Field of view calculation help

[Peter Connell]

Hi guys, wondering if someone can help me check my numbers here please.

I am planning to use an anamorphic lens designed for a super 35 mm DIGITAL SENSOR on a super 16mm FILM camera and want to know what the field of view will be. Does the following make sense...

1. A Super 35 DIGITAL SENSOR measures 24.89mm x 18.66mm. The manufacturer says the lens has a 70 degree HORIZONTAL field of view.
2. A Super 16 FILM measures 12.52mm x 7.41mm.
3. The horizontal crop factor is 12.52 : 24.89 = 0.52.
4. Can I apply this crop factor to the field of view as well? If so, the horizontal field of view if I use this lens on a super 16mm film format would be 70 degrees * 0.52 = 36.4 degrees.

Thoughts !?
Thank you in advance.

[Dom Jaeger]

More or less correct, except if you are planning to crop for 2.39 then the capture area is 1.195:1 so you would be cropping the S16 frame considerably at the sides. 

Assuming the 70 degree angle of view relates to a S35 sensor in 2.39 anamorphic mode, then the width is more like 21.2mm for something like an Alexa Mini. You'd need to crop the S16 frame down to 8.85mm wide for 2.39 extraction. So the crop factor then becomes 8.85 / 21.2 or around 0.42 x. So 70 degrees would be cropped down to about 29 degrees. 

[Peter Connell]

Thank you Dom. I hadn’t factored in the adjustment of the aspect ratio which is not insignificant. Some say its better to crop a non anamorphic super 16 image and not bother with the 1.5x anamorphic. But I have observed there is still a difference and that the anamorphic does feel more familiar. 

[Dom Jaeger]

Ah, if it's a 1.5x anamorphic then that changes the S16 capture area dramatically. The native 1.66:1 frame will expand out to 2.49:1, so barely any cropping needed to get to 2.39. 

[David Mullen ASC]

I assume that the 70 degrees FOV is based on the 1.5X horizontal expansion of view due to the anamorphic element.

If so, then you just have to figure out the crop factor for the same areas used to create the same aspect ratio in both formats.

[Peter Connell]

Yes I should specify it is a 1.5x anamorphic. The horizontal field of view is 70 degree due to the 1.5x anamorphic element. Thank you Dom and David. I've seen a chap called Nkosi Roma do this on Youtube, it did have an interesting look. I've never been obsessed with lens flares but I do find the anamorphic look appealing. 

[David Mullen ASC]

If you want to calculate crop factor using area of film used, then you'd have to calculate the area used to create a 2.39 frame (if that's your final aspect ratio) after a 1.5X de-squeeze.  This means that the actual area used has a 1 : 1.59333 (divide 2.39 by 1.5).

So if you are comparing to shooting in 4-perf Super35:

Full Aperture is 24.89 x 18.67mm, so knowing that is close to 1.33, you figure that for a final 2.39 image after a 1.5X de-squeeze, you're going to have to crop the top & bottom a little because all you need is 1.59333. It works out to be a 24.89 x 15.621mm area.

If comparing to shooting in 3-perf 35mm:

Full Aperture is 24.8 x 13.87mm, so knowing that is close to 1.78, you figure you're going to crop the sides because all you need is 1.59333. It works out to be 22.099 x 13.87mm.

1.59333 on Super16 (which is 12.35 x 7.42mm full aperture) is 11.823 x 7.42mm.

So comparing horizontal view for crop factor, compared to 4-perf Super35, that's a 2.1X crop factor. Compared to 3-perf 35mm, that's a 1.87X crop factor.

That would help you calculate focal lengths for each format to get to 2.39 : 1 for a final project.  But in terms of using that 70 degree AOV figure, you'd have to know specifically for what format area that number applies to.