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| p.1 #1 · p.1 #1 · Lens size: sensor size, registration distance, aperture |
My wife has an Olympus EM-5 and I have a Canon 5DII, which means I have tried to follow pretty closely the available lenses for both systems. It is clear from our two kits that I not only have a much larger camera, but much larger lenses. I took this basically as a given, after all my camera has a much larger sensor and a much longer registration distance. The received wisdom is that this means larger lenses. As I looked at the lens options, however, I made some observations that surprised me. When thinking about a normal type lenses, my wife has the wonderful Panny/Leica 25mm f/1.4. I have a Rokkor 58 f/1.2 which is wonderful as well, but it is over twice the size. Does it have to be that way? When I thought about it I realized it doesn't have to be that way. I could get a C/Y Zeiss 50mm f/1.7, which is a wonderful lens and it would actually be lighter, have a smaller diameter, and be shorter than my wife's Panny/Leica. The same could basically be said about any FF 50 f/1.8 or 2.0 lens. Maybe that is just normal lenses, what about an Oly 12 f/2 for m4/3rds? Well it is a lot smaller than something like a Zeiss ZE 25 f/2, but it really isn't smaller than the Oly OM 24 f/2.8 that I used to have. Maybe it is just m4/3rds? How about we compare the Fuji 14 f/2.8 to FF lenses. It is way smaller than the Zeiss ZE 21 f/2.8, but it isn't really any smaller than the Oly OM 21 f/3.5 or the Voigtlander 20 f/3.5. Maybe if we switch to telephoto lenses we will see the difference? The Oly 75 f/1.8 is a brilliant and relatively small lens. It is way smaller than the Zeiss ZE 135 f/2 APO, but it really isn't any smaller than the Olympus OM 135 f/3.5 or the Minolta MD 135 f/3.5. As I started to do these comparisons what became evident is that if you equate lenses for the depth of field they can produce m4/3rds and FF lenses (and APS-C lenses as well) all end up being a similar size. Of course some manufacturers generally make bigger lenses (e.g., Zeiss) and some generally make smaller lenses (e.g., Olympus), but it seems to me that whether a manufacturer is making a m4/3rds lens with a max aperture of f/1.4, or an APS-C lens of f/2.2, or a FF lens of f/2.8 and they all have a similar field of view, the lenses will all end up being about the same size. Said another way, it is the aperture of the lens and not the size of sensor it was designed for, nor the registration distance, that accounts for sizes of lenses. More practically, the reason my wife has a great kit of really small lenses is that the lens makers for m4/3rds have made (and we have bought) lenses that have a lot less possibilities for depth of field. The wonderful Oly 45 f/1.8, doesn't really have a counterpart with the same limited depth of field possibilities for FF (there are no small 90 f/3.5 lenses--I know there is the Voigtlander 90 f/3.5 APO, but this lens is larger than it would need to be if it didn't have excellent and short close focus and very high levels of correction). Neither does the Panny 14 f/2.5, nor the Oly 17 f/1.8. M4/3rds just makes some very tiny lenses that no one has tried to make something with similar imaging possibilities for FF. On the other hand, my FF lenses are partly large because no one (not even Voigtlander) has tried to make a m4/3rds lens with the imaging capabilities of a 58 f/1.2, or a 35 f/1.4, or even a 135 f/2. In the middle, however, when lenses have similar imaging capabilities they have similar sizes irrespective of the format or the registration distance. It seems that making lenses with very shallow depth of field (i.e., wider apertures) is what makes lenses big quick.
This should be good news for those who want a small mirrorless FF. When such a camera is made there is no reason that a very small 21 f/4, 24 f/3.5, 28 f/2.8, 35 f/2.8, 50 f/2, 85 f/2, 135 f/4, and 200 f/5 could not be made to match it and if they make constant aperture f/5.6 zooms, a 24-85, and a 70-200 even could be quite small. These lenses could all be excellent as well as it is much easier to make lenses with these smaller apertures.