Focal length prospective and crop factor confusion (help)

Kendrick Gray · August 29, 2016

I wanted to upload some examples but I can't for some reason. I have screenshots not urls. I can't seem to search the answer to this question considering I wouldn't exactly know how to search it. I don't know what to look for.

So my question is about perspective (I think this is the proper term to use). I noticed that 16mm, 35mm, and 85mm lenses not only have different field of views, but they have a different look. 16mm makes the face look skinnier, and the higher focal lengths made the faces wider. This I already knew but my question requires that I bring this up.

The Question: If I am using a camera with a super35 sensor with a 85mm FF lens attached, will the 85mm FF lens give me the same prospective of the face considering the crop factor from the sensor? I hope this is not a dumb question.

Usually somebody may get a 50mm lens or something close to that to have the same field of view as the 85mm on the crop sensor. Im afraid that doing this will make my picture change thats all.

Edited August 29, 2016 by Kendrick Gray

Dom Jaeger · August 29, 2016

If you're worried that on a S35 sensor camera an 85mm lens designed to cover full frame will look different to an 85mm designed for S35, they won't. On the same size sensor, the lenses will produce the same sort of image, with the same field of view. The FF lens simply has a larger image circle than is needed for the S35 sensor, but whether the image circle is cropped by the lens design or the sensor, it's still an 85mm lens.

The distortion you're talking about is due to the distance from the subject, it's not a function of the lens itself. With a longer focal length you can fill the frame with a subject from a relatively far distance. With a shorter focal length you have to get closer to make the subject appear the same size in the frame, and that's what causes things to look different.

Kendrick Gray · August 29, 2016

Thank you for your answer. So let me get this straight, 85mm is 85mm. But what if I wanted the same field of view of the full frame camera with an 85mm lens. Getting a smaller prime lens is ok and is only widening the image on the super35 right?

Stuart Brereton · August 29, 2016

If you wanted to match the FOV of an 85mm on a s35mm sensor with a full frame sensor, you'd need something like a 120mm lens so maybe a 135mm would be the closest solution. Going the other way, matching an 85mm on a full frame sensor with s35mm, you'd need a 58mm, so either a 50mm or 65mm would be closest.

Robin R Probyn · August 29, 2016

have a look at this site.. it shows very clearly the difference between FF and other sensor sizes..

http://www.abelcine.com/fov/

Crop factor is about 1.6 s35 -FF35.. the lens itself of course stays the same but the FOV changes.. all started with DSLR camera,s shooting video..

Edited August 29, 2016 by Robin R Probyn

Kendrick Gray · August 29, 2016

Thanks, I was just making sure that distortion wasn't a lens issue. I appreciate the info.

David Mullen ASC · August 29, 2016

It's the field of view and whether it creates a wide-angle view that is linked to the distortion, not the focal length number in the abstract. But in terms of wider-angle lenses, some distort more than others even if they have the same focal length and are on the same format -- distortion in terms of artifacts like barrel distortion, corner fall-off, etc. -- not distortion in terms of shooting a face with a wider-angle lens.