[URGENT] Image brightness changing when changing Focal/Target distance

[Art48]

Hi,

I assume this is a nasty bug and not a feature.

Situation:
Rendering a product shot using VRayLights and SpotLights and the VRayPhysical Camera

Problem:
When changing the focal length of a camera from 45mm to 85mm while changing NO other settings darkens the image.
There is no vignetting activated, shutter and ISO are the exact same.

Apparently there are several bugs here, or at least I think so:
1) Changing the focal distance shouldnt affect the image brightness at all
2) I got "specify focus" enabled by accident, but we're rendering without DoF anyways so it shouldn't matter - anyways if I switch it off, some brightness creeps back into the image, but not all of it.
3) Most significant one: Changing the target distance affects brightness! Going from 15cm to 50cm really raises the highlights to the point of burning out.

Steps to reproduce:
Open provided scene, duplicate the camera "Detail_v010", change focal length to 85mm

See all that in the screenshots provided.
I will send the scene to Vlado.



This is the basic. The look shouldn't change from here.


Only thing changed: "specify focus" turned OFF now


Changed target distance from around 15 to around 41


Changed compared to the fist image (the reference image): changed focal length from 45mm to 85mm

It would be awesome if we could get a hotfix for that ASAP - I dare to say this is a pretty serious bug and I cannot imagine that this is intended in any ways even if there is some reality in this behaviour, this is definitely not artist-friendly at all.

Edit: See my system specs and software versions in my signature.

[Art48]

Just sent the mail to Vlado containing a download link for the scene files (30MB)

[joconnell]

Yep, I think I got this before too and apparently there is some darkening naturally in changes of focal length, but I agree it's not helpful for us at all.

[vlado]

That's normal for the physical camera. See this page for a demonstration of the same effect in a real camera:
http://docs.chaosgroup.com/display/V...dFocusDistance

The physical camera in 3ds Max 2016 allows you to override this by specifying the exposure in EV.

Best regards,
Vlado

[Art48]

You gotta be kidding me... by all means I love the PhysicalCamera and VRay in general.
But...seriously? Could we at least get an option to disable this?
I don't want to sound ungrateful at all but this feature does not make any sense from a usability point of view.

At least I know what's happening now... thanks :P

[vlado]

We won't be adding an option, I'm afraid. You can disable the physical camera exposure and use V-Ray color mapping settings instead to bring the exposure down. Or, if you are not using DOF, just use the "specify focus" option to lock the camera focused at some fixed distance.

Best regards,
Vlado

[Art48]

Well thanks anyways for the clarification .
Just a quick question though: When did the help section on that lens breathing effect appear there? Didn't notice it before.

[vlado]

I'm not sure when we added it exactly; it was some months ago.

In any case, the physical camera in 3ds Max 2016 deals with these issues more elegantly, so eventually I hope people will move over to that one.

Best regards,
Vlado