How come no other cheapies like Nifty Fifty?

Started Feb 14, 2012 | Discussions thread
photonius Veteran Member • Posts: 6,895
Re: How come no other cheapies like Nifty Fifty?

jvkelley wrote:

photonius wrote:

Another point about longer focal lengths. If you go from 50mm to 100mm, and want to maintain f1.8, you need to double the diameter of the lens (at least front).

I think is true for longer focal lengths, but it doesn't seem to be true in the 50mm range. The 50mm f/1.8 II has a filter diameter of 52mm. The 100mm f/2 USM has a filter diameter of 58mm.

Well, the filter diameter is only a rough approximation, and of course we are talking about a hypothetical thin lens, which none of the above lenses are.
Here are the measurements (focal length divided by max aperture):
100mm / 2 = 50mm the diameter needs to be 50mm. (100 / 1.8 = 55.56mm)
50mm / 1.8 = 27.8 mm
200mm / 2 = 100mm
500mm / 2 = 250mm
500 mm / 8 = 62.5mm

If you look at the block diagrams of the lenses, you will see that the glass diameter in the 50mm is a lot smaller than the mechanical diameter (especially the front lens), while for the 100mm lens, the front lens goes very close to the edge of the barrel.

For wide-angle lenses it doesn't work anymore either, since they are retro designs. Otherwise a 24mm f2 lens would only need to be 12mm in diameter - would be nice. Well, you have some smaller wide angle lenses for mirror-less cameras.

block diagrams are at the canon museum.

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J.V.

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