# How long of a lens needed...

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### #1 Derek Van Gorder

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Posted 19 September 2011 - 04:21 PM

Seeing THX 1138 again recently, I'm struck by the classic final shot:

Roughly, how long of a lens did they need to get a shot like this? Anyone have any experience shooting something similar?
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### #2 John Sprung

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Posted 19 September 2011 - 07:53 PM

That could be about 1000mm on Academy 1.85. The sun and moon look about the same size from earth, about half a degree.

-- J.S.
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### #3 David Mullen ASC

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Posted 19 September 2011 - 09:02 PM

Though being a Techniscope movie, i.e. a half-frame 2-perf format, they probably got away with something in the 600mm to 800mm range -- I'd get something in the 1000mm to 1200mm range for standard 35mm / Super-35 if I wanted the sun that big.
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### #4 Patrick Cooper

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Posted 19 September 2011 - 10:56 PM

Wow, what a captivating image. I admit that Ive never seen this film have heard good things about it.

Should be fairly simple to work out what focal length you'd need for a shot with similar magnification of a sunset. With whatever format you'e shooting with, grab a lens and photograph a sunset. Note how much of the frame the sun occupies....you could even measure the image of the sun in millimeters if you really wanted to be precise. Say the sun measures 10mm on your recorded frame. If you use a lens that has double the focal length of the one that you initially photographed the sun with, the sun would measure 20mm. Determine how many millimeters you would like the sun to ultimately be (on your recorded frame) and then do the maths to work out the appropriate focal length. Eg. if you need the sun to appear five times bigger than your initial test shot, then you need 5x the focal length.

Edited by Patrick Cooper, 19 September 2011 - 10:59 PM.

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