5d3, cpl and flash

I'm using a 580 ex2 flash set to ettl on my new 5d3 (set on P) with a 24-105L lens and a cpl. The photos are all coming out dark. I took off the cpl and the photos are fine. Shouldn't the ettl compensate for the cpl? It doesn't seem to happen using the 7D. It also doesn't seem to happen in Av or Tv mode.

Since we are left to guess what your exposure settings are, all I can comment on is if the flash is at it's max output already and you place a filter on the lens, there is no magic in the eTTL system that can make the flash produce more power.

Have you tried opening up the aperture or increasing the ISO?

dedsen wrote in post #15416188
Since we are left to guess what your exposure settings are, all I can comment on is if the flash is at it's max output already and you place a filter on the lens, there is no magic in the eTTL system that can make the flash produce more power.

Have you tried opening up the aperture or increasing the ISO?

This is exactly what came to mind when I read that. I have no idea what sort of restraints P mode puts on the exposure to max out a flash, but its certainly possible.

In the 'P' mode it's registering f4 at 1/60 second with or without the cpl. I can increase the flash by about 1 1/3 stops using the camera menu and the photos look much better. Shouldn't this happen automatically?

DanThoman wrote in post #15416268
In the 'P' mode it's registering f4 at 1/60 second with or without the cpl. I can increase the flash by about 1 1/3 stops using the camera menu and the photos look much better. Shouldn't this happen automatically?

I am going to suggest posting a photo with the exif intact. Same shot with filter, and without. It is difficult(for me) to guess how many stops might be added by the cpl filter.

110yd

Here are two photos with nothing changed except that I took the cpl off.

No suggestions/ideas?

DanThoman wrote in post #15423467
No suggestions/ideas?

I pulled out my camera, 580ex flash and CPL to try and duplicate your photo. I am , but am going to take a guess that the flash is actually maxed out power wise. (in general my camera underexposes) I did not have time to try and tinker with the ISO or Flash compensation. I was getting a slightly underexposed frame at 1/60 F4 ISO 400 with or without the CPL. I don't think the CPL comes in to play very much, unless you have a significant amount of reflected light.

Regards,

110yd

The camera uses distance information from the lens as part of its calculations for flash output in E-TTL mode (when using direct flash). Since it doesn't know about the polarizer, it's going to underexpose a little.

E-TTL isn't perfect. Crank up your FEC and drive on.

I don't think that for the fireplace photo the 580 would have maxed out.

I am not surprised that in Av, Tv the results are better, because the camera exposes for the ambient and the flash is 'fill'.

I read somewhere that for the fully automatic mode you get less flash power, I can't remember exactly.

I wonder whether it has something to do with the ETTL measuring a reflected light wave through the polarizer. Try to shoot in portrait and see whether there is a difference (or turn your CPL 90 degrees...

Curtis N wrote in post #15423959
The camera uses distance information from the lens as part of its calculations for flash output in E-TTL mode (when using direct flash). Since it doesn't know about the polarizer, it's going to underexpose a little.

E-TTL isn't perfect. Crank up your FEC and drive on.

Curtis may I say sir that for as long as I've been on these forums it has always been a pleasure to read your helpful contributions. Thanks for your willingness to share the wealth of lighting knowledge you have with the rest of us.

Curtis N wrote in post #15423959
The camera uses distance information from the lens as part of its calculations for flash output in E-TTL mode (when using direct flash). Since it doesn't know about the polarizer, it's going to underexpose a little.

E-TTL isn't perfect. Crank up your FEC and drive on.

Sounds like a plausible explanation to me...

I tried to duplicate the OP's problem with my 60D, the onboard flash and a CPL shot at 0 and 90 degrees, in Av, Tv, M and Green Rectangle.

I got no lighting differences from 0 and 90 degrees, all shots perfectly lit. So there goes my theory about polarized light...

Av and Tv used the flash as fill (much longer speed or open aperture).

Green Rectangle and P recorded properly in all shots.

However, my distance to the subject was about 4 ft, so maybe at larger distances, Curtis' theory may come true.

The flash wasn't maxed out because I could increase the output by about 1 stop and the photo was much better. Rotating the cpl did not make a difference. The distance did not make a difference as I first noticed this taking photos of people from about 20 to 25 feet away and the fireplace was less than 10 feet away.