Why are fast APS-C telephoto zooms uncommon beyond about 55mm?
Asked 1/29/2012
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I use a Nikon D300 with a Tamron 17-50mm and was looking for a matching longer, fast zoom for APS-C. Aside from lenses like the Tokina/Pentax 50-135mm f/2.8 and Sigma 50-150mm f/2.8, there seem to be very few fast APS-C telephoto zooms in this range.
Is there a physical reason APS-C-specific telephoto zooms like a smaller DX equivalent to a 70-200mm f/2.8 are rare, or is it mainly a market/design decision? I’ve heard that beyond roughly 100mm there’s little advantage in making a crop-only lens, but I’m not sure whether that’s actually true.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
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Actually the same 50-135 f/2.8 lens was sold by Tokina for other mounts, but it was discontinued in 2009.
I'd say the primary reason is that there's no significant savings between making a telephoto lens just for APS-C or one that's also good for full frame. In fast telephoto lenses, the majority of glass goes towards achieving the big aperture needed, the smaller image circle won't introduce very significant differences.
Another reason is that since a fast telephoto zoom is an expensive lens, many of the buyers are already considering getting a full-frame body in the future, and would dismiss an APS-C lens. This leaves a smaller pool of potential buyers, meaning less potential profit. Pentax doesn't have to worry about it, since they don't have a full frame body, nor have they announced any plan of making one.
Originally by user4390. Source · Licensed CC BY-SA 4.0
user4390
14y ago
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Mostly it’s a design-and-market issue, not a hard physical limitation.
For a fast telephoto zoom, a lot of the lens size is driven by the wide aperture itself. Once you get into lenses like 50-135mm f/2.8 or 50-150mm f/2.8, reducing the image circle for APS-C doesn’t save nearly as much size and weight as it does with wide-angle lenses. So an APS-C-only telephoto often ends up not being dramatically smaller than a full-frame 70-200mm-class lens.
That makes the business case weaker: fast telephoto zooms are expensive, and many buyers in that market also want compatibility with full-frame bodies now or in the future. A crop-only version appeals to fewer people, so manufacturers have less incentive to produce one.
So the idea that there’s “no advantage” beyond about 100mm is an overstatement, but there is less advantage. APS-C telephoto zooms are possible and have existed, just not in large numbers because the size savings are modest and demand is more limited.
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