Loading ...
Sorry, an error occurred while loading the content.

GTF81 focal length

Expand Messages
  • dan_kordella
    Hello - I m new to the group here. I ve been an enthusiastic amateur for a long time, but in the past year and a half have become an addicted astrophotographer
    Message 1 of 18 , Oct 3, 2013
    View Source
    • 0 Attachment
      Hello - I'm new to the group here. 

      I've been an enthusiastic amateur for a long time, but in the past year and a half have become an addicted astrophotographer and have gone as "all-in" as my budget will allow. 

      I recently purchased a GTF81 from Agena to be my main imaging scope, to go with my Atik 383l+ monochrome camera.

      While the scope is beautifully made (I have never owned a scope with this caliber of craftsmanship), I have gotten some odd results from imaging that concern me.

      I use Ron Wodalski's CCD calculator and figured that based on the stated specs of the telescope (478mm focal length, f/5.9 optics) I should get an image scale of about 2.33 arcsec/pixel.

      I've done some imaging, and immediately noticed that not only is it a bit more challenging to guide this telescope because of the weight, my images seemed to have been a bit grainier, as if the signal-to-noise ratio isn't great (up until recently I had been using a Stellarvue scope working at f/5.6 - should not be a dramatic difference to f/5.9!). 

      When I plate-solve my images, I find I get an image scale of 2.05 arcsec/pixel, which corresponds to ~550 mm focal length and f/6.7!

      Has anyone else gotten similarly odd results with this scope? 

      Thanks,

      Dan 
    • sberrada_99
      Yes you are correct I get 553mm using single sub measured from astrometry.net That is quite a difference to F6.8 vs F5.9 ... Hello - I m new to the group here.
      Message 2 of 18 , Oct 12, 2013
      View Source
      • 0 Attachment

        Yes you are correct

        I get 553mm using single sub measured from astrometry.net

        That is quite a difference to F6.8 vs F5.9 



        ---In William-Optics@yahoogroups.com, <william-optics@yahoogroups.com> wrote:

        Hello - I'm new to the group here. 

        I've been an enthusiastic amateur for a long time, but in the past year and a half have become an addicted astrophotographer and have gone as "all-in" as my budget will allow. 

        I recently purchased a GTF81 from Agena to be my main imaging scope, to go with my Atik 383l+ monochrome camera.

        While the scope is beautifully made (I have never owned a scope with this caliber of craftsmanship), I have gotten some odd results from imaging that concern me.

        I use Ron Wodalski's CCD calculator and figured that based on the stated specs of the telescope (478mm focal length, f/5.9 optics) I should get an image scale of about 2.33 arcsec/pixel.

        I've done some imaging, and immediately noticed that not only is it a bit more challenging to guide this telescope because of the weight, my images seemed to have been a bit grainier, as if the signal-to-noise ratio isn't great (up until recently I had been using a Stellarvue scope working at f/5.6 - should not be a dramatic difference to f/5.9!). 

        When I plate-solve my images, I find I get an image scale of 2.05 arcsec/pixel, which corresponds to ~550 mm focal length and f/6.7!

        Has anyone else gotten similarly odd results with this scope? 

        Thanks,

        Dan 
      • sberrada_99
        YES YOU ARE CORRECT. As an owner of the GTF81 which has a specification of F5.9 (478mm FL) Overall it is a good telescope with sharp images edge to edge.
        Message 3 of 18 , Oct 12, 2013
        View Source
        • 0 Attachment

          YES YOU ARE CORRECT.

          As an owner of the GTF81 which has a specification of F5.9 (478mm FL)

           

          Overall it is a good telescope with sharp images edge to edge.

           

          However the first time I used it, I was a little surprised that the images looked bigger than my previous ES80 (480mm) but never thought much of it.

           

          When I saw your email, I did the following verification\;

          - I took a single sub and ran it in astrometry.net

          - This gave me a FOV of 1.57 x 2.35 degrees

          - When I convert for the sensor I get a FL of 553mm, which equates to F6.8

          fl =(  SensorSize/2) * tan( FOV/2)

          fl = (22.3/2)*tan-(2.35/2) = 553mm

           

          I have a friend who took the same DSO with a new Esprit 80mm F5; and to revalidate, I measured the relative distance between 2 stars and came up with a ratio of 1.35... which again leads me to F6.7.

           

          So we should be asking the builder / designer why that is ?

           

          This makes a difference of 30 percent on a single sub exposure, to get the same light intensity.... this means that subs need to be 8 min (at F6.8) long instead of 6 min (at F5.9) for the same result

           

          Thanks,
          Sam

           

          ---In William-Optics@yahoogroups.com, <william-optics@yahoogroups.com> wrote:

          Hello - I'm new to the group here. 

          I've been an enthusiastic amateur for a long time, but in the past year and a half have become an addicted astrophotographer and have gone as "all-in" as my budget will allow. 

          I recently purchased a GTF81 from Agena to be my main imaging scope, to go with my Atik 383l+ monochrome camera.

          While the scope is beautifully made (I have never owned a scope with this caliber of craftsmanship), I have gotten some odd results from imaging that concern me.

          I use Ron Wodalski's CCD calculator and figured that based on the stated specs of the telescope (478mm focal length, f/5.9 optics) I should get an image scale of about 2.33 arcsec/pixel.

          I've done some imaging, and immediately noticed that not only is it a bit more challenging to guide this telescope because of the weight, my images seemed to have been a bit grainier, as if the signal-to-noise ratio isn't great (up until recently I had been using a Stellarvue scope working at f/5.6 - should not be a dramatic difference to f/5.9!). 

          When I plate-solve my images, I find I get an image scale of 2.05 arcsec/pixel, which corresponds to ~550 mm focal length and f/6.7!

          Has anyone else gotten similarly odd results with this scope? 

          Thanks,

          Dan 
        • Dan Kordella
          Thanks - so I know I m not crazy :) I ended up returning the scope. I bought it because of the additional flattener. It seems kind of absurd to add a focal
          Message 4 of 18 , Oct 13, 2013
          View Source
          • 0 Attachment
            Thanks - so I know I'm not crazy :)

            I ended up returning the scope. I bought it because of the additional flattener. It seems kind of absurd to add a focal reducer/flattener to a scope that already has the flattener built in. I hope WO gets this thing worked out because it really is a beautifully made scope. I know of a couple other people that have returned this scope very soon after buying it. 

            I ended up going with an Explore Scientific 80mm instead...

            Dan


            On Sat, Oct 12, 2013 at 10:12 PM, <sberrada99@...> wrote:
             

            Yes you are correct

            I get 553mm using single sub measured from astrometry.net

            That is quite a difference to F6.8 vs F5.9 



            ---In William-Optics@yahoogroups.com, <william-optics@yahoogroups.com> wrote:

            Hello - I'm new to the group here. 

            I've been an enthusiastic amateur for a long time, but in the past year and a half have become an addicted astrophotographer and have gone as "all-in" as my budget will allow. 

            I recently purchased a GTF81 from Agena to be my main imaging scope, to go with my Atik 383l+ monochrome camera.

            While the scope is beautifully made (I have never owned a scope with this caliber of craftsmanship), I have gotten some odd results from imaging that concern me.

            I use Ron Wodalski's CCD calculator and figured that based on the stated specs of the telescope (478mm focal length, f/5.9 optics) I should get an image scale of about 2.33 arcsec/pixel.

            I've done some imaging, and immediately noticed that not only is it a bit more challenging to guide this telescope because of the weight, my images seemed to have been a bit grainier, as if the signal-to-noise ratio isn't great (up until recently I had been using a Stellarvue scope working at f/5.6 - should not be a dramatic difference to f/5.9!). 

            When I plate-solve my images, I find I get an image scale of 2.05 arcsec/pixel, which corresponds to ~550 mm focal length and f/6.7!

            Has anyone else gotten similarly odd results with this scope? 

            Thanks,

            Dan 


          • timm_bottoni
            Hi all, I emailed William directly and he is Taiwan right now working on production of new scopes. He is working with the optical designers and optical
            Message 5 of 18 , Oct 14, 2013
            View Source
            • 0 Attachment

              Hi all,


              I emailed William directly and he is Taiwan right now working on production of new scopes.   He is working with the optical designers and optical manufacturers to figure out where the discrepancy occurs, and he will reply as soon as he cans but it seems like the field flattener is actually lengthening the focal length of the original optics by as much as 10%.


              I suggested to him that he post a full reply for anyone interested, and for anyone who might be unhappy to contact him.


              As for me, I'm really pleased with the GTF102, and even though it may have a slightly longer focal length than specified, it has amazing optics, flat across the entire field.   Most of the objects I have imaged (or tried) actually benefit from more magnification, but I'm in really light polluted skies, and not really able to image the large fainter nebulae anyway.  I can see why some might want a shorter focal length if you want to image things that won't fit in your camera chip.  I know I can't fit the Andromeda Galaxy in mine now, but that is about the only thing that I can think of that is just too big.


              For those new to photography, or astrophotography, don't think of the focal ratio as being "faster" like a camera lens, it isn't.  The real light gathering ability is based on the aperture of the front lens, the focal ratio is just a ratio.  What matters is how big the object is you want to image, and how long the focal length is.  There are some really good calculators online, or built into some of the programs like SkySafari Plus, that I use on my table.  They will show you exactly how the image scale looks relative to your scope and camera chip size.


              Hope that helps,


              Timm



              ---In William-Optics@yahoogroups.com, <william-optics@yahoogroups.com> wrote:

              Thanks - so I know I'm not crazy :)

              I ended up returning the scope. I bought it because of the additional flattener. It seems kind of absurd to add a focal reducer/flattener to a scope that already has the flattener built in. I hope WO gets this thing worked out because it really is a beautifully made scope. I know of a couple other people that have returned this scope very soon after buying it. 

              I ended up going with an Explore Scientific 80mm instead...

              Dan


              On Sat, Oct 12, 2013 at 10:12 PM, <sberrada99@...> wrote:
               

              Yes you are correct

              I get 553mm using single sub measured from astrometry.net

              That is quite a difference to F6.8 vs F5.9 



              ---In William-Optics@yahoogroups.com, <william-optics@yahoogroups.com> wrote:

              Hello - I'm new to the group here. 

              I've been an enthusiastic amateur for a long time, but in the past year and a half have become an addicted astrophotographer and have gone as "all-in" as my budget will allow. 

              I recently purchased a GTF81 from Agena to be my main imaging scope, to go with my Atik 383l+ monochrome camera.

              While the scope is beautifully made (I have never owned a scope with this caliber of craftsmanship), I have gotten some odd results from imaging that concern me.

              I use Ron Wodalski's CCD calculator and figured that based on the stated specs of the telescope (478mm focal length, f/5.9 optics) I should get an image scale of about 2.33 arcsec/pixel.

              I've done some imaging, and immediately noticed that not only is it a bit more challenging to guide this telescope because of the weight, my images seemed to have been a bit grainier, as if the signal-to-noise ratio isn't great (up until recently I had been using a Stellarvue scope working at f/5.6 - should not be a dramatic difference to f/5.9!). 

              When I plate-solve my images, I find I get an image scale of 2.05 arcsec/pixel, which corresponds to ~550 mm focal length and f/6.7!

              Has anyone else gotten similarly odd results with this scope? 

              Thanks,

              Dan 

            • bee_em_oh
              Any reply from the manufacturer on this topic yet ? Will the effective FL of the GTF102 be affected by this as well ?
              Message 6 of 18 , Nov 11, 2013
              View Source
              • 0 Attachment
                Any reply from the manufacturer on this topic yet ? Will the effective FL of the GTF102 be affected by this as well ?

                --- In William-Optics@yahoogroups.com, <t.bottoni@...> wrote:
                >
                > Hi all,
                >
                >
                > I emailed William directly and he is Taiwan right now working on production of new scopes. He is working with the optical designers and optical manufacturers to figure out where the discrepancy occurs, and he will reply as soon as he cans but it seems like the field flattener is actually lengthening the focal length of the original optics by as much as 10%.
                >
                >
                >
                > I suggested to him that he post a full reply for anyone interested, and for anyone who might be unhappy to contact him.
                >
                >
                > As for me, I'm really pleased with the GTF102, and even though it may have a slightly longer focal length than specified, it has amazing optics, flat across the entire field. Most of the objects I have imaged (or tried) actually benefit from more magnification, but I'm in really light polluted skies, and not really able to image the large fainter nebulae anyway. I can see why some might want a shorter focal length if you want to image things that won't fit in your camera chip. I know I can't fit the Andromeda Galaxy in mine now, but that is about the only thing that I can think of that is just too big.
                >
                >
                >
                > For those new to photography, or astrophotography, don't think of the focal ratio as being "faster" like a camera lens, it isn't. The real light gathering ability is based on the aperture of the front lens, the focal ratio is just a ratio. What matters is how big the object is you want to image, and how long the focal length is. There are some really good calculators online, or built into some of the programs like SkySafari Plus, that I use on my table. They will show you exactly how the image scale looks relative to your scope and camera chip size.
                >
                >
                >
                > Hope that helps,
                >
                >
                > Timm
                >
                >
                >
                > ---In William-Optics@yahoogroups.com, <william-optics@yahoogroups.com> wrote:
                >
                > Thanks - so I know I'm not crazy :)
                >
                > I ended up returning the scope. I bought it because of the additional flattener. It seems kind of absurd to add a focal reducer/flattener to a scope that already has the flattener built in. I hope WO gets this thing worked out because it really is a beautifully made scope. I know of a couple other people that have returned this scope very soon after buying it.
                >
                >
                > I ended up going with an Explore Scientific 80mm instead...
                >
                >
                > Dan
                >
                >
                >
                > On Sat, Oct 12, 2013 at 10:12 PM, <sberrada99@... mailto:sberrada99@...> wrote:
                > Yes you are correct
                > I get 553mm using single sub measured from astrometry.net http://astrometry.net
                > That is quite a difference to F6.8 vs F5.9
                >
                >
                > ---In William-Optics@yahoogroups.com mailto:William-Optics@yahoogroups.com, <william-optics@yahoogroups.com mailto:william-optics@yahoogroups.com> wrote:
                >
                > Hello - I'm new to the group here.
                >
                > I've been an enthusiastic amateur for a long time, but in the past year and a half have become an addicted astrophotographer and have gone as "all-in" as my budget will allow.
                >
                >
                > I recently purchased a GTF81 from Agena to be my main imaging scope, to go with my Atik 383l+ monochrome camera.
                >
                > While the scope is beautifully made (I have never owned a scope with this caliber of craftsmanship), I have gotten some odd results from imaging that concern me.
                >
                >
                > I use Ron Wodalski's CCD calculator and figured that based on the stated specs of the telescope (478mm focal length, f/5.9 optics) I should get an image scale of about 2.33 arcsec/pixel.
                >
                >
                > I've done some imaging, and immediately noticed that not only is it a bit more challenging to guide this telescope because of the weight, my images seemed to have been a bit grainier, as if the signal-to-noise ratio isn't great (up until recently I had been using a Stellarvue scope working at f/5.6 - should not be a dramatic difference to f/5.9!).
                >
                >
                > When I plate-solve my images, I find I get an image scale of 2.05 arcsec/pixel, which corresponds to ~550 mm focal length and f/6.7!
                >
                >
                > Has anyone else gotten similarly odd results with this scope?
                >
                >
                > Thanks,
                >
                >
                > Dan
                >
              • timm_bottoni
                Yes, sorry, I forgot to post an update on this. Weeks ago William updated the specifications on the WO website to reflect the corrections here for the GTF102
                Message 7 of 18 , Nov 11, 2013
                View Source
                • 0 Attachment

                  Yes, sorry, I forgot to post an update on this.  Weeks ago William updated the specifications on the WO website to reflect the corrections here for the GTF102

                  http://www.williamoptics.com/telescopes/gtf102ddg_spec.php


                  And here for the GTF81

                  http://www.williamoptics.com/telescopes/gtf81_spec.php


                  The optical triplet specs are correct on the lens cell, and the flatterner isn't a reducer, but actually lengthens the focal length.   William also mentioned that it could be possible to remove the built in flattener and instead use a flattener/reducer at the focuser.  I'm fine with mine the way it is for both visual and photographic use, but I would be happy to test this if William wants me to.


                  Removing the flattener would be a simple matter of unscrewing it from the built in holder.  


                  Timm

                   



                  ---In William-Optics@yahoogroups.com, <bamark@...> wrote:

                  Any reply from the manufacturer on this topic yet ? Will the effective FL of the GTF102 be affected by this as well ?

                  --- In William-Optics@yahoogroups.com, <t.bottoni@...> wrote:
                  >
                  > Hi all,
                  >
                  >
                  > I emailed William directly and he is Taiwan right now working on production of new scopes. He is working with the optical designers and optical manufacturers to figure out where the discrepancy occurs, and he will reply as soon as he cans but it seems like the field flattener is actually lengthening the focal length of the original optics by as much as 10%.
                  >
                  >
                  >
                  > I suggested to him that he post a full reply for anyone interested, and for anyone who might be unhappy to contact him.
                  >
                  >
                  > As for me, I'm really pleased with the GTF102, and even though it may have a slightly longer focal length than specified, it has amazing optics, flat across the entire field. Most of the objects I have imaged (or tried) actually benefit from more magnification, but I'm in really light polluted skies, and not really able to image the large fainter nebulae anyway. I can see why some might want a shorter focal length if you want to image things that won't fit in your camera chip. I know I can't fit the Andromeda Galaxy in mine now, but that is about the only thing that I can think of that is just too big.
                  >
                  >
                  >
                  > For those new to photography, or astrophotography, don't think of the focal ratio as being "faster" like a camera lens, it isn't. The real light gathering ability is based on the aperture of the front lens, the focal ratio is just a ratio. What matters is how big the object is you want to image, and how long the focal length is. There are some really good calculators online, or built into some of the programs like SkySafari Plus, that I use on my table. They will show you exactly how the image scale looks relative to your scope and camera chip size.
                  >
                  >
                  >
                  > Hope that helps,
                  >
                  >
                  > Timm
                  >
                  >
                  >
                  > ---In William-Optics@yahoogroups.com, <william-optics@yahoogroups.com> wrote:
                  >
                  > Thanks - so I know I'm not crazy :)
                  >
                  > I ended up returning the scope. I bought it because of the additional flattener. It seems kind of absurd to add a focal reducer/flattener to a scope that already has the flattener built in. I hope WO gets this thing worked out because it really is a beautifully made scope. I know of a couple other people that have returned this scope very soon after buying it.
                  >
                  >
                  > I ended up going with an Explore Scientific 80mm instead...
                  >
                  >
                  > Dan
                  >
                  >
                  >
                  > On Sat, Oct 12, 2013 at 10:12 PM, <sberrada99@... mailto:sberrada99@...> wrote:
                  > Yes you are correct
                  > I get 553mm using single sub measured from astrometry.net http://astrometry.net
                  > That is quite a difference to F6.8 vs F5.9
                  >
                  >
                  > ---In William-Optics@yahoogroups.com mailto:William-Optics@yahoogroups.com, <william-optics@yahoogroups.com mailto:william-optics@yahoogroups.com> wrote:
                  >
                  > Hello - I'm new to the group here.
                  >
                  > I've been an enthusiastic amateur for a long time, but in the past year and a half have become an addicted astrophotographer and have gone as "all-in" as my budget will allow.
                  >
                  >
                  > I recently purchased a GTF81 from Agena to be my main imaging scope, to go with my Atik 383l+ monochrome camera.
                  >
                  > While the scope is beautifully made (I have never owned a scope with this caliber of craftsmanship), I have gotten some odd results from imaging that concern me.
                  >
                  >
                  > I use Ron Wodalski's CCD calculator and figured that based on the stated specs of the telescope (478mm focal length, f/5.9 optics) I should get an image scale of about 2.33 arcsec/pixel.
                  >
                  >
                  > I've done some imaging, and immediately noticed that not only is it a bit more challenging to guide this telescope because of the weight, my images seemed to have been a bit grainier, as if the signal-to-noise ratio isn't great (up until recently I had been using a Stellarvue scope working at f/5.6 - should not be a dramatic difference to f/5.9!).
                  >
                  >
                  > When I plate-solve my images, I find I get an image scale of 2.05 arcsec/pixel, which corresponds to ~550 mm focal length and f/6.7!
                  >
                  >
                  > Has anyone else gotten similarly odd results with this scope?
                  >
                  >
                  > Thanks,
                  >
                  >
                  > Dan
                  >
                • drollain
                  Timm, You always seem to say the right thing about these scopes. Because of your review on the 102GTF I purchased one. I am going marry that up to a QHY12
                  Message 8 of 18 , Dec 10, 2013
                  View Source
                  • 0 Attachment

                    Timm, 


                    You always seem to say the right thing about these scopes.  Because of your review on the 102GTF I purchased one.  I am going marry that up to a QHY12 OSC.  I believe that with the size of that chip,  I may be able to fit Andromeda corner to corner... 


                    The scope that I am getting are the ones marked f/6.9.  I am not really sure if its actually f/7.68 like the later 102GTF's I am guessing that it is.


                    Sorry,  did mean to hijack the thread...  =)


                    Kind Regards,

                    -Doug

                  • timm_bottoni
                    Hi Doug, Yes, the effective focal ratio is actually F/7.68 with a focal length of 783mm. The optical triplet is the same in both the GT102 and GTF102, but
                    Message 9 of 18 , Dec 11, 2013
                    View Source
                    • 0 Attachment

                      Hi Doug,


                      Yes, the effective focal ratio is actually F/7.68 with a focal length of 783mm.   The optical triplet is the same in both the GT102 and GTF102, but the GTF102 has the built in flattener which actually adds to the focal length.


                      I'm not familiar with the camera you have, but I have a Canon 60D (unmodified) and I tried some Andromeda shots in September that didn't turn out that good due to my light pollution, but it looks like it fits corner to corner.  If I can get out now that it's much higher in the sky I will try again.  We've have really bad weather here in Chicago so far this Winter, so I haven't been out in over a month.


                      Timm

                    • drollain
                      I thought so, even tho the scope is marked f/6.9... The QHY12 is 4610 x 3080 active pixels... with an effective area of 24mm*16.4mm... a rather large
                      Message 10 of 18 , Dec 11, 2013
                      View Source
                      • 0 Attachment

                        I thought so,  even tho the scope is marked f/6.9...  The QHY12 is 4610 x 3080 active pixels...   with an effective area of 24mm*16.4mm...  a rather large chip...  =)  


                        I really can't wait to get it and setup... However,  being that I am in Western NY the skies are not clear too often.  Here is a shot of M42 that I took with the 81GTF and QHY12.


                        http://www.astrobin.com/full/66388/0/


                        I processed it HDR in PIX so the coloring is off,  but I got a lot more detail.


                        -Doug

                      • salmanazam69
                        I am considering getting the GTF102 for pure astroimaging. I am stuck between getting this model and the GT102 but I very much like the idea of a built in
                        Message 11 of 18 , Mar 3
                        View Source
                        • 0 Attachment
                          I am considering getting the GTF102 for pure astroimaging. I am stuck between getting this model and the GT102 but I very much like the idea of a built in flattener as an external one can be problematic. I'm curious if anyone has gotten good results imaging wise with the GTF. Is the higher focal ratio a cause for concern or should I be ok? I'm using an Atik 383L monochrome for imaging. 

                          Thanks, 
                          Sal
                        • timm_bottoni
                          Hi Sal, I posted my review of the GTF102 last year. It s very good for astroimaging but I have been out only once all Winter here in Chicago. I wish I could
                          Message 12 of 18 , Mar 3
                          View Source
                          • 0 Attachment
                            Hi Sal,

                            I posted my review of the GTF102 last year.  It's very good for astroimaging but I have been out only once all Winter here in Chicago.  I wish I could have done some more. I have severe light pollution, and just got an Astonomik CLS Clip filter for my Canon 60D DSLR, 

                            What questions do you have for me?  Did you see my review?

                            If you are looking for a wider field of view, then the GT102 with the WO FLAT6A would be the better option.

                            Timm
                          • salmanazam69
                            Hi Timm, Yes, I did read your review and others like it. I am strongly considering this model since I already own the WO 80mm Megrez Triplet, so I guess I
                            Message 13 of 18 , Mar 3
                            View Source
                            • 0 Attachment
                              Hi Timm, 

                              Yes, I did read your review and others like it. I am strongly considering this model since I already own the WO 80mm Megrez Triplet, so I guess I wouldn't need the GT model. My only concern at this point is it being an F/7.7, which in the imaging world is considered slow. However, I'm hearing mixed information regarding this scope's ability to image. That's why I would like to see more images and make a judgement off that. 

                              -Sal
                            • dan_kordella
                              I use the GTF81 with an Atik 383l camera. What really cinched it for me was that it was becoming difficult to fit all the components of my optical train using
                              Message 14 of 18 , Mar 4
                              View Source
                              I use the GTF81 with an Atik 383l camera. What really cinched it for me was that it was becoming difficult to fit all the components of my optical train using a scope with an added field flattener/reducer and not search all over creation for the bits to get all the spacing right. With the GTF81 (and the GTF102) this is not at all a concern. The optics are sharp, the field is pancake-flat, and I really like the feel and strength of the focuser (I don't use the DDG version). 

                              Attached is a recent image I did using that pair.
                            • salmanazam69
                              Dan, That is a really good image. Thanks for sharing it. I am leaning more towards the GTF model now. -Sal
                              Message 15 of 18 , Mar 4
                              View Source
                              • 0 Attachment
                                Dan, 
                                That is a really good image. Thanks for sharing it. I am leaning more towards the GTF model now. 

                                -Sal
                              • timm_bottoni
                                Hi Sal, I don t think the F/7.7 is an issue for imaging unless you have a mount that can t handle the size and focal length. I m actually thinking of selling
                                Message 16 of 18 , Mar 5
                                View Source
                                • 0 Attachment

                                  Hi Sal,

                                   

                                  I don't think the F/7.7 is an issue for imaging unless you have a mount that can't handle the size and focal length.  I'm actually thinking of selling mine, and moving up to an FLT132 to be honest.   I have the iOptron iEq45 and it can handle a bigger scope, and with my light pollution here in Chicago, I think a bigger aperture combined with an Astronomik CLS EOS clip filter might be a better bet.    I just got the filter and haven't even tried it yet, and this has been the worst Winter I can remember in our area, for snow, cold, clouds so I am itching to get out and try it. 


                                  Email me if you are interested in buying my GTF102 or having you send me some of the less than perfect images (full size is quite large even in JPG) that I have saved.  I'm still very much learning AP, but I am also thinking that going bigger would allow me to do more observing.

                                   

                                  Thanks,

                                   

                                  Timm

                                • salmanazam69
                                  Hey Timm. Sent you an email. -Sal
                                  Message 17 of 18 , Mar 5
                                  View Source
                                  • 0 Attachment
                                    Hey Timm.

                                    Sent you an email.

                                    -Sal
                                  • timm_bottoni
                                    Hi Sal, Sent you an email reply Timm
                                    Message 18 of 18 , Mar 5
                                    View Source
                                    • 0 Attachment
                                      Hi Sal,

                                      Sent you an email reply

                                      Timm
                                    Your message has been successfully submitted and would be delivered to recipients shortly.