Michael Reichmann's take on smaller full frame Sony FE mount lenses

Started Dec 18, 2013 | Discussions thread
blue_skies Forum Pro • Posts: 11,708
Re: Michael Reichmann is absolutely correct wrt/ non-retrofocal lenses....

Michael's comments make a lot of sense: the most popular focal lengths on Leica FF cameras were between 20mm and 50mm - and these were all of a non-retrofocal design.

Non-retrofocal means that the lens length (measured from sensor) roughly equaled the focal length.

On FF DSLR, these FL had to be retrofocal to clear the mirror box, which led to large and heavy glass, especially if the lens was a fast lens.

Only from about 50mm and up, the camera construction (mirror vs. mirrorless) hurdle begins to disappear and lens size versus sensor size comparisons become more valid. The crop factor helps with reach, e.g. APS-C requires 2/3rd and MFT requires 1/2 the FL for the same FOV, or, if you have a 200mm lens, the APS-C FOV would be that of a 300mm lens, and the MFT FOV would be that of a 400mm lens. The crop factor helps with reach, to some extent. You also have to take sensor resolution into account: MFT is at 16Mp, APS-C at 24Mp and FF at 36Mp - it offsets things somewhat if you need to crop.

Back to non-retrofocal design. On Leica mount (44mm), the lens was protruding into the camera, and compact lens design essentially was made possible because of the mirror box removal. MFT and APS-C (Nex, Fuji) have all fairly similar registration distances, and lens design follows a similar non-retrofocal versus retrofocal curve. Or, if you go wider than 20mm, you have to go retrofocal again, due to mechanical construction limits.

This hampers MFT lenses: to match 20mm - 50mm on FF, it needs a 10mm - 25mm lens length. That is, assuming a cut-off at 20mm, most MFT lenses cannot be non-retrofocal, and they will have to get larger than their actual FL, especially if the lens is fast. The (WA) non-retrofocal FF lenses are actually very compact.

The A7 is more forgiving than the A7r, and with the new Sony app, even suspect lenses such as the Voigtlander 21/4 or the Contax G 28/2.8 become usable on the A7 (the A7r struggles with smearing).

If you are not convinced, compare e.g. this Camera size: OM+17/1.8 versus A7+35/2.8

There is also confusion as to fast FF lenses. Except for the Voigtlander Nokton 35/1.4, (which is very small), most fast FF lenses tend to 'bring out' the lens to capture more light. But you are getting f/1.4 lenses on FF! To bring this in perspective, you would need a f/0.7 (or faster, due to digital sensor in-efficiency at such apertures) and such a lens will be very bulky.

So yes, you can point to large and fast FF lenses, but these are not proper comparisons, because they essentially bring 'more' to the FF camera, and cannot be matched by smaller format cameras.

If you look at Leica, Zeiss Ikon and Contax G shooters, you notice that there is almost no interest for lenses that go beyond 90mm. Why? Because FF cameras were better for long telephoto. The compactness of the range-finder system was given up at such long telephoto lengths.

You will find lenses wider than 20mm for range-finder, but usability is questionable - rectilinear lenses only go to about 17mm, wider than that and they all have (fisheye) distortion.

But in the 20-50mm length (plus or minus a few lengths), range-finder systems were very compact - you could carry the camera with three or four lenses in a minuscule small camera bag.

The Sony A7/r bring this back to digital cameras. Your only other FF choice is the Leica M9 or M240, and this will set you back quite a bit more. The A7/r is cheap in comparison - it makes the E-M1 even look expensive.

Putting it all together - if you go out with a FF camera and non-retrofocal lenses between 20mm to 50mm (FF FOV), the overall system is very hard to beat in terms of compactness and IQ (including lens speed).

I hope that Sony releases a set of lenses that follow in this spirit, and does not simply revert to putting out this myriad of zoom lenses (yes, zoom lenses sell more than prime lenses). If not, using RF lenses on the A7 is definitely possible today - in this FL range (avoid the A7r for wider than 35mm for now).

BTW - the same discussion is happening wrt/ the Nex-7 versus the A7. In this case the resolution is the same (24Mp), and there are a number of good prime lenses out for the Nex-7 now. There are pros and cons to either format (APS-C and FF), not dissimilar from comparing MFT versus FF.

In the end, rangefinder cameras were nichy, partially due to pricing, but also due to limited focal length, and the incompleteness of such systems (studio setup, flash, specialty lenses, not for sports/action, etc.). It is possible that A7/r systems will be relegated to a similar use pattern - and MFT and APS-C cameras will take center stage.

But, in the heart of his comment, I think that Michael Reichmann is dead-on - the A7/r is a true game-changer for FF inclined photographers. And already, the system is quite capable of adapting a large plethora of past and present lenses, from almost all manufacturers. This is not something to sneeze at, not by anyone.

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