[MF3D.FORUM:1053] Re: Mounting issue

[Alan Lewis <3-d@xxxxxxxx>]

Bill Glickman wrote:
> 
> George...
> 
>        It is very easy to align the cameras... After you put them
> > on the bar, make sure that the center of the viewfinder of
> > each camera is pointing to the same object at infinity.
> > (It is important that the object is far away because the
> > lenses will be converging to this object.)
> 
>           For SLR's this work fine, but I forgot to mention my M7's are
> rangfinders.  That is why I suggested shining a light through the lens on to
> a wall?   About how accurate should they be.. say one camera should not be
> more than 3 deg. off from the other? If so, that is easy to eyeball... I was
> trying to be more accurate than that..

On my twin SLR rig I would just fasten one of the cameras to the bar as
parallel to the bar as practical, then to align the second camera I
would use a ruler (6" or 12" or anything) and place it onto the face of
the lens of the first camera (which is already fastened) then twist the
second camera on the bar until it's lens face is also parallel and
touching the ruler.  The lens face is usually the filter thread ring.

I would use the lens without any filter on it to make it more accurate,
and make sure both lenses are focussed at infinity.

What this does is to align both lenses to be parallel and also prevent
one camera from being offset in front of or behind the other.

The ruler is just a straigtedge, no actual measuring is done.  Any
straight, sturdy bar will do.

I would also do this in the field as a check to make sure that the
cameras are still aligned properly.  Unless you somehow lock the cameras
on the bar (with more than just the tripod screw) you will eventually
find that one camera has twisted after being used a lot.

One other check is to make sure that the cameras are aligned
vertically.  You don't want one camera pointing down and one pointing
up.  I checked this by visually looking across the lens faces from the
side.  I can easily spot if one lens face is tilted from the other.
You could also use the straightedge method for this if your straigtedge
is at least as wide as the lens face diameter.  You hold the
straightedge onto one lens face and then look for daylight between the
other camera lens face and the straightedge.

To reduce this vertical problem I would not use a rubber facing on the
twin bar, I just used bare metal.  I don't think I ever had a vertical
alignment problem when fastening the camera directly to metal.

Lot's of words for a very quick and simple procedure, so it sounds
complicated!

If you only want to do this once in your lifetime then you will need to
add some kind of adjustable fences/stops onto your bar.  These could be
angle brackets or anything else that lets you butt your camera rear
panel against it.  Adjust once and that's it.
Stricly homemade stuff though.

A diagram:
			straightedge
	__________________________________________
		|	|		|	|
		|	|		|	|
		|	|		|	|
		________		_________

		Lens			Lens


-- 
Alan Lewis  
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