close camera target makes rendered image almost go black (VrayPhysicalCam)

[VI_MOVE]

I noticed something about the VrayPhysicalCamera which took me a while to figure out. During an animation zooming closely to a product detail the rendered image got darker and darker the closer I got. Because I couldn't find the reason for this I was almost about to try raising up the ISO settings. Since this was in an animation that would have been only the worst case solution.

But after a lot of testing the only thing that could be the reason for getting the dark frames was the camera target. I don't know if that has anything to do with some behavior of a real life camera but I still don't really understand it. I started with a target distance of about 480 and the closest point had a disctane of about 50. But then the image is almost pitch black.

Anyone else had that experience before?

[vlado]

Have you tried turning off the vignetting option for the camera?

Best regards,
Vlado

[simmsimaging]

This has happened to me before too. It was not vignette that was causing it. If I have time I'll try and reproduce it again.

b

[VI_MOVE]

Thanks, but vignetting was off already... I could provide a scene showing this. But it's easy to see, just create a scene with somewhat midgrey background (to quickly see the differences). The background will get darker the closer the target gets to the camera. Lights or models won't be necessary to get this effect but if there's any model in the scene it will show the same result.

[bardo]

I've tested now.

It happens also if you disable the target option and you set the target distance (and if you set also the focus distance, this override the target distance).

I think it's very strange because I've set the target distance to different values (1 - 2 - 3 - 10 - 10000 cm) and the background value from the VFB are respectevly :

target distance (cm) background VFB values

1 2.984
2 0.332
3 0.037
10 0.119
100000 0.332

The scene contains only a vrayphyscam with only exposure ON and a neutral white balance and a background mid grey (136,136,136).

[vlado]

Can you post the scene?

Best regards,
Vlado

[bardo]

vlado is quite simple to reproduce.

Now I am not at the office so I can't send you the scene but I did it as follow:

empty scene in centimeters scale with a mid grey as environment background color.
VFB enabled
3dsmax with gamma corrections enabled ( with affect material editor ON and input gamma 2.2)
Linear color Mapping with 1,1,2.2 and sub-pixel enabled
GI off or on is the same
a vrayPhysCam with vignetting off, exposure ON, color balance to "Neutral" and with target off or on to test the "target distance" and "focus distance" values.

Tomorrow I can send you a file.

[bardo]

Hi vlado,
I've attached a sample file.
Play with different target distance and focus distance from 1cm to 100000cm and you'll obtain different RGB values in the VFB.

[VI_MOVE]

While working with the current version 2.0.2 I noticed the problem is present still. But I found a workaround by ticking "specify focus" and setting the "focus distance" to whatever suiting your scene lighting best.

Just in case anyone faces this problem...

[3ddesign]

I am having the same problem but have found that it only happens with Vray Camera with Vray Sun and Sky. No checking or unchecking of camera settings makes any difference. Checking Specify Focus then entering a close focus also turns the image dark. (Vray 1.5 SP5) Edit: Just discovered that deleting the Vray Sun but keeping the Vray Sky solves the problem. This is a pain because I need to get in close to a detail.

[vlado]

Well, in V-Ray 2.0 you have the V-Ray exposure control which can help in such cases.

Best regards,
Vlado