I posted this same mesage at dpview, but thought it was important enough to post here as well. Plus, if anyone here can help out, I'd really appreciate it. Thanks.
"Ok first let me state that I have no way to post my pictures so if someone wants to post them for me that would be a big help; just let me know what your email is.
Anyway, I just got my 20d a few days ago and have noticed some slight, but very visable banding at iso 3200. It's really kind of annoying because part of the reason I upgraded from my rebel was because 3200 seemed usable, now it does not. It's pretty inconsistent but usually it happens when the image is underexposed by about a stop or there is a dark shadow area in a correctly exposed image. However if I take back to back images sometimes it will show up in one and not the other. This happens regardless of whether the flash is used or not.
However, and here is where some help posting pictures would really show had bad this is, I took some long exposures tonight at iso 100 and 200. Most of the shots were 30 seconds long and most came out wonderfully with no banding at all. In a handful of shots, I used the internal flash to see if I could expose the foreground and then let the long exposure take care of the background lights. The effect didn't work too well but.....
....on the pictures where the internal flash was used, the banding is horrible. It reminds me of a crappy printer with really bad microbanding. It's not just slightly noticable, we're talking huge obvious bands that completely ruin the picture.
So....a few questions:
1) Does this happen with all 20d's? Maybe a few people want to try this out. My camera was set to iso 200 with 30seconds @f14 in manual with second curtain flash. Try it on a dark night exposure where most of the histogram is pushed to the left...or underexpose by a stop or two. Even if you don't underexpose by this much, the banding is still really bad, but this will really bring it out.
2) What should I do? I suppose I can live with the banding if this is normal and can make sure not to use flash on long exposures (which I wouldn't do very often anyway). However, I don't think it's really exceptable at all and I don't want to see any banding at iso 3200 or at least want to understand why it is happening only sometimes.
Will canon fix this problem or is this just a problem that all the camera's have? I'd really appreciate any help you guys can give.
I don't think it has to do with the flash. I just took some photos at ISO 3200 at -2EV and got some fairly noticeable banding. Also, I don't want to overstate the problem... it's NOT a problem in 99.5% of the shots I've taken, and I've never seen it at anything below ISO 3200 (although I haven't undertaken any long exposures yet, like you have). But when it's there, yeowee! It's THERE.
Yeah, Softechie said he would post the pictures for me so check back here again. However, I was using iso 100 and 200 and I got extremely visible banding only when using the flash. I took about 30 pictures tonight with the same setting and only the ones with flash showed banding. At iso 3200 without flash it was there, but it was not nearly as bad as this. Also, I've done a bit more testing and at iso 3200 I get banding in 50% of shots that have dark areas, even if the subject is properly exposed.
I don't think this is exceptable at all. My rebel never did this and I think I'll be calling Canon tomorrow.
For this picture it was completely unnecessary, I'm not sure what I was thinking However, in a few pictures I took tonight, I was able to light up the bottom of the bridge with the flash and still have the long exposure for the lights in the background. Also, I sometimes take pictures at 24 hour mountain bike races and doing a long exposure and popping the flash as the rider goes by creates really cool light trail effects.
Like I said before, I don't do this too often, but I did buy the 20d to take pictures at iso 3200 when needed and if half the shots have banding in them, I'm better off just using my Rebel and saving the cash.
Same settings for both pictures, except the one with the banding had the flash fire. Like I said, I didn't need it for this one, but a few others I took tonight where the flash helped also showed banding. I think the flash causes some kind of interference.
Softechie: The banding in those pictures is at ISO 200.
After reading banding on DPR, they have it at ISO 1600 w/o flash as well. So banding isn't necessary with internal flash. Maybe it's defected on the unit level and not wide across all units.
I can imagine that a discharging flash is quite likely to be an electrically noisy event. At ISO 3200, the sensor could be sensitive to this noise. OTOH, the regularity of the banding could suggest something else, like a bug in the firmware or a flaw in the amplifier stage.
With the 10D, ISO 3200 used to be obtained by the camera doing the equivalent of shooting at ISO1600 with 1 stop underexposure then pushing the result by 1 stop. So if you underexpose by 1 stop at 3200, it's actually like shooting at 1600 then trying to push it 2 stops afterwards, so it isn't too surprising that the results are poor.
I expect the 20D's ISO 3200 works the same way, and that's why it's an option to enable it at all. Correct exposure is absolutely essential at high ISO, there really is very little scope to push it afterwards.
If you see banding with a correctly exposed high ISO shot, rather than after having pushed the image in post-processing, then there's definitely a problem.
jdee, can you post some full-rez shots for us to download? This looks similar to an issue I've had with the 20D and my 50MM f/1.4 - most likely connected to electrical interference with the motor. I'd like to see if it's the same distinct pattern - it's hard to tell look at these resized shots.
The pattern I see is much different than the usual banding you see with the 20D - much more fine, and usually only occurs along the top or bottom edge of the frame.
On dpreview, another user posted he got banding when he used AF with a certain lens.... When he switched to MF, it went away. My theory is that the banding is due to voltage reductions across the camera body due to various things... in the dpreview guy's case... the AF was probably draining voltage... while in your case, it is use of the camera flash. Under this theory, off camera flash shouldn't impact any photos since the flashes have their own power supply. For whatever reason (I'm not an EE), the voltage reduction apperas to cause the sensor to band.
However, in a few pictures I took tonight, I was able to light up the bottom of the bridge with the flash and still have the long exposure for the lights in the background. Also, I sometimes take pictures at 24 hour mountain bike races and doing a long exposure and popping the flash as the rider goes by creates really cool light trail effects.