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XTI seems to underexpose

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Thread started 23 Apr 2007 (Monday) 10:38   
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wilded
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Is this a problem? Is there a fix? Thanks, ET

Post #1, Apr 23, 2007 10:38:30


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mrbigisbudgood
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I've been noticing that my XTi likes a positive (.3 to 1.0 depending on the situation) white balance where my old Kodak liked a negative WB. I'm still learning the XTi, but this was one of the first things I learned.

Post #2, Apr 23, 2007 10:46:52


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angryhampster
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mrbigisbudgood wrote in post #3089729external link
I've been noticing that my XTi likes a positive (.3 to 1.0 depending on the situation) white balance where my old Kodak liked a negative WB. I'm still learning the XTi, but this was one of the first things I learned.



Do you mean exposure compensation? XTi is made from the factory to underexpose. This creates naturally more constrasty, saturated images.

Post #3, Apr 23, 2007 10:58:47


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mrbigisbudgood
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angryhampster wrote in post #3089791external link
Do you mean exposure compensation? XTi is made from the factory to underexpose. This creates naturally more constrasty, saturated images.

Yes, I meant EC, sorry. I'm eating lunch at home, thinking about work, thinking about go-karting tomorrow night, waiting for my wife to get home.....I'm here 'cause I'm not all there.

Post #4, Apr 23, 2007 11:00:50


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Hellashot
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angryhampster wrote in post #3089791external link
Do you mean exposure compensation? XTi is made from the factory to underexpose. This creates naturally more constrasty, saturated images.

Exucse me but why are you posting such fabricated nonsense?

Post #5, Apr 23, 2007 11:31:28


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Tee ­ Why
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Generally, I don't think this is a consistent issue. I have heard that it maybe a problem if you used eval metering though.

A quick fix would be to check the histogram and adjust for exposure compensation.

I too heard that Canon prefers to underexpose with tricky lighting to prevent overexposure and loss of details from UK magazine, I think it was the last issue of Photography Monthly, where they did a comparison of entry level dslrs.

Post #6, Apr 23, 2007 12:07:12


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angryhampster
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Hellashot wrote in post #3089953external link
Exucse me but why are you posting such fabricated nonsense?



Sorry for fabriacting such nonsense.

http://www.google.com ...xpose+&btnG=Google+​Searchexternal link

For subjects with high contrast containing a white element, the Rebel XTi tends to underexpose to keep the highlight within the histogram.

http://www.dcviews.com ...-XTi-Nikon-D80-review.htmexternal link

http://forums.dpreview​.com ...rum=1031&message=21​603849external link

http://photography-on-the.net ...ghlight=rebel+under​expose
http://photography-on-the.net ...hlight=rebel+undere​xposed

It's fairly common for the rebel series to underexpose images up to a full stop.

Post #7, Apr 23, 2007 12:08:08


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Bill ­ Boehme
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My XTi is also doing some of that "fabricated nonsense". I should have a talk with it and tell it to stop fabricating all of that nonsense.

I sent it back to Canon a couple months ago when the underexposure was severe (about 1.67 stops). They confirmed the problem and repaired the camera. Now it is at the "normal" (.33 to .67 stop) underexposure.

Contrary to some Internet lore on exposure, it is preferrable to slightly overexpose an image as long as it doesn't result in objectionable blown out highlights. Overexposure will afford you more lattitude in post processing the darker areas of an image. I learned this tidbit from the late Bruce Fraser.

Post #8, Apr 23, 2007 12:28:02 as a reply to angryhampster's post 19 minutes earlier.


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angryhampster wrote in post #3090157external link
Sorry for fabriacting such nonsense.
It's fairly common for the rebel series to underexpose images up to a full stop.

User comments is in no way official word from Canon that they designed the XTi to under expose. All SLRs need exposure compensation with different shooting situations.

Do a few people who hit the accellerator in a car instead of the brake mean that the car maker designed the pedals in opposite positions? :)

Post #9, Apr 23, 2007 21:01:19


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angryhampster
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Hellashot wrote in post #3093071external link
User comments is in no way official word from Canon that they designed the XTi to under expose. All SLRs need exposure compensation with different shooting situations.

Do a few people who hit the accellerator in a car instead of the brake mean that the car maker designed the pedals in opposite positions? :)



Is it common for people to hit the brake pedal and the car keep going?

Post #10, Apr 23, 2007 21:14:12


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The sheer volume of postings on various forums about the XTi/400D shooting slightly underexposed is enough to suspect that there is something more than speculation to this conjecture. Offhand, I do not recall any postings about the camera overexposing.

Post #11, Apr 23, 2007 21:18:16 as a reply to Hellashot's post 16 minutes earlier.


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liquefied
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I think the nonsense being pointed out was that the XTi is supposed to underexpose. That is a ridiculous claim and if Canon actually designed a camera to underexpose then I'm tempted to switch to Nikon. The camera has a light meter for a reason, that light meter should be accurate. I've only heard that it's a defect with the light meter. My XTi consistently underexposes by 2/3 stops and I've tested this several times with a gray card (a gray card is not 'tricky lighting', it is 18% gray - right in the middle of a correctly exposed histogram). The problem is there and a solution needs to be provided by Canon soon.

Post #12, Apr 23, 2007 22:12:10



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Robert_Lay
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liquefied wrote in post #3093476external link
I think the nonsense being pointed out was that the XTi is supposed to underexpose. That is a ridiculous claim and if Canon actually designed a camera to underexpose then I'm tempted to switch to Nikon. The camera has a light meter for a reason, that light meter should be accurate. I've only heard that it's a defect with the light meter. My XTi consistently underexposes by 2/3 stops and I've tested this several times with a gray card (a gray card is not 'tricky lighting', it is 18% gray - right in the middle of a correctly exposed histogram). The problem is there and a solution needs to be provided by Canon soon.

Bravo - well said!

I have posted a graphic of a carefully measured transfer characteristic for my XTi, which clearly shows two things of interest - underexposure of about 2/3 to 1 f-stop, and a decidedly abrupt shoulder.

Now that I am seeing more and more comments that corroborate my own findings, I am becoming more convinced that it is intentional - my explanation being that it keeps you further from that abrupt shoulder.

Post #13, Apr 23, 2007 22:27:47


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angryhampster
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Yea shoulda worded it differently. I suppose "does underexpose from the factory" would have been more appropriate than "is meant to"

Post #14, Apr 23, 2007 22:32:09


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Robert_Lay wrote in post #3093538external link
Bravo - well said!

I have posted a graphic of a carefully measured transfer characteristic for my XTi, which clearly shows two things of interest - underexposure of about 2/3 to 1 f-stop, and a decidedly abrupt shoulder.

Now that I am seeing more and more comments that corroborate my own findings, I am becoming more convinced that it is intentional - my explanation being that it keeps you further from that abrupt shoulder.

Robert,

Thanks for the information. Could you provide a link to the graphic? I have heard numerous "stories" about reasons for underexposure in the XTi, but as an engineer, none of them really sounded very plausible to me. This explanation, however, sounds very logical. It is easy to envision a scenario in which getting a product to market trumps working out all of the bugs in a sensor design. I presume from what you say here that beyond the "shoulder", all pixel data are saturated.

Post #15, Apr 23, 2007 22:56:47


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