vraysky at night

[RayOfLight]

is it just me, or doesn't this work?
I place a daylight system, put it to vraysun, in setup, I enter a time of 0:00 hours, midnight.
I render with a vrayphysical camera, (in the scene a plane or vrayplane and a teapot, both with a default vraymtl). I render, everything black, logical, there is no light, so I place a photometric light, vrayshadows, 200lx at target distance (teapot).
Of course we have to set the camera exposure to match the light in the scene...A possible night setting on a real camera could be, f-number 2.8, shutterspeed 1/15s and Iso at 400.
This results in a nice teapot, shadows and groundplane...and a sky, bright blue (0.0, 0.0, 100.x)(up to 100 that is).
Why is this? The sun is below the horizon, everything should be dark, the vraysky will lighten the scene a bit, just a little bit, but it should look black.
With a real world camera, an Iso 800 film, a f-number at 2,8 and a shutterspeed of 20 seconds, still results in a pitchblack nightsky, with bright lit stars...but the sky is dark..
Am I doing something wrong? Or is this a bug?

(and yes, I know, I could make a nightscene with the sun and sky turned of..but with a day/night simulation this doesn't make sense. I don't turn the sun and sky of IRL, I only adjust my camera..)

[vlado]

The V-Ray sun and sky are based on a model for daylight illumination; they do not really attempt to model night-time illumination from the Moon and the stars.

Best regards,
Vlado

[RayOfLight]

so it should only be used during daytime...hmmm, it would be nice to have the "moon, planets&stars"-option too...perhaps it can be scripted..like, a new and correct "day&night System"..

maybe I should do some research on it (perhaps someone else already made it, like in Vue)

[vlado]

Well, technically you can write your own night-time environment map as a texture for 3ds Max, which you can use inside a V-Ray dome light for the illumination.

Best regards,
Vlado

[RayOfLight]

I haven't done any scripting yet...(I used to make programs for a living once), but this might be a nice one to start with...although it also might be way too much

[Morne]

@Vlado
OK so this should only be used for daylight?
how much of an effort is it to fix the VRaySky to be dark at night?
I often use the sun below the horizon (kinda semi dark) and the VRaySky never seem to be correct. As soon as I go below the horizon, I get "incorrect" Sky colours.

[^Lele^]

The simples way would be to use an external application to render and HDRI of the moonlit sky (like Vue, or similar), and then add it to the domelight, as Vlado said.
I very much doubt anything like that is of easy scriptability.
It will need some serious coding abilities, and the VRay sdk to create one.

Another method can be that of "abusing" the sky parameters: lower turbidity to 2, and raise ozone to 1.
Then, compared to a default Physcam exposure, lower the Sun multiplier to something like .1-.4 (depending on sun height onthe horizon).
That looks much like a night sky to me.
To help the tinting when the sun(moon!) gets low on the horizon, a camera White Balance color similar to Peach can help (255,211,184)
On the shadows / moon image size, while there's no current way of directly adding a texture to the sun disc, raising the size multiplier to something like 25 will help soften the shadows and make the reflections take into account the disk, and adding a disk (self-illuminated, and not shadow-casting) in front of the sun will do the trick is the moon has to be visible and detailed.

[RayOfLight]

good explanations, and thanks Lele for the warning about the scripting
I'd better start with something easier..

[jujubee]

Do you suppose Vlado it would be difficult to include somethin in Vraysky which would simulate night conditions under clear sky?

I suppose the horizon would start to turn a faint blue and the rest of the sky would start to turn darker around a sun's target as it moves to the opposite end of the earth.

Perhaps we can have something such as a 'VrayMoon'?

I realize this sun/sky work is based on technical research papers - but isn't that mostly about falloff and gradients that change with an object (in this case a sun)?

Seems simple to me - but then again I can't program.

[vlado]

It is about falloff and gradients, but they are still based on actual measurements of the sun/sky luminance.

There was, in fact, a paper on night-time illumination and we may think about it, just don't expect to see all the stars by their names Not sure if the moon texture should be included either, as it will need to be based on a photo or something.

Best regards,
Vlado

[Aldaryn]

Actually I think adding a basic star database would be easier than many might think.

Anyway, it would be nice to see the sky system working with a sun below the horizon. For me especially for dusk shots. you know, fun time for architectural photographing starts half an hour after the Sun has set.

Best regards,
A.

[werticus]

google earth covers the sky i believe now.

[jujubee]

Wow - this would be fantastic. As for 'stars', that wouldn't be that important to me as long as the general illumination would be there.

Most of the time in the city, you will not see stars anyways. Which I suppose may bring up a different issue entirely. Perhaps a 'light pollution' parameter is added lol.

If you were to add stars that would be a 'bonus', but the option to turn it off would be needed as well.

[Aldaryn]

But the timelapse stars image just looks too darn sexy... But the moon is definitely a photo.

Best regards,
A.

[RErender]

or textured sphere