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Topic: Focusing trouble.

Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 02-21-2002 01:20 PM

Sure hope David gets back with the info we asked. If his problem was an on-going thing for a long time, I would bet it is the Sankor Lense. He should also check the lense to see if it is burned, separating, has loose elements or has been dropped.

I think the key is how long has this been going on. If he has no problem with a scope primary having the same f-stop as the flat lense, then I would say he definately has a problem with the flat lense, and a replacement for that may be indeed needed.

In the lense area, my knowledge is anal. But it is just a thought.

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Dave Williams
Wet nipple scene

Posts: 1836
From: Salt Lake City, UT, USA
Registered: Jan 2000

posted 02-21-2002 03:07 PM

I have had this same problem in the past. What I found was that the xenon bulb was focused too tight and burned the flat lense in the center. As a result, the image on screen was soft and yellow in the center, and impossible to focus throughout the image. We had the lense resurfaced and it was just great after that.

The reason the effect was not noticed on the scope lense, was because the scope lense was manufactured using different grade optics and did not burn.

Dave

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David Whitbeck
Film Handler

Posts: 70
From: Tempe, AZ
Registered: Jun 2001

posted 02-21-2002 03:19 PM

The problem I believe has been there for a long time. Some movies it's more noticable in than others. Paul, you're talking about a scope primary? Is that the the flat lense that is attached to the anamorphic? If that's the case, we have a Schneider 4.13 inch F 2 attached to a Cine Navitar Animorphic. The aperture plate never feels like it's overly hot, I pull it all the time and it's decently warm, but I don't think it would burn me, I'll find out after this next show. The Sankor looks OK, but my knowledge is less than... But it looks OK. Seems to be tight all around, too.

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Joe Beres
Jedi Master Film Handler

Posts: 606
From: Minneapolis, MN, USA
Registered: Nov 2000

posted 02-21-2002 03:25 PM

It sounds to me like it could be the lens. Is it more noticeable is darker films, scenes, and shots, and less noticeable in brighter ones? Brighter shots will allow more light to be projected, sometimes allowing more contrast and make focus troubles more apparent.

This post was edited, because due to a lack of clarity and my own scattered mind, it made very little sense.

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David Whitbeck
Film Handler

Posts: 70
From: Tempe, AZ
Registered: Jun 2001

posted 02-21-2002 03:30 PM

The best time to see the problem is when there are words on the screen such as the credits.

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 02-21-2002 03:35 PM

Sankor lens are not the most durable or high quality until very recently they were still cemented elements

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David Whitbeck
Film Handler

Posts: 70
From: Tempe, AZ
Registered: Jun 2001

posted 02-21-2002 04:16 PM

I have lowered the gate tension to 1 with no change. If it is just a cruddy lense, I would have to say that it will make me happy because then I'm not to blame

. We're about to be getting new screens and installing some Christie P35C's so hopefully we'll acquire some new lenses at the same time.

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Pat Moore
Master Film Handler

Posts: 363

Registered: Mar 2000

posted 02-21-2002 08:05 PM

I'd have to vote on the lens being the bad guy as well. Those were not the greatest lenses ever made, problems with coatings as well as the glass. No depth of focus at all with them.

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David Whitbeck
Film Handler

Posts: 70
From: Tempe, AZ
Registered: Jun 2001

posted 02-21-2002 10:04 PM

Well guys, if the lense is at fault then thanks for all your help. I'm going to try to run some test loops through tomorrow with our other flat lense, I'll let you know the results I guess. We only have two screens here so it's kinda tough switching the lenses when they are both in use. Thanks again.

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Stan Gunn
Expert Film Handler

Posts: 176
From: Clematis, in the hills near Melbourne Australia
Registered: Aug 2000

posted 02-21-2002 11:29 PM

I did not want to be that blunt.

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 02-22-2002 01:24 AM

David W.
If you have the f-2 lense as the scope backup, you will have a good focus field. You said the aperature felt ok temperature wise, so I don't think you have any serious mis-alignment problems.

I now change my view and agree many of the forum members. I think it is time to get another flat lense. But remember one thing.....The faster the lense is, less focus depth you have to play with. However, the faster lense will pass more light. Conversly, the slower the lense is (higher f-stop) the better the focus depth, but the light loss will be greater. It is all a trade-off. If you have a high power xenon and have light to "burn", you would probably be better off with a slower lense.

As far as the flat lense is concerned, (the Sankor) it is more than likely the culprit giving you all your grief.

Hey guys, correct me if I am wrong.

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David Whitbeck
Film Handler

Posts: 70
From: Tempe, AZ
Registered: Jun 2001

posted 02-22-2002 03:53 PM

Just so everyone knows, I swapped our two flat lenses and ran a loop through and sure enough, the other flat focused fine. So, I guess we have a shitty lense, you wouldn't be surprised if you saw our theatre... Anyway, thanks for all your help. Too bad it wasn't something easilly fixable. Take it easy.

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Joe Beres
Jedi Master Film Handler

Posts: 606
From: Minneapolis, MN, USA
Registered: Nov 2000

posted 02-22-2002 04:57 PM

Well, obviously you will need to replace that lens. If you're strapped for cash, you should be able to find a good-quality, used lens at a good price. We have all Isco lenses here, some of which were purchased used, and they have not given us any trouble.

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Jerry Chase
Phenomenal Film Handler

Posts: 1068
From: Margate, FL, USA
Registered: Nov 2000

posted 02-22-2002 05:04 PM

I didn't say this, but lenses can be accidently dropped...

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David Whitbeck
Film Handler

Posts: 70
From: Tempe, AZ
Registered: Jun 2001

posted 02-23-2002 06:06 PM

I'm not going to be the one to drop it... We'd be screwed if we lost that lense, we're running to flat movies right now that both play at the same time so you get the picture, but I suppose if I really got tired of it, it would be an option

. Well, we're supposedly getting new stuff in April, so I think we can hold out a little longer, I was just hoping it could be fixed.

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