI, then the CCD gear. Racked the Celestron
      main focus knob all the way clockwise (mirror moved all the way
      back toward the rear). The image was moving toward focus, but
      could not get all the way focused.
      2) Mounted JMI focuser first, then the reducer, then the CCD gear.
      Same result.

      Note: I CAN get focus with the F/3.3 reducer through the eyepiece and
      a star diagonal visually (NO CCD attached).

      Is my problem that the focal reducer lens is too far away from the
      CCD chip with all the gear attached? Or, is it too close to the CCD
      chip? It seems from the visual eyepiece check that the reducer is
      too far away from the CCD chip. I can't get it any closer without
      removing some of the CCD attachments, which is not feasible for me
      (can't do without the color wheel or adaptive optics).

      Anybody have any ideas on what the cure for this is? If this specific
      focal reducer is incompatible, anybody have any suggestions for brands
      that will work and are faster than F/6.3 (already have a .63 from
      Celestron that works fine--just need shorter focal lengths than this
      with such a long main focal length to work with!). Would like to get
      down to at least F/4 or 4.5 if possible, as F/6.3 just is not
      desirable with some objects on the CGE-1400.

      Thanks for any help you all can give me on this!

      Clear skies,
      Wade Van Arsdale
      Little Rock, AR.
      (Registered NewAstro Customer)




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    • Roger Hamlett
      ... Too far from the CCD chip. ... You will allready be using a compressor that is more extreme than F*.63. The reduction acheived by a compressor, is
      Message 2 of 9 , Dec 1, 2003
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        > Hi,
        > I cannot achieve focus with a Meade F/3.3 focal reducer used with
        > the following:
        > 1) Celestron CGE-1400 OTA. 3910mm focal length @ F-11 when no focal
        > reducer used.
        > 2) CCD setup is an ST-7/CFW-8/AO-7 all attached together.
        > 3) JMI SmartFocus elecric micro-focuser.
        >
        > I've tried the following already:
        > 1) Mounted the reducer directly onto the visual back of the OTA first,
        > then attached the JMI, then the CCD gear. Racked the Celestron
        > main focus knob all the way clockwise (mirror moved all the way
        > back toward the rear). The image was moving toward focus, but
        > could not get all the way focused.
        > 2) Mounted JMI focuser first, then the reducer, then the CCD gear.
        > Same result.
        >
        > Note: I CAN get focus with the F/3.3 reducer through the eyepiece and
        > a star diagonal visually (NO CCD attached).
        >
        > Is my problem that the focal reducer lens is too far away from the
        > CCD chip with all the gear attached? Or, is it too close to the CCD
        > chip? It seems from the visual eyepiece check that the reducer is
        > too far away from the CCD chip. I can't get it any closer without
        > removing some of the CCD attachments, which is not feasible for me
        > (can't do without the color wheel or adaptive optics).
        Too far from the CCD chip.

        > Anybody have any ideas on what the cure for this is? If this specific
        > focal reducer is incompatible, anybody have any suggestions for brands
        > that will work and are faster than F/6.3 (already have a .63 from
        > Celestron that works fine--just need shorter focal lengths than this
        > with such a long main focal length to work with!). Would like to get
        > down to at least F/4 or 4.5 if possible, as F/6.3 just is not
        > desirable with some objects on the CGE-1400.
        >
        > Thanks for any help you all can give me on this!
        You will allready be using a compressor that is more extreme than F*.63. The
        reduction acheived by a compressor, is dependant on it's own focal length,
        and the distance to the target. Assuming you have the F*.63, mounted with
        the normal "captain's wheel" on the AO7, the compressor will be running at
        about F*.5. The final focal ratio achieved though, is dependant on the scope
        itself. As the back focus increases (which with the compressor and the
        distances involved with the focusser, will be at perhaps 300mm), the scope
        itself give higher than design focal ratios. It's design ratio is F/11, and
        with the extended backfocus, it will probably be working more like F/12.5,
        giving you a final ratio close to F/6.3. You will not get much more extreme
        than the ratio you are allready using, without severe problems elsewhere
        (you will be getting some shading of the main CCD, by the 'pick off' for the
        guide CCD, vignetting from the filters and compressor etc. etc..).
        The 'key' of the AO7, is that it allows detailed imaging at quite long focal
        lengths, by giving fast accurate guiding. You have two basic choices:
        1) Stick with the high focal ratio, and use the AO7.
        2) Remove the AO7 and image at perhaps F/4 (which should be fine with normal
        guiding).
        You _can_ 'do without' the adaptive optics, when running at shorter focal
        lengths.

        Best Wishes
      • uwpf23
        Hi Roger, Thanks very much for your help on this. That is the same thing that I (being a CCD novice) had concluded--too far away from the CCD chip. I m
        Message 3 of 9 , Dec 1, 2003
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          Hi Roger,
          Thanks very much for your help on this. That is the same thing that
          I (being a CCD novice) had concluded--too far away from the CCD chip.
          I'm considering one other option--I have a Celestron ST-80 F/5
          refractor mounted on the main 14 inch OTA. If I can find the proper
          T-Ring to adapt it's focuser tube to the captain's wheel of the AO-7,
          (even though the AO-7 wouldn't be needed here--just don't want to
          mess with taking it apart every time!), I will try imaging and
          manually focusing with an aperature mask through the ST-80 for the
          very large sky objects (M42, etc...), then just go with the setup you
          recommended below for the fainter, smaller objects. I may wind up
          having a similar distance problem with the ST-80 though, even without
          the reducer and JMI focuser: focus may be too far away from the CCD
          chip to rack the drawtube in far enough to get there. I may not have
          any other choice but to take the AO-7 off when using the refractor.
          Any comments on this setup with the ST-80 refractor would be greatly
          appreciated, as well.

          Thanks also for the information on the 14 inch OTA F-values with the
          .63 compressor. This will aid greatly in fine-tuning the proper
          binning mode to get a more reasonable arc-sec/pixel value with such
          long focal lengths! Looks like I'll be using 3x3 binning most of the
          time with this long focal length.

          Clear skies,
          Wade Van Arsdale

          //////////////////////////////////////////////////////////////////




          --- In ccd-newastro@yahoogroups.com, "Roger Hamlett" <roger@t...>
          wrote:
          > > Hi,
          > > I cannot achieve focus with a Meade F/3.3 focal reducer used with
          > > the following:
          > > 1) Celestron CGE-1400 OTA. 3910mm focal length @ F-11 when no
          focal
          > > reducer used.
          > > 2) CCD setup is an ST-7/CFW-8/AO-7 all attached together.
          > > 3) JMI SmartFocus elecric micro-focuser.
          > >
          > > I've tried the following already:
          > > 1) Mounted the reducer directly onto the visual back of the OTA
          first,
          > > then attached the JMI, then the CCD gear. Racked the Celestron
          > > main focus knob all the way clockwise (mirror moved all the way
          > > back toward the rear). The image was moving toward focus, but
          > > could not get all the way focused.
          > > 2) Mounted JMI focuser first, then the reducer, then the CCD gear.
          > > Same result.
          > >
          > > Note: I CAN get focus with the F/3.3 reducer through the eyepiece
          and
          > > a star diagonal visually (NO CCD attached).
          > >
          > > Is my problem that the focal reducer lens is too far away from the
          > > CCD chip with all the gear attached? Or, is it too close to the
          CCD
          > > chip? It seems from the visual eyepiece check that the reducer is
          > > too far away from the CCD chip. I can't get it any closer without
          > > removing some of the CCD attachments, which is not feasible for me
          > > (can't do without the color wheel or adaptive optics).
          > Too far from the CCD chip.
          >
          > > Anybody have any ideas on what the cure for this is? If this
          specific
          > > focal reducer is incompatible, anybody have any suggestions for
          brands
          > > that will work and are faster than F/6.3 (already have a .63 from
          > > Celestron that works fine--just need shorter focal lengths than
          this
          > > with such a long main focal length to work with!). Would like to
          get
          > > down to at least F/4 or 4.5 if possible, as F/6.3 just is not
          > > desirable with some objects on the CGE-1400.
          > >
          > > Thanks for any help you all can give me on this!
          > You will allready be using a compressor that is more extreme than
          F*.63. The
          > reduction acheived by a compressor, is dependant on it's own focal
          length,
          > and the distance to the target. Assuming you have the F*.63,
          mounted with
          > the normal "captain's wheel" on the AO7, the compressor will be
          running at
          > about F*.5. The final focal ratio achieved though, is dependant on
          the scope
          > itself. As the back focus increases (which with the compressor and
          the
          > distances involved with the focusser, will be at perhaps 300mm),
          the scope
          > itself give higher than design focal ratios. It's design ratio is
          F/11, and
          > with the extended backfocus, it will probably be working more like
          F/12.5,
          > giving you a final ratio close to F/6.3. You will not get much more
          extreme
          > than the ratio you are allready using, without severe problems
          elsewhere
          > (you will be getting some shading of the main CCD, by the 'pick
          off' for the
          > guide CCD, vignetting from the filters and compressor etc. etc..).
          > The 'key' of the AO7, is that it allows detailed imaging at quite
          long focal
          > lengths, by giving fast accurate guiding. You have two basic
          choices:
          > 1) Stick with the high focal ratio, and use the AO7.
          > 2) Remove the AO7 and image at perhaps F/4 (which should be fine
          with normal
          > guiding).
          > You _can_ 'do without' the adaptive optics, when running at shorter
          focal
          > lengths.
          >
          > Best Wishes
        • Roger Hamlett
          ... You are obviously interested in going for quite wide fields . At least with the ST7, you won t get microlens artefacts, (which can get quite bad on the
          Message 4 of 9 , Dec 2, 2003
          • 0 Attachment
            > Hi Roger,
            > Thanks very much for your help on this. That is the same thing that
            > I (being a CCD novice) had concluded--too far away from the CCD chip.
            > I'm considering one other option--I have a Celestron ST-80 F/5
            > refractor mounted on the main 14 inch OTA. If I can find the proper
            > T-Ring to adapt it's focuser tube to the captain's wheel of the AO-7,
            > (even though the AO-7 wouldn't be needed here--just don't want to
            > mess with taking it apart every time!), I will try imaging and
            > manually focusing with an aperature mask through the ST-80 for the
            > very large sky objects (M42, etc...), then just go with the setup you
            > recommended below for the fainter, smaller objects. I may wind up
            > having a similar distance problem with the ST-80 though, even without
            > the reducer and JMI focuser: focus may be too far away from the CCD
            > chip to rack the drawtube in far enough to get there. I may not have
            > any other choice but to take the AO-7 off when using the refractor.
            > Any comments on this setup with the ST-80 refractor would be greatly
            > appreciated, as well.
            You are obviously interested in going for quite 'wide fields'. At least with
            the ST7, you won't get 'microlens' artefacts, (which can get quite bad on
            the lensed CCD's at fast focal ratios). :-)

            > Thanks also for the information on the 14 inch OTA F-values with the
            > .63 compressor. This will aid greatly in fine-tuning the proper
            > binning mode to get a more reasonable arc-sec/pixel value with such
            > long focal lengths! Looks like I'll be using 3x3 binning most of the
            > time with this long focal length.
            I'd have expected the compressor to be showing some noticable aberrations at
            the large spacing. The 'design' spacing, is about 90mm from the base of the
            threads, to the CCD (to give 0.63*). The AO7 body itself adds nearly this
            much, while the colour wheel, distance to CCD inside the camera body, and
            the long front port on the AO7, all extend this distance. Generally, to get
            reasonably good images, to the edge of the field with the compressor and the
            AO7, it is necessary to reduce this distance as much as possible. Hence the
            adapter here:
            http://www.ziplink.net/~lester/FLR.html
            Though this will reduce the focal compression you get from the existing
            unit, the scopes focal ratio will drop a little, and the overall field will
            not be that different, but the quality across the field will be better.
            For really wide fields, a shorter focal length scope will be the answer.
            However remember you can allways take a sequence of images binned 3*3 (say),
            and make a mosaic.
            Once you get the suitable adapter to try this, rain will be guaranteed for a
            few weeks... (personal depressing forecast).

            Best Wishes
          • uwpf23
            Thanks for the info Jim! Clear skies, Wade ... a c14and ... because ... 3Robo ... first, ... and ... CCD ... specific ... brands ... this ... get ...
            Message 5 of 9 , Dec 2, 2003
            • 0 Attachment
              Thanks for the info Jim!

              Clear skies,
              Wade

              ////////////////////////////////////////////////////////////////
              --- In ccd-newastro@yahoogroups.com, "Jim Thibert" <thibertj@h...>
              wrote:
              > I have found with all the ccd optical train, especially when using
              a c14and
              > st7 that .63 is tough enough let alone 3.3 R/C
              >
              > For the .63, I went to a VSE focuser where the R/C is zero offset
              because
              > its inside
              >
              >
              >
              > Good skies-clear eyes
              >
              > JImmy
              > http://www.forterieobservatory.com
              > formerly, www.frenchriverobservatory.com
              >
              > W78-55-12 N42-54-25
              > C-14@f... (st7-i/cfw8)and TV101(st7-e) on ParamountME with VSE m-
              3Robo
              >
              >
              >
              >
              >
              > ----Original Message Follows----
              > From: "uwpf23" <uwpf23@y...>
              > Reply-To: ccd-newastro@yahoogroups.com
              > To: ccd-newastro@yahoogroups.com
              > Subject: [ccd-newastro] Need focal reducer help!
              > Date: Mon, 01 Dec 2003 04:29:25 -0000
              >
              > Hi,
              > I cannot achieve focus with a Meade F/3.3 focal reducer used with
              > the following:
              > 1) Celestron CGE-1400 OTA. 3910mm focal length @ F-11 when no focal
              > reducer used.
              > 2) CCD setup is an ST-7/CFW-8/AO-7 all attached together.
              > 3) JMI SmartFocus elecric micro-focuser.
              >
              > I've tried the following already:
              > 1) Mounted the reducer directly onto the visual back of the OTA
              first,
              > then attached the JMI, then the CCD gear. Racked the Celestron
              > main focus knob all the way clockwise (mirror moved all the way
              > back toward the rear). The image was moving toward focus, but
              > could not get all the way focused.
              > 2) Mounted JMI focuser first, then the reducer, then the CCD gear.
              > Same result.
              >
              > Note: I CAN get focus with the F/3.3 reducer through the eyepiece
              and
              > a star diagonal visually (NO CCD attached).
              >
              > Is my problem that the focal reducer lens is too far away from the
              > CCD chip with all the gear attached? Or, is it too close to the
              CCD
              > chip? It seems from the visual eyepiece check that the reducer is
              > too far away from the CCD chip. I can't get it any closer without
              > removing some of the CCD attachments, which is not feasible for me
              > (can't do without the color wheel or adaptive optics).
              >
              > Anybody have any ideas on what the cure for this is? If this
              specific
              > focal reducer is incompatible, anybody have any suggestions for
              brands
              > that will work and are faster than F/6.3 (already have a .63 from
              > Celestron that works fine--just need shorter focal lengths than
              this
              > with such a long main focal length to work with!). Would like to
              get
              > down to at least F/4 or 4.5 if possible, as F/6.3 just is not
              > desirable with some objects on the CGE-1400.
              >
              > Thanks for any help you all can give me on this!
              >
              > Clear skies,
              > Wade Van Arsdale
              > Little Rock, AR.
              > (Registered NewAstro Customer)
              >
              >
              >
              >
              > To unsubscribe from this group, send an email to:
              > ccd-newastro-unsubscribe@egroups.com
              >
              >
              >
              > Your use of Yahoo! Groups is subject to
              http://docs.yahoo.com/info/terms/
              >
              > _________________________________________________________________
              > Add photos to your e-mail with MSN 8. Get 2 months FREE*.
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            • uwpf23
              Thanks Mark. I think I m going to use a Celestron ST80 guide scope mounted piggyback for the larger objects (with the AO-7 removed), and use the .63
              Message 6 of 9 , Dec 2, 2003
              • 0 Attachment
                Thanks Mark. I think I'm going to use a Celestron ST80 guide
                scope mounted piggyback for the larger objects (with the AO-7
                removed), and use the .63 reducer/AO-7 with the C-14 the rest of the
                time. Appreciate the help from everybody who responded!

                Clear skies,
                Wade
                ///////////////////////////////////////////////////////////////////

                --- In ccd-newastro@yahoogroups.com, "Mark de Regt" <deregt@e...>
                wrote:
                > You can't use a Meade .33 reducer with the AO-7--the distance is
                too great
                > from reducer to chip, and you won't be able to focus (even if you
                could, the
                > distortion would be horrible).
                >
                > The .63 reducer should work; it does with my LX200 with an AO-7.
                I don't
                > know about the optec filters, except that I understand that they
                will not
                > work with the CFW-8.
                >
                > Mark de Regt
                > Redmond, Washington, USA
                > 47.7 N. Latitude; 122 West Longitude
                > Astro Images: http://home.earthlink.net/~akilla/MAD
                >
                >
                >
                >
                > > -----Original Message-----
                > > From: uwpf23 [mailto:uwpf23@y...]
                > > Sent: Sunday, November 30, 2003 8:29 PM
                > > To: ccd-newastro@yahoogroups.com
                > > Subject: [ccd-newastro] Need focal reducer help!
                > >
                > >
                > > Hi,
                > > I cannot achieve focus with a Meade F/3.3 focal reducer used with
                > > the following:
                > > 1) Celestron CGE-1400 OTA. 3910mm focal length @ F-11 when no
                focal
                > > reducer used.
                > > 2) CCD setup is an ST-7/CFW-8/AO-7 all attached together.
                > > 3) JMI SmartFocus elecric micro-focuser.
                > >
                > > I've tried the following already:
                > > 1) Mounted the reducer directly onto the visual back of the OTA
                first,
                > > then attached the JMI, then the CCD gear. Racked the Celestron
                > > main focus knob all the way clockwise (mirror moved all the
                way
                > > back toward the rear). The image was moving toward focus, but
                > > could not get all the way focused.
                > > 2) Mounted JMI focuser first, then the reducer, then the CCD
                gear.
                > > Same result.
                > >
                > > Note: I CAN get focus with the F/3.3 reducer through the
                eyepiece and
                > > a star diagonal visually (NO CCD attached).
                > >
                > > Is my problem that the focal reducer lens is too far away from
                the
                > > CCD chip with all the gear attached? Or, is it too close to the
                CCD
                > > chip? It seems from the visual eyepiece check that the reducer
                is
                > > too far away from the CCD chip. I can't get it any closer
                without
                > > removing some of the CCD attachments, which is not feasible for
                me
                > > (can't do without the color wheel or adaptive optics).
                > >
                > > Anybody have any ideas on what the cure for this is? If this
                specific
                > > focal reducer is incompatible, anybody have any suggestions for
                brands
                > > that will work and are faster than F/6.3 (already have a .63 from
                > > Celestron that works fine--just need shorter focal lengths than
                this
                > > with such a long main focal length to work with!). Would like
                to get
                > > down to at least F/4 or 4.5 if possible, as F/6.3 just is not
                > > desirable with some objects on the CGE-1400.
                > >
                > > Thanks for any help you all can give me on this!
                > >
                > > Clear skies,
                > > Wade Van Arsdale
                > > Little Rock, AR.
                > > (Registered NewAstro Customer)
                > >
                > >
                > >
                > >
                > > To unsubscribe from this group, send an email to:
                > > ccd-newastro-unsubscribe@egroups.com
                > >
                > >
                > >
                > > Your use of Yahoo! Groups is subject to
                http://docs.yahoo.com/info/terms/
                > >
                > >
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