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Choosing a coma corrector for 8" f/4 telescope?


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Hello

I have a Telescope Service newtonian 8" f/4 telescope and I have a DSLR camera with a 36x24 mm sensor. And I need a coma corrector, I have looked at the Skywatcher f4 Aplanatic Coma Corrector and I think it is good with a M48 thread to the camera.

The sensors diagonal is 43,3 mm is a M48 thread to narrow for my camera? If I screw the corrector into the M48 thread, I guess the opening would be something about ~45 mm?

Any suggestions about which corrector that I should buy? Ofcourse I want the best optical correction. I have borrowed a MPCC Mk II from a friend but I don't want that with a small T-thread (M42) it does not work so good on my scope, it is made for f/4,5 and I have f/4 and it is also to narrow with that T-ring.

Any ideas?

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Oh it was M48 thread, I saw it on another web shop and it was only a T2 thread there, maybe it was an older one or wrong text.

Why is the Aplanatic one much more expensive than this one? Is it better or the same?

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no idea of the differences. I cannot really help with imaging applications as I am solely a visual astronomer. adding a single baader ring (28mm) between corrector and the visual top means that I have the correct spacing for eyepieces too. will be interesting to see the visual images cf the paracorr.

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I understand what you mean, the only thing I want to do with my 8" f/4 telescope is astroimaging with my DSLR (or a cooled CCD if I buy one in the future). I have a much better scope for visual and planeteray use, its a Cave Astrola Deluxe B 8" f/8 that is outstanding for everything except deep sky imaging with a DSLR.

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Hello

It seems like the ASA 2 0,77 corrector only can 22 mm field.

http://shop.textalk.se/en/article.php?id=19067&art=18083982

In the text here I think the GPU Aplanatic corrector is the best one. It covers a full frame view, I know it could be some vignetting but maybe it could be corrected with flats and a little crop of the image.

http://shop.textalk.se/en/article.php?id=19067&art=20214199

I saw some very interesting comparision here! And I think it could help many people to choose the right correcotor.

http://www.teleskop-austria.at/shop/index.php?lng=de&m=2&kod=bar2-kom-kor-4

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Hello

It seems like the ASA 2 0,77 corrector only can 22 mm field.

http://shop.textalk.se/en/article.php?id=19067&art=18083982

In the text here I think the GPU Aplanatic corrector is the best one. It covers a full frame view, I know it could be some vignetting but maybe it could be corrected with flats and a little crop of the image.

http://shop.textalk.se/en/article.php?id=19067&art=20214199

Tjena Stoffe!

On the ASA homepage there are three 2" coma correctors. The one with the largest field is the Quattro x1.175 with a 30mm field (specs @ http://www.astrosysteme.at/images/Corr_2Zoll_ComaCorr.pdf) that can be extended to 40mm with some vignetting and a minor loss in performance. For optimal performance on 36x24 mm chips 2" is just a little to small but then again so is the secondary mirror on you scope. ;)  

/Patrik

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Tack Patrik! (we are both Swedes and are IRL friends)

The ASA for 550€ looks really nice but of course, expensive. I think with a magnification of 1,175x it would reach focus on my scope without any problems. Actually it would cost more the my telescope :) I can change my secondary mirror as well, it is a 63 mm mirror.

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I just saw that 550€ is without VAT and shipping. To bad, it would be nice with that corrector. But I still wonder what the difference is between the ASA corr and the Skywatcher (GPU) corr. Both are 4-element designs and correct the field very good.

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I also saw this thread about the Aplanatic corrector, but I haven't found anyone that have acctually bought it and used it?

Btw, 55 mm backfocus, is that to tight if I want to upgrade to a dediceded CCD with filterwheel and offaxis guider?

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