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Old Oct 16, 2006, 7:29 AM   #1
Join Date: Aug 2004
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While this message is intended for Steve, if anyone else out there has the 400d AND another Canon DSLR, please feel free to chime in with results.

In looking at some posts on another forum, several people have made this rather disturbing claim:

At ISO 1600, the XTi appears to underexpose shots by about 2/3 stops. The problem of course being that after you adjust the exposure to be correct in PP, noise levels are higher than they were with the XT.

Now, I don't know the people who made these claims, so I thought it best to ask some folks I'm more familiar with.

Again, the ideal test would be to pit the XTi against the XT to see if there are indeed expopsure differences at ISO 1600.

As a shooter who takes a lot of high ISOshots I'm curious if this is a trend Canon may have started to deal with the noise issues putting 10mp on the same size sensor brings about.
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Old Oct 16, 2006, 11:02 AM   #2
Join Date: Jun 2003
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Yes... I've noticed the posts, too. Some of it may boil down to metering differences.

But, what bothers me, is if you look at some of the photos taken in controlled conditions in the reviews, for example, the "Studio Scenes" over at "that other site" ;-), the 400D is using slower shutter speeds for roughly the same brightness shooting Aperture Priority at f/9 compared to some other models in some photos.

The aperture and ISO speed are the same in some of them. Yet, the shutter speed for the new 400D is slower compared to the Sony DSLR-A100 and older Canon 350D in some, even at lower ISO speeds (for example, an ISO 100 series). That's not the case compared to the Nikon D80 though (at least not the images I've looked at yet), as it's shutter speeds are slower, too.

The biggest difference was between the 350D and 400D. But, it could be that the older 350D is significantly more senstiive than rated at lower ISO speeds in those specific conditions (lighting temperature, subject type).

Metering could be a culprit with some of them, though (although that doesn't appear to be the case with all of them). For example, I looked at a series of images not long ago in low light, where the Sony DSLR-A100 was getting shutter speeds almost as fast at ISO 400, compared to a Nikon D80 at ISO 1600, with both cameras set to the same aperture. lol That could be because the Sony's metering is geared more towards protecting highlights. The Sony's photos were a bit darker. But, they were not 2 stops darker. So, there are more differences than just metering involved.

Lighting temperature could also play a role. AA Filter differences, and even lens coatings can come into the equation, and the tone curve being applied by the camera may differ, depending on conditions and settings. So, you'd need to look at images taken in a greater variety of controlled conditions to draw any useful conclusions.

I'll admit that sometimes I wonder if cameras are "tuned" for specific tests they know reviewers are going to make, since exposure tends to be more consistent in some tests (for example "ISO series") versus others (for example "studio scenes").

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