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SMC Pentax-M 50mm f/1.7 Lens Review

Fast, sharp 50mm M Series vintage lens from Pentax. John Riley reviews this easily adapted, widely available f/1.7 classic, sharing sample photos, MTF & CA performance charts along with his verdict of this standard length K mount lens.

Posted: 18/01/2024 - 09:25

Handling and Features

1976 saw the introduction of the new Pentax ME and MX camera bodies, incredibly compact and thirsting for the new range of M series compact lenses to go with them. The M series duly replaced almost all of the previous range of SMC Pentax lenses. Almost every camera body sold would have been offered with the ubiquitous 50mm standard lens, or the new 40mm pancake lens for those who wanted a truly pocketable option. The standard lens has always been a key optic, demonstrating the quality of a manufacturer's system and whetting the appetite for more of the same. Here we look at the f/1.7 lens, not a budget price like the f/2, nor a premium price like the f/1.4 and f/1.2. Let's see how it holds up in our current digital world, coupling the lens up with the 36MP Pentax K-1 body.

SMC Pentax-M 50mm f/1.7 Handling and Features

In many ways the M series lenses reach a pinnacle of manufacturing quality, with beautiful precise etched markings, solid construction and more extensive use of metal than many of its peers. There is a deliciously smooth focusing action that, as commented on previously in other reviews, is a silky smooth tactile pleasure. Even this fairly well used copy retains that smoothness, some 48 years or so after it was made.

The lens is a compact 63mm x 31mm and weighs in at just 185g. The dedicated lens hood is a clip on design, not cheap by any means and not included with the lens when new. However, it is by far the best hood to use for both efficiency and convenience and was used throughout this review. The hood just clips into place on the rim of the lens and there is also a standard 49mm filter thread, an economical size and standard to many Pentax lenses of the period. There is just one thing to watch about the hood and that is to make sure it is sitting square to the lens, as it can rotate without becoming loose and if it rotates too far then some vignetting might occur.

This is of course a manual focus lens and the focusing ring is, as expected, beautifully slick and smooth. Focusing is down to 45cm, or 1.5 feet, for a maximum magnification of 0.15x. The distance scale is in a cut out in the lens barrel and is clearly marked in feet and metres. There is also a well spaced depth of field scale that is quite usable. The infra-red focusing mark is a red line at the f/5.6 spot, indicating how much IR focus deviates from visible light. The aperture ring has precise click stops at half stop intervals, except between f/16 and f/22 where we find a full one stop interval. There is the usual white raised dot on the barrel that gives a tactile indication of the position of the lens for insertion into the bayonet mount.

The bayonet mount is made of high quality stainless steel that fits with firm precision on the K-1 as well as it does on every other model of Pentax K bayonet camera. It is a plain K mount with no electronic contacts, so the camera must be used in stop down mode with DSLRs to ensure correct stopping down of the lens.

The metering process with the K-1 and other DSLRs is simple enough though. Switching on the camera, we are asked what the focal length is for the purposes of the shake reduction system. Then, with the mode dial set to M, select the aperture required on the lens and press the green button on the back of the camera. The camera will meter and set the appropriate shutter speed and when the shutter is released the lens will stop down correctly to the selected value. This soon becomes second nature and makes the use of these fine lenses absolutely viable.

Optical construction is a fairly standard 6 elements in 5 groups, with the diaphragm having 6 blades. The lens is Super-Multi-Coated, abbreviated by now to SMC in the lens description. This version of the lens was, as mentioned introduced with the ME and MX compact bodies and was manufactured from 1977 to around 1984, after which it was replaced with the A series version, with electronic contacts and an “A” on the aperture ring. There is no denying that the A lens is more convenient to use on DSLRs because it links with the camera electronics and the exposure modes may be used as normal. However, the M series are less plasticky, maybe not exactly better made, but constructed with more metal and having a definite feeling of traditional quality that can be lacking on later offerings.

On a full frame DSLR, using the SMC Pentax-M 50mm f/1.7 lens is a real back to roots experience and a total pleasure. For APS-C format we get a “35mm equivalent” field of view of 75mm, or a short telephoto that could be ideal for portraits and other close range telephoto shooting. Either way, a great experience awaits us.

SMC Pentax-M 50mm f/1.7 Performance

Central sharpness is very good all the way through the aperture range, rising to excellent at f/8 and f/11. The edges are just fair at f/1.7 and f/2.8, good at f/4, very good at f/5.6, excellent at f/8, very good at f/11 and f/16 and good at f/22. A very creditable performance.

How to read our MTF charts

The blue column represents readings from the centre of the picture frame at the various apertures and the green is from the edges.

The scale on the left side is an indication of actual image resolution and sharpness as LW/PH and is described in detail above. The taller the column, the better the lens performance.

For this review, the lens was tested on a Pentax K-1 using Imatest.

CA (Chromatic Aberration) is centrally very well controlled, the edges straying somewhat at wider apertures but coming under better control as we stop down. Overall, CA is not much of a problem except perhaps where we have extremely challenging subjects such as bare branches against bright sky.

How to read our CA charts

Chromatic aberration (CA) is the lens' inability to focus on the sensor or film all colours of visible light at the same point. Severe chromatic aberration gives a noticeable fringing or a halo effect around sharp edges within the picture. It can be cured in software.

Apochromatic lenses have special lens elements (aspheric, extra-low dispersion etc) to minimize the problem, hence they usually cost more.

For this review, the lens was tested on a Pentax K-1 using Imatest.

Distortion measures -0.89% barrel, pretty much what we would expect from this lens design and very acceptable.

Bokeh is the smoothness of the out of focus areas in an image, and in its day was not something often discussed, not aquiring the name yet. The bokeh is rather pleasant though and here too the lens performs well.

The SMC coating has improved over the years, but even at this relatively early stage it does the job of reducing flare very well. There are some quite attractive artefacts that can be generated if we work at it, but generally there is little sign of flare.

Vignetting is there, especially with the lens wide open, but it soon settles to a reasonable level and could easily be reduced further using software if desired.

Aperture Vignetting
f/2.8 -1.6
f/4 -1.3
f/5.6 -1.1
f/8 -1.1
f/11 -1.1
f/16 -1.1
f/22 -1.1

Value for Money

Given that a 50mm lens was supplied with most camera bodies, and this was often the f/1.7 version, huge numbers will have been made and finding a good example should not be a problem. If lucky, a free one might be found attached to a camera body purchase, but in any event picking up a great example from £20 to £50 should be quite possible. Excellent value.

SMC Pentax-M 50mm f/1.7 Verdict

Many photographers started off with just the 50mm standard lens and to revisit that is a very liberating experience. No heavy camera bags loaded with equipment and options, no decisions regarding focal length and much greater freedom in low light with fast, bright lenses. 50mm lenses also lend themselves well to adding other optical devices. So, bellows, close up lenses, reversing wide angle lenses on the front for huge magnifications, extension tubes...the list goes on.

Why 50mm? This is the focal length that most closely mimics the perspective that is similar to the human eye, so images look natural. It is also long enough to use for portraits, yet wide enough to include a small group in the shot. Crop sensor users will look to the 35mm lens for a similar effect, but the 50mm is still useful as a fast, short telephoto.

In summary, a very versatile, high performance lens and this SMS Pentax-M 50mm f/1.7 is an excellent choice, with great results and a very satisfying character to the images.

Another Highly Recommended M series lens.


SMC Pentax-M 50mm f/1.7 Pros

  • Very good overall sharpness
  • Compact and light
  • Full frame format
  • Excellent value
  • Beautifully made
  • Very pleasing imaging characteristics
  • Excellent flare resistance
  • Low central CA
  • Modest distortion
  • Lovely tactile handling

SMC Pentax-M 50mm f/1.7 Cons

  • Manual focus
  • Stop down metering
  • Wider apertures soft at edges

Features: 4/5
Handling: 4.5/5
Performance: 4.5/5
Value: 5/5
Overall Verdict: 4.5/5

Pentax SMC Pentax-M 50mm f/1.7 Specifications

Manufacturer Pentax
Lens Mounts Pentax K
Focal Length 50mm
Angle of View No Data
Max Aperture f/1.7
Min Aperture f/22
Filter Size 49mm
Stabilised No
35mm equivalent 50mm
Internal focusing No
Maximum magnification 0.15x
Min Focus 45cm
Blades 6
Elements 6
Groups 5
Box Contents
Box Contents No Data
Weight 185g
Height 31mm

Members gallery photos using: smc PENTAX-M 50mm F1.7

Posted 31/01/2024 - 18:01 Link
Interesting review thanks John. I still have the one that came with my ME Super bought in1983.

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