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Basic anamorphic question ?


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#1 Elliot Beach

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Posted 29 August 2014 - 12:56 PM

Hello everyone I have a basic question concerning anamorphic lenses as I've never worked with them before.

 

I may have a job in which some Kowa, or better, Hawk anamorphic lenses will be used and I wanted to know something about focal length.

 

A 40mm anamorphic lens in comparison to a 40mm normal lens gives you more space on the side edges? Or another way of putting it, will a 40mm anamorphic be equivalent to say a 32mm normal lens? (32mm is just a random number for the example).

 

Trying to figure out what length I will need for each shot as most of the companies start at 40mm unless we go to Arri here in London.

 

Thanks,

 

El


Edited by Elliot Beach, 29 August 2014 - 12:58 PM.

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#2 Mark Dunn

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Posted 29 August 2014 - 01:26 PM

The horizontal angle of view is increased by the anamorphic ratio, so a 40mm. 2x anamorphic will have the horizontal angle of view of a 20mm.; a 1.5x, about the same as a 25. The vertical angle of view is unchanged.

It's as simple as that


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#3 David Mullen ASC

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Posted 29 August 2014 - 03:26 PM

On the same sized sensor, then yes, a 2X anamorphic would be double the horizontal view of the non-anamorphic version of the same focal length, hence why a 40mm anamorphic, similar to a 20mm spherical in horizontal view, is considered a typical wide-angle lens.  Anamorphic lenses tend to suffer from barrel distortion so people are less inclined to use the 35mm anamorphic or even shorter focal lengths unless they don't mind the barrel distortion (even the 40mm anamorphic can be somewhat distorted on the sides.)

 

However, keep in mind that if a final aspect ratio of 2.40 is desired, then this means you will be using a 1.20 : 1 area of the sensor with a 2X anamorphic.  On some cameras, this means cropping the sides of the sensor in camera or in post later, which in turn loses some of the width of the image, so your 40mm anamorphic on a Red Epic, for example, won't use as wide a sensor area as on a 4x3 Alexa, and would therefore be less wide-angle.

 

So you really need to know the actual dimensions of the 1.20 : 1 area of the sensor to know what the horizontal field of view will be compared to something like the 22mm width of 4-perf 35mm anamorphic, if that's your frame of reference.


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#4 Elliot Beach

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Posted 02 September 2014 - 10:05 AM

Hi guys.

 

Ok perfect that’s exactly what I needed to know. So just find out which anamorphic lenses are 2x or 1.5 and that will give me the ‘actual’ length.

 

Cheers for that further insight David, I new it would never be that simple. Although I should of known this already. When it comes to sensor size would you know of any websites, apps, etc, that have already made these calculations? To get some rough ideas before doing some pre shooting if that time is available.


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#5 David Mullen ASC

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Posted 02 September 2014 - 11:56 AM

You'd have find out the vertical dimensions of the sensor that gets recorded, then multiply by 1.20 to figure out the horizontal area you'd actually be using to get a 2.40 image using 2X anamorphic lenses. Then you can figure out the crop factor compared to whatever is your normal frame of reference.
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#6 Elliot Beach

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Posted 02 September 2014 - 01:06 PM

So as of now I am shooting with Kowa's on an Alexa XT Plus, which offers 4:3 recording at ProRes, thats then down sampled to 2048x1536, but that shouldn't affect he original recored sensor space i believe.

 

3rd frame down in purple text - http://matchmoversca...nes_SUP_9_1.jpg

 

Im not sure if its making full use of the sensor and won't crop it or will there be a crop of 2.3mm?


Edited by Elliot Beach, 02 September 2014 - 01:11 PM.

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#7 cole t parzenn

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Posted 02 September 2014 - 01:17 PM

You'd have rind out the vertical dimensions of the sensor that gets recorded, then multiply by 1.20 to figure out the horizontal area you'd actually be using to get a 2.40 image using 2X anamorphic lenses. Then you can figure out the crop factor compared to whatever is your normal frame of reference.

 

Why aren't sensors 21 by 17.5 millimeters?


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