Some shots overexposed, no changes made to equipment

[mishmatta]

Equipment: Pentax k20d, Alien Bee 800, 2 slave flashes, 50mm manual lens & 24mm manual lens.

So I was doing this shoot indoors in a tiny living room. The alien bee was directly over camera, pointing down onto the subjects. The 2 slaves were pointing from the sides to the wall, sides of tree. I used my 50mm, f8, 1/125 at ISO 100.

I'd take a few shots that looked ok, and then noticed that every few shots in between were terribly overexposed. I'm enclosing a sample so you can see what I mean.

NO changes to the camera/lens. NO changes to the lighting. The slaves and the alien bee fired each time.

I kept double checking my lens to see if I accidentally bumped it down to 1.4 or something, but it was still at 8! What was strange was that I switched it to 11 and even 16. When it captured the correct image, it was darker than what it should have been for each of those settings, BUT when it captured it as "overexposed" there was no difference in the overexposed images at 8, 11 and 16. They all looked like the overexposed image below???

I swapped out my lens at one point to my 24mm, and got the same results.

First time I've ever seen this, and I've used this lighting setup before without this issue.

Ideas?

Lighting, camera, lens???

[zona5101]

Ever noticed it when not using flash? Try some shots without any strobes and see if you get similar results...At least that will let you know if your AB is freaking out or if it's your camera/lens. My first thought was sticky diaphragm blades on the lens...but same results on a different lens makes me think it's the camera body or flash. Testing with just ambient will eliminate the strobe as the culprit.

[mishmatta]

Originally Posted by zona5101

Ever noticed it when not using flash? Try some shots without any strobes and see if you get similar results...At least that will let you know if your AB is freaking out or if it's your camera/lens. My first thought was sticky diaphragm blades on the lens...but same results on a different lens makes me think it's the camera body or flash. Testing with just ambient will eliminate the strobe as the culprit.

Nope, this was the only time. Never had this happen with ambient lighting. Never had this happen with the strobes before either...so....

Both lenses are old slr lenses. Manual focus, but generally pretty sharp glass and decent images.

Maybe it IS the lenses since they're so old? However.....I've used these lenses for a while now, even with external hotshoe flashes without ever having this result.

[sk66]

You didn't have bracketing activated did you?

[mishmatta]

No bracketing.

[sk66]

What's the exif for the two shots? The difference there should point to the problem.

[autofocus]

just curious, how are you communicating to the light(s), radios, hard wired?? Almost seems like a communications issue. Are the slaves Pentex, or third party?

[scootermcq]

Are you sure your AB fired each time? I look at the image and there is not indication of a main light. No catch lights etc. There are shadows on the wall camera left from your kicker striking the tree, which would be knocked down with a main light.

If it is firing, were you allowing it to charge the capacitor before firing? It really looks like no main in the underexposed image.

[mishmatta]

Originally Posted by sk66

What's the exif for the two shots? The difference there should point to the problem.

Here's a pic comparison - no differences except the time taken. Oh, and the ISO was 140, not 100. But for both shots.

Originally Posted by autofocus

just curious, how are you communicating to the light(s), radios, hard wired?? Almost seems like a communications issue. Are the slaves Pentex, or third party?

Hard wired to the alien bees. The slaves are ac flashes from Adorama.

[autofocus]

f/0.0???? what's with that?