vrayPhysicalCam issues.

[re:FORM]

I'm a bit confused (now there's a change!)...

I noticed a variation in my background colour in an animation which I just couldn't explain. After much digging around I narrowed it down to the fact that when my camera is animated, the distance between camera and target varies. I didnt previously consider this to be a problem as I thought exposure was only affected by film gate, focal length, f-stop,iso, and distortion. so... fair enough, the camera is physically correct, so the amount of light hitting the lens when the target is closer to the lens will be less.... Obviously, this is a bit of a problem when you are trying to work on colour balance on an animation and you find that things that were nicely white at the beginning of the animation become dark by the end.

The parameter I would assume to use to fix the target distance is "target distance" which is actually greyed out when you are in 'targeted' mode.

Looking at the vray docs, it is described as "the distance to the camera target for a targeted camera." which makes absolutely no sense when you can only ever use this parameter when the camera doesnt have a target! (perhaps 'targeted' should be 'free').

So.... when I click targetted off, my camera looses its target animation I assume Im going to have to create a new camera(same settings but with targetted off), and parent it to the old camera?

[re:FORM]

Actually, I think I might have found a bug....
If I have a vrayPhysicalCamera (targetted), and I want to find the target distance at any point in the animation, I need to untick the 'targetted' box. This removes the camera target from the scene, and looses all animation that it had. Even undo doesnt bring back the camera target's animation.

I'm not sure why adjusting the camera target distance affects the field of view(or the focus distance for that matter).... surely this is set purely with the camera film gate, and focal length. Adjusting the distance of the target to or from the camera shouldn't effect the zoom should it? It should only effect the focal point used in DOF calculations. <edit> It seems alot more complicated to deal with than a normal camera where you have the camera point at an object(target), and you use the focal length to adjust zoom level, if the object moves towards or away from the camera, it just becomes larger or smaller in the frame, the frame captured in the camera would remain the same.... apart from the obvious refocussing required to keep the object in focus (which only applies in the vray cam when you have DOF on).

<edit> I think the best way to describe it is that adjusting the 'focus distance' doesnt have the same effect you would get in a normal camera when you adjust your focus. It would be like if you changed focus and the exposure was effected, which just doesnt happen in real life.

I think I've found the solution to my previous issue though.... I should be using 'specify focus'

[Neilg]

Adjusting the distance of the target to or from the camera shouldn't effect the zoom should it?

I'm a bit lost with the rest of your point, but i'm just chiming in to add that on slr's it does make a subtle difference.

[re:FORM]

Ah, it turns out my problem with the 'focus distance' is that I am using the camera at a very small scale (some objects are 1mm or less, ie a macro lens situation ). I created a clean scene, and changing the focus distance does change the zoom level by the subtle amount you would expect from a real lens. It appears that when the subject is very close to the vraycamera adjusting the focus distance has a very large impact on the zoom of the lens. I guess I need to use a different film gate to remove this effect.

To any experienced photographers out there... how does a macro lens compare with the default vraycamera? to emulate a macrolens would I need to use a zoom factor (thus decreasing the degree of perspective)?

Thanks for your help

[tricky]

I am using vray cameras for my current animation. I am worried from your post that I may experience some 'exposure flickering' as the camera moves through the scene - is this true?? (i really hope not and I hope I have misunderstood your post!)

[re:FORM]

I think you have misunderstood my post.

The problem is related to the distance of the camera from the target. At extrememly small distances, small changes in distance can have a large effect on the amount of light hitting the 'sensor' as it were.

Try it out, if you're working in metres, make a camera that's less than a millimeter away from the target, and render at different focus distances.... you 'should' see what I'm talking about.
For scenes with standard sizes, I dont think you'll have any problems.

When I get a chance I'll render some examples, and screenshots to explain the issue.

[tricky]

cheers fella!