40D exposure problem

I was messing with my 40D tonight trying to under exposing some test pictures. I just wanted to see what a couple steps under would do to the picture. When I started to under expose the picture things started going bad. Take look at these pictures.

They start to get this yellow hazing on them. This has never happened before. What could be causing this strange effect?

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My guess is white balance? did you set it on auto?

Yes it set to auto. If I change the WB it gets even worse.

I could venture a guess and say that you have fluorescent lighting? I can't find the post right now about it, but there was a good thread on shooting under fluorescent lighting, and combating the banding with shutter speed.

I would guess it's probably fluorescent lighting.

Fluorescent lights aren't continuous. They pulse (how quickly depends on the ballast). Because you were trying to underexpose, you were probably increasing your shutter speed (making it faster), and eventually increased it to the point where it would be able to capture only part of a single pulse from the lighting.

In your case, you'll want to decrease your shutter speed and narrow your aperture.

Wow thanks guys. I never even knew about the fluorescent light issue. Add another fact that I leanred from the great people of the this site. Thanks again.

Donte wrote in post #4857208
Wow thanks guys. I never even knew about the fluorescent light issue. Add another fact that I leanred from the great people of the this site.

I didn't either until I started shooting indoor high school basketball a couple of months ago. Talk about WB all over the place.

That's what it looks like to me, too. At 1/320 second you'll get about 1/3 of a light pulse, with variation between top and bottom.

Yep, that's what your shots look like...

-js

Damn, I was going to ask how did you do that background.

Yep, fluorescent lighting. It happens to all cameras.

I have those little screw in florescent lights you replace the other kind with and I don't get anything like this. Yes, the color is not exactly right, but it's even throughout, not like a ND filter.

canonloader wrote in post #4857372
I have those little screw in florescent lights you replace the other kind with and I don't get anything like this. Yes, the color is not exactly right, but it's even throughout, not like a ND filter.

I've heard that from others, too. Guess it's time to do some tests on a compact fluorescent.

If the phosphor in the lamp has a slow decay time it'll even out the cyclic variation - I suppose there's a difference between tube-type fluorescents too.

The worst are arc-discharge lamps, like the mercury or sodium vapor street lights.

-js

You mean, like it still glowing after you turn it out? Yep, it sure does that. In a dark room, it fades out over a second or so, cool looking.

That would solve the problem. I suppose there are tube-type fluorescents that have slow decay too, but you never see that specified on the package...

-js

I have seen some, but you only see them glowing if there is no other light in the room, like in a basement at midnight.