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[MF3D.FORUM:1069] Re: Mounting issue


  • From: "David W. Kesner" <drdave@xxxxxxxxxx>
  • Subject: [MF3D.FORUM:1069] Re: Mounting issue
  • Date: Thu, 10 Aug 2000 22:41:15 -0600

Bill Glickman writes:

> Once again, I am confused....
> 
> > Just remember that no matter how "square" your two cameras
> > they will always have the problem with the chips.
> 
> Why?  If the cameras were perfectly square wouldn't the left
> chrome alwasys show more left image every time?

Remember "LLL" the left image shows less on the left side.

The problem is that with two separate cameras there is no 
"built-in" window or the window is set at infinity. That means 
that the infinity points will be at the window and the entire 
scene will be in front of it (coming through it). That is what 
all that "excess" image is that you see in one film chip and 
not the other. The only way to get rid of it is:

1) to have the camera lenses and film gates offset to provide 
a "built-in window"
2) to toe-in the cameras to achive the same thing (sort of)
3) to mask the excess out with the mount (some times this 
means going to a small width mount - such as a 6x4.5 portrait)

Think of the spacing like this:

You have an object that is 12 inches wide in front of two 
parallel cameras. At the closest the lesnes can be the right 
camera "sees" only the right most 11 inches and the left 
camera "sees" only the left most 11 inches. When you go to 
mount these film chips you will need to have the inner most 
edges show the most amount of image, but the extra image in 
each is the outside edge.

The confusion may come from the fact that as you move film 
chips away from each other in the mount it exposes more of the 
inside of each chip which is setting the window closer and 
moving the scene behind it. When you move cameras away from 
each other you are losing image material from the inside edges.

With my past history of confusing people, I hope you 
understand this. I know what I am saying, but may not be 
conveying it very well. Perhaps someone else can do a better 
job.

> Why would one want to toe in the cameras?  

I DO NOT advocate toe in as I don't like the keystone 
distortion it can cause. However, done judiciously under the 
right circumstance the effect can be hardly noticed.

> I thought perfectly square would be the ultimate, right?


Yes, square, parallel, flush, matched cameras are the 
ultimate. Having a built in window just allows more of the 
image to be used without cropping.

That's all for now,

David W. Kesner
Boise, Idaho, USA
drdave@xxxxxxxxxx