GoPro 3 equivalent lens and photography theory.

[ShinySideUp]

I'm trying to find out what the 35mm (full-frame) equivalent of a GoPro (Hero3+ in this case) lens is. The sensor is 1/2.3", or about 10mm but that doesn't really help as I have no idea what the GoPro focal length is...ah, found it. It's 2.92mm. I think it's all to do with 'crop factor' or some such. Apparently the equivalent in full-frame is a little over 16mm and a fixed aperture of f15.7.

I really need to brush up on my photography theory, anyone know of a good, single, source to learn this stuff? A reference book would be good, you know, one of those heavy things that we used to read.

 

[StephenM]

I come up with a different answer based on your information.

For basic theory, I'd go with Michael Langford's Basic Photography and Advanced Photography with the caveat that different people will have different ideas of exactly what is included in that.

My reasoning on your specific question runs:

At infinity, image size is directly proportional to focal length. Double the focal length, the image becomes twice as large, so to get the same amount in you have to double the size of the image recording area. In 35mm terms, if you move from a 50mm lens to a 100mm one, you record exactly the same amount of the scene if you move up to a negative (or sensor) that is 72mm x 48mm in size.

Hence, it's simply applying a ratio. If your sensor size is 10mm (I assume 10mm wide, the longer side?) then a 35mm frame is 36/10 the size of a GoPro frame. Therefore, the amount included by the lens will be the same if the GoPro focal length is multiplied by 36/10. On my Windows calculator, this comes out at 10.5mm.

 

[Nod]

According to Wiki, a 1/2.3" sensor measures 6.17mm x 4.55mm with a diagonal of 7.66mm. Crop factor is 5.64. That puts the effective (FF) focal length at about 16.5mm.