Half-Frame lens field of view and crop factor

[polka]

35mm half-frames are not 18x24 (the exact half of 24x36, but in general a little more than 17x24 because you need at least 1mm to separe two adjascent frames. It depends on the camera.
POLKa

 

[Alan Edward Klein]

I put together this detail to explain crop factor.

 

[Chan Tran]

And since 24x36 is actually a crop of all the larger formats, the 'crop factor' is proven to be a mental crutch for FL 'equivalence' to change from format to format for those unaccustomed to working in different formats. (I shot in 4 formats but never previously used any 'crop factor' -- except initially when going from 135 to digital APS-C...using the same set of lenses for both, which had never happened before.)

That's why I think we should not use the crop factor any more. We had all the different formats before and didn't need the crop factor. One thing I don't like about the crop factor because it makes the 35mm format as the one all other formats are measured by. I often joke that I only use full frame because I can't figure out the crop factor.

 

[wiltw]

I often joke that I only use full frame because I can't figure out the crop factor.

I only used 135 film when I could not afford to routinely shoot anything larger !