Variable light control switch for projectors - anyone tried this?

[Tom Fales]

I am looking to control the light projected through the film gate on a number of projectors. These projectors all have different specs; some use a 120v lamp, others utilize 8v or 12v lamps. Unfortunately, I don't have schematics for them, so I'm opening a discussion with the experts to see if anyone has any experience with doing this and what I should be looking for (or to avoid).

As further clarification, I am looking to modify these projectors for direct film gate transfer using a camcorder. Light control is critical in getting a good print. To date, I have been removing the existing lamp module and installing MR16 (GU5.3) type halogen or LED lights and running them through a separate dimmer control powered by a DC power supply. Works well, but I'd like to see if I can eliminate a component.

Thanks
Tom

[Terry Sills]

Tom
I always run my projectors through a variac transformer, not for film transfer, but just to save bulb life. I reduce the voltage as much as I can but high enough to allow the projector to run. This is usually about half the normal voltage and seriously dims the
lamp brightness and somewhat reduces the speed of the projector. You can then slowly wind up the voltage to the correct one.
as I say it works for me in saving the lamp from that initial voltage surge. May not work for your purposes, though worth a try maybe.

[Brian Fretwell]

Doesn't the dimmer give trouble by changing the colour temperature of the lamp? Or are the sensors you use wide range enough to cope.

[Tom Fales]

Brian - I've not seen any noticeable color temperature change. The dimmer that seems to have the most control is the one pictured below:


I went to the 30A control (and typically 16 or 18 gauge wire) to allow for a wide variety of halogen and LED lamps to be used. This particular dimmer seems to allow sensitive light adjustments. In the case of using LEDs, there is a variety of different temperatures available.
Terry - most all of the projectors I work on already have variable speed control so I don't really want to mess with the motor speed, just the feed to the lamp.

Tom

[Tom Fales]

I guess I'm just going to have to experiment with this.

[Lee Mannering]

Hi Tom. You really want a cold light LED.

For fun a few years back I converted a Eumig sound projector for 8mm transfers which i loaned out from time to time.

Get some pcb and draw the outline of a A1231 lamp round it. Cut it out.
White margarine tub cut a circle and fit to front of lamp bracket to act as diffuser
Fit a small array of leds to it and run a power cable.
I put a 12v dc power unit in both a small circuit the a pot to vary volts from zero to 12v.
The optical side will depend on what sort of camera you use. I put a hd camcorder on mine, but the new owner has put a 4K unit in place. Still works well and sound.
Hope this helps you on your way.
Take care