This is topic Conversion from Arc Lamps to Xenon in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Randy Loy (Member # 112) on 10-28-2000, 05:25 AM:
One of the performing arts centers I'm affiliated with is considering converting from carbon arc to xenon in the booth. I sort of hate to see the arc lamps go because I enjoy working with them but I also realize how practical xenon lamps are in modern motion picture exhibition.Does anybody know what the xenon equivalent for an Ashcraft arc lamp (8mm positives, 7mm negatives at 60 amps) would be? We have access to some good used xenon lamp houses but I'm not sure exactly how many watts we need. Our screen is 34 by 17 and our throw is about 100 feet.
Posted by Carl King (Member # 398) on 10-28-2000, 09:40 AM:
I don't know what the equivelant to arc lamps would be but I believe that it does not apply here. The important info is the throw and the size screen. Without having a proper calculating device with me I can't say for sure but I would guess with a 100' throw and that size screen you would need a lamp of more than 200W. Three of my houses have 53' throws and I use 200W lamps in them with good results. Your longer throw would require more light of course.Maybe a good service tech will see your question and answer it properly for you.
Posted by Carl King (Member # 398) on 10-28-2000, 09:41 AM:
sorry. the wattage should read 2000W not 200W.
Posted by Scott Norwood (Member # 30) on 10-28-2000, 09:59 AM:
But the throw distance isn't the determining factor for lamp size--the screen size is far more important. For a screen just over 30 feet, you probably could get away with 2k lamps, but 3k lamps would probably be preferable. You'll want to have a tech come out and do measurements, though.
I would make the point, though, that if you are only running films occasionally you will probably save money by keeping the arc lamps, as long as they are in good shape. The cost of buying xenon lamphouses (even used ones) and havign them installed, along with the cost of a set of lamps, will probably be far more than the cost of a couple years' worth of carbons. If you're running five shows a day, though, xenons will make far more sense, of course...
I agree that carbons make no sense in a new installation, but if you already have the lamps installed and they seem to work fine, why bother changing? There's nothing worse than a theatre that is getting good illumination with carbon and then installs underpowered xenon lamps, causing brightness to drop from "acceptible" to "nonexistant."
Posted by Randy Stankey (Member # 64) on 10-28-2000, 10:13 AM:
I'd say either 2,000W or 2,500 W, depending on your screen. I was running 2,000W on a 12' X 28' specular screen and that was great. Then we bought a new screen. It was 13' X 31' and it was only a 1.5 gain. There was quite a difference. I would have liked to have had a 2,500W.If you get a 2,500 W you can always turn the power down a bit but you can't turn the power UP if you get a 2,000W then find out it's too dim!
Also, don't forget what the auditorium is like. Is it good and dark in there when the movie runs? If not you might need a little more power. Stray light can be a killer.
Posted by Ken Layton (Member # 133) on 10-28-2000, 10:33 AM:
Scott's right. If they only plan on occassional films, they are better off to keep the carbon arc.If they convert to xenon you have to factor in the cost of the lamphouses, power supplies, new bulbs, cost of electrician for wiring in the new power supplies (especially if 3 phase), etc.
For that size of screen and throw a minimum of 2000 watts is needed, but a 3000 is prefered. Usually a 3000 watt power supply is 3 phase. What are these used lamphouses you have a lead on? If they are the old Christies with the deep dish reflector you would actually be getting LESS light than sticking with carbon arc.
Posted by Randy Loy (Member # 112) on 10-28-2000, 10:51 AM:
Hmmm...Scott and Ken have me thinking that maybe we should stick with what we've got...Scott hit the nail right on the head when he mentioned only doing a few films per year. The theatre does mostly live stuff these days and films aren't as frequent as I'd like. I'm trying to change that though.
In answer to Ken's question about the lamp house types that we have a line on, we know where there are a set of 3,000 watt Xenex lamps and a set of 1,500 watt Strong lamps. (rectifiers available for both). I figured the 1,500 watters were too small for the application but bet the 3,000's would work.
My only hesitation about hanging onto the arc lamps is a concern about continued availability of carbons. If it looks like we can still get them, even if a bit pricey, I wouldn't mind sticking with carbon arc. I just love the sound of the lamp running when I throw the knife switch and the "poof" when I stike the arc!
Posted by Randy Loy (Member # 112) on 10-28-2000, 11:10 AM:
My mistake! The Strong lamps are SIXTEEN hundred watts, not fifteen.
Posted by Ken Layton (Member # 133) on 10-28-2000, 11:16 AM:
The Strong 1600 watt is too small.You should not have any problem getting carbons. They are still widely available and you should be able to find the longer ones that will burn for an hour so you could use 6000 foot reels with only one changeover.
Posted by Gordon McLeod (Member # 33) on 10-28-2000, 01:04 PM:
Actually carbons are starting to get difficult to get as national only does periodic runs
The 3Kw Xenex will do the job very well
Posted by Steve Guttag (Member # 268) on 10-28-2000, 06:06 PM:
Do you find that you have a lot of particulate matter (low flying clouds/fog/heavy smoking)in your air? If not, throw has next to 0 effect on lamp size required (as others have now pointed out).With a 34' wide screen, you are going to want about 3000 watts. Try and avoid 2500 watts since they are often the xenon lamp manufacturer's worst lamp in the cost/hour range...normally a 3000 can be run like a 2500 without any difficulty in any event.
I would tend to agree with others that you should look at the total cost of going over to xenon and add up how many carbons you could get for that much (also factor in lamphouse parts and possible part failures to which no replacement parts are available). I wouldn't convert to xenon just because it is trendy.
You will have to determine if converting is cost effective.
Steve
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"Old projectionists never die, they just changeover!"
Posted by Gordon McLeod (Member # 33) on 10-28-2000, 07:44 PM:
Actually throw does matter only when it get to useing the extreme ends of the lens focal length range. Not a big difference in the middle range
Posted by Steve Guttag (Member # 268) on 10-28-2000, 09:24 PM:
All right smartty-paints... (that would be Gordon)...then let him use 101.6mm (4") lenses....there you can have a less efficent f/1.7 which should yeild about as much light as a modern f/2.0-f/2.4 :-)In all seriousness...the B&L Super-Cinephores (Silver and Red) in the 4" dia. were excellent lenes...they were even coated.
Steve
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"Old projectionists never die, they just changeover!"
Posted by Randy Loy (Member # 112) on 10-29-2000, 06:43 AM:
I've really enjoyed this discussion and you've all made some really good points.I talked with our 86 year old Chief Projectionist last night (he's been running film at the theatre since 1932) and we agreed that we will stay with carbon arc as long as we can. He's actually the one that posed the question about switching to xenon so he's certainly not afraid of change (actually our 16mm machine has a 1,000 watt Xetron xenon lamp). However, we both agree about weighing the costs of going to xenon with the two 35mm machines against the number of films we run each year.
Also, he mentioned something that made me smile when he equated the conversion from carbon arc to xenon to the conversion from steam locomtives to diesels. The diesel is cetainly the modern efficient way to go but the old locomotives hold all the romance of the glory days of railroading. We're sticking with our arc lamps as long as they remain practical!
Posted by Carl King (Member # 398) on 10-29-2000, 07:45 AM:
Well, my mistake, sort of. I said that the throw was important and I got an e-mail from David Johnson correcting me. As an operator, not a tech, I do not have to calculate this kind of thing. I was thinking of the large single screen house that I used to work in that had a 120' throw and comparing it to the 50' range that I use now.In the case we are discussing, Scott may be correct in thinking that this booth may want to keep the carbon arcs. The conversion cost could be high for just an occasional showing.
Posted by Gordon McLeod (Member # 33) on 10-29-2000, 11:53 AM:
Actually Steve that was the basis of my point throw only will matter in the transission of light when one reach's the extremes of the focal length scale
Also 4" dia lens don't count since no one makes them now and the coatings on some of them are getting fairly brown
Not to knock them though
Posted by Dave Bird (Member # 490) on 10-29-2000, 12:13 PM:
What diameters do they make now? For what purpose were the 4" lenses made?
Posted by Gordon McLeod (Member # 33) on 10-29-2000, 12:42 PM:
The 4" lens was designed to allow for the larger diameter to maintain a decent F stop number with the longer focal lengths
In driveins in particular with real long throws lens of 7-8" fl were sometimes used
The larger diametre allow better light transmision
Posted by Bill Enos (Member # 440) on 10-29-2000, 11:27 PM:
Getting carbons is NO problem so far. We've been getting them from Marble for years. We compared theirs with Nationals using a meter and couldn't tell any difference. Their number is 800 759 5905.
Posted by John Walsh (Member # 168) on 10-30-2000, 10:26 AM:
Personally, I didn't care for the Marble rods. While I didn't compare them according to light, (brightness and tempeture) I found they would break easier while both handling and running.I also liked the Nationals because you could join them together. IMOHO....
Posted by John Pytlak (Member # 331) on 10-31-2000, 10:10 AM:
Brad has the excellent National Carbon Bulletins posted in the "Manuals"
section. Lots of good information on the theory and practice of running
carbon arcs.
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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