Film-Tech Forum ARCHIVE: Ashcraft 35/70 focusing data

This is topic Ashcraft 35/70 focusing data in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Kenneth Wuepper (Member # 1174) on 05-23-2004, 06:34 AM:

We need the critical distance from the back of the reflector to the aperture plate when installing the Ashcraft Carbon Arc Lamp.

The usual critical distance is 29 1/2 inches. I believe that this lamp is different.

Could anyone please supply this information?

Thanks
KEN

Posted by Stephen Furley (Member # 1277) on 05-23-2004, 06:47 AM:

What model of Ashcraft lamp? There are manuals for a couple of them in the Film-Tech manuals section; they give this information.

Posted by Robert Throop (Member # 61) on 05-23-2004, 09:35 AM:

Kenneth,
The Core Lite series of lamps specified 29.5-29.75 inches as the working distance. I recently installed a pair of Core Lites on Motiograph bases. Due to the design of the base the closest I could get the lamp was 31". It works fine although I'm sure there's some light loss. We nearly doubled the light from the old Strong Mighty Nineties at the same current.

Posted by Steve Kraus (Member # 476) on 05-23-2004, 10:54 AM:

Bless you all for perpetuating the art.

Posted by Gordon Bachlund (Member # 124) on 05-23-2004, 01:55 PM:

Amen!

Posted by Kenneth Wuepper (Member # 1174) on 05-23-2004, 02:34 PM:

OK!
Thanks for all of the responses. We are still running carbon arc and single reels. If we can get the light output where it was before, we will continue until there are no more carbons. Running two Xenon lamps for the entire showing is not a pleasant nor efficient option for us.

The lamp nameplate says 35/70. The current is 150 Amps and we have the matching Ashcraft power supplies with silicon diode rectifiers. The backup power supplies are Ashcrafts with Copper Oxide stacks.

These machines are Cinemeccanica V-10 and it is not possible to get the lamps much closer to the aperture plates. I measured the light and it is less than we were getting before the theatre was idled for restoration.

These specific lamps are not covered in the Manuals section here, that is why I have posted this thread.

Your help is sincerely appreciated.

KEN

Posted by Robert Throop (Member # 61) on 05-24-2004, 09:05 AM:

Kenneth,
The Cinex which I think was sold as the 35/70 had a working distance of 34.5".

Posted by Gordon McLeod (Member # 33) on 05-24-2004, 01:15 PM:

Post a picture of the beast as the cinex and the super cinex and some of the corelites get a bit confusing

Posted by Kenneth Wuepper (Member # 1174) on 05-24-2004, 01:49 PM:

Thanks Robert for that piece of information. I am certain that there is no way to get the reflector within 29 inches of the aperture. It is possible to move it to the dimension you suggest and that is not where it is now.

Gordon, I will take some photos of the booth later this week. We have run "Titanic" and "Casablanca" for two performances each. The images are not up to our old standards for brightness and sharpness.

Thanks again, KEN

Posted by Gordon McLeod (Member # 33) on 05-24-2004, 06:47 PM:

The Vic10 had a rather small drum shutter and it may be thottling the light as well
Somewhere in the dark mists of the past I remember reading something about issues with certain lamphouses on vic10's

Posted by John Walsh (Member # 168) on 05-24-2004, 10:10 PM:

There was a note in the Ashcraft Corelite 150's we used saying that projectors with barrel shutters would prevent the lamphouse from being positioned forward enought for correct distance.

Posted by Robert Throop (Member # 61) on 05-25-2004, 09:44 AM:

The Cinex manual specifically refers to using the Motiograph AAA with no problems.

Posted by Kenneth Wuepper (Member # 1174) on 05-26-2004, 10:06 PM:

Recent trip to the booth yields this information: The Ashcraft series is a Cinex Special. The model number is CS-35/70.

I cannot attach the photos but I can e-mail them if you want to see the nameplate and the mounted lamp.

KEN

Posted by Gordon McLeod (Member # 33) on 05-27-2004, 08:32 AM:

Well since it appears it is a Cinex try positioning it at the 34.5" mark and see what happens
The Cinex was an excellent lamphouse

Posted by Kenneth Wuepper (Member # 1174) on 05-27-2004, 03:31 PM:

Thanks Gordon.

I have no manual for this beast and although the innards appear as all other Ashcrafts, that distance seems more logical. This unit has a very large dichroic mirror reflector. I believe we got two of the last ones out there.

I believe there is a special arcscope graticle for this lamp also. Both of the original paper ones were lost over the years and so the two in there now may not be correct. The Positive position is different for the two formats.

A distance of 6 3/4 inches from back of reflector to the crater edge appears best for 35mm on the screen.

KEN

Posted by Tim Reed (Member # 137) on 05-28-2004, 09:29 AM:

The Cinex Special was a very fast lamp that used short 18" positives, as I recall (anything longer would protrude from the front of the lamp and hit the shutter). The working distance was very close.

HOWEVER... another fly in the ointment is that the proper reflector for that lamphouse hasn't been available for 20 years or so (broken master mold?). To get an appreciable amount of light with the replacement mirror, operators were forced to move the positive crater back, precariously close to the contacts. If you run the arc where it was designed to be run in this lamp, the f1 point of the reflector misses the crater entirely. Sad situation.

Just scoot it up against the shutter guard and tweak the crater distance to spread the beam, as I'd venture to say you'll never get it where it should be with that lamp/reflector/projector combination. The reflector(s) you have now (for a Core Lite?) probably will work fine at the shutter guard distance, although the light this lamphouse originally output will never again be realized.

Posted by Kenneth Wuepper (Member # 1174) on 08-31-2004, 01:12 PM:

Thanks to all for the input.

The Reflector to Aperture plate distance is 35" and the light output is very satisfactory. The entire 35mm frame is evenly iluminated right out to the corners. We have not had a 70mm print in a few years so I have not followed up on that format as yet.

KEN

Posted by Steve Kraus (Member # 476) on 08-31-2004, 02:42 PM:

I wonder if this would provide any useful information: Illuminate the screen as brightly as possible, the most practical way being by running the opposite projector sans film (using a junk lens in case it gets burned); maybe even briefly with the machine stopped if you can get away with it.

With the booth lights out look inside the lamp of the non operating machine and using a white card or tape on the end of the positive and see where the light from the screen is focused into the smallest spot. In theory this should be where the positive is when in operation, give or take a few millimeters on account of depth of crater or corrections needed for uniformity across the screen. Sounds like you are there already but who knows.

Posted by Kenneth Wuepper (Member # 1174) on 08-31-2004, 03:25 PM:

Steve,

We can illuminate the screen with the three Super Trooper spotlights and then perform your test. I think that is a really "cool" way to get some data. I too wonder how useful that will be.
KEN