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Using a Canon T3i with full-spectrum mod and IDAS UV/IR cut filter?

Rudy_Pohl
30 Jan, 2019 18:11
Due to the amazing generosity of a good friend I now am the happy owner of Canon T3i that has been full-spectrum modded and has an IDAS UV/IR cut filter in it to maintain focusing ability on regular photography lenses, which is what I use for AP.

All my gear up until now has been Nikon and I have been using an unmodded Nikon D5500 for astrophotography with a Nikon 300/F4 ED IS lens as my main DSO optic. I have just purchased a recommended, good quality Nikon F-mount to Canon EOS lens adapter so I can use my Nikon lenses on the T3i. Here's hoping that it will work out well.

QUESTIONS:
  1. How should I acquire Ha-rich images with my modded T3i so I can add them to my RGB images taken with my stock Nikon D5500? Should I simply take the Ha images with the modded T3i as it is, or should I additionally add some kind of special Ha filter to to it as well, and if so, which filter?
  2. Sould I expect bloated stars?
  3. Can I do narrowband astrophotography with this T3i, and if so, how do I do that and what filters, holders, adapters should I get? There is already a clip-in filter in the camera body enabling focusing so I presume any additional filter must be somehow be screwed onto the front of the lens. As you can see, I really don't know very much about this kind of stuff.
Thanks very much for your help.
Best regards,
Rudy
dciobota
31 Jan, 2019 17:55
Hi Rudy and congrats!

Now, I'm not a narrowband guy, so take my advice with a grain of salt.

For Ha, you don't really need a filter.  Just pull out the red channel from the t3i image and that should be sufficient I think.  Hb does tend towards blue, but if it's just Ha, then the red channel is all you need.  Note that the reason these cameras are modded to capture more Ha is to extend the light transmission into the deep red.  One caveat though, red tends to pull a bit more than just Ha.  If you want a very well defined Ha band, then a narrowband filter would be the way to go, since it limits the bandpass to just a portion of the Ha band.

Bloated stars.  If you use an uv/ir cutoff filter like you mentioned, you should be ok, the stars should be no worse than with an unmodded camera.  However, for very tight stars, a dedicated Ha narrowband filter (like say a 5nm one) will produce smaller stars simply because it cuts off any starlight outside the band.

3.  Yes.  You can either use a front mounted filter (like a 2" ) and use one band at a time.  Or, you can try one of the more expensive filters like the triad series (three or four band) which are multiple bandpass.  The difficulty with those is separating the narrowband channels afterwards.  I believe someone has created a color mapping action though that makes that process easier.  The advantage of those multiple bandpass filters is that you image all bands at the same time, which eliminates filter changes (and refocusing) and also uses all the pixels in the camera at once, since the different bands show up in different colors.

Hope this helps.

Daniel
Edited 31 Jan, 2019 17:55
Rudy_Pohl
31 Jan, 2019 20:18
Hi Daniel,

Thanks so much for this really practical reply, it's exactly the kind of information I was hoping for!

Best regards,
Rudy
dciobota
31 Jan, 2019 23:04
Glad to help Rudy.  Looking forward to even more awesome images from you.  Loved the ones you've been posting on CN.

Daniel
Rudy_Pohl
01 Feb, 2019 10:29
dciobota
Glad to help Rudy.  Looking forward to even more awesome images from you.  Loved the ones you've been posting on CN.Daniel

Thanks Daniel, that means a lot!
Cheers,
Rudy
 
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