Stupid Question - F8 is F8 right?

Not sure if this was a lens question or lights, think it fits here? If not please move

I know this may sound like a dumb question but I just came back from a local workshop and working out the lighting they had figured it was set up for ISO100 125th @f/5.6. I started shooting and was getting the blinkies of things being blown out and was quite hot. So I dropped down to F8 and things seemed to mellow out. When I verified what they set it up for I was told that being I was shooting with a 2.8 lens (24-70 f2.8) my settings would be off. I asked isnt F8 "f8" no matter what, 2.8 may help me focus faster but shouldn't make any difference then that right?

so yea, if I have a 85mm f/1.2 lens @F8 and a 85mm f/5.6 (if there is such a thing) @F8 they should be the same right?

Ive always thought that if it meters F8 who cares what lens it is and just want to see if ive been misunderstanding this entire time or not

You're correct. f/8 will yield the same exposure for all lenses (at the same shutter speed).

You're absolutely correct. F/8 will ield the same exposure for all lenses. However exposure could very a little bit depending on the camera. For example if you use a light meter you might not get the "right" exposure if you simply set your exposure to what the meter says as there may be a bit of difference between the light meter and your camera.

Tawcan wrote in post #9792239
You're absolutely correct. F/8 will ield the same exposure for all lenses. However exposure could very a little bit depending on the camera. For example if you use a light meter you might not get the "right" exposure if you simply set your exposure to what the meter says as there may be a bit of difference between the light meter and your camera.

There will also be a slight difference if you're comparing two very different lenses, like a big zoom and a fast prime. The prime will yield a slightly brighter image at the same exact settings due to less glass in the way absorbing or reflecting light.

mike_d wrote in post #9792331
There will also be a slight difference if you're comparing two very different lenses, like a big zoom and a fast prime. The prime will yield a slightly brighter image at the same exact settings due to less glass in the way absorbing or reflecting light.

This is "not supposed" to be true. However, some lenses may not be calibrated all that closely, just like some bodies are slightly different when set to same ISO

440roadrunner wrote in post #9800790
This is "not supposed" to be true. However, some lenses may not be calibrated all that closely, just like some bodies are slightly different when set to same ISO

Nothing to do with the calibration; like Mike said, the amount (and type) of glass can affect things. With thoroughly multicoated lenses like we're getting nowadays it's less a factor, and TTL metering can compensate for it without your intervention, but in the film industry where maintaining continuity includes keeping the exposure consistent from shot to shot, lenses used to be calibrated in "T-stops" (Transmissivity stops) which allowed much closer matching of shots from different lenses and film stock.