Dichroic Reflector vs. IR heat filter.

[Frank Angel]

We are still using Peerless Magnarcs for both XLs -- yes, I am not kidding - still using carbon arc. Unfortunately a steam pipe broke during covid and the 14" dichroic glass reflectors in both lamphouses were damaged. The new glass reflectors are hard to come by and when you can find them, they are pretty expensive. I was resigned to buying new ones, but then I found that we have two brand new metal reflectors in storage. Now I know the metal units won't have the heat mitigating properties of the dichroics and so they will pass more heat thru to the film, but I was wondering, would I be able to use the metal and just add IR heat filters at the mouth of the lamphouse to the same end, i.e., reducing heat that reaches the film. We run archival prints (I guess almost any 35mm print at this stage of the game is an "archival" print eh?!) and I want to make sure I aim the least amount of heat at that precious celluloid strip, especially on B&W prints. IR filters are pretty standard for xenon lamphouses, so getting a set for the two Magnarcs should he easy enough and, I am assuming, less costly than new dichroic reflectors. BUT would they be as effective? Waddyathink? And, BTW, yes, I still have boxes and boxes of carbons that should last me until I go to that big movie theatre in the sky, so NO reason to switch to xenon with it's skinny little arc and weird spectrum spikes all over the place in the green area. I'll keep that beautiful FAT plasma arc with it's much smoother waveform with barely any spikes anywhere -- true sunlight illumination between those two carbons..thank you very much!

[Sam Chavez]

I'm still running carbons in the warehouse cinema but our schedule is lighter than yours. Using dichroic reflectors. Someone here must have done a IR filter install on these lamps. Hope they are still alive to tell the tale.

[Mark Gulbrandsen]

I have seen both dicro reflectors and heat filters in a few Chicago 70mm booths that ran road shows for months on end. JJ's had a slot at the rear of the shutter housing for the heat filters. Lamps were Super Cinex.
You could call Jac Roe here in Nashville to see if they might have a line on some new reflectors.

[Phillip Grace]

Taking a step sideways for a minute, is it possible to have dichroic reflectors re-coated anywhere? I'm looking at ageing Kinoton reflectors and as far as I know they can no longer be obtained new.

[Sean McKinnon]

Phiilip, Boston Light & Sound has Kinoton reflectors some new some good lighly used depending in the size you need.

[Paul H. Rayton]

Optiforms, in Temecula, Calif. (an exurb of San Diego) is an OEM mfr. of many such reflectors, as well as re-surfacing existing reflectors. It's been over 10 years since I had one done, and it wasn't cheap, but you can get a current quote from them if you want to use your existing damaged reflectors. Presumably they can make the surface either dichroic or silvered, though the layering for dichroic-type surfaces are kind of their specialty. This is their website for contact: https://www.optiforms.com/

[John Eickhof]

note that optiforms exclusively coats metal formed reflectors, not glass reflectors like the peerless magnarc would use, they were balcold reflectors made by bausch and lomb. heyer shultz used to make metal replacements but they were uncoated and ran very hot on the aperture especially when running larger amperage trims. ir filters were the norm with the metal reflectors. i may still have a pair of decent balcolds, however, it was very difficult to match up a pair due to inconsistency of coating, color and brilliance varied more excessively than silvered reflectors.

[Mark Gulbrandsen]

John is correct. Metal only. I actually was standing and looking at the lamp house of Christie S-1 projector at the show in Vegas many years back. Another gentleman was also gazing into it as well. That person turned out to be the President of Optiforms. We got to talking and he told me that the projector manufacturers were foolish to go with glass, he said that he actually had a better system designed and tested that was all metal. He sort of hinted that glass reflectors were yesterdays designs...

[Frank Angel]

Yes, someplace back in the archival part of my brain I seem to remember that -- glass, while they were great for reducing heat, were inconsistency with matching pairs. I can't recall if anyone ever sold premium versions as matched pairs; perhaps that's what I got because I never saw any significant difference in light output between the two machines. Color matching, especially with carbons, is difficult to determine without test instruments.

These days running film here is certainly a rarity, although we continue to look for film engagements whenever we can with the classics. All of a sudden, running "the glory of film" has now become a hot marketing hook, but those engagements are far and few between in our big theatre. Our two screening rooms are digital only, although in one of them I did put in a xenon 16mm Eiki just before covid to run archival thesis films that student shot on 16mm. But when we do run archival 35mm film in the 2500 seater, I want to be sure to reduce the heat at the gate to as minimum as possible, especially now that I've put the metal reflectors back in. Years ago I upped the trim in the Magnarcs to 80 amps; that's when I put in the glass dichroics. I suppose finding IR heat filters today should be easy enough; I'll rig something simple at the back of the XLs to hold the filters in place. I've got water cool gates but to be honest, even with going thru the trouble of using that "wet water" additive to the tanks, I am not sure in the XLs at least, it really makes much difference in reducing heat on the image emulsion in the aperture. Then again, those Ashcrafts burn 120amps so maybe my worrying about heat is overkill.

Anyone know if there is a spec on the top limit of how hot the aperture area can be before the emulsion starts to blister? You should be able to put a heat probe in the aperture with the lamp on and the motor running to take a reading. That should be an easy way to determine whether your light output has a dangerous IR component...in other words --"Its to damn hot." It would be helpful If we had hard Fahrenheit figure that we need to stay below.

[Stefan Scholz]

Reflectors, the difficult part for film projection these days, as many manufacturers have ceased existence.
Kinotone and Ernamann mirrors were made at Weule in Goslar/ Germany, one of the oldest specialist companies to do dichroic reflectors. They ceased operation shortly after digital won internationally in 2013.
At the time being, they could deliver matched pairs, sorted from a production batch. A hefty premium on the price, but worth it, quite good match and close to requested color temp.

This is easier with silvered mirrors, they also have better color than many dichroic reflectors.
Dichroic mirrors areb made of manz layers of individual material, up to 30 layer are required. And many layers are hydroscopic, so humidity or condensation kills the surface. Some designs use a quartz (SIO2) protective top layer, which adds also scratch resistance.
Dichroic mirrors have a better light efficiency than rear coated glass mirrors.

I feel, not many specialists remaining, and the prices they ask for their service will not be low. Mirrors and Xenon bulbs might eventually be the items that end film projection.

[Mark Gulbrandsen]

I feel, not many specialists remaining, and the prices they ask for their service will not be low. Mirrors and Xenon bulbs might eventually be the items that end film projection.

There will likely be be laser sources adapted to film in the not to distant futurel... Plus there are a multitude of other uses for Xenon lamps, so those will not be going away any time soon.

[John Eickhof]

frank, unfortunately, there are too many variables pertaining to film buckling point temp, ie shutter dwell and exposure time, distance of shutter from aperture, ambient cooling at aperture and most of all film density and, emulsion and base ! a b&w print will bubble faster then color, and triacetate will bubble faster than estar....thus and a light scene will hold up better than a dark one and so forth!

[Frank Angel]

True, but seems that over the years every conceivable aspect of the physical structure of the film has been documented, one would think the SMPTE, for example, would have done testing to quantify at least some of those heat related variables, if not at least the tolerance of the two film base types, and come up with a maximum temperature at the aperture that should not be exceeded in order to protect all types of film that might be run on a projector. And no matter what all the other parameters might be, things like shutter dwell, distance from the lamphouse to the aperture, etc, none of that would matter if the temperature was taken at the aperture itself. Thing is, in real life situations, no one is going to readjust the lamphouse depending on if they are running acetate or mylar, color or B&W, so coming up with a nominal safety "universal" temperature that would be safe for all film certainly would have been a helpful stat for us back then. Then of course no matter how well the tech adjusts everything so that the "red-line" temp would be set and maintained, the projectionist no doubt will readjust the lamphouse to get the brightest picture on the screen no matter how the lamphouse was adjusted -- much like the gain levels of the surround channels. Theatre supply houses could then sell $3 oven meat thermometers as Professional Cinema Temperature Probes for $60.

[Sam Chavez]

Well stated John and Frank. And once the film is embossed or burnt, it's over. Plus, you may not know you've damaged the film until you show the film the next time.