F4 shots brighter than F2.8?

Is it normal that if I take two pictures of the same thing, with flash or not, one at F4 and one at F2.8, that the F2.8 shot is always slightly less exposed/darker (i'm guessing 1/3 stop) than the F4 shot?

What mode are you shooting in? Manual, AV, Tv? Is this a controlled setup with a tripod shooting the same subject, at the same focal length? AWB?

This will help. But in general, no, it shouldn't be any darker.

If all settings, environmentally and the camera settings (i.e. manual mode), are the same, and the only thing that changes is the aperture between the two shots, then the 2.8 should be brighter.

Could you post the two pics using "Go Advanced" and/or post the exif data so we can compare?

if you are in full manual, with the same shutter speed, and ISO, then the larger aperture can only make the image brighter.

Billginthekeys wrote in post #2748831
if you are in full manual, with the same shutter speed, and ISO, then the larger aperture can only make the image brighter.

As above. If that's not the case, then your computer is not consistenly processing your photos.

I will assume you are shooting in Av mode.

Are you sure its not a metering issue? If you are not on a tripod with a subject that isn't moving, the metering would easily change.

Even the tiniest shift could make the light meter change by 1/3 stop.

Also, as discussed with certain lenses, the vignetting at 2.8 could be allowing less light in. This has been noticed with lenses like the 50 1.4 and 50 1.2 where one is brighter (1.2) at the same f/stop.

This is a case where some example photos would be most beneficial. Show us what you have...with exif data intact.

The question here is ... are the images really always darker on the f/2.8 than on the f/4?

Or did you see that in some cases the f/2.8 images were darker than the f/4 images. As already mentioned, a tiny difference in the light can change metering ... and if your camera did select a longer shutter speed in some cases than in others, it might explain it.

If you get these results consistantly, then something might be amiss with your camera/metering system/lens/...

Best regards,
Andy

I shoot in Av. If the camera is supposed to give an identical shot at F2.8 1/50 and F4 1/25 then mine is not, lens is a 17-55. The F2.8 shots often come out slightly darker, it may not be 1/3 of a stop but the difference is noticable (although somewhat negligible at the same time). When using my 430ex in Av with 1/250 sync the difference is noticable in a different way (they're illuminated a bit different) but I guess thats unavoidable as at F4 (compared to F2.8 ) the flash has to fire brighter so you get slightly more flash lighting/glare/reflect​ions/shadows and less ambient lighting. Correct?

The ambient light exposure will be the same either way, but it's possible the flash metering changed slightly.

bieber wrote in post #2749194
The ambient light exposure will be the same either way, but it's possible the flash metering changed slightly.

Right but what I mean is the flash will have to fire stronger at F4 to get the same exposure as it did at F2.8, so there's more flash light bouncing around which can change the look of the picture, correct?

Would your 17-55 lens focal length setting (for the f:2.8 shots) happen to be towards the 55mm range?

Chigger wrote in post #2749800
Would your 17-55 lens focal length setting (for the f:2.8 shots) happen to be towards the 55mm range?

yes

For some reason, I read 17-55 & my mind said 18-55. I assumed the kit lens with it's variable max f:stop. My mistake.

I did a lens test at different apertures in AV. Each setting from 2.8 up got darker. I used a tripod and shot the in quick succession.

In AV 2.8 should be the brightest.