dark raw files - canon XT

quark

I have an XT that is acting odd.

When I shoot in raw (non-idiot modes) I occassionally get a very dark photo that is completely un-usable. Seems to be less than 25% of the time and seems to occur completely randomly as far as I can tell. The flash is firing correctly and works fine with my other cameras.

I do have a new memory card that I have been using that I got a really good deal on, any chance this is the cause? I am not sure if the LCD is after the photo hits the card? If so it could be the card because I can see the ruined photo on the LCD.

Any thoughts appreciated.

ziggy53

quark wrote:

I have an XT that is acting odd.

When I shoot in raw (non-idiot modes) I occassionally get a very dark photo that is completely un-usable. Seems to be less than 25% of the time and seems to occur completely randomly as far as I can tell. The flash is firing correctly and works fine with my other cameras.

I do have a new memory card that I have been using that I got a really good deal on, any chance this is the cause? I am not sure if the LCD is after the photo hits the card? If so it could be the card because I can see the ruined photo on the LCD.

Any thoughts appreciated.

Review the EXIF information of the dark frames versus the normal frames around the dark frames. Look especially at the mode to see if the problem mostly occurs when shooting Aperture Priority, Shutter Priority or whatever.

Try to correct the image as much as possible to see if there is a flash sync problem. If the flash illumination is not contributing to the exposure, try to find out why that might be. Don't assume that because the flash fired, it contributed to the exposure. There are several scenarios where the flash will fire and not add to the exposure.

Do you have a gallery with examples? Even JPGs will help us to help you if they have EXIF information intact.

I don't think that the memory card is the culprit, but leave no stone unturned.

quark

Thanks Ziggy. I have posted an example in a gallery. I took these at intermission of the concert I was shooting in an attempt to diagnose the problem. I was using P-mode, and reflecting back it may be occuring only in this mode but I can't be sure.
example

The exif did not carry over so I am trying to hunt the data.

If the problem is flash sync why would it occur only in specific modes? As I mentioned I don't notice this in the auto modes so I assumed the flash was not the culprit ....

ziggy53

quark wrote:

... I was using P-mode, and reflecting back it may be occuring only in this mode but I can't be sure. ...

"P-mode" is almost certainly part of the problem. Do not use P-mode if you want consistant results.

I use Aperture Priority and Manual modes only.

A lot of good information here:

http://photonotes.org/articles/eos-flash/
http://photonotes.org/articles/eos-flash/index2.html

(First mentioned in this thread:
http://www.dgrin.com/showthread.php?t=507)

quark

Hmm. Very suspicious. I will stay away from P and report back if it happens again.
Thanks much!

digismile

A couple of things.

First, f/22 is maybe a little bit too much for an indoor flash photo! You will get better results at a much lower f-stop. See what that does for you ...

Second, it's hard to tell whether this is a malfunction or not. It looks a bit like a corrupted file, but the very faint image may just be because there was really no light due to a high shutter speed and a very high f-stop. Maybe the flash hadn't recycled to full charge and therefore gave very little light.

I think if it was a card malfunction, you would see this problem with daylight shots (I assume you're not).

Let's start with opening the lens up, slowing down the shutter speed to 1/30 to 1/60 of a second and the let's see if you get the same problem.

ziggy53

digismile wrote:

A couple of things.

First, f/22 is maybe a little bit too much for an indoor flash photo! You will get better results at a much lower f-stop. See what that does for you ...

Second, it's hard to tell whether this is a malfunction or not. It looks a bit like a corrupted file, but the very faint image may just be because there was really no light due to a high shutter speed and a very high f-stop. Maybe the flash hadn't recycled to full charge and therefore gave very little light.

I think if it was a card malfunction, you would see this problem with daylight shots (I assume you're not).

Let's start with opening the lens up, slowing down the shutter speed to 1/30 to 1/60 of a second and the let's see if you get the same problem.

Exactly! I see the EXIF on the first image now.

The Canon dRebel 350D/XT built-in flash has a guide number of 13, so at f22 it will only reach out about 2 ft. or so at ISO 400. It also looks like you were using the EF 18-55mm, f3.5-f5.6 "kit" lens, not a very good choice for an indoor venue. I highly recommend something more like the EF 50mm, f1.8 for indoor events, and it's about as inexpensive as it gets.

Tee Why

I don't see any shots or any EXIF, but if you take two quick shots with the onboard flash, the second one probably didn't have the flash go off as it needs to be given enough time to recycle.