Film-Tech Forum ARCHIVE: Adjustable shutter blades

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Posted by Randy Stankey (Member # 64) on 04-17-2004, 11:52 PM:

My Simplex (PR-1003) has a shutter that can be adjusted so the blades are wider or narrower.

I've got a new lamp (Superior Quartz Prod.) and new lenses. (Isco Ultra Star HD+) I'm shooting a (approx.) 13' X 31' Cinemascope screen with a 2,000 watt lamp. I'm burning at 85-90 amps. That's just about as far as I can push her. (Use your "Scotty" voice.)

The light is pretty good. It has gotten a lot better with the new lamp and lenses. Now, I'd like to see if I can squeeze that last bit of light out of it.

There's still room for me to narrow the shutter blades by almost an inch and still have the aperture covered when the intermittent is at rest. What are the pros and cons, here?

Of course, I'll get a bit more light but it will put more heat on the film. It'll also make shutter timing that much more critical, lest I have problems with travel ghost.

I'd like to be able to scale the power supply back to 80-85 amps if I can. Things seem to run just a bit smoother when I do but that's just a bit less light I get on the sreen. (I notice it, at least.) I think it would be good to have a little overhead, too.

Is the amount of light and/or power savings I stand to gain worth the potential problems? Or, should I leave it as-is?

Posted by Zach McQuaid (Member # 613) on 04-18-2004, 12:39 AM:

What does your photometer read at the screen? I know that's hell of a throw at M'hurst, so if you've got good light there I would leave her alone. You may shorten the bulb life if you try to push it too hard. Xenons are like Chrysler vehicles. They're fine if you don't drive them. [Wink]

Posted by Randy Stankey (Member # 64) on 04-18-2004, 12:49 AM:

Can I borrow your photometer, Zach? Mine is in the shop for recalibration. [Wink]

I don't want to drive the xenon any harder than I have to. That's why I am thinking about narrowing the shutter. I'm hoping to get more light, or at least the same light with less lamp.

In other words, let the shutter be open longer so that more light can get through. However, hotter film, increased chance of travel ghost and more noticable flicker are the down sides I can think of.

I'm looking for the balance between two possibilities.

Posted by Jack Ondracek (Member # 1466) on 04-18-2004, 01:19 AM:

I don't know what math applies here, but if you turn the lamp down, yet decrease the shutter width to compensate, wouldn't the net effect re: heat be somewhat the same?

Posted by Zach McQuaid (Member # 613) on 04-18-2004, 01:42 AM:

I don't mean to sound like the nit-wit that I am, but the heat to the film would be a bulb focus issue, right? I usually don't worry about heated film unless I think the bulb needs re-focused. I can't imagine that the amount of light hitting the film makes all that much difference. (Outside of microscopic proportions)Anyway, the travel ghosting would obviously be a crapshoot. Trial and error may be the best way to go with this one. [Smile]

Posted by Frank Angel (Member # 248) on 04-18-2004, 06:18 AM:

If you are burning 2000w bulbs, unless your lamp is way out of alignment and youv'e got a serious hotspot, you shouldn't have any concerns about excessive heat. I would bet that if you looked at some test footage, you will not see any signs of heat stress. Make your changes with the shutter and check again. I still think you will find there is no sign of embossing of the emulision, not at a mere 2000W. If you do see heat stress, then back off your change (and check your optical system).

You also might want to run some black and white footage for the stress test -- footage that has frames which are completely black. Run it with a 1.37 apeture plate. If no embossing is found on B&W film; this is the worse case scenario as it is film emulsion that absorbs the most heat because of the silver content, then you are doublely safe with color stock which absorbs much less. But again, we are talking 2000w here -- it should get you safely 'round to home plate without as much as a hiccup.

As for travel ghost....if your shutter is only opened for the intermittent null cycle and closed for the pull-down, travel ghost simply will not be an issue. In fact, I can't really see the advantage of being able to extend the shutter into the null cycle at all, except perhaps for much higher wattage lamps to perhaps cut down heat, but to tell you the truth, I have never heard of using "more" shutter over the null cycle as a means of heat abatement. In fact, in DIs, which routinely used a lot higher wattages than you are, they would even shave down the shutters to wring out that extra bit of light, accepting the resultant travel ghost, and still not burn film (well, in some of the cases). In fact, they even would use high speed intermittents to allow an even longer null period in the aperture by reason of faster pull-down speeds; and they STILL could get away without damaging film. Well, let's just say they didn't blister the print. As for embossing....that might be another story; many a DI print would warrant a place in the YOU SUCK thread. But for what you are talking about, you are way under the heat radar.

Correct infrared heat filtering and water cooling will make a significent difference in the amount of heat that reaches the film without negatively impacting the light transmission. Grossly blocking the amount of white light at the apeture as a means of reducing heat seems a rather primative and crude way of dealing with a problem that has much more elegant solutions.

Posted by John Walsh (Member # 168) on 04-18-2004, 07:52 AM:

I think Frank is right... at 2000 watts, you shouldn't have a heat problem. Using the rough screen size vs. bulb wattage formula, (height of the screen, squared, times 12) your 13 foot high screen needs about 2000 watts to light. The larger the reflector, the larger the shutter needs to be. On older projectors, the shutter can oscillate back and forth slightly while it's running, so you might not be able to reduce it's angle to it's theroical minimum. I don't see any harm trying.

Posted by Gordon McLeod (Member # 33) on 04-18-2004, 10:35 AM:

85-90 amps exceeds the rating of a 2K lamp
I believe you have a LP xelamp system which is a hot mirror so watch out for exess heat
check the lamphouse and rectifier current rating as you may want to switch to the 2500HS lamp

Posted by Randy Stankey (Member # 64) on 04-18-2004, 11:19 AM:

My lamphouse has a straight shot from the lamp/reflector out to the aperture. (L.P. Associates "Xe-Lamp") No water cooler. No heat shield in the snoot.

As long as the film is running at-speed I haven't had problems with heat, so far. The film is a little hot when it comes out the bottom of the projector. When the film is dark it is still a bit warm to the touch when it gets back to the platter. At this point I don't see heat as being an insurmountable problem. As it is set up right now, the moment the projector gets below half speed it burnss film RIGHT NOW!

I suppose I could get some old trailers, run them through and tune for minimum smoke.

Posted by Richard Fowler (Member # 893) on 04-18-2004, 11:43 AM:

The LP lamphouse you have should have a dichoric reflector but I know it can be ordered without one. That model, with the small reflector is very efficient and is capable of being focused down to a 16mm aperture so hot spotting has to be considered.

Posted by Floyd Justin Newton (Member # 1316) on 04-18-2004, 11:44 AM:

Randy--

I would consider puting in a heat shield and possibly water cooling.

My .002 worth.

fjn
Local 294 Ret. [beer]

Posted by Randy Stankey (Member # 64) on 04-18-2004, 01:46 PM:

It burns at 85A and 24V. 2040 watts. Right at the limit. It's a Strong switching rectifier so it run pretty darned stable. In the first few minutes it does fluctuate a bit as the lamp warms up but once it does, it never goes over what I set it at.

I won't be getting a heat shield or water cooler any time soon. The budget is tight and I've got other fish to fry with the money that I do have.

Yes, I do want to back the lamp down a bit. Like I said:

<Scotty Voice>
I'm givin' her all she's got Cap'n! If I push 'er any harder the dilithium crystals will blow apart!
</Scotty Voice>

I hope narrowing the shutter will help me throttle back the antimater reactor. [Wink]

Posted by John Pytlak (Member # 331) on 04-18-2004, 09:29 PM:

You can certainly get a bit more light by opening up the shutter, as long as you avoid getting any travel ghost. That will allow you to back off on the current at bit, and not overdrive the lamp. Do you have the dichroic mirror?

A water cooled gate does not affect radiant energy absorbed by the film, and so won't help heat-related focus issues. It will make the gate more comfortable to work with, and reduce projector abrasion from hot film-contacting components. At 2000 watts, you'd really need to badly hot spot to get permanent damage to a color print.

Posted by Randy Stankey (Member # 64) on 04-20-2004, 04:35 PM:

I just did the dirty deed today.

Narrowed the blades by almost a 1/2 inch. I was able to back the power supply down to 80 amps and still have the same light. At least as far as I can tell by eye.

Now, when Zach brings comes over with that photometer I'll be all set! [Big Grin]

Posted by Gordon McLeod (Member # 33) on 04-21-2004, 09:36 AM:

I hope you checked for travel ghostas well

Posted by Randy Stankey (Member # 64) on 04-21-2004, 04:36 PM:

Yep! Matter of fact, I had to redo it because I narrowed the blades just a bit too much.

I readjusted the blades and rechecked for ghosting and it's all good, now!

It was actually a lot easier than I thought it was going to be at first.