using a russian collimator

daniel mahlknecht · November 6, 2010

Hi,

I yust bought an russian collimator.

see a picture at: www.dapalmerfilm.com/fotos/autocollimator.jpg

I have only what you see in the picture. Do I need anything else to check the lenses?

Does this collimator work with anamorphic lenses (I should have checked this before I bought it...).

Actually what I want to do with this collimator is check my lens set after I have changed the lensmount, as I might quiet frequently have to switch between OCT19 and PLmount.

The lenses I want to test are the lomo roundfront anamorphic primes 35mm, 50mm and 75mm, the OPF18 Zoom (40-240 anamorphic) and the OPF7 zoom (50-500 anamorphic).

As the next lenstech is abouth 300km away from where I work, and changes might have to be done over night, I thought I should learn to do them by myself.

As far as I understand, I have to put the lens in front of the collimator, then put the mirror in the focal plane where the filmgate shound be, and evaluate the reflection. Am I right so far, or didn't I understand nothing at all? Unfortunately the manual is only russian.

thanks

daniel

Dom Jaeger · November 7, 2010

As far as I understand, I have to put the lens in front of the collimator, then put the mirror in the focal plane where the filmgate shound be, and evaluate the reflection. Am I right so far, or didn't I understand nothing at all? Unfortunately the manual is only russian.

I'm not familiar with that collimator, but it looks a little like one of the collimators I have in my workshop, an old 50's model that was set up for Bolex mounts. Unless you have a mount set up in line with it with a mirror behind at exactly where the film plane would be, I think it's more of a field collimator. With a lens mounted on a camera, set wide open and at infinity, you point the collimator down the lens and adjust the knob until the reticule visible in the collimator eyepiece is at its sharpest. Turning the knob should move a marker on the scale to tell you exactly how far out the back focus is, so you can adjust or shim the lens accordingly. The camera flange depth needs to be correct, and while film in the gate will reflect a little, ideally you put a mirror at the film plane or use a very reflective backing plate such as is used to measure the camera flange depth with a depth gauge. You also need to adjust the collimator eyepiece to your eye - on my old version you focus so the texture is visible. If the camera flange depth is set a fraction under the nominal depth (on a 35mm Arri it is usually 2 to 3 hundredths of a mm under 52.00 for example, to allow for film breathing in the channel and to penetrate into the emulsion) you need to take that into account. By turning the mirror in front of the gate aperture you can check the ground glass depth, although being less reflective it can sometimes be hard to see. Wider and slower lenses (like Lomo anamorphics) are also harder to see.

Hope that helps a little.