06-01-2013, 08:40 AM
The focal lengths provided by the Tri-mar are relatively close together though. A range of 1.3x and it's relatively slow at f/4. A stepped 35-85 would be 2.4x, so quite a bit more.
I guess the possible advantage to a stepped zoom as opposed to a continuous one, is the former means the lens designers only have to concentrate on a few fixed points. A continuous zoom need to be optimised for all points. However I suspect the performance at intermediate points can be better controlled with today's optical design tools than historically, so they would rather aim for a more marketable continuous zoom.
It's a tough balancing act. We're balancing zoom range and speed here. Longer zoom, slower lens. Faster means shorter, until you hit primes. How little zoom can you get away with at what speed?
I do feel that a fast up to 2x tele zoom is possible and useful, which would steer it towards the short-mid portrait range. This is the 45-85 as originally proposed by soLong. But that's ideally for FF. So as not to step on the toes of the existing f/2.8 zooms, I think it would need to be f/2 to offer enough reason for existing. For APS-C, it could be a 30-55mm instead, where I suspect the wide angle would be hardest to implement so maybe it could start at 32 or 35mm and go a bit longer. But this should be easier to go fast than on FF. Given Sigma already have the 18-35 f/1.8, then something like a 35-60mm f/1.8 could be a nice follow up lens for the future, and people could start building up a f/1.8 lens system for APS-C, as a parallel to looking at f/2.8 sets on FF.
I guess the possible advantage to a stepped zoom as opposed to a continuous one, is the former means the lens designers only have to concentrate on a few fixed points. A continuous zoom need to be optimised for all points. However I suspect the performance at intermediate points can be better controlled with today's optical design tools than historically, so they would rather aim for a more marketable continuous zoom.
It's a tough balancing act. We're balancing zoom range and speed here. Longer zoom, slower lens. Faster means shorter, until you hit primes. How little zoom can you get away with at what speed?
I do feel that a fast up to 2x tele zoom is possible and useful, which would steer it towards the short-mid portrait range. This is the 45-85 as originally proposed by soLong. But that's ideally for FF. So as not to step on the toes of the existing f/2.8 zooms, I think it would need to be f/2 to offer enough reason for existing. For APS-C, it could be a 30-55mm instead, where I suspect the wide angle would be hardest to implement so maybe it could start at 32 or 35mm and go a bit longer. But this should be easier to go fast than on FF. Given Sigma already have the 18-35 f/1.8, then something like a 35-60mm f/1.8 could be a nice follow up lens for the future, and people could start building up a f/1.8 lens system for APS-C, as a parallel to looking at f/2.8 sets on FF.
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