Film-Tech Forum ARCHIVE: Flat and Scope

This is topic Flat and Scope in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Evan T. Ryan (Member # 945) on 11-14-2001, 01:11 PM:

I run a Large Format(8/70) Domed theater inside a science center. We are considering getting a 35mm adaptation on our existing projector head. Because it is a dome we have a fixed fisheye lense. This means that without purchasing a completely different lens, we will only be able to show flat films. The only thing I've had to worry about until now is if a film is available in 8/70. Are all 35mm films usually available in both flat(letterboxed) and scope?

Posted by Ken Lackner (Member # 1002) on 11-14-2001, 01:43 PM:

Not that I am in any position to answer your questions, but out of curiosity, are you at an Omnimax theatre?

Posted by Evan T. Ryan (Member # 945) on 11-14-2001, 01:46 PM:

No, Our equipment was made by MegaSystems. Also we use a different film format(8/70 instead of 15/70).

Posted by Jerry Chase (Member # 660) on 11-14-2001, 02:06 PM:

"Are all 35mm films usually available in both flat(letterboxed) and scope?"

No, not to the best of my knowledge. IMO, any conversion kit should be designed to allow for both flat and scope films.

Posted by John Pytlak (Member # 331) on 11-14-2001, 02:11 PM:

Obviously, for 35mm "scope" films, you will need an anamorphic lens.

But if you use the SAME lens for both 8-perf 70mm and "flat" 35mm, the image size on the screen for 35mm will be very small, proportional to the image size difference of the two formats.

You might be better off with a dedicated projector for 35mm use.

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
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Posted by Evan T. Ryan (Member # 945) on 11-14-2001, 02:21 PM:

Unfortunately, this one does not. We put a test aperature plate in to see how big a 35mm picture would be and it looks good.Obviously smaller than the 8/70 image, but good. The problem w/ a dedicated 35mm machine is space. The doghouse has only enough room for Me, the existing projector and a hogie. But that is still one of our options. I think the problem with a scope lens is the approx. 30ft throw. I am worried we would need a custom lens, or adapter for the fisheye... both options mean $$$$$.

Posted by John Pytlak (Member # 331) on 11-14-2001, 02:29 PM:

Many modern anamorphic projection lenses can be focused for throws shorter than 30 feet:
http://www.schneideroptics.com/projection/cinema_projection/anamorphics/
http://www.iscooptic.de/english/products/indexprod_eng.htm

Posted by John Walsh (Member # 168) on 11-14-2001, 03:10 PM:

To answer your question:

Regular 35mm films are usually only avaiable in one format. IE: They will all be flat only or 'scope only. I'm guessing managment is consitering this to enable them to run current films and make more money. If so, they will almost have to purchase an anamorphic ('scope) lens. Usually, the director chooses the formmat, and that's it.

The 35mm image projected (using the existing 8/70 lens) will be much smaller than your current 8/70 image. While I don't know details (like your lens focal length or size of the image on 8/70 film) I would guess the 35mm projected image could be 13 times smaller than the screen ... possiably so small customers would object. The problem is compounded by your curved dome screen, that is, even if you put the correct lens in (to fill the screen) it will distort without the fisheye.

A suggestion would be to try shorter and shorter focal length lenses until you have an acceptable balance between picture size and distortion.

I don't know what the audio sound track assignments are, or where the speakers are placed behind the screen. For example, 15/70 format has three across the center, with a top center. Can the projector play back 35mm optical soundtracks?

Posted by Evan T. Ryan (Member # 945) on 11-14-2001, 03:31 PM:

Thank You, John P. for the leads, and John K. for the clarification.
We tested What the size would be if we used the existing wideangle lens. Our dome has a 60ft diameter and the image filled a little under 40ft. So about 90 degrees of the arc of the dome for the image and approx 45 degrees of nothing on each side. We are speaking w/ schneider to see what our options for scope are. None of the options are easy and might not be possible. We are thinking of testing a normal 19mm lens w/ an anamorphic adaptation to get a larger image w/ such a short throw. The only problem will be the distortion and/or focus difficulty. We have DTS for digital and with the install(if it happens) we will be getting an optical reader. If it all works out I will send pictures.

Posted by John Pytlak (Member # 331) on 11-14-2001, 03:48 PM:

A 19mm lens will have VERY shallow depth of focus. Good focus will be difficult to maintain, especially with a large lamp. The unique design of the two-intermittent MegaSystems projector may help, but I'd favor a longer lens to get better image quality, even if it means a smaller image.

Posted by Dave Macaulay (Member # 813) on 11-14-2001, 10:39 PM:

I have some doubt that any anamorphic adapter will work with a 19mm lens, even the reverse ones have a limited acceptance angle. All the extremely short FL scope lenses I've seen are the integrated type - I don't have a catalog here but I can't recall one as short as 19mm.