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"too sharp" is a nice problem to have

An old Pentax-M series lens, the SMC Pentax-M 50mm f/4 Macro was produced between 1977 and 1984, and is a good choice if you are prepared to put up with the lack of in-camera aperture setting.

SMC Pentax-M 50mm f/4 Macro. Note the reproductions ratios on the ring in front of the focusing ring, a nice touch. The five-blade aperture mechanism produces Componon-like pentagons when stepped down which don't float my boat.

Specifications

The SMC Pentax-M 50mm f/4 Macro is a classic Tessar design: 4 elements in 3 groups. The lens uses 5 aperture blades with apertures ranging from f/4 to f/32.

The lens has a minimum focusing distance of 23cm, and can (almost) produce 1:2 macro.

Macro Performance

The SMC Pentax-M 50mm f/4 Macro is sharp corner to corner from wide open (f/4). Its main advantage is a flat field, with no distortion, it has reasonable contrast with almost no chromatic aberration.

a neatly thought out lens - the reproduction ratios are on the front of the focus ring

It is a neatly thought out lens - the reproduction ratios are on the front of the focus ring, making them easier to read on their own scale than having them mixed in with the focus scale. This makes this lens much easier to read than many other macro lenses.

SMC Pentax-M 50mm f/4 Macro Lens. The steeply recessed front lens is typical of good macro lenses, and also means that a lens hood is not always as neccessary as on non macro lenses. The maximum magnification of .45:1 can easily be overcome with extension tubes or bellows.

The bokeh of the SMC Pentax-M 50mm f/4 Macro is typical Tessar style which gives a beautiful romantic / artificial component to flower shots or similar.

But, the five-blade aperture mechanism also produces Componon-like pentagons when stepped down, they don't float my boat.

The maximum magnification of .45:1 can easily be overcome with extension tubes or bellows.

The lens has a large, accurate and sensitive focus throw and a deeply recessed front element. No lens hood is required.

What's It Good For?

a large, accurate and sensitive focus throw On APSC, the SMC Pentax-M 50mm f/4 Macro gives roughly a FF 75mm lens view, very close to portraiture. But, if anything, it might be a little too sharp for this application, although "too sharp" is a nice problem to have. It is sometimes mentioned as a nice sharp sleeper lens for landscape work, but there are also reports of soft edges at infinity.

Pentax Compared

SMC Pentax-M 50mm f/4 Macro (l) compared with Nikon el-Nikkor 50 f/2.8(r).

In some tests I did, the Pentax-M 50 compares very favourably with the classic el-nikkor 50 enlarging lens.

As you'd expect with an older lens, the contrast of the Pentax shot had to be helped a little bit in postprocessing, but in terms of sharpness and detail there's really nothing in it.

For a four element design, that's pretty good work by Pentax.

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