Calculating FOV

Jon O'Brien · September 7, 2023

This might sound like a very basic question but what's a good formula for calculating FOV?

I'm filming an orchestra concert soon and have just been told I can set up the camera in the sound room at the back of the theatre, or alternatively set the camera up amongst the audience, in the auditorium if necessary. I'd prefer to shoot the wide angle shot of the entire orchestra from the sound room if possible as the height is good and it's centred on the stage. The sensor size of the camera is Super 35. I'm wondering what the field of view will be of the stage, in other words how wide in metres from one side to the other will be the field of coverage of the stage, given the lenses I've got. I can hire various focal length range lenses. I could go to the venue and check but it would be good to know in advance. The distance of the camera to the stage will be 50m. If anyone has any advice I'd be glad to read it. Thanks.

Dom Jaeger · September 7, 2023

You’ll need to know the width of the stage, then calculate what angle of view you need to cover that width from 50m. Basic trigonometry.

Then use any of the online angle of view calculators to determine what focal length has the required angle of view on a S35 sensor.

David Mullen ASC · September 7, 2023

There are free FOV calculators online. You can also use your smart phone on the location and a director's viewfinder app like Artemis or Cadrage, there are quite a few (not free though.)

APS-C is the same sensor size as Super35 so you could also take an APS-C still camera with a zoom to the location and determine the likely focal-length. (Of course, you could use any camera format and then calculate the crop factor to find the equivalent focal length...)

Phil Rhodes · September 7, 2023

The thing is, this does get quite sensitive to exact sensor sizes, especially if you're talking about short focal lengths.

Not everything that has a "Super-35" sensor has something that's exactly as wide as the Academy gate. The Blackmagic Ursa Mini series is pretty big, for instance. It doesn't often have a sufficiently significant impact to really affect things like lens coverage, but the field of view will be more affected. If it's bigger, no big deal, you can always crop in if you've a spit of resolution spare, but if you find an unusually ungenerous sensor size, I could see it being at least noticeable.

Jon O'Brien · September 8, 2023

Yes good point Dom about the trig, I will ask for the stage width from the venue. It's funny I wasn't good at maths at school but later on really got into it, but then later after that I forgot a lot of it. Haha. Too much into the art side I am I think sometimes. Thank you David and Phil, your posts are very helpful and very much appreciated.