Real World Camera to VRayPhysical Camera

[Morne]

I have a wide angle photo taken with a Nikon D40 and in the properties of the jpg it says:
focal length: 10mm
max aperture: 4
35mm focal length: 15

so to match that in VRayPhyscial cam I put my focal length to 15 but its nowhere near the foto. To get a more accurate match I have to set my vray cam to 18.135 focal lenght. Something is off here or am I missing something?

match was done with manual measurements. (spot was marked on site where person was standing and I matched this spot on the plan) viewing direction was manually done in viewport. Its pretty accurate match (well about 85% to 90%). I would love to get it 95%

so the question is do I have my focal lenght wrong or whats up?

[vlado]

What is the censor size (film gate)?

Best regards,
Vlado

[Dave_Wortley]

You will also want to do a lens correction to remove the likely large warping you'll get on a 10mm lens. I would expect it to be a 16mm lens not 15mm as it's a 1.6x conversion normally for cropped cameras.

[Morne]

What is the censor size (film gate)?

its the vrayphysicalcam default: film gate (mm) 36.0

You will also want to do a lens correction to remove the likely large warping you'll get on a 10mm lens. I would expect it to be a 16mm lens not 15mm as it's a 1.6x conversion normally for cropped cameras.

I can live without the warp, but not sure what u talking about in the 2nd part about the 1.6 conversion and how does that help me?

[vlado]

I meant the film gate on the actual camera...

Best regards,
Vlado

[Morne]

I dont know, it doesnt say. But I have the RAW NEF file if that helps?

[Morne]

can I somehow get EXIF info out of the raw nef file and pump that into the vrayphysicalcam?

[Macker]

The sensor size affects crop factor, the default VRay sensor size (film gate) is 35mm, the equivilent to a full frame camera. You need to find out the sensor size of the camera (shouldn't be very hard at all) and input that as the film gate on the Vray Cam.

[edit] A quick google search says the sensor size is 23.7 x 15.5 mm, so put 23.7mm in your film gate et voila.

[Morne]

then for my focal length
jpg properties
----
focal length: 10mm
35mm focal length: 15
----

do I then use 10mm or 15mm for my vrayphyscialcamera focal lenght?

[zeronove]

according to manufacturer specs the D40 sensor size should be 23.7 x 15.6 mm

EDIT1: ops, sorry ...too late

[chriserskine]

you should be able to do either.

leave film gate as is and do a 1.5 times to get 15mm (nikon is 1.5, canon 1.6)

or change the film gate and leave at 10mm.

[Morne]

ok I got a pretty accurate match I'd say about 95% or so

the problem now is the exposure. If I put those exposures into my VRayPhysicalCam, it looks like a nuke went off - everything is extremely over exposed. Using the VFB's exposure correction, I have to go down by as much as -2 to get it more or less same as the real foto. It seems the problem lies in F-Stop which doesnt seem to be correct. The photo has Fstop of 14, but with vraycam I have to double that number to get similar results

Recommendations? Just wing it?

(could the problem lie in the VRaySky that is too bright?)
I have vraysyn/sky with default settings and sun time of day and position same as photo

[tehamnes]

It's almost impossible to directly share exposure values between a real-world- and the Vray Camera. This i due to your real-world camera is measuring the light using its own matrix or area evaluation of the light. The light meter in a real camera considers 18% grey as the neutral which give the "correct" exposure". That's why photographers use a neutral grey card to set the correct exposure manually. So what matters is what you point your camera at to measure the light to get the exposure value (combo of f-stop, iso, and shutter speed).
To match the vray camera exposure values to a real camera exposure is therefore difficult or "meaningless", but if lucky the values from real photo can get you close in some ideal situations.
I would suggest you adjust the vrayphyscam iso f-stop or shutter speed until it looks right. You only have to consider one of these parameters at a time.