Cinematography Mailing List - CML

Image size V Focal Length & Aperture

This is the first of a series of pages and videos where I will try and explain simple concepts that people seem to find hard to understand but which are in fact really simple.

The main problem is that the basic ideas are drowned in BS from either people who don't know what they are talking about or people with vested interests.

This is the software that I use to generate these images.

The image is the same, it doesn't matter if you shoot Full Frame or S35. It's the combination of image size, focal length and aperture that matters.

If you shoot with a 100mm lens on Full frame at T2.8 you will get exactly the same framing and DoF on S35 with a 66.7mm lens at T1.8.

Or the other way, if you shoot on S35 with a 66.7mm lens at T1.8 you will get exactly the same image size and DoF with a 100mm at T2.8 on FF.

OK, you can't get a 66.7mm lens but you can get a 65mm.

It's not rocket science it's very basic maths. On S35 open up 1.3 stops and you get the DoF and image size you would have on FF with a lens 1.5 times the focal length. Everything else is BS.

This also explains why ARRI has a 47mm lens in the Signature series and not a 50mm. They understand image matching across formats.

It was a simple rule in the S16 or S35 days, use half the focal length and open up 2 stops and nobody can tell S16 from S35. Especially if you make use of having to open up 2 stops and use a slower stock!

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