Film-Tech Forum ARCHIVE: Question regarding light output

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Posted by Mitch Davis (Member # 474) on 05-14-2000, 11:30 AM:

Got a newbie question for the group:

I'm about to be getting a home 35mm projector with a 1000 Watt lamphouse. The thing is, I live in an apartment, and 1K might be a bit too bright for a 32 foot throw! The guy selling me the projector told me to just power the light on low, but I just read that this will kill the bulb much quicker. I realize that I can always defocus the bulb for a dimmer light output, but for some reason, I feel strange about doing that. I'm thinking about just using a 500 watt bulb instead. The big question is, if I install a 500 watt bulb in a lamphouse designed for 1K, am I asking for trouble?

Cheers,

Mitch Davis

Posted by Gordon McLeod (Member # 33) on 05-14-2000, 11:43 AM:

The rectifier may not turn down that much
Get a piece of stanless steel wire mesh(muchlike window screen) and place it between the lamphouse and the projector head.
Who are you buying it from?

Posted by Mitch Davis (Member # 474) on 05-14-2000, 12:18 PM:

I'm buying it from Robert Miniaci. He's the guru behind Robert Film Service, a supplier that services nearly every cinema and film festival in Montreal. The unit that I'm about to get is kind of a Frankenstein job of a Chinese portable, so to speak, as it's been modified from the bottom up. I'm just getting a bit uncomfortable with the notion of having such a bright lamp in an apartment. Am I wrong in thinking that 1K will be too bright from 30 feet? The last thing that I'd want to have is a unit that flares out its own image, or desaturates colours.

Cheers,

Mitch D.

Posted by Scott Norwood (Member # 30) on 05-14-2000, 01:48 PM:

The necessary light output isn't determined by throw distance, but rather by image size. Whether you have a 20-foot throw or a 100-foot throw, you'll still need (roughly) the same light output to properly illuminate a given screen area.

Posted by Mitch Davis (Member # 474) on 05-14-2000, 02:49 PM:

In very (and I do mean VERY) rough approximation, a scope image would be about six feet tall and 15 feet wide. Not huge, but perfect for an apartment screening room.

Posted by Brad Miller (Member # 2) on 05-14-2000, 03:38 PM:

You will be fine if you run it at 80-100% of it's rated power. That won't be too bright.

Posted by Mitch Davis (Member # 474) on 05-14-2000, 03:48 PM:

Really? Even when I'm projecting at 1:66 or 1:85? I'd always figured that 800-1000 watts of xenon would wash the colours out of such a small image. If it can be that bright, and still retain deep colours, it's going to look AMAZING!

I feel much, much better now.

Posted by Brad Miller (Member # 2) on 05-14-2000, 04:06 PM:

You will have far more light with scope (2.35) than you will with conventional 1.66 or 1.85. If anything will be a problem, it will be scope. But it shoudn't be. You can always defocus the lamp just a bit if necessary.

Posted by Gordon McLeod (Member # 33) on 05-14-2000, 04:43 PM:

Be very crefull of any of the chineese portables as they are almost all junk and very light inefficient and har to get parts for
Also be wary of the supplier I sujest that you contact other theatres that have bought from them

Posted by Mitch Davis (Member # 474) on 05-14-2000, 04:51 PM:

Actually Gordon, RFS supplies allthe gear for two cinemas that I regularly work with as a programmer, as well as special outdoor projections for the World Film Festival. I've heard mixed things about the Chinese models too, but Montreal's biggest film lab, Covitech (formerly Astral) have one of these units in one of their projection suites. I've played with one, and it was more gentle on film than any of the other portables that I've seen (which granted, aren't many - Mignons and Ranger tones). I realize its a generalization, but are most of the Chinese portables unreliable? I'm getting a bit concerned.

Posted by Mark Gulbrandsen (Member # 72) on 05-14-2000, 06:59 PM:

Mitch, Definately be careful. You could get a DeVry 35mm and be alot happier. I've never seen a portable that was any good at all. Ihave a pair of Russian machines that are copies of the Ziess portables and they are only so-so. I've had Tokiwas, Prevosts,and even a Norelco FP-4 and non of them were worth the money spent on them. I only have the russian machines because the price was cheap....250.00US for both machines. Where will you get parts for the Chineese machine? I know where you can get DeVry parts.
mark

Posted by Scott Norwood (Member # 30) on 05-14-2000, 07:15 PM:

Oh, one more thought--if brightness really _is_ a problem (and it doesn't sound like it will be, given the specs that you list), you can always get a couple of stops' worth of ND (neutral density) filters at your local camera store and build some sort of bracket to hold them in front of your lenses...

Posted by Greg Mueller (Member # 17) on 05-14-2000, 09:27 PM:

I am running 1KW with a 25' throw and a 14' X 6' screen. Scope looks great.

Posted by Mitch Davis (Member # 474) on 05-14-2000, 11:38 PM:

Thanks to everyone for their kind replys!

I feel good about the 1K issue now, but I'm getting really hung up about everyone's bad experiences with portables. Has ANYONE had a portable that they found reliable and fantastic?? The Chinese unit that I played with a while back was incredibly forgiving with old, damaged film (I even watched it project a horribly irresponsible masking tape "splice" - without a hitch!), had a rock solid image and bright light output. The only thing I didn't like about it was the rectifier.

Posted by Michael Barry (Member # 237) on 05-15-2000, 12:04 AM:

Mitch:

I've seen 2K lamphouses illuminate screens of roughly the size and throw that you describe with spectacular results. I don't think that 1K is out of the question (from what I gather).

A little too bright is a far better proposition than too dark (ahem!). If highlights flare or strobe then you can always cut back the current a little (as Brad suggested).

If you get a chance, try experimenting with different screen surfaces because that will have a huge effect on the image.

Posted by John Pytlak (Member # 331) on 05-15-2000, 08:29 AM:

Mitch:

As you know, SMPTE Standard 196M specifies 16 footlamberts as the aim, and allows a range of 12 to 22 footlamberts. So having a bit too much light won't really hurt, and for most pictures, may actually look better! Going above 22 footlamberts with a two-blade shutter makes flicker more noticable.

You can always defocus the lamp somewhat to get less light output and better uniformity. You could also "cash in" the excess light and use a three-blade shutter to reduce flicker.

Generally, "Brighter is Better":
http://www.kodak.com/US/en/motion/newsletters/reel/spring98/pointers.shtml

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com

Posted by Tim Reed (Member # 137) on 05-15-2000, 12:19 PM:

Continuing along the lines that John suggests, in addition to a 3-bladed shutter, you would do good to look for slower lenses (i.e., numerically higher than f/2.0, like f/2.5, f/3, etc...). You'll lose all kinds of light, and get fantastic depth of field, too.

------------------
Better Projection Pays!

Posted by John Pytlak (Member # 331) on 05-15-2000, 12:59 PM:

Tim: AFAIK, the IscoOptic "Ultra-Star HD Studio" lenses are selected stopped-down versions of their standard lenses, trading some light efficiency for greatly improved optical quality. Great choice for smaller screens, where getting enough light is easy to do.

My "ultimate" small-to-mid size screen theatre would use a three-blade shutter (to get rid of flicker), Isco Ultra-Star Studio HD lenses, and run at 22 footlamberts.

Posted by Brad Miller (Member # 2) on 05-15-2000, 03:34 PM:

I'd rather defocus the bulb, reduce the current or even put a ND filter inline before adding a 3 bladed shutter. Reducing the flicker takes a little bit of that film look away.

Posted by Pat Moore (Member # 380) on 05-15-2000, 07:08 PM:

I'll side with John on this one. I think the 3-blade shutter adds a bit to the "look" of film. 72 images per second looks a lot nicer than 48, and you can run some higher light levels and look great. Problem is they are light hungry -- you need more horsepower to make it happen. Shouldn't be too much trouble in this application, though.
Good luck!

Posted by Josh Jones (Member # 447) on 05-15-2000, 08:26 PM:

I hate to get off the subject but how good are those tawakia machines? a guy in minneapolis wants to sell me his TSR for 500 bucks. Is it worth it?

Josh

Posted by Michael Barry (Member # 237) on 05-15-2000, 11:21 PM:

I've used Tokiwas. I would suggest an alternative even if space or portability is at a premium since they're not necessarily more compact than other models and they're just as heavy.

They run quite noisily, too, and aren't that gentle on film. For what they are, they're not all that bad, but you could do much, much better.

Posted by Christopher Seo (Member # 7) on 05-16-2000, 02:15 AM:

Regarding the triple-bladed shutters: I can understand what that would be for single shutters, but is there such a thing as a triple-bladed double counter-rotating shutter such as would fit the Century JJ or DA? That sounds like it would be pretty rare and exotic at best.