Thursday, May 22, 2014

Wide Is Back - Pentax-M 20mm f4 on Sony A7

The most aggravating issue for manual focus lens lovers who do not have a full frame digital camera, is the lack of ultra wide angle lenses. The 20mm lens that you treasured from the film days, which gives you an immense and expansive field of view, is a measly 30mm mini-wide on crop sensor.  The experience between 20mm and 30mm is like day and night. The good news is that Sony has now lowered the price of its full frame A7 camera to a much more affordable level and with that, your 20mm lens has the 20mm field of view again!

I tested out the Pentax-M 20mm f4. This has been my favourite lens for IR on the 20D and it's extremely sharp corner to corner on crop sensor, especially the IR 20D that has no AA filter. Amazing for it's tiny, pancake like size. This lens works on the 5D Mark II as well, but it would hit the mirror at infinity if not used in Live-View; too much of a hassle and that's the reason it's been used only a couple of times on the 5D II.  As it turns out, the Pentax-M 20mm f4 works perfectly on the A7; a good match for the A7 sensor too.

This lens has very good resolving power, even near the edges in smaller apertures. By f8, the far edges are quite sharp with good definition. The amount of detail you can dig out from the 24MP sensor of the A7 is incredible, and I am sure it's even more so for the A7R. If shooting landscape is your thing, go for the A7R. For sure, this lens is no Distagon 21mm f2.8, but it puts up a good fight at the fraction of the cost, not to mention it's a millimeter wider :)

The Good:
- Very good resolving power
- Good edges around f11-f16
- Small size and well made

The Bad:
- Relatively small maximum aperture at f4
- Vignettes at larger apertures
- Needs ultra-thin polarizing filters if you use it


  1. An almost film-like rendering. Nice.

  2. Congrats to your Sony A7 ... i fevered with you and watched this long and complicated birth of your fourth child Sony A7. My heart beats as much as yours for this different an promising system; it may be forgiven, that, two month ago you bitched around with an Olympus model (I even can't remember its name).

    Polarizer filter renders blue really really blue ... skies are fantastic blue. It renders as well the building face with a cast (first picture - over the tulips field). As every and everybody complains about A7 and wide and ultrawide lenses: what about the trees behind the tulip field? Chromatic aberations? I am sure you will do extensive testing on that. So my title for one of you next threads could be ... CA on Sony A7 - much ado about a minor niggle?

    Shot 2+4 are a demonstration: Pentax 20mm F4 is very sharp on the edges.

    1. The Olympus E-M5 is for long lenses, and A7 is for wide angle! Best of both worlds :)

      As for the tulip pictures, this is normal for all cameras when you have very strong back lit scene. Surprisingly, the Pentax-M 20mm f4 is very well controlled with CA. I like this lens a lot.