Most viewfinders are short-range telescopes that view the inverted image on
the ground glass. On straight through doors the mirror shutter and 45-degree
mirror act as a simple periscope and do not effect the image.
If you are shooting with an Arri II or III, with the camera upside down (if
shooting with a relay lens) and want the image right side up relative your eye,
you can remove the optic tube and replace it with a simple lens to view the
ground glass. A 3 to 5 inch focal length lens will do. (The viewfinder tube
inverts and reverses the image while relaying it from the ground glass to in
front of the eyepiece.) You will have to adapt the lens to fit the 1" plus viewfinder
tube hole. Watch for light leaks back to the film if your eye doesn't block
all the light.
You can't do this with an Arri 16 S because the image is relayed to a ground
glass just in front of the eyepiece. This image is larger than 16 mm format.
The Arri 35 ground glass image relayed from the ground glass is reduced so that
the 16 and 35-mm eyepieces and periscopes will work interchangeably.
If you want a smaller image of the ground glass to your eye, a 75 mm lens as
an eyepiece works well. Matching the metric threads of the Arri eyepiece is
a metric lathe job.
A periscope finder can be made by placing a prism where the light trap goes
and a second prism to make a tube that will tilt up. A 3 to 4 inch lens will
do for a viewfinder.
For shooting sports hand held, seeing much more than the camera sees is very
handy. Cut the film chambers off of an old interchangeable ground glass still
camera and use it as a parallax finder. Some means to align the two images is
necessary. With wide lenses at a distance the parallax error is no problem.
If you shoot with the same focal length on the still/finder as the film camera
you will see double the area. You can scribe the TV, 85 or academy frame size
on the still ground glass. Align the still image with what the film camera sees.
This worked well with the Photosonics 4ML 200-FPS camera. There are a lot of
junk still lenses around.
We tried a fiber optic remote finder years ago with little success. The image
was too dark and the resolution poor.
Extension finders for Arris can be made with Porro or roof prisms and short
range telescopes. You can also use the prisms and eyepiece from mono and binoculars.
Replace the front element with a shorter focal length lens extended to focus
on the image at the end of the viewfinder optic tube where the eyepiece attaches.
Half of binoculars with individual eye focus is best.
If you are shooting very slow frame rates of moving objects, information is
lost while the shutter is open and no image is coming to your eye. A parallax
finder is helpful. This can be a monocular with the front element replaced with
a cheap still zoom. You will have to put a frame size reticule at the focus
of the eyepiece. This focus is usually just in front of the eyepiece optics.
Position this reticule after the new front zoom section is done. You don't want
the reticule image to move when you change your eye position.
© Copyright 1999-2004 Ron Dexter. All Rights Reserved.