DSLR backfocus

[Haggis]

First, please forgive my lack of knowledge. I have read tons of information on the internet but I'm still clueless about many things regarding astrophotography. Right now, I'm struggling with a difficult situation. At least, to me it's difficult so I was hoping an experienced imager could help me out here.

As many of you are undoubtedly aware, there are ways to turn normal DSLR camera's into monochrome camera's by removing the bayer matrix from the sensor. From what I've read so far, a modded DSLR is still not quite as sensitive and "good" as a dedicated CCD astro camera. But a peltier cooled and debayered DSLR seems like an affordable alternative and I've seen many pretty pictures taken with monochrome DSLR's.

Right now I'm using a very simple Canon EOS 1000D with Backyard EOS but since I've just upgraded from a GSO 200 to a TS ONTC12 F4 Newtonian telescope with 3 inch JMI focuser and 3 inch 0.95x Wynne Corrector, I have to start looking for a more serious camera, preferably 35mm, to get the most from it. So I was wondering... maybe save money for a few months and buy a used Canon 5D MK2, have it modded with a JTW ice cube system and have it "debayered" (total cost about 2000 - 2500 euro) or save money for twice as long and go for a Moravian G3-11000FW or something equally nice?

In case of going for a modded 5D MK2 I'm stuck with a dillema. The 0.95x Wynne corrector requires a distance of about 58mm from surface to chip. Right now, I'm using a short TS extension piece to put my DSLR in the correct focusposition (Wynne corrector -> short extension adapter -> T-Ring -> DSLR). But if I put a filterwheel between the corrector and the DSLR, won't the distance be too far even with the extension adapter removed? Is there a way to adjust the backfocus of a Canon camera or would I simply be better off with a CCD camera with filterwheel?

[Tinker1947]

I think spending that sort of money on a converted DSLR, you would be better off buying a dedicated CCD....also there more back focus than a DSLR..

[lensman57]

First, please forgive my lack of knowledge. I have read tons of information on the internet but I'm still clueless about many things regarding astrophotography. Right now, I'm struggling with a difficult situation. At least, to me it's difficult so I was hoping an experienced imager could help me out here.

As many of you are undoubtedly aware, there are ways to turn normal DSLR camera's into monochrome camera's by removing the bayer matrix from the sensor. From what I've read so far, a modded DSLR is still not quite as sensitive and "good" as a dedicated CCD astro camera. But a peltier cooled and debayered DSLR seems like an affordable alternative and I've seen many pretty pictures taken with monochrome DSLR's.

Right now I'm using a very simple Canon EOS 1000D with Backyard EOS but since I've just upgraded from a GSO 200 to a TS ONTC12 F4 Newtonian telescope with 3 inch JMI focuser and 3 inch 0.95x Wynne Corrector, I have to start looking for a more serious camera, preferably 35mm, to get the most from it. So I was wondering... maybe save money for a few months and buy a used Canon 5D MK2, have it modded with a JTW ice cube system and have it "debayered" (total cost about 2000 - 2500 euro) or save money for twice as long and go for a Moravian G3-11000FW or something equally nice?

In case of going for a modded 5D MK2 I'm stuck with a dillema. The 0.95x Wynne corrector requires a distance of about 58mm from surface to chip. Right now, I'm using a short TS extension piece to put my DSLR in the correct focusposition (Wynne corrector -> short extension adapter -> T-Ring -> DSLR). But if I put a filterwheel between the corrector and the DSLR, won't the distance be too far even with the extension adapter removed? Is there a way to adjust the backfocus of a Canon camera or would I simply be better off with a CCD camera with filterwheel?

Hi,

Spending £1000.00 +on a used MKii and then a similar amount of money for the ice box, and some more for the mods, then you end up with a camera that is half baked . Save your money for a bit longer and go for a proper cooled CCD. An Atik 11000 is about £3900..00 . This will also give you time to research what it is exactly you want to do and what is required to achieve it. You must also make sure that your new scope and reducer can actually cover a flat coma free field of at least 44 mm diameter to cover the 35mm sensor field.

Regards,

A.G

[Haggis]

Thanks for the advice! I agree that it may be better to save money for a good CCD camera. I'm pretty sure my new ONTC telescope is up to the job. I went with the 3 inch focuser and Wynne corrector for that reason. According to the specs, the Wynne gives a 50mm corrected field. I think I'll save money for an Atik 11000 or other KAF 11000 based CCD then. In the mean time, it stinks to have a great telescope and a lousy camera  .

[lensman57]

Thanks for the advice! I agree that it may be better to save money for a good CCD camera. I'm pretty sure my new ONTC telescope is up to the job. I went with the 3 inch focuser and Wynne corrector for that reason. According to the specs, the Wynne gives a 50mm corrected field. I think I'll save money for an Atik 11000 or other KAF 11000 based CCD then. In the mean time, it stinks to have a great telescope and a lousy camera  .

The scope is now fast enough so you can both lower the exposure time and decrease the ISO to reduce the noise of the 1000 d. This will also give you the opportunity to test the set up on starfields and fine tune for any orthogonality issues. A large format chip is highly unforgiving of the slightest misalignment or collimation errors. You may also decide that a smaller but very sensitive chip such  as the ICX 694 is sufficient from a FOV point of view for your intended targets which may be small galaxies. Good luck.

A.G

[Haggis]

To get started with my new telescope I have decided that for now I will be using a non-modded 5D MK2 and maybe in the future I will buy a dedicated CCD camera. I just bought a used 5D MK2 body with only 9000 clicks for 850 Euro's so it was a bargain that I couldn't resist. I haven't tried it yet on my new ONTC telescope but I hope it won't cause any problems with vignetting. I may have to swap my T2 connector for a M48 to EOS connector though.

Thanks again for the advice everybody.

[lensman57]

To get started with my new telescope I have decided that for now I will be using a non-modded 5D MK2 and maybe in the future I will buy a dedicated CCD camera. I just bought a used 5D MK2 body with only 9000 clicks for 850 Euro's so it was a bargain that I couldn't resist. I haven't tried it yet on my new ONTC telescope but I hope it won't cause any problems with vignetting. I may have to swap my T2 connector for a M48 to EOS connector though.

Thanks again for the advice everybody.

Excellent buy, look forward to seeing the images produced by that combination.

A.G

[Haggis]

Well, I'm back to where I started. Apparently, the deal was too good to be true because the seller told me he accidentaly dropped the camera while preparing to send it to me. According to him it's probably damaged beyond repair so the deal's off. I personally think he got himself a better deal with another interested buyer but I'll give him the benefit of the doubt.

But maybe I'm fortunate I didn't get the camera. It seems the combination fast Newtonian + 0.95x Wynne corrector and full frame EOS gives heavy vignetting because of the mirror box. I read this on CN forums, 2 users have tried it. One has an ASA newt + 5D MK2 and the other one has a self made newt + a Canon 6D. Both had fairly large black bars around the entire image. That's too bad! Full frame imaging is the main reason I bought this telescope. I just hope I don't get these problems with a dedicated CCD camera like the ATIK 11000 or Moravian G3-11000. I wish I could try before I buy.

At least I now know that a full frame DSLR is not an option.