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canon xt vs t31 pixel size

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#1 ky1duck


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Posted 12 February 2013 - 03:30 PM

i have a chance to get a old rebel xt(350d) free. i am looking for a camera to mod. been using my t3i. but dont really want to mod it because i use it for more than astro. my question is going from a

unmoded t31 4.3um at 2.05arcsec/pix

to a

moded rebel xt 6.4um at 3.05arcsec/pix

what kind of image quality changes could i see. or witch is better. i am having a hard time understanding the pixel size to quilty/detail stuff

both numbers using my AT72ED i am also planing on getting a 8" f4 that would give me t3i(1.11arcsec/pix) or xt( 1.65 arcsec/pix)

any ideas or sugestions will help thanks for taking the time to read


#2 Falcon-



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Posted 12 February 2013 - 04:04 PM

i am having a hard time understanding the pixel size to quilty/detail stuff

If you have two sensors build with the *exact* same technology with the same electronics reading from it put in identical cameras and one sensor has physically larger pixels then the other then the one with the larger pixels *will* produce a higher quality signal simply because the larger pixel area allows more photons to be collected for a given exposure time.

That said the sensor technology does not stand still (thankfully) so in reality the smaller pixels of the T3i do not actually give you any disadvantage. Yay for technological advance! :D

So as to your actual dilemma.... I would absolutely get that XT and mod it! I use both an XT and a more modern XS, the XT is moded and the XS not (yet).

Here is what you can expect with the XT (vs a T3i)

- Pro: You can mod it!!! BIG difference!! Worth suffering the cons IMHO.
- Pro: the XT/350D does perform well for astro-capture despite it's age
- neutral: "average" seeing is reported to often be in the 2-4 arc-second range. 3-arc seconds per pixel sounds fine there most of the time. :shrug:
- Con: the XT does not have live-view (not too big of a deal with a computer and 1s looping test exposures)
- Con: the XT requires a long exposure adaptor cable & computer or an interval timer remote to get exposures longer then 30s (minor inconvenience only)
- Con: the XT does *not* have drivers for 64bit windows (and never will). If you have a brand-new Win8 machine you may need something like XP in a VM to do computer based camera control.
- Con: the XT has amp-glow. This makes well-match dark frames very important.

Hope that helps!

#3 Sean13


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Posted 12 February 2013 - 04:07 PM

Look into modding your T3i with an Astrodon NIR/UV filter. You get a good increase in red response and keep the ability to use the camera in daylight with autofocus.

#4 Jerry Lodriguss

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Posted 12 February 2013 - 04:35 PM

Don't worry about pixel size, it is vastly over-worried about.

Smaller pixels in the same size sensor don't produce more signal. The same number of photons (the signal) fall on the same size of the sensor no matter what the pixel size is. So the signal is the same. It is just divided up into more pixels.

Some will argue that means more readout noise contribution, but the engineers usually improve the readout noise every time they shrink the pixels, so it's a wash.

As far as arcseconds per pixel, don't worry about that either. Seeing will obliviate any difference that will make in long exposure images.

I have shot with everything from 16mm to 3,000mm all with the same size pixels, and you will never see a difference.

The only time arcseconds per pixel matter is with high-resolution planetary imaging.

If you can get a 350D for free, go for it. That camera has taken some nice pictures. It's not as nice as the new cameras, because it has amp glow, and it doesn't have live view, and it has more noise, but you can't beat free.


#5 Campos



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Posted 13 February 2013 - 05:10 AM


I'd say go for the 350D, I have done all my deep sky imaging with one (Baader modded and recently TEC cooled) with very good results IMHO.
When modified it's very sensitive to red nebulas, and with carefully matched darks it will give you nice clean images, it will only suffer a bit on very hot summer nights, that why I built the TEC cooler, here in Portugal it's quite hot :)

Here goes one example image I made in 2011, with a 200mm f/4 newt. and Baader MPCC, stack of only 11x 7 min. @ 400 ISO:




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