Problems with Target Distance on VRayPhysCam

[MoonDoggie]

We are having issues with VRay 2.20 and the target distance on VRayPhysCam.

We are re-creating shots in reality for a composite photoshoot. Because of the sensitive nature of the work, I'm using another file to illustrate the problem.

We are test shooting with a Cannon with known lens sizes of 18mm, 28mm, and 50mm. So we recreate our 3d in reality and everything is crazy off.

So we checked and the problem is the "target distance". It changes the composition completely. Here is the target distance at 24cm

Here's the renders with the target distance at 24cm, and 7cm

24cm:


7cm:


Here are the screenshots of my viewport:

24cm


7cm


We are under the impression this is a bug. If it's not, how can we correctly recreate our scene in reality if changing the target distance changes the composition so much? Thanks for your replies.

-Colin

[vlado]

Are the units set up correctly in 3ds Max, and is the scene modeled in the correct scale?

For the FOV change, check out this post: http://www.chaosgroup.com/forums/vbu...882#post548882

Also, it's a silly question, but is the target distance correctly the distance to the point you want to focus on?

Best regards,
Vlado

[MoonDoggie]

Vlado,
Thanks for your quick response. The scene is modeled correctly at the correct scale. I'm sorry I posted the image of the really blurry pens, it's not pertinent to this discussion. We are just trying to figure out why the shift in perspective is happening. Thanks for the link, we'll check out that thread now.

[MoonDoggie]

Vlado,
We're about to go do another photoshoot and this issue is still a problem. I checked the thread you posted about FoV changing and am sitting here with my Canon 40D (which it looks like you are using too) and changing my focus does not change the FoV at all. Is the correct workflow to matching a Hasselblad medium format camera this:

Sensor size: x - 53.7mm, y - 40.2mm
Resolution: 8956 x 6708

So we set our VrayCamera to this for a photo we took on a 28mm prime lens:

Film Gate: 53.7, Focal Length: 28.9

But now what do we set the Focus Distance to? It's changing the composition so drastically that we are confused. Thanks!

[MoonDoggie]

Also, is the FoV Toggle in the VRayPhysicalCamera a diag/horizontal/vertical Fov?

[vlado]

It is horizontal FOV.

Best regards,
Vlado

[MoonDoggie]

So I still don't understand why a focus point changes the composition and framing of the shot. If I move my focus ring on my 40D, it just adjusts the focus. Maybe we're having a term problem? Anyway, as a temporary solution Vlado, do you suggest we get the Horizontal FoVs of our lenses and just plug them into the vray camera so we can stop worrying about it?

Cheers,
Colin

[vlado]

do you suggest we get the Horizontal FoVs of our lenses and just plug them into the vray camera so we can stop worrying about it?

Yes, that would be the best thing to do.

Best regards,
Vlado

[MoonDoggie]

Thanks Vlado for your help.