How do you handle the inconstant exposure by different lens length at V-Ray Next?

[Micha]

Hi,

I'm using V-Ray for Rhino Next and often I render scenes and products from views based on different lens length. But V-Ray 3/Next makes, that the output brightness is dependent from the lens length if exposure is enabled. This means a tele lens cause a to dark output and a wide angle lens a to bright if the setup was adjusted for a standard lens.

How do you handle this situation at 3dsmax? Readjust the exposure for every view? Are you using auto exposure? This doesn't work well for me, a bright window or a strong light in the background and anything is changed. Did I have overseen something?

At VfR2 I disabled the exposure for years and the white balance was still usable. At V-Ray Next the white balance is disabled if the exposure option is disabled. Also at VfR2 I used the color mapping multiplier if I need to readjust the brightness of a complex scene with many lights. This option isn’t available anymore.

I wished the lens length wouldn't influence the output brightness like a at cheap lenses and I could render without to fight against this effect.

Ciao,
Micha

[^Lele^]

Could it be optical vignetting?

[Micha]

It's not a kind of vignetting. I think the effect in the real world is that a tele lens magnify the projected image at the sensor moreover the sensor area, so that less light, which is coming through the lens, is used at the area of the sensor. At basic zoom lenses can be found for example 28mm-210mm F2,8-5,6. Expensive profi lenses support constant F-stop. Unfortunately V-Ray simulate the cheap lenses and the user need to fight against this effect. So, you can render a white object at 28mm and at 210mm is much to dark.

[^Lele^]

https://en.wikipedia.org/wiki/Vignet...cal_vignetting
It is, and like in the real world, if the focal length variation is too big to recover in post, you do it in camera by lowering F, or raising ISOs.
You can, alternatively, use a non-physical camera, and the VrayExposure effect, which won't be sensitive at all to the camera focal length.

[Micha]

There is no non-physical camera, only standard (physical) and VR (pano). It's not possible at V-Ray Next to control the exposure without the cumbersome real world side effects. Also the white balance can't be used, if the physical camera exposure is disabled. It's serious problem and a pain to work with the side effect of inconstant exposure. I hope a solution will be possible. It looks like at 3dsmax the user don't need to live with the side effects.

[^Lele^]

Wrong forum section.
Rhino devs won't read this, and i cannot help you, besides acknowledging it's what it is in Rhino.
My answer, of course, was for Max.

[Micha]

Your answer helps me so far it looks like there is a solution at 3dsmax. I ask at the Rhino side too, but there is no interest to provide a solution. I don't know why. The problem is the goal at V-Ray Next seems to be to keep the UI so simple as possible and this cause that the workflow breaks quite hard and cause a lot of trouble some times.

Do you have an idea how I could get V-Ray Next working, so that I can adjust the exposure and white balance without camera dependent exposure jumps? It's quite difficult to get contact to the chaosgroup at the Rhino forum. The only answer one week before was - it's the expected behavior. But it's not practicable in a daily professional use.

(https://forums.chaosgroup.com/forum/...ent-brightness)

[^Lele^]

I'm looking into it, give me a few minutes while i set myself up with Rhino and VfR.
EDIT: Micha I'll need a bit more time, it's a national holiday today in Bulgaria, so the office is quite empty.
I have ideas, but need to speak to the devs.

[^Lele^]

Micha so the devs are looking into possible ways of decoupling the physical camera model from exposure, in Rhino, similarly to what Max can already do.
It may not be a quick fix, but it's likely to happen.

[Micha]

Great, thank you very much for spending your time and bring it on the way.

[^Lele^]

I did nothing, in fact, if not discovering they were already looking into it.
We almost always hear everyone here, just that some things take a bit, and the outcome is often not known, so we prefer to keep a low profile until we have tangible results.
But yeah, i'm good at kicking wasp nests!