A reminder for some memebers as to what the F stop is all about.

Started Jan 26, 2014 | Discussions thread
bobn2 Forum Pro • Posts: 62,181
Re: Glad that you had such big aperture

philosomatographer wrote:

Anybody still participating in the "equivalence" debate have a serious dead-horse-beating fetish - they should get out and take some photos, possibly with a "full-frame" system. Just remember to stop down those lenses to f/8 for a nice and even performance across the frame!

If someone were to perform their photography at f/8 all the time, then there is no point to having an FF system. I suspect that a lot of people who don't understand equivalence have wasted their money that way. You can get the same results using FT at f/4, and have a smaller, lighter, cheaper system. Then again, you could get the same results using a top-end 1/1.8" compact at f/2, and have an even smaller lighter system. I've got FF, APS-C, Four Thirds and 1/2.4" interchangeable lens cameras. So long as the DOF is in a range they can all do, they'll produce almost identical results (given there is about 1 stop variation between them in sensor efficiency). So, apart from the benefit of more pixels, my Pentax Q at f/2 produces very, very similar results to my D800 at f/11 and is very much smaller.

I use four thirds, 35mm "full-frame" (Leica), 6x7cm Medium Format (Mamiya), and 4x5in (Linhof) all on a regular basis. There are no optically better lenses than the Olympus SHGs when looking across all optical parameters.

That is disputable. Certainly, the Olympus SHGs are very, very good, but 'there are no better' is a very strong statement that I don't believe you can substantiate.

As it stands, we have junk like the Nikon 16-35mm f/4.0 that is not only huge like a telephoto lens, but distorts like a fisheye. See - only if they severely compromise on one parameter (distortion) do they manage a good showing with the others.

Calling it 'junk' is simply extreme. It is of course a compromise lens, in Nikon's equivalent of the HG, not SHG lens, and it is giving the equivalent of an 8-17.5 f/2 lens on four thirds. It's worthwhile noting that the much vaunted Olympus equivalent, the 7-14 is only an f/4 lens, equivalent to an f/8 on FF. If Nikon were to make a 14-28/8, no-one would buy it, because it would be a simply pointless lens on FF.

Truly uncompromising lenses are very rare in the 35mm world, yet we have them in the form of four zooms covering 7mm to 250mm in the four-thirds system.

Yet the four thirds lenses are indeed 'compromised' in terms of light gathering power with respect to FF lenses. But then, making such lenses for FF would be pointless because you'd get the worst of both worlds, lower light gathering and large size. In the end, equivalence isn't at all about whether FF or FT is 'better' or 'compromised' it's about knowing what the tradeoffs are (in both cases) and deciding for yourself.

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