Vray light meter

[rajdarge]

please add a feature to allow scripted access to the light meter to trigger a calculation

Raj


BTW the directional property of vray lights is very nice now.
Raj

[vlado]

please add a feature to allow scripted access to the light meter to trigger a calculation

Yes, made a note to do it.

BTW the directional property of vray lights is very nice now.

Glad to hear it

Best regards,
Vlado

[rajdarge]

is the light meter a cardiod or flat sensor type?

if I convert ISO, SS and A to Exposure Value with Vrayphyscam
ie A= 8.0 ISO = 200, SS = 125
I change A to 8.1 and back to 8 keeping EV constant and SS fixed, the ISO jumps to 210

Is this a rounding error in max, the Vray Physcam or somewhere else?

I found that setting lights to watts was a fair approximation of my studio setup (with real studio lights, reflectors and lightmeters) in v 2.01
but in 2.02 it is 4 stops too low ( I can fix this with a fudge factor that I am already using, but is this behaviour between the versions what you wanted ?)


Raj

[rajdarge]

I found the source of the error:
here is my fixed code
EVnum = (log10 (ap^2.0*SS) + log10 (ISO/100.0) )/log10 2

I was dividing ISO by 100 and not 100.0
I still get an error but its on the 3rd significant number
so I will have to start adding some roundings

Raj

looking at the Vrayutils.ms

why does
renderers.current.showlastVFB()

pop up the VFB window and this
command
showproperties(vray())
not reveal this command.

are there others undocumented ?

[chicoone]

While on the subject and if possible; can I get a standalone light meter for Vray 1.5 and Max 9...? Not even Santa helped me this year to upgrade.

[rajdarge]

you can make your own scripted light meter with a fisheye camera lens and 180degree FOV and a small 1x1pixel render .

by the way that formula up there is completely wrong (dont trust wikepaedia)
this is the correct one:
EV = log(ap^2.0 * SS * 100.0 / ISO)/log 2.0
also I'm a bit rusty as I haven't done any serious maths in 25 years.

Raj

[chicoone]

I'm totally rusty as i never have done any scripting... Ok, will see but all I want is the foot-candles on an area or point.

[rajdarge]

depends on what you want to achieve.
If its to render and expose the image properly:
make a camera at the subject,
point it towards the main camera,
make it a fisheye lens of 180 degrees.
render a 1x1 pixel render
this pixel will tell you approximately how much light is falling on that point. If its out of the range you want - its over exposed.
adjust the lighting appropriately as the pixel is in HDRI format.

Just like you can use a camera as a crude light meter

It will not give you foot candles.

I think the light meter in Vray 2.0 does something similar
but then vlado converts it to LUX ( similar to foot candles)
he used some conversion formula that is highly dependant on the way that vray has been created
Not sure how he calibrated it .

Maybe he will give you the conversion formula.
When I am finished my current script mebe I could try and write that light meter one for max 9. I would have to be careful to only use commands for that
Since I never used max 9 - I might have to get you to send me the Online Max script reference.

Raj

[vlado]

looking at the Vrayutils.ms

why does
renderers.current.showlastVFB()

pop up the VFB window and this
command
showproperties(vray())
not reveal this command.

are there others undocumented ?

Most of the MaxScript methods are listed here: http://www.spot3d.com/vray/help/200R..._maxscript.htm

Best regards,
Vlado

[rajdarge]

thanks I was looking for something like that.

any idea on how long it might be before I have a trigger for light cal available ?
I have a workaround but its cumbersome and I'd rather not write it if the trigger is just around the corner.

Also I just made some calibrated photos with my light meter, a model and a calibrated colour chart from x-rite

Using the studio strobes that I have with the diffusers that I have
I get pretty similar results using Power set to watts, but I have pretty well precisely 2 stop difference between what I get with vray and what I get with my camera and lightmeter

I should have done distortion maps for all my lenses while the studio was set up, but I forgot.
once I have done such a thing, is there some kind of database of such files that I could upload to?
Raj