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SMC Pentax-M 135mm f/3.5 Lens Review

Looking for some additional reach for your photography? This affordable vintage 135mm f/3.5 Pentax-M Series K mount lens could just be the answer. John Riley put the lens to the test and provides sample photos, MTF & CA charts along with his verdict.

Posted: 27/02/2024 - 13:02

Handling and Features

We continue our look at the M series compact lenses, introduced along with the then-new Pentax ME and MX compact SLR cameras. 1975 had seen a new range of bayonet mount Pentax cameras and lenses, largely based on the screw thread lenses that preceded them, but by 1977 the new paradigm was for compact kit and gradually the M series replaced the larger K series. These new compact lenses were arguably some of the smoothest and classiest lenses Pentax had ever produced, and the sheer silky movement of the focusing rings is in itself a pure tactile pleasure.

Having been seduced by the qualities of the standard lens provided with most camera bodies sold, the hobbyist photographer would eagerly look to expanding their collection and one of the most popular choices for the first extra lens would be the 135mm. Thus it had always been as 135mm was the longest lens that could be used with the rangefinder focusing systems of the Leica and others and in terms of simple tradition this leaked over into the aspirations of the SLR photographer.

Here we have a fine example of the SMC Pentax-M 135mm f/3.5, kindly loaned for this review by SRS Microsystems in Watford. Let's see how the lens handles and performs and whether it can deliver the quality along with its new, trim dimensions and undeniably slick handling. The camera body used is the 36MP Pentax K-1.

SMC Pentax-M 135mm f/3.5 Handling and Features

What is sometimes evident in reading reviews and articles from various sources is that it can be forgotten (if it was ever known in some cases) just how compact and elegant in design Pentax lenses could, and can be, even to this day. Whilst it may not be as small as some rangefinder lenses, the SMC Pentax-M 135mm f/3.5 is truly tiny. Weighing in at just 270g and measuring a svelte 63mm x 66mm it adds little bulk to the K-1 body, balancing extremely comfortably in the hands.

The lens has few features , but nonetheless some refinements that prove to be useful. The 49mm filter thread is a modest size making the purchase of filters more affordable. There is a built in slide-out lens hood that offers enough protection to the front element to make a difference and reduce flare, whilst of course shielding the front of the lens from impact damage. The wide focusing ring is truly gorgeous in its action and generally remains so over the years, a testament to the high quality of manufacture. Production dates were 1977-1986 so this sample is at least 38 years old and maybe as much as 47 and yet still in superb condition.

The distance scale lies in a cut out, showing feet in blue figures and metres in yellow. Engravings are crisp and clear. Focusing is down to 1.5m, or around 5 feet, for a maximum magnification of 0.11x. This is reasonably close and much better than some earlier SLR lenses such as Voigtlander's 135mm f/4 Dynarex that only offered 13 feet and had to be supplied with a special close up lens to move in further. However, it is no competition in the close up stakes to almost any current kit zoom.The depth of field scale also shows the IR correction mark, here at the f/16 point, whereras shorter lenses usually show this at around the f/4 point. Clearly more IR focusing correction is needed with the telephoto lens. This is probably a moot point for most users but was relevant when IR film was well known.

The aperture ring has well defined click stops at f/4, f/5.6 and then half stops till f/22 is reached and we have one final click onwards to f/32. The M series lenses generally have one further stop when compared to the previous K series and also when compared to the norm across the other manufacturers. Many 135mm lenses would stop at f/22 or even f/16, but the Pentax M goes all the way down to f/32. This is fine for maximising depth of field, but there will likely be quite a drop in sharpness at these small apertures due to diffraction. At least we are given the choice.

Finally, there is the solid steel mount, jointly designed with Zeiss and still proving itself today, albeit with the addition of various levels of electronic contacts. This basic mount was introduced in 1975 with the K series of cameras and lenses, and replaced the long established and ubiquitous 42mm screw mount. At the time this caused some consternation, but there were good reasons to make the change. The lens throat was increased in diameter from 42mm to 45mm, thus enabling more ambitious lens designs, especially fast primes and new wider ranging zooms. There is also the obvious convenience of faster lens changing. In typical Pentax form, an adapter allows the use of older screw mount lenses and we still make use of this today, opening up a huge number of screw thread options going back well over 60 years.

Optical construction is 5 elements in 5 groups, with the diaphragm comprising 8 blades. This is a slight increase in sophistication of design as many 135mm lenses at this time only had a 4 element contruction. There is also an SMC Pentax 135mm f/2.5 lens with 6 elements in 6 groups and a lower cost Takumar (Bayonet) 135mm f/2.5 with 4 elements in 4 groups.

Being a manual focus lens with no electronic communication with the camera, there are some handling pointers to think about. When the camera is switched on it will ask what the focal length is, for the purposes of setting the shake reduction system correctly. Then we need to focus the lens, and this may be a lost art for many that needs relearning, but with no visual aids in the viewfinder to help. No microprisms to shimmer when out of focus, no split image rangefinder to align to find perfect focus, just the eye judging the point of sharpness. Unfortunately most eyes are quite poor at this and the amount of variation when finding that point of focus is significant, especially with a telephoto lens where depth of field is reduced. The answer is Live View, and using LV with magnification reveals that point of focus easily and also shows up how dismal the ability of the human eye can be. This has always been known and in the past various magazines have demonstrated this in tests. At longer distances and smaller apertures we get away with it, but close up with wide apertures or where precision is necessary then the use of LV with magnification is the way forward.

Shake reduction is very welcome with even a 135mm lens, or alternatively a tripod with SR switched off. If the self timer is used SR is automatically disengaged and the time delay allows any vibration from pressing the shutter release to die away. In addition, the mirror is raised before the exposure when the self timer is used, thus removing any shutter vibration from the equation.

As there is no communication with the camera, exposure is via stop down. Focus the lens, set the aperture on the lens, press the green button and the lens will briefly stop down, exposure will be measured and the camera will set the shutter speed. The lens opens up again. Press the shutter release and the lens stops down, the exposure is made and the lens opens up again. With practice, the process is simple and quick.

We can also use an APS-C crop sensor DSLR of course, in which case the “35mm equivalent” field of view will be around 200mm.

SMC Pentax-M 135mm f/3.5 Performance

Central sharpness is good at f/3.5, very good at f/4, excellent at f/5.6, very good from f/8 to f/16 and then, as expected, tails off to being good at f/22 and just fair at f/32. The edges are generally softer, being good from f/3.5 to f/5.6, very good at f/8 and f/11, good at f/16 and fair at f/22 and f/32. The empasis is clearly on central sharpness, but stop down to f/8 or f/11 for very good even 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 showing some colour fringing in demanding subjects such as branches against bright sky. For most subjects this will not be too intrusive, but software correction is available if needed.

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 +0.69% pincushion which is very satisfactory and it is unlikely that further correction will be needed. Software is the answer if necessary.

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. However, it is inescapably part of the magic of a lens, and this one has some of that Pentax quality about it. The rendition is very pleasing indeed and bodes well for portrature and flower studies, which will be enhanced by the smoothness of out of focus backgrounds.

The SMC coating has improved over the years, but is already working well for lenses such as this 135mm. Flare resistance is excellent and it is very difficult to generate any artefacts. This also aided by the smaller number of elements compared to current lenses. Less elements means fewer glass surfaces to cause internal reflections.

Vignetting is kept to a very reasonable one stop or so, despite the compact construction of the lens.

Aperture Vignetting
f/3.5 -1.1
f/4 -1.1
f/5.6 -1.1
f/8 -1
f/11 -1
f/16 -1
f/22 -1
f/32 -1

Value for Money

This particular very fine sample of the lens has been kindly loaned from SRS Microsystems Ltd and is on their website priced at £69. Including 12 months guarantee and this free thorough lens test that is pretty good value.

Over in the world of eBay a variety of price levels exist, from the very cheap to the adventurously unrealistic, but with careful buying there will be bargains to be had.

SMC Pentax-M 135mm f/3.5 Verdict

It is arguable that some of the finest classic Pentax lenses have come from the compact M series. There is a predominance of metal construction under the skin, probably less plastic than the A series onwards, and a certain elegance and smoothness of design and construction. We have been looking at new reviews of the M series partly because of this and partly because they are the last Pentax lenses before the A series made the connection electronically with the cameras, so there are very reasonable bargains to be had, and plenty of options with very hig standards of performance.

The 135mm f/3.5 is a classic example of a lens that delivers, is available freely for a very reasonable cost and which is a real pleasure to use.

Another Highly Recommended M series lens.

Thanks again to SRS Microsystems for kindly loaning this lens for review.

SMC Pentax-M 135mm f/3.5 Pros

  • Very good to excellent central 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 135mm f/3.5 Cons

  • Manual focus
  • Closer focusing would be useful
  • Stop down metering
  • Edge sharpness lags behind centre

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

Pentax SMC Pentax-M 135mm f/3.5 Specifications

Manufacturer Pentax
Lens Mounts Pentax K SMC-M
Pentax K
Focal Length 135mm
Angle of View No Data
Max Aperture f/3.5
Min Aperture f/32
Filter Size 49mm
Stabilised No
35mm equivalent 135mm
Internal focusing No
Maximum magnification 0.11x
Min Focus 150cm
Blades 8
Elements 5
Groups 5
Box Contents
Box Contents No Data
Weight 270g
Height 66mm

Members gallery photos using: smc PENTAX-M 135mm F3.5

Posted 09/03/2024 - 22:42 Link
Excellent review! I still have my SMC Pentax-M 135 f3.5 from an old MX (from the 1980s).
Sometimes I use it coupled to a K100D or K-3 with excellent results (manual mode).
SMC Pentax-M 135 f3.5 is still a great lens.
(I also have the SMC Pentax-M 50mm f1.4)

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