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Re: Questions on focal reducers

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  • Charles
    The link in my previous post is to the tests Michael did with an LX90. Here is a subsequent test he did with an LX200 ACF scope.
    Message 1 of 17 , Feb 22, 2013
      The link in my previous post is to the tests Michael did with an LX90. Here is a subsequent test he did with an LX200 ACF scope.
      http://www.weasner.com/lx200acf/accessory_reviews/focal_reducers.html
      So based on his experience it seems to work well.

      :)

      --- In LX200GPS@yahoogroups.com, "Charles" <charlesgriffith1@...> wrote:
      >
      > Hi Ian,
      >
      > Michael Weasner has a review he did of the Antares using an ACF scope here: http://www.weasner.com/lx90/accessory_reviews/focal_reducers.html
      >
      > So it CAN work, apparently. Also, it need not be mounted between the scope and focuser, it can be mounted to the back of the focuser if you use the SCT thread adapter that comes with the focuser. In fact, for it to work properly, getting the spacing correct between the reducer and the camera chip being critical, it'd probably HAVE to be behind the focuser. I don't know what the spacing requirement of the Antares is, but the old Meade, and the Celestron 6.3 reducers were 105mm or so. (105 is what Sky and Telescope published in an article about reducers) I'd guess the Antares is similar. Putting it in front of the focuser would likely make that spacing problematic. But the point is you shouldn't have an issue with attaching and detaching as needed.
      >
      > Clear skies,
      > Charles
      >
      > --- In LX200GPS@yahoogroups.com, Ian Roberts <itrmail2003@> wrote:
      > >
      > > I intend to acquire a focal reducer for my LX200R 8" and Canon DSLR combo.
      > >
      > >
      > > So far the Antares  F6.3 reducer seems suitable - it is "neutral" in terms of field flattening and is fine for the LX200R which has its own built-in field flattening.
      > > The disadvantage is it is SCT only and will not work with other scopes, it is also mounted between the scope and focuser so is semi-permanent in operation. Price around $90
      > >
      > > OPT has recommended the Optec Lepus 0.62.  The Optec Lepus Reducer is a four element reducer designed specifically for corrected SCTs like the Meade ACF and Celestron EdgeHD.
      > >
      > > Being 2" I believe it slides directly into the focuser, but the DSLR needs a special adapter. The combined price of reducer and adapter is $294 so its not cheap.
      > > The advantage is the easy operation - it can be removed at any time and other lens or camera elements inserted into the focuser.
      > >
      > > I see that Meade has announced a F5 reducer/flattener for the LX600/LX800 F8 scopes above 10", so I guess this will not work with my LX200R 8".
      > >
      > > Is this summation correct and is there anything else available I should consider?
      > >
      > > Thanks,
      > > Ian.
      > >
      > > [Non-text portions of this message have been removed]
      > >
      >
    • P. Clay Sherrod
      The Antares reducers are not designed for the field of the R optics. Where are you getting this neutral information and the fact that this reducer is
      Message 2 of 17 , Feb 22, 2013
        The Antares reducers are not designed for the field of the "R" optics. Where
        are you getting this "neutral" information and the fact that this reducer is
        suitable for the LX200R optics?

        Dr. Clay
        _____
        Arkansas Sky Observatories
        MPC H45 - Petit Jean Mountain South
        MPC H41 - Petit Jean Mountain
        MPC H43 - Conway West
        http://www.arksky.org/

        ----- Original Message -----
        From: "Ian Roberts" <itrmail2003@...>
        To: <LX200GPS@yahoogroups.com>
        Sent: Friday, February 22, 2013 3:02 AM
        Subject: [LX200GPS] Questions on focal reducers


        I intend to acquire a focal reducer for my LX200R 8" and Canon DSLR combo.


        So far the Antares F6.3 reducer seems suitable - it is "neutral" in terms of
        field flattening and is fine for the LX200R which has its own built-in field
        flattening.
        The disadvantage is it is SCT only and will not work with other scopes, it is
        also mounted between the scope and focuser so is semi-permanent in operation.
        Price around $90

        OPT has recommended the Optec Lepus 0.62. The Optec Lepus Reducer is a four
        element reducer designed specifically for corrected SCTs like the Meade ACF and
        Celestron EdgeHD.

        Being 2" I believe it slides directly into the focuser, but the DSLR needs a
        special adapter. The combined price of reducer and adapter is $294 so its not
        cheap.
        The advantage is the easy operation - it can be removed at any time and other
        lens or camera elements inserted into the focuser.

        I see that Meade has announced a F5 reducer/flattener for the LX600/LX800 F8
        scopes above 10", so I guess this will not work with my LX200R 8".

        Is this summation correct and is there anything else available I should
        consider?

        Thanks,
        Ian.

        [Non-text portions of this message have been removed]



        ------------------------------------

        Yahoo! Groups Links
      • Michael Weasner
        I use the Antares focal reducer a lot with my 8 LX200-ACF and a DSLR. I removed the Microfocuser a few years ago, so it is not my focus chain. ... Mike
        Message 3 of 17 , Feb 22, 2013
          I use the Antares focal reducer a lot with my 8" LX200-ACF and a DSLR. I removed the Microfocuser a few years ago, so it is not my focus chain.

          On Feb 22, 2013, at 03:50, Charles <charlesgriffith1@...> wrote:

          > The link in my previous post is to the tests Michael did with an LX90. Here is a subsequent test he did with an LX200 ACF scope.
          > http://www.weasner.com/lx200acf/accessory_reviews/focal_reducers.html
          > So based on his experience it seems to work well.


          Mike Weasner Email: mweasner@... / Twitter: @mweasner
          LX200-ACF-8" ETX-125AT ETX-105PE ETX-90RA ETX-70AT PST GPOD-XL5
          Cassiopeia Observatory: http://www.weasner.com/co
        • P. Clay Sherrod
          I would be interested in see a full frame shot of a star field using the Antares focal reducer; it is the same design as the Meade and Celestron and is really
          Message 4 of 17 , Feb 22, 2013
            I would be interested in see a full frame shot of a star field using the Antares
            focal reducer; it is the same design as the Meade and Celestron and is really
            not made for the "corrected" optics of Meade and Celestron. Other than those
            promised, but not yet produced by the manufacturers, the only one that is
            specifically designed to NOT introduce aberrations from the reducer itself is
            the OPTEC Lepus.

            Dr. Clay
            _____
            Arkansas Sky Observatories
            MPC H45 - Petit Jean Mountain South
            MPC H41 - Petit Jean Mountain
            MPC H43 - Conway West
            http://www.arksky.org/

            ----- Original Message -----
            From: "Michael Weasner" <mweasner@...>
            To: <LX200GPS@yahoogroups.com>
            Sent: Friday, February 22, 2013 7:45 AM
            Subject: Re: [LX200GPS] Re: Questions on focal reducers


            >I use the Antares focal reducer a lot with my 8" LX200-ACF and a DSLR. I
            >removed the Microfocuser a few years ago, so it is not my focus chain.
            >
            > On Feb 22, 2013, at 03:50, Charles <charlesgriffith1@...> wrote:
            >
            >> The link in my previous post is to the tests Michael did with an LX90. Here
            >> is a subsequent test he did with an LX200 ACF scope.
            >> http://www.weasner.com/lx200acf/accessory_reviews/focal_reducers.html
            >> So based on his experience it seems to work well.
            >
            >
            > Mike Weasner Email: mweasner@... / Twitter: @mweasner
            > LX200-ACF-8" ETX-125AT ETX-105PE ETX-90RA ETX-70AT PST GPOD-XL5
            > Cassiopeia Observatory: http://www.weasner.com/co
            >
            >
            >
            > ------------------------------------
            >
            > Yahoo! Groups Links
            >
            >
            >
          • grantcblair
            I echo Dr. Clay s interest. I read Mike s review pretty thoroughly but somewhere I don t seem able to grasp a good apples to apples comparison. At one point,
            Message 5 of 17 , Feb 22, 2013
              I echo Dr. Clay's interest. I read Mike's review pretty thoroughly but somewhere I don't seem able to grasp a good 'apples to apples' comparison. At one point, the Antares gives the impression of only about a 0.8x focal reduction but in other places, it seems significantly closer to 0.6. There ought to be an "ideal spacing" between the reducer and the sensor which, when coupled directly to the back of a moving-mirror scope, will yield a particular reduction. This may or may not be close to the same result yielded by the Meade or Celestron reducer under identical circumstances - the focal plane (hence prime focus image scale) is going to move when the primary mirror is moved. I'm not even sure true 'apples to apples' is possible as a comparison.

              I'd also be curious to see vignetting comaprisons between the reducers, on identical primary optical setups. This would require sharp, well-exposed, dark-subtracted fields for optimal comparison.

              Anyone up for this? :)


              Grant



              --- In LX200GPS@yahoogroups.com, "P. Clay Sherrod" <drclay@...> wrote:
              >
              > I would be interested in see a full frame shot of a star field using the Antares
              > focal reducer; it is the same design as the Meade and Celestron and is really
              > not made for the "corrected" optics of Meade and Celestron. Other than those
              > promised, but not yet produced by the manufacturers, the only one that is
              > specifically designed to NOT introduce aberrations from the reducer itself is
              > the OPTEC Lepus.
              >
              > Dr. Clay
              > _____
              > Arkansas Sky Observatories
              > MPC H45 - Petit Jean Mountain South
              > MPC H41 - Petit Jean Mountain
              > MPC H43 - Conway West
              > http://www.arksky.org/
              >
              > ----- Original Message -----
              > From: "Michael Weasner" <mweasner@...>
              > To: <LX200GPS@yahoogroups.com>
              > Sent: Friday, February 22, 2013 7:45 AM
              > Subject: Re: [LX200GPS] Re: Questions on focal reducers
              >
              >
              > >I use the Antares focal reducer a lot with my 8" LX200-ACF and a DSLR. I
              > >removed the Microfocuser a few years ago, so it is not my focus chain.
              > >
              > > On Feb 22, 2013, at 03:50, Charles <charlesgriffith1@...> wrote:
              > >
              > >> The link in my previous post is to the tests Michael did with an LX90. Here
              > >> is a subsequent test he did with an LX200 ACF scope.
              > >> http://www.weasner.com/lx200acf/accessory_reviews/focal_reducers.html
              > >> So based on his experience it seems to work well.
              > >
              > >
              > > Mike Weasner Email: mweasner@... / Twitter: @mweasner
              > > LX200-ACF-8" ETX-125AT ETX-105PE ETX-90RA ETX-70AT PST GPOD-XL5
              > > Cassiopeia Observatory: http://www.weasner.com/co
              > >
              > >
              > >
              > > ------------------------------------
              > >
              > > Yahoo! Groups Links
              > >
              > >
              > >
              >
            • Michael Weasner
              There is a little distortion at the edge with the Antares on the ACF. There is also some vignetting with the DSLR D7000. Here s an example (Virgo Galaxies
              Message 6 of 17 , Feb 22, 2013
                There is a little distortion at the edge with the Antares on the ACF. There is also some vignetting with the DSLR D7000. Here's an example (Virgo Galaxies Cluster):

                http://www.weasner.com/co/Photos/DSO_Galaxies/images/Virgo_Cluster.jpg

                When possible, I usually just crop out the edges during image processing.

                On Feb 22, 2013, at 06:58, "P. Clay Sherrod" <drclay@...> wrote:

                > I would be interested in see a full frame shot of a star field using the Antares
                > focal reducer; it is the same design as the Meade and Celestron and is really
                > not made for the "corrected" optics of Meade and Celestron.


                Mike Weasner Email: mweasner@... / Twitter: @mweasner
                "Home Page": http://www.weasner.com
                "Cassiopeia Observatory": http://www.weasner.com/co
              • P. Clay Sherrod
                That is really a nice photo Mike.....I wish that you would take some Flats to apply to the images; Your focus and resolution are excellent. I am seeing some
                Message 7 of 17 , Feb 22, 2013
                  That is really a nice photo Mike.....I wish that you would take some Flats to
                  apply to the images; Your focus and resolution are excellent. I am seeing some
                  distortion, but with this field that could easily be cropped out.

                  Dr. Clay
                  _____
                  Arkansas Sky Observatories
                  MPC H45 - Petit Jean Mountain South
                  MPC H41 - Petit Jean Mountain
                  MPC H43 - Conway West
                  http://www.arksky.org/

                  ----- Original Message -----
                  From: "Michael Weasner" <mweasner@...>
                  To: <LX200GPS@yahoogroups.com>
                  Sent: Friday, February 22, 2013 8:08 AM
                  Subject: Re: [LX200GPS] Re: Questions on focal reducers


                  > There is a little distortion at the edge with the Antares on the ACF. There
                  > is also some vignetting with the DSLR D7000. Here's an example (Virgo
                  > Galaxies Cluster):
                  >
                  > http://www.weasner.com/co/Photos/DSO_Galaxies/images/Virgo_Cluster.jpg
                  >
                  > When possible, I usually just crop out the edges during image processing.
                  >
                  > On Feb 22, 2013, at 06:58, "P. Clay Sherrod" <drclay@...> wrote:
                  >
                  >> I would be interested in see a full frame shot of a star field using the
                  >> Antares
                  >> focal reducer; it is the same design as the Meade and Celestron and is really
                  >> not made for the "corrected" optics of Meade and Celestron.
                  >
                  >
                  > Mike Weasner Email: mweasner@... / Twitter: @mweasner
                  > "Home Page": http://www.weasner.com
                  > "Cassiopeia Observatory": http://www.weasner.com/co
                  >
                  >
                  >
                  > ------------------------------------
                  >
                  > Yahoo! Groups Links
                  >
                  >
                  >
                • Michael Weasner
                  Thanks Dr. Clay. Someday I may work harder on my astrophotography. I m more a visual person at the telescope than an astrophotographer . I tend to just
                  Message 8 of 17 , Feb 22, 2013
                    Thanks Dr. Clay. Someday I may work harder on my astrophotography. I'm more a visual person at the telescope than an "astrophotographer". I tend to just "play" at doing astrophotography, but I can still get some good results with my limited imaging equipment.

                    On Feb 22, 2013, at 07:12, "P. Clay Sherrod" <drclay@...> wrote:

                    > That is really a nice photo Mike.....I wish that you would take some Flats to
                    > apply to the images; Your focus and resolution are excellent. I am seeing some
                    > distortion, but with this field that could easily be cropped out.


                    Mike Weasner Email: mweasner@... / Twitter: @mweasner
                    LX200-ACF-8" ETX-125AT ETX-105PE ETX-90RA ETX-70AT PST GPOD-XL5
                    Cassiopeia Observatory: http://www.weasner.com/co
                  • P. Clay Sherrod
                    Good results for playing around! Must be those dry, dark skies you have. Dr. Clay _____ Arkansas Sky Observatories MPC H45 - Petit Jean Mountain South MPC H41
                    Message 9 of 17 , Feb 22, 2013
                      Good results for playing around! Must be those dry, dark skies you have.

                      Dr. Clay
                      _____
                      Arkansas Sky Observatories
                      MPC H45 - Petit Jean Mountain South
                      MPC H41 - Petit Jean Mountain
                      MPC H43 - Conway West
                      http://www.arksky.org/

                      ----- Original Message -----
                      From: "Michael Weasner" <mweasner@...>
                      To: <LX200GPS@yahoogroups.com>
                      Sent: Friday, February 22, 2013 8:16 AM
                      Subject: Re: [LX200GPS] Re: Questions on focal reducers


                      > Thanks Dr. Clay. Someday I may work harder on my astrophotography. I'm more
                      > a visual person at the telescope than an "astrophotographer". I tend to just
                      > "play" at doing astrophotography, but I can still get some good results with
                      > my limited imaging equipment.
                      >
                      > On Feb 22, 2013, at 07:12, "P. Clay Sherrod" <drclay@...> wrote:
                      >
                      >> That is really a nice photo Mike.....I wish that you would take some Flats to
                      >> apply to the images; Your focus and resolution are excellent. I am seeing
                      >> some
                      >> distortion, but with this field that could easily be cropped out.
                      >
                      >
                      > Mike Weasner Email: mweasner@... / Twitter: @mweasner
                      > LX200-ACF-8" ETX-125AT ETX-105PE ETX-90RA ETX-70AT PST GPOD-XL5
                      > Cassiopeia Observatory: http://www.weasner.com/co
                      >
                      >
                      >
                      > ------------------------------------
                      >
                      > Yahoo! Groups Links
                      >
                      >
                      >
                    • Michael Weasner
                      Much appreciated. Yep, being at 4370 elevation and in southern Arizona does help! ... Mike Weasner Email: mweasner@mac.com / Twitter: @mweasner Home
                      Message 10 of 17 , Feb 22, 2013
                        Much appreciated. Yep, being at 4370' elevation and in southern Arizona does help!

                        On Feb 22, 2013, at 07:24, "P. Clay Sherrod" <drclay@...> wrote:

                        > Good results for playing around! Must be those dry, dark skies you have.


                        Mike Weasner Email: mweasner@... / Twitter: @mweasner
                        "Home Page": http://www.weasner.com
                        "Cassiopeia Observatory": http://www.weasner.com/co
                      • paul valleli
                        Ian, Whichever brand you select you will be faced with technical limitations and practical limits. Being able to change a telescope s F/ratio is a significant
                        Message 11 of 17 , Feb 22, 2013
                          Ian,
                          Whichever brand you select you will be faced with
                          technical limitations and practical limits.
                          Being able to change a telescope's F/ratio is a
                          significant advantage which few current amateurs
                          appreciate. A century ago, one would have to
                          regrind and repolish the mirrors or be satisfied
                          to just be able to change magnification with
                          different eyepieces.
                          Starman Paul


                          [Non-text portions of this message have been removed]
                        • Ian Roberts
                          Thanks for all the good advice on this thread. It was most informative. I ve decided on the Optec because Optec has left plenty of room to accommodate any CCD
                          Message 12 of 17 , Feb 23, 2013
                            Thanks for all the good advice on this thread. It was most informative.
                            I've decided on the Optec because "Optec has left plenty of room to accommodate any CCD and filter wheel combo or DSLR with room to spare!" and being standard 2" mounting there is a vague chance it might work with my Celestron refractor and Canon DSLR combo as well.

                            I did not mention the need to do astrometry, so the option of cropping distorted outer fringes of an image, OK for casual use, will probably cause astrometric reduction to fail.

                            Ian.

                            [Non-text portions of this message have been removed]
                          • John Mahony
                            ... I don t think so.  I ve always heard it is optically the same as the C or (old style) M 6.3. ... With the right adapters you can put it anywhere.  The
                            Message 13 of 17 , Feb 23, 2013
                              ----- Original Message -----

                              > From: Ian Roberts <itrmail2003@...>

                              > I intend to acquire a focal reducer for my LX200R 8" and Canon DSLR combo.

                              > So far the Antares  F6.3 reducer seems suitable - it is "neutral" in
                              > terms of field flattening

                              I don't think so.  I've always heard it is optically the same as the C or (old style) M 6.3.

                              > and is fine for the LX200R which has its own built-in
                              > field flattening.
                              > The disadvantage is it is SCT only and will not work with other scopes, it is
                              > also mounted between the scope and focuser so is semi-permanent in operation.

                              With the right adapters you can put it anywhere.  The Meade microfocuser comes with an adapter so you can put an SCT-threaded reducer (or other SCT-threaded parts) after the focuser.  Similar adapters are available elsewhere.  

                              > OPT has recommended the Optec Lepus 0.62.  The Optec Lepus Reducer is a four
                              > element reducer designed specifically for corrected SCTs like the Meade ACF and
                              > Celestron EdgeHD.
                              >
                              > Being 2" I believe it slides directly into the focuser, but the DSLR needs
                              > a special adapter. The combined price of reducer and adapter is $294 so its not
                              > cheap.
                              > The advantage is the easy operation - it can be removed at any time and other
                              > lens or camera elements inserted into the focuser.
                              >
                              > I see that Meade has announced a F5 reducer/flattener for the LX600/LX800 F8
                              > scopes above 10", so I guess this will not work with my LX200R 8".

                              It might work reasonably well, since both would use R/ACF optics.  The only diff is the f/

                              -John 
                            • John Mahony
                              ... Why would that matter? -John
                              Message 14 of 17 , Feb 23, 2013
                                ----- Original Message -----

                                > From: Ian Roberts <itrmail2003@...>

                                > I did not mention the need to do astrometry, so the option of cropping distorted 
                                > outer fringes of an image, OK for casual use, will probably cause astrometric
                                > reduction to fail.


                                Why would that matter?

                                -John
                              • paul valleli
                                Ian, There is always the possibility to photograph a standard star field, measure it, and determine the distortion as a function of field radius. Then subtract
                                Message 15 of 17 , Feb 23, 2013
                                  Ian,
                                  There is always the possibility to photograph a standard star field,
                                  measure it, and determine the distortion as a function of field
                                  radius. Then subtract the correction factors for unknown fields.
                                  A lot of extra work, of course, and each time the focal reducer
                                  is installed, it must be set to the same optical settings as for the
                                  calibration series.
                                  Another approach would be to have a lens designer calculate
                                  the telescope/reducer combination for distortion. But that is $$$$.

                                  Starman Paul


                                  [Non-text portions of this message have been removed]
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