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Which OTAs can give good corner stars with a Canon 6D?

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16 replies to this topic

#1 Henry from NZ

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Posted 12 July 2019 - 05:01 AM

I am very close to pulling the trigger to buy a second hand 6D.

However I am not sure if all my OTAs would support the full frame?

If the majority of them would support full frame, I think this would be a good investment.

If the majority do not, I guess there are more economical APS-C size alternatives which may actually be better in terms of image quality e.g. Nikon D5300.

So before I invest the $$ on a full frame camera, I would like to see some sample images from 6D using the following OTAs in particular:

 

1. Tak FS60CB with reducer

2. Tak FS60CB with flattener

3. Astrophysics 130GT with flattener

4. Astrophysics 130GT with reducer

5. Tak e130D

6. 8" EdgeHD with reducer

7. 8" EdgeHD at native f/10

 

Would appreciate any real life experience.

 

PS - I do know about and have seen spot diagrams and the image circle specs of my scopes, but the technical specifications and spot diagrams do not always reflect real life.


Edited by Henry from NZ, 12 July 2019 - 05:04 AM.


#2 Ishtim

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Posted 12 July 2019 - 06:13 AM

I think you could answer many of your questions (from an image standpoint) using Astrobin and applying the proper filters to a search. 

https://www.astrobin.../search/?d=i&q=



#3 Henry from NZ

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Posted 12 July 2019 - 06:16 AM

I tried Astrobin but the problems are: 1. The search function is rather limited and 2. I cannot tell how much of the images have been cropped.

#4 sg6

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Posted 12 July 2019 - 07:52 AM

From reading and assorted aspects I would say very few support a full frame right to the edges/corners.

Somewhere in all the blurb will be a clause saying something like 95% or flat within x%.

 

From the DSLR side I recall that to get a good flat field on an aps sensor the advice was buy a lens that handles a full frame and use it on an aps sensor. The central part is then really flat and the not so flat bits are not on the sensor so don't count. Really good advice.

 

I seriously suspect that a flat field on a full frame means get an imaging circle that is "flat" for a size about 1.4 to 1.5 times greater.

 

If you select a system that sort of just scraps in the "full frame" dimension, 43.3mm dia circle, I do not think the result will be a flat full frame image. A flat image circle of 50mm might, just do not expect to find any that produce such.


Edited by sg6, 12 July 2019 - 07:53 AM.


#5 maxmir

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Posted 12 July 2019 - 08:18 AM

I tried Astrobin but the problems are: 1. The search function is rather limited and 2. I cannot tell how much of the images have been cropped.

Yes, you can tell how much is cropped.

Compare the FOV plate solution in Astrobin with the CCD calculator FOV for the scope/camera combo.



#6 Henry from NZ

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Posted 12 July 2019 - 05:13 PM

To answer my question in part, I have checked Astrobin:

 

e130D definitely support full frame

 

Samyang 135 almost cover full frame

 

Still on the search for the others



#7 bnickeson

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Posted 12 July 2019 - 08:09 PM

The 8" Edge with reducer won't and I doubt it will at its native f/10 either.  While it would probably have a flat field, you'd get such severe vignetting that it wouldn't matter.  I just bought an 8" Edge and got an astro camera with a APS-C chip for this very reason.

 

For my 6D, I have a Stellarvue 102mm f/7 that has a quite flat field out to the corners.  It's not perfect but it does a decent job.  I would expect most other 4"+ refractors with at least a 2.5" or 3" focuser and a field flattener would work well for a full frame camera.



#8 whwang

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Posted 12 July 2019 - 09:22 PM

The problem of E130D is not whether the design supports FF.  Rather, it's whether the user can maintain the collimation.  It's hyper sensitive.  So be careful.


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#9 jeff.bottman

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Posted 12 July 2019 - 09:30 PM

Astro-Tech AT65EDQ covers full frame with good stars. Not super fast at f/6.5, but also not super expensive.

#10 rockstarbill

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Posted 14 July 2019 - 07:05 PM

The AP130 GTX can cover a full frame with both the flattener and reducer. It's image circles are 65mm and 50mm respectively.

#11 Henry from NZ

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Posted 15 July 2019 - 02:07 AM

I do not have a GTX but the older GT. I am pretty sure the Flattener will cover full frame no problem. The reducer is just the 27TVPH which is not as good as the quad reducer. So it may not cover full frame. I don’t know for sure.

#12 Samir Kharusi

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Posted 15 July 2019 - 02:50 AM

In my limited experience with different OTAs I have come to the conclusion that IF the manufacturer advertises that it will cover a full 35mm format then it will. If the manufacturer does not claim that in his ads, e.g. when using a reducer or not, then it will not. It is so expensive to make an OTA that does cover a full 35mm format that no manufacturer will miss it out of his adverts. Just hoping that the OTA will isfalse hope. E.g. just go carefully through the adverts/specs by Tak. No such claim for a specific OTA? It will not. The ones that do will be shouted about.


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#13 AtmosFearIC

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Posted 16 July 2019 - 07:30 AM

In my limited experience with different OTAs I have come to the conclusion that IF the manufacturer advertises that it will cover a full 35mm format then it will. If the manufacturer does not claim that in his ads, e.g. when using a reducer or not, then it will not. It is so expensive to make an OTA that does cover a full 35mm format that no manufacturer will miss it out of his adverts. Just hoping that the OTA will isfalse hope. E.g. just go carefully through the adverts/specs by Tak. No such claim for a specific OTA? It will not. The ones that do will be shouted about.

There is different levels of acceptability though. I have a Zeiss 50mm F/1.4 Milvus that covers full frame and for daylight photography works fine but at the extreme edges it's HORRID. Crop the full frame into a square format at F/2.8 and it looks very good but that last but into the extreme corners is very poorly corrected.

 

Is the Milvus 50mm corrected for full frame? Yes. I'd say very well corrected out to about 18-20mm off-axis but the extreme corners on a Nikon D810 require cropping. On a Canon 6D with it's anti-aliasing filter and larger pixels? It may very well be acceptable remembering that the older 12-16 megapixel cameras are no where near as demanding as the newer 36-50mp cameras.


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#14 calypsob

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Posted 16 July 2019 - 02:19 PM

I am very close to pulling the trigger to buy a second hand 6D.

However I am not sure if all my OTAs would support the full frame?

If the majority of them would support full frame, I think this would be a good investment.

If the majority do not, I guess there are more economical APS-C size alternatives which may actually be better in terms of image quality e.g. Nikon D5300.

So before I invest the $$ on a full frame camera, I would like to see some sample images from 6D using the following OTAs in particular:

 

1. Tak FS60CB with reducer

2. Tak FS60CB with flattener

3. Astrophysics 130GT with flattener

4. Astrophysics 130GT with reducer

5. Tak e130D

6. 8" EdgeHD with reducer

7. 8" EdgeHD at native f/10

 

Would appreciate any real life experience.

 

PS - I do know about and have seen spot diagrams and the image circle specs of my scopes, but the technical specifications and spot diagrams do not always reflect real life.

the sharpstar 150 f2.8 was designed for full frame, a bit more bang for the buck than an epsilon.



#15 Henry from NZ

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Posted 16 July 2019 - 02:21 PM

Thanks for the OTA suggestions, but those are the OTAs I already have.

#16 calypsob

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Posted 16 July 2019 - 09:54 PM

Thanks for the OTA suggestions, but those are the OTAs I already have.


My bad lol. In that case I think of the epsilon takes the cake. I have seen firsthand the combination of a 6D and 130D and the light gathering power was phenomonal.

#17 t-ara-fan

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Posted 16 July 2019 - 10:51 PM

The original 6D is a very good camera. Even if the corners are not perfect, personally I don't care.  I rarely use the full frame anyway.  I crop a lot of images to 1000x1000 or 2000x2000 for looking at on a computer. 




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