bjornthun Offline Upload & Sell: Off
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DavidBM wrote:
Fred someone else (Bjorn? Not sure) calculated that given the published MFD the focal length at 1:1 must be about 40mm, which suggests strongly that there is an FLE or at least some reconfiguration of elements to allow the focal length to change. That makes it very likely it doesn't unit focus, and might explain the limited extension. If they have been very clever it might mean fast focus in the non macro range.
I don't mind the reduced focal length - one reason to have a shorter macro as well as the 90 (aside from as a light dual purpose hiking optic) is to have something with the slightly less flat perspective, at cost of course to working distance.
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Yes, I did that calculation. At 1:1 magnification a symmetrical lens will give a distance of 4 times its' focal length between film and object. So with a MFD of 160mm we see that 4 x 40mm = 160mm. At 1:1 the Sony 50/2.8 behaves like a symmetrical 40mm lens. That's why I think it's a floating element construction or as you say, the distance between the lens elements is reconfigured.
I'm fine with the shrinkage of the focal length here. Most modern macro lenses show this behaviour, so it's the price we pay to get 1:1 magnification built in without using extension tubes. The old Olympus Zuiko 50/3.5 goes only to 1:2 magnification, and is fairly symmetrical, if memory serves.
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