Film-Tech Forum ARCHIVE: Would I use a regular flat lens to project 1.77:1?

This is topic Would I use a regular flat lens to project 1.77:1? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Justin Hamaker (Member # 2165) on 10-29-2008, 08:50 PM:

If I'm going to be projecting at 1.77:1, would I use my regular flat lens with an aperture plate filed to 1.77:1?

Posted by John Wilson (Member # 269) on 10-29-2008, 08:53 PM:

You'd need a larger lens than your 1.85:1 to do this properly as you need to make your image slightly smaller on screen. Masking would also need to be adjusted in addition to your new aperture plate.

What are you running? Can you not get away with 1.85:1?

Posted by Justin Hamaker (Member # 2165) on 10-29-2008, 09:46 PM:

It's a loop of film that someone else is brining to our drive-in related to something they will be filming. Unfortunately I will not be able to see the film prior to the day it's going to be projected. Masking is not an issue since the drive-in screen doesn't have any. With our flat picture, the film just fills the screen top to bottom and the sides are black.

For what it's worth, this is a one time only deal so doing it "right" isn't as much of a priority as if we were going to be showing a movie to a paying audience.

Posted by Monte L Fullmer (Member # 2797) on 10-29-2008, 10:20 PM:

..then, you'd need a slightly longer lens to do 1.77/1 if your 1.85/1 fills to the top of the screen.

If you're doing a f:3.97 now for 1.85/1, at 400ft, you'd need something slightly over 4inches to do the task.

The 1.77/1 will flow over the top and the bottom masking line on the drive-in screen with your present lens.

Posted by John Hawkinson (Member # 1135) on 10-29-2008, 10:22 PM:

To be clear, for common-height projection, you would like a lens that makes the same-sized image smaller on the screen, which is a longer focal length.

1.77 is taller than 1.85:1, so if your 1.85:1 image fills the screen completely, then running 1.77:1 will be off the top and bottom of the screen.

If you really "just want to see it on screen," you should be able to use your scope lens without the anamorphic attachment (assuming it is not an integrated anamorphic). Of course this will give you a substantially smaller image, but at least you'll be able to see the full thing.

A lot "depends." Obviously the right answer is to rent or borrow the correct lens. An alternative is to find a "MagnaCom" (more properly a "variable converter"), which is basically an adjustable zoom attachment. For some compromise in optical quality and potential loss of light, you'll be able to adjust your image size to fit your screen (well, within some limits).

Without additional equipment, your only choices are to run 1.85:1 with the top or bottom (or both) cropped, or to run your scope lenses (or academy, if you have them) with the image half the size it should be.

Monte: the notation "f/3.97" refers to the aperture, not to the focal length, and is pretty much independent of the focal length. You might indeed find a 4.00" (inch) focal length lens, but that is not f/4.00 (and generally f/ numbers don't have that much precision).

P.S.: Justin, what is your focal length?

--jhawk

Posted by Monte L Fullmer (Member # 2797) on 10-30-2008, 03:56 AM:

Wow, did it again - got focal and inches turned around once more.

Thx "Mr. JHawk" for setting me straight.

Still, 400' to the screen from lens. That takes quite a bit of light to hit that distance.