Film-Tech Forum ARCHIVE: Guidelines for maximum magnification?

This is topic Guidelines for maximum magnification? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Jeffry L. Johnson (Member # 453) on 04-09-2003, 02:41 PM:

I have a colleague who wants a list or chart that indicates when a given lens will provide an unacceptable image. For example he wants to know at what screen distance will a 50mm lens stop providing a quality image. Does such a list or chart exist?

I showed him SMPTE EG-5, SMPTE Engineering Guideline--Projected Image Quality of 70-, 35- and 16-mm Motion-Picture Projection Systems, and ANSI/SMPTE 196M, SMPTE Standard for Motion-Picture Film--Indoor Theater and Review Room Projection--Screen Luminance and Viewing Conditions. But that's not what he wants. He wants a list of focal lengths and maximum screen distance limit before the "image falls apart" due to graininess or other problems.

Posted by Steve Kraus (Member # 476) on 04-09-2003, 10:50 PM:

Um...why can't I project an image to any size whatsoever by way of whatever lens I choose? Okay, in reality there are limits to the amount of light you can pump through a given film size and lens glass, and if we are talking about mile wide pictures then maybe atmospheric haze would come into play. That aside, if a lens produces adequate resolution then it's not going to vary with the size of the projected picture. The recommended viewing distance is going to change but as long as it subtends only the same portion of the viewer's field of view why would there be a limit on the physical size of the image? Your colleague's question is without merit. The picture will not "fall apart" if you stay the same distance away in proportion to its size. And you can walk up close enough to a picture of moderate size to have this happen just like with a giant image. If the illumination requirements can be met then it's going to be the same picture and look the same at the same relative distance.

Posted by John Pytlak (Member # 331) on 04-10-2003, 06:14 AM:

What really counts is the viewing distance from the image. For example, I find NTSC television generally looks okay if you are at least four or five screen heights away. I personally find current digital cinema systems look okay as close as about two screen heights, but any closer and the artifacts and lack of resolution become bothersome. I feel that good 35mm productions ("film done right") still look pretty good as close as one screen height. Large format film supports much closer viewing (e.g., IMAX theatres have most seats closer than one screen height).

A 10 x 24 foot image viewed at 20 feet will give the same visual impression as a 20 x 48 foot image viewed at 40 feet. The only limitation on screen size is how much light you can put on the screen --- larger print formats allow spreading the energy over a larger area of film, and so allow much more light for larger screens.

Posted by Jeffry L. Johnson (Member # 453) on 04-11-2003, 02:29 PM:

Thanks for your comments. EG-18 appears useful also.

Posted by John Hawkinson (Member # 1135) on 04-12-2003, 01:39 AM:

For those curious, SMPTE EG-18 is "EG 18-1994 Design of Effective Cine Theaters."

--jhawk