Curved Film Gate - what radius?


#1

Hi all,

I’m starting on a gate design and am thinking about making it curved since it’s all the rage with the commercial scanners.

Does anyone know what radius the curvature should be? I want it to be be slight enough that we don’t have to correct the image in post but also enough of a curve to help flatten warped film.

Any help is much appreciated!

Matthew Epler


#2

The gate design is dependent on the type of camera you are using. An area-scan camera would like to see the film perfectly flat as it captures the frame. A line-scan camera like the Spirit and others use only captures a single (or three) line/s of the image, so a line-scan can take advantage of the curve.

Having said that, the issue you are trying to solve, how to capture a warpy film, can be dealt with to an extent. The gates that use a pressure plate, as in a camera or projector, can give us guidelines. The Richardson movement that was mentioned in another thread is a good example. A version of that idea would help many films. If a truly terrible film needs capture, another approach would be to make a sandwich between two pieces of optical glass, like microscope slide glass, or similar. This idea needs a stop-frame capture, as you would need time to open and close the glass as the film moves.

many choices, and maybe separate gate designs for different situations. This implies a quick-change type of mounting, so you can change gates as required.


#3

Thanks, Grace! That makes perfect sense. I have a good gate here from a 35mm machine with pressure “rails” instead of a full plate. It seems to work really well. I’ll see what I can come up with.

Any visual references to existing solutions are most welcome!

M


#4

Also, I wonder if just a slight curve would be acceptable and/or effective with warped film? I suspect that any radius qualifies as a distortion and therefore should be avoided (since we’re using a full frame camera).

We could switch to a line-scan camera at some point but it’s too late for now as I’ve already spent the money on a full frame option based on some other recommendations.

M


#5

With an area-scan camera you could get away with a little bit of curve if your depth-of-field is greater than the curvature. To get a larger depth of field, you need more light, maybe a lot of light, and speed up the shutter, and close down any iris you have in the lens. I am projecting for my lighting system, a 400watt light, with a shutter speed of somewhere around 20 microseconds. This may be enough. My Spirit has a 300 watt xenon lamp, but the newer ones went to a 700 watt.