Quick Lens Focus Check

On 23 Feb, 2009, Steve Morton had this fairly simple and easy solution to a problem I was having after taking a lens apart for a quick check and lube the day before a 35mm shoot. My problem was that I had a "multi-start" thread lens, and I couldn't tell which thread was the correctly started thread when I'd put it back together, and thus had no way of telling if my lens was properly focusing or not. I was using a desqueezer that was not trustworthy, which didn't help. I didn't have time to shoot film and process it, nor did I have time to send the lens/camera out for inspection, nor did I have a collimator. So here was Steve Morton's answer:

"Tape a scrap of 35mm neg or post in the gate, set the camera up on a tripod and point it at a light coloured (white) wall in a darkened room. Grab a bright torch or small desk lamp. Shine the light onto the film in the gate (without a mag present) turning your camera into a projector. You can then see EXACTLY what your lenses are doing.

I decided to share with everyone and add a few pics. I put it on a tripod, broke out my projection screen, a tape measure, some gaffers tape, a 600w lamp with barn doors, and a still 35mm negative.

Here's a close-up of the Gate with a frame of negative taped to it. Be sure the film is held tight and flat against the gate:
Tape Negative to Gate

Tape your film to the gate

Light shines through negative onto screen:
Shine light through gate and negative

Shine light through gate and negative

Screen is 1.5 meters away. I used a Negative with small/fine wires on the wagon to be sure of sharpness:
Projecting negative to screen

Projecting the negative through the lens and on to the screen

Matched up perfectly:
The markings matched perfectly

The lens marks matched my perfectly focused projected image

The original thread can be found here: http://konvas.org/pipermail/cinema_konvas.org/2009-February/006046.html