DOF etc with S100fs

Started Jul 7, 2008 | Discussions thread
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M87 Regular Member • Posts: 456
DOF etc with S100fs

The next part of educating Andy.......................

The aperture size = the focal length divided by a dimensionless number i.e. f/2.8

So for my S100fs, where the max aperture is f/2.8 but the actual focal length 7mm, then the aperture is 7/2.8 = 2.5mm.

Doing the conversion to 35mm equivalent which means multiplying the focal length by 4, to keep the aperture the same we must also multiply the 2.8 by 4 giving in reality a 35mm equivalent f/11.2 (28/11.2).

This is why we cannot achieve the same shallow depth of field as a consumer DSLR for which the relative numbers would 18/2.8 and equating to 35mm 28/4.2.

So full frame at f/2.8 gives shallower DOF than cropped DSLR at f/2.8 which in turn gives much shallower DOF that my S100fs and continues in this vein as we move down the sensor size.

Therefore, if I want shallower DOF (and that is a big if) then I really need to go to DSLR and get glass with a maximum possible aperture (i.e. fast glass).

Is my understanding accurate. (More to the point, does my attempt at an explanation actually make the same sense in writing as it does in my head).

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Andy

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