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Canon 800D (T7i) experience? tests?

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#1 Michael Covington

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Posted 05 June 2017 - 06:06 PM

Is anyone out there using a Canon 800D (T7i) for astrophotography?  How well is it serving you?

What I'd really like to see is a DxOmark or PhotonsToPhotos test to confirm that its sensor is at least as good as the 80D.  None have been published yet.  But it looks like a promising camera.

 



#2 Gary Honis

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Posted 08 June 2017 - 01:38 PM

Hi Michael,

 

The T6i and T7i has issues for long exposures because of the AF pixels on the sensor, see here:

 

https://www.cloudyni...ing-help/page-3

 

The T5i model does not have the problem.

 

Gary


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#3 Michael Covington

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Posted 08 June 2017 - 03:20 PM

Thanks.  Does the 80D?



#4 Michael Covington

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Posted 08 June 2017 - 04:15 PM

[Edited]  If that is so, it looks like Canon takes one step forward, one step back.  Just when they get nearly ISOless sensors, they add rows of pixels that don't match the surrounding pixels, for Dual Pixel AF.

That thread seemed to indicate that calibration did not fix the problem.  Even when flats and flat darks are included?  I'd like to know more.

I am having a hard time imagining a problem that wouldn't actually be fixed by proper application of darks, flats, and dark flats.  Actually I can imagine one -- nonlinearity -- but it's a very improbable one.  "Canon banding" until now has largely been a difference in bias, in my experience.


Edited by MCovington, 08 June 2017 - 08:05 PM.


#5 Gary Honis

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Posted 08 June 2017 - 06:03 PM

Hi Michael,

 

Thanks.  Does the 80D?

 

According to astro images posted on this site, I don't see the AF pixels:

 

http://www.jtwastron..._canon_80D.html

 

Gary



#6 Michael Covington

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Posted 08 June 2017 - 06:31 PM

Very interesting, because if I understand Canon's literature right, it works the same way.  Maybe we are looking at a problem that was solved.  Or maybe someone's flat-fielding method takes care of it and someone else's doesn't. I'll keep my eyes open!



#7 Gary Honis

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Posted 10 June 2017 - 07:25 AM

Hi Michael,

 

I ordered a 80D with kit lens from Canon to test the model and to modify.  I plan to post modification instructions on my website if the model passes my tests.

 

Gary


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#8 ccs_hello

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Posted 10 June 2017 - 08:39 AM

Canon started from T4i era to use PDAF pixels on camera's main image sensor.

I.e., the "damage" stated since T4i/650D.

 

I guess Canon fixes those by cloning the neighboring pixels and probably done inside DIGIC ISP.

 

Don't know what happens in T7i and onward.

May be there are way too many to fix, RAW out starts not to fix them, or may be Canon expects post will do a good job???

 

Clear Skies!

 

ccs_hello



#9 Michael Covington

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Posted 10 June 2017 - 08:53 AM

Hi Michael,

 

I ordered a 80D with kit lens from Canon to test the model and to modify.  I plan to post modification instructions on my website if the model passes my tests.

 

Gary

Excellent!  What I want to know, of course, is whether these stripes exist on the 80D and, if so, whether they are correctable with careful darks, flats, and dark flats.  I might ask you to send me a flat and a dark flat for further analysis.

 

My experience is that traditional irregular "Canon banding" seems to be largely bias variation and is greatly helped by flat fielding with dark flats included.



#10 jgraham

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Posted 10 June 2017 - 10:27 AM

Do flats help correct the AF pixels?



#11 ccs_hello

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Posted 10 June 2017 - 10:34 AM

Previous T4i PDAF discussion thread:

https://www.cloudyni...cmos-af-pixels/



#12 Michael Covington

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Posted 10 June 2017 - 10:47 AM

Thanks.  So far it can be summed up thus: In the past we have had to deal with a lot of random pixel-to-pixel variation in sensitivity and bias.  Now we also have some that is intentional.  The question is whether standard calibration methods will deal with it equally well.




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