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Old Feb 23, 2007, 2:14 AM   #21
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Just got my black XTI the other day and never had problem with underexpose photos.
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Old Feb 23, 2007, 9:29 AM   #22
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Imacer wrote:
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Just got my black XTI the other day and never had problem with underexpose photos.
I'm glad you don't have any problems. I sent my Camera off to Canon yesterday, should be there today. I'm hoping it will come back with better results. Looks like a lot of people who have had Canon check them out have came back working much better.

What I finally ended up doing was taking shots of a white piece of paper (Only because I don't have a gray card and this works very close to using a gray card for this purporse) under tungsten lighting. I took 7 shots, in P mode, using evaluative metering, manual focus.

I opened them all in Photoshop and looked at the Histogram means on them.

At 0 EC, my mean was 82.2 . This, I am told, is low. It should be somewhere around 110. I didn't get to 110 until I increased my EC by 2/3 stops. It was also very low while using full auto/green box mode. Sure, I can just increase my EC every timeI take a shot when not using full auto mode, however I feelit should expose properly w/out having to do that for almost every shot I take.

So, camera is sent, I'll wait to see how it turns out when I get it back.
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Old Feb 24, 2007, 11:40 PM   #23
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hopkinsg wrote:
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What I finally ended up doing was taking shots of a white piece of paper (Only because I don't have a gray card and this works very close to using a gray card for this purporse) under tungsten lighting. I took 7 shots, in P mode, using evaluative metering, manual focus.
Using a white card will guarantee the camera to underexpose !
In fact all cameras will, including mine - This is like shooting in the snow or white wedding gown and expect the camera not to underexpose...

-> A Grey card is 18% grey for areason not a white card (or a black card): :idea:
http://www.luminous-landscape.com/tu.../dig-exp.shtml
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Old Feb 25, 2007, 2:00 PM   #24
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I'm no expert and this could totally be inaccurate information, but from what others have said, a white piece of paper should work the same as an 18% gray card.

If the camera sees all white, as I did since the frame was filled 100% with the piece of paper, even lighting, the camera will expose it to be 18% gray. After it does that, the histogram should show a result similar to that of using an 18% gray card.

In any event, I did send my camera in to Canon last week to have them check it out. If there is a problem I'm sure they will fix it, or if it's working properly then I'm going to spend less time testing for problems and more time shooting and learning to adjust any exposure manually.

Gary

NHL wrote:
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hopkinsg wrote:
Quote:
What I finally ended up doing was taking shots of a white piece of paper (Only because I don't have a gray card and this works very close to using a gray card for this purporse) under tungsten lighting. I took 7 shots, in P mode, using evaluative metering, manual focus.
Using a white card will guarantee the camera to underexpose !
In fact all cameras will, including mine - This is like shooting in the snow or white wedding gown and expect the camera not to underexpose...

-> A Grey card is 18% grey for areason not a white card (or a black card): :idea:
http://www.luminous-landscape.com/tu.../dig-exp.shtml
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Old Mar 4, 2007, 12:59 PM   #25
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Thought I would post an update:

I sent my Camera into Canon for service on the underexposure problem, and also an issue where my RAW ISO 1600 pics were quite a bit more noisy than JPG ones. This could be normal, however I thought I'd have them check anyways.

I rec'd the camera back on Friday, and it works 100% better ! My pictures are no longer underexposed and my histograms on my "white paper" test now show much higher and acceptable numbers.

This is what Canon did to the camera:

"We have examined the product according to your request, and, it was found that the part had shorted noise appeared in the image from time to time The cmos sensor assembly was replaced. repaired exposure unit Other electrical adjustments and inspection and cleaning were carried out."

Here is a copy of the repair sheet:

http://gary.cybernetik.net/images/xtirepair.jpg

If anyone thinks they are getting dark pictures, or if their tests show really low values on the histogram, I would definitely send the cam into Canon for evaluation.

-Gary
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Old Mar 16, 2007, 6:46 PM   #26
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I have my 400D back home! And now it works well with all lenses.
NO MORE UNDEREXPOSURE!
Also 18-55 works as I expected when I bought the camera in december. I know that the kit lens is not comparable with the high quality series, but it will no more produce dark pictures with my 400D.

The first test i made this afternoon, in P, AV e TV:
http://www.diegocuoghi.it/test400d/400D_FIXED.jpg
Thumbnails are blurred because Digital Photo Professional shows only the preview of the JPG files.

Here is the same test, made in January, in the morning:
http://www.diegocuoghi.it/test400d/400d_lens_test1.jpg

Now I am very happy. I know that I will trust my camera and lens, an I will have good exposed pictures even in Full Auto.

I talked with Canon technicians in the two labs where my camera was tested. They found it was defective and they fixed the underexposure issue. If I understand well (I am not a technician) the cause was an incompatibility between the camera software and the focusing screen mounted. Maybe I must say "my" camera because they said not all the 400D mount the same identical focusing screens. These parts were produced in different factories and the camera have to recognize them. If this not happens the light mesaurement, with some lenses having not a great aperture (ie 5.6), give wrong reading and produces underexposed pictures. The underexposure was more noticeable with 18-55, they said, most at long focal lenght (around 50mm) than at short (18mm). They found the same issue also with other 5.6 lenses.

The underexposure can be corrected changing the focusing screen or changing some part of the software related to its functions. In my case they corrected the software. The technician said also that I was not alone... the same issue was found in other 400D cameras.
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Old Mar 17, 2007, 10:46 AM   #27
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Software or firmware?
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Old Mar 17, 2007, 11:20 AM   #28
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Diego Cuoghi wrote:
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If I understand well (I am not a technician) the cause was an incompatibility between the camera software and the focusing screen mounted.
Very interesting. This is an issue I see come up from time to time when users go with third party split image micro-prism type focusing screens (metering sometimes needs to be recalibrated to work correctly, which is not normally something a user could do unless they have access to the manufacturer's service software and test equipment needed).

I see it with manufacturer installed focus screens from time to time, also (because the service techs didn't notice the part in the manual about recalibrating the metering when installing a different screen). lol

I'm glad they got it working for you.


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Old Mar 17, 2007, 4:05 PM   #29
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dequardo wrote:
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Software or firmware?
They said they changed the software that tells to the camera the kind of fosusing screen used. In the report I read "Verifica WE. Taratura accurata sistema esposimetro" (WE verification. Accurate light metering calibration).
I do not know what is "WE" but I know that now my camera works perfectly and I have no more underexposure with 18-55.

Some test pictures made with the fixed 400D.
http://www.diegocuoghi.it/test400d/fullauto/
Here some pictures before sending to assistance:
http://www.diegocuoghi.it/test400d/under/
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Old Apr 2, 2007, 7:37 AM   #30
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canon xti service 4days.i had the same underexsposure problem ,dropped camera off monday morning picked it up friday morning.perfect service was excellent.asked about 1.05 firmware was told they do not have the program yet.was told firmware will not fix exsposure problem.they are located 5 minutes off n.j. turnpike 5 minutes from rt#130 and twenty minutes from rt#1.its worth the trip .you save shipping and insurance and TIME.
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