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Anamorphic stretch/crop math


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#1 Steven C. Boone

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Posted 27 November 2016 - 06:15 PM

Hello,

 

I'm shooting a microbudget short with a couple of old 2X anamorphic lenses. I would prefer to use the crop sensor (APS-C) Nikons and Sonys at my disposal but recognize that the 2X squeeze would un-squeeze at a much wider than standard 2.35:1 ratio.

 

What I'd like to know: Cropping the sides to 2.35:1 in post from the un-squeezed footage, exactly how much resolution would I lose? And is there a resolution figure (i.e. 1080p, 720p) one could draw from the resulting crop?


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#2 David Hessel

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Posted 27 November 2016 - 07:09 PM

The crop horizontally we would be aprox 1.5 assuming a 16:9 source. Basically you need to crop away about 1/3 of the horizontal resolution if shooting with a 16:9 camera and a 2x anamorphic at 2.35:1.
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#3 David Mullen ASC

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Posted 27 November 2016 - 08:49 PM

Let's say that you did an HD recording, standard 1920 x 1080 pixels (1080P), which is a 1.78 : 1 (16x9) aspect ratio... but you had a 2X anamorphic lens on the camera.

 

You can figure it out a couple of ways, the math is easy, but if your image has a 2X horizontal squeeze to it and you want the final unsqueezed image to be 2.40 : 1, then that means the unsqueezed image area is 1.20 : 1.  So ignoring the squeeze for a moment, you can think of this as only using a 1.20 : 1 area of your 1.78 : 1 recording.

 

Another way to think of it is if the vertical remains 1080 pixels, then the width used to get 1.20 : 1 is 1080 x 1.2 = 1296.  So this means you'd be cropping 1920 pixels to 1296 pixels.

 

Of course, at some point, 1296 x 1080 pixels has to be converted to a standard format and unsqueezed -- for example, maybe a 1920 x 1080 HD recording with a 2.40 letterbox.  Or maybe a scope 2K DCP, which is 2048 x 858 pixels.


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#4 Steven C. Boone

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Posted 02 December 2016 - 02:54 PM

Let's say that you did an HD recording, standard 1920 x 1080 pixels (1080P), which is a 1.78 : 1 (16x9) aspect ratio... but you had a 2X anamorphic lens on the camera.

 

You can figure it out a couple of ways, the math is easy, but if your image has a 2X horizontal squeeze to it and you want the final unsqueezed image to be 2.40 : 1, then that means the unsqueezed image area is 1.20 : 1.  So ignoring the squeeze for a moment, you can think of this as only using a 1.20 : 1 area of your 1.78 : 1 recording.

 

Another way to think of it is if the vertical remains 1080 pixels, then the width used to get 1.20 : 1 is 1080 x 1.2 = 1296.  So this means you'd be cropping 1920 pixels to 1296 pixels.

 

Of course, at some point, 1296 x 1080 pixels has to be converted to a standard format and unsqueezed -- for example, maybe a 1920 x 1080 HD recording with a 2.40 letterbox.  Or maybe a scope 2K DCP, which is 2048 x 858 pixels.

 

Thanks to both of you for the very helpful answers.

 

It sounds like I'd end up with an image that would still hold up on large displays and moderately sized cinema screens. As enthusiastic as I am about using modest equipment to deliver a cinematic look, I still want to leave my director with as many options as possible in the finish.


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#5 Stuart Brereton

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Posted 02 December 2016 - 03:50 PM

Although you are going to lose some resolution by cropping left and right , it's not actually that much more than you would lose by shooting spherically, and then letterboxing to 2.40:1

 

Spherical Crop. 1920 x 800 = 1.53 MP

 

Anamorphic Crop 1296 x 1080 = 1.39 MP


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#6 Steven C. Boone

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Posted 08 December 2016 - 08:55 PM

Although you are going to lose some resolution by cropping left and right , it's not actually that much more than you would lose by shooting spherically, and then letterboxing to 2.40:1

 

Spherical Crop. 1920 x 800 = 1.53 MP

 

Anamorphic Crop 1296 x 1080 = 1.39 MP

 

Thanks so much, Stuart. I can live with those numbers. Another question for this math dropout: What resolution figure might I arrive at with a 1.75X squeeze on the same crop sensor?


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#7 Phil Rhodes

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Posted 08 December 2016 - 09:02 PM

Presumably you could shoot a 4K camera - pretty easily available, these days - and have enough excess resolution yield a good-looking 2:1 anamorphic extraction if your final is HD. A PL-mount Ursa Mini, or something.

 

P


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#8 Stuart Brereton

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Posted 08 December 2016 - 09:25 PM

 

Thanks so much, Stuart. I can live with those numbers. Another question for this math dropout: What resolution figure might I arrive at with a 1.75X squeeze on the same crop sensor?

A 1.75x squeeze would need a sensor that was 1.37:1 to get a 2.40:1 frame. 1.37 x 1080 = 1479. So, your final frame would be 1479 x 1080, or 1.6 MP


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#9 David Mullen ASC

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Posted 08 December 2016 - 10:58 PM

Who makes a 1.75X anamorphic lens?
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#10 Stuart Brereton

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Posted 09 December 2016 - 12:08 AM

Some of the anamorphic projector lenses that people commonly adapt to use with DSLRs seem to have a roughly 1.75 squeeze. I had one a few years ago that was definitely in that ballpark.


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#11 David Mullen ASC

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Posted 09 December 2016 - 12:17 AM

A 1.3X anamorphic is the best way to fit a 2.40 image into a 16x9 recording with minimal cropping.
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#12 Steven C. Boone

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Posted 12 December 2016 - 04:37 PM

A 1.3X anamorphic is the best way to fit a 2.40 image into a 16x9 recording with minimal cropping.

Yes I'm aware. I happen to be working with an unusual lens, a DO Industries "Close Up" anamorphic that focuses within 2 feet. It's my cheap alternative to getting anamorphic close-ups without diopters. For whatever reason it squeezes 1.75X.

 

I most prefer 2X lenses over 1.3X because there seems to be more anamorphic "character" the higher the squeeze factor. The 1.33X lenses I've seen tested all seem rather lackluster in texture. And a lot more expensive than a well-kept vintage projection lens.


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#13 David Mullen ASC

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Posted 12 December 2016 - 04:41 PM

You can't really have it both ways, worrying about resolution but wanting the lens to have more character -- if you want the funky characteristics of old anamorphic lenses then I wouldn't worry so much about resolution.


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#14 Steven C. Boone

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Posted 12 December 2016 - 06:02 PM

You can't really have it both ways, worrying about resolution but wanting the lens to have more character -- if you want the funky characteristics of old anamorphic lenses then I wouldn't worry so much about resolution.

Oh believe me, I'm with you. I just wanted to know how much actual resolution I'd be getting at each squeeze factor, as it's something to consider in planning shots. But not even the aspect ratio is as important an anamorphic characteristic to me as the visual texture. Thanks again.


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#15 S Carlton

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Posted 26 December 2016 - 01:49 PM

One last thing. So I've been testing the lens and love it--a beautiful compromise between 1.33X and 2X. BUT on the post end, can anyone recommend a software or plug-in to get my 1.75X squeezed footage to un-squeeze properly? The closet setting in Adobe Premiere gets me close (1.5X) but obviously resulting in slight vertical elongation. There seems to be no custom option inside Premiere Pro's Interpret Footage or Sequence settings, and Google turns up no suggestions about handling 1.75X footage in post.

 

Any ideas?


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