Film-Tech Forum ARCHIVE: Question about slide projectors

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Posted by Sam Hunter (Member # 1119) on 10-20-2003, 02:22 PM:

What is the common method of fading or whatever used on slide projectors when the projector advances slides? Is the bulb being killed or is there an mechanical type shutter being used?
Thanks.

Posted by John Pytlak (Member # 331) on 10-20-2003, 02:31 PM:

Usually, a mechanical "dark shutter" is used. Kodak Ektagraphic slide projectors also allowed the use of an external "dissolve control" to fade between two projectors electrically:

Kodak Ektagraphic Slide Projector Manual

Posted by Stephen Furley (Member # 1277) on 10-20-2003, 02:36 PM:

Both systems are used; most simple projectors just use a shutter to cut off the light while the slode is changed. Projectors which can fade to black, or be used in pairs for disolving between slides normally dim the lamp. At least this is the case with halogen lamps. Xenon projectors have to be dimmed mechanically.

Posted by Sam Hunter (Member # 1119) on 10-20-2003, 03:09 PM:

I have an Sawyers 500 series in which I was trying to come up with a way to fade between slides instead the picture sliding back and forth. There is a cam operated advance unit that I was gonna control a relay that kills the bulb during changes. The only problem I see is the abuse of the bulb as which I was going to run bulb current through a resister during the off cycle to help protect the bulb.

Posted by Scott Norwood (Member # 30) on 10-20-2003, 05:13 PM:

Sam--just get a commercially manufactured dissolve unit. These things are dirt cheap on Ebay right now. Most are designed to sync with two projectors and a tape recorder. You can use it with one projector and a cheapo Radio Shack-type tape recorder to record a tape with only dissolve cues and then play it back during the show to automate the fade-out/change slide/fade-in process. It's easier to do than to describe.

Alternatively, there's a particular model of Telex projector that has a built-in timer which will fade out the slide, advance to the next slide, and fade in (by dimming the lamp) at regular intervals, usually ranging from about 3 seconds to about 15 seconds. I believe that there is a Kodak model that does this, too. This is simpler, but probably more expensive, since it requires buying a whole new slide projector. Both the Kodak and Telex models use the same type of slide tray.

Posted by Sam Hunter (Member # 1119) on 10-20-2003, 09:28 PM:

So far I have been outbid on every Kodak I have bid on as I do not wish to spend a whole lot for one. For something that is so out of fashion slide projectors sure seem to be popular on Ebay.

Personally, I like making things and I want to try modifying my Sawyer.

With that what do you think about killing the bulb during slide change and dimming the bulb to almost extinction?

Posted by Travis Hubrig (Member # 1745) on 10-20-2003, 10:17 PM:

We use Telex Caramate, 3150? Halogen bulbs that dim on slide change... bulbs last for something like 250 hours.
approx. 90 days on or off for 3-4 hours between shows.

Posted by William Bunch (Member # 1040) on 10-21-2003, 05:10 PM:

We use Telex projectors too. The bulb dims between slides. Our machines use the "EXY" type halogen lamp. We get nowhere the life that Travis is getting out of his. Maybe only 50 hours. It could be the extra vibration on the filament. We are on 50 Hz over here.

Bill BuncH
Misawa, Japan

Posted by Travis Hubrig (Member # 1745) on 10-24-2003, 08:41 PM:

The bulbs are very touchy, we use surge protectors.
It increases the life dramatically. The slide proj bulbs, can't handle much variation in current when operating, small surges would almost certainly wreck a bulb.