Film-Tech Forum ARCHIVE: What is a reverse anamorphic lens?

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Posted by Adam Martin (Member # 641) on 10-18-2003, 06:33 AM:

Someone in the Equipment Forum wants to buy a reverse anamorphic lens. Is this a lens that compresses the image? And what on earth would this be used for outside of camera or optical printing use?

Posted by John Pytlak (Member # 331) on 10-18-2003, 06:44 AM:

In most cases, the 2X squeeze anamorphic lens used for "scope" projection MAGNIFIES the image by a factor of 2X horizontally. The focal length of the "prime" lens is chosen based on the HEIGHT of the image.

In long throw situations, an anamorphic lens may be oriented such that it REDUCES the magnification in the vertical direction by a factor of 1/2. The focal length of the "prime" lens would then be based on the WIDTH of the screen image desired. Reverse anamorphics are used when the throw is so long that there is no suitable long focal length prime lens available for the more commonly used 2X widthwise magnification.

Posted by David Kilderry (Member # 142) on 10-18-2003, 07:37 AM:

John is correct Adam. Here at the Lunar Drive-in Theatre we have throws up to 500 feet, finding the very tall focal length prime lenses for regular anamorphics is difficult hence us using reverse anamorphics on two of our screens. One is a Kollmorgen, popular brand from the 1960's era not often seen today, the other is a Kowa. Both let good light through to our big screens.

David Kilderry

Posted by Robert Throop (Member # 61) on 10-18-2003, 09:05 AM:

The first reverse anamorphs were made by B&L. Those had to be factory adjusted for throw AFAIK. The later Kollmorgan, Isco, Schneider lenses can be field adjusted just like any scope lens.

Posted by Pete Lawrence (Member # 130) on 10-18-2003, 09:33 AM:

In a pinch, a regular anamorphic lens can also simply be reversed end for end and used. Take a look at the Skyline Drive-in in the Pictures section. About half way down you'll see Ken Layton's smiling face holding what looks like a B&L 4" scope lens on the front of the projector. It's mounted backwards.

Posted by Paul G. Thompson (Member # 655) on 10-18-2003, 12:33 PM:

I have two Kollmorgans. They are one big hunk of glass. Very heavy. They may need support to keep them from sagging when they are used.

Posted by Adam Martin (Member # 641) on 10-18-2003, 04:17 PM:

Interesting ... the longest throw I've worked with was about 350 feet at a drive-in, where I was able to find "standard" lens configurations.

Posted by Gordon McLeod (Member # 33) on 10-18-2003, 08:31 PM:

the problem was as the trow get to a certain length the focal length of the lens gets so long that they are inefficient even at 4" in diameter so the reverse anamoprhic drops the focal length back into the ball park of reasonably efficient lens design

Posted by Barry Floyd (Member # 385) on 10-19-2003, 12:43 AM:

I'm using a brand new Schnieder(sp?) Reverse Anamorphic Scope at our drive-in. Kind of pricey.... but it puts a great picture on the screen.

Our screen is 25' x 60' with a 325' throw, and finding other lenses for that throw was almost impossible.

Posted by Ron Keillor (Member # 1790) on 10-19-2003, 01:02 AM:

Back in my univerity days we screened 16mm. in an auditorium whose screen could not be widened. To use 'Scope pictures we squashed the picture down using an anamorphic adapter installed at 90° to keep the width constant. The old Bay and Colonial Theatres had to do that, their screen widths were fixed by proscenium arches. We referred to the process as "SquashoScope".