Vray cam exposure & photoshop exposure

[AlexP]

Is there a way to "convert" the vray physical camera exposure settings to a value used in photoshop with the exposure tool?

Im on max 2015 still, so, old vray camera.

Essentially, if I have rendered an exr without exposure, is there a way to find out what the photoshop exposure needs to be, in order to match the render output *with* exposure.

I know I can go by eye, but I prefer a mathematical way if possible

[Morne]

Why don't you just open the EXR in the VFB, add the exposure and resave it?

Not exactly what you're looking for, but if you found a nice exposure in the VFB and want to match it to your CAM in Max, you can use this formula:
Stick this in Google: 160*(2^-0.5)

In this example, the shutter is currently set to 160. In the VFB you adjusted the exposure to 0.5. So you're new cam exposure will be 113. If you went the other way and it was -0.5 in the VFB, then your new exposure will be 226.
(the + and - get reversed in the formula)

Not sure how that will translate into PS or if the formula will work for PS as their's go all the way down to -20 and up to 20

[AlexP]

This is a good tip, but wont apply here I dont think.
Basically, I have render to texture a few different elements. Some of these come out at the correct exposure, some of them do not, so I wanted to add an exposure adjustment layer in photoshop that matched whatever exposure was being applied by the Vray camera settings

[Morne]

You could take the image that saved with exposure, and rerender without.

Then in PS stick the no exposure one over the exposure one and set the blending mode to difference. Add an exposure adjustment to the no exposure one and adjust until you get a black image. You'll now have your exposure value

Use that exposure then as an adjustment on the other images where exposure was not saved

[AlexP]

Ah so obvious! Thanks