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SMC Pentax-M 75-150mm f/4 Zoom Lens Review

John Riley reviews the SMC Pentax-M 75-150mm f/4 Zoom vintage Pentax K mount lens, with the full-frame Pentax K-1.

Posted: 25/06/2019 - 08:31

SMC Pentax-M 75-150mm f/4 ZoomThe zoom lens is now so ingrained in our photographic world that it can be hard to remember that this was not always so. However, by the mid 1970s computer lens design was already making possible some remarkable advances. It was Olympus who started the short telephoto zoom on its way, advertising their 75-150mm f/4 for the OM system as compact and every bit as good as the prime lenses it replaced. Pentax were hot on their heels and here we are looking at the SMC Pentax-M 75-150mm f/4 zoom lens, marketed in exactly the same way as being remarkably compact and on a par with the 85, 100, 120, 135 and 150mm lenses that it theoretically could replace. It will be interesting to see where this lies today, using the full frame 36MP Pentax K-1 DSLR, so let's hone our manual focusing skills and zoom in on one of the first of what was a new breed of telephoto zoom lenses.

SMC Pentax-M 75-150mm f/4 Zoom Handling and Features

Smc Pentax M 75 150mm F4 At Full Zoom On K 1There is a certain satisfaction in opening the box and finding a 40 year old lens in absolutely perfect condition, with that glint of newness about it. We are talking here about the first of the really good zoom lenses, where before this the prime lens was the absolute quality choice. We will see how close this gets to that quality as we proceed. In current terms, at 465g the lens is satisfyingly heavy, but quite compact, the weight coming from metal and glass. In terms of the 1970s it is more bulky than any of the primes it might replace, and Pentax had lenses of 85mm, 100mm, 120mm, 135mm and 150mm that were contemporary and much smaller. They were also generally faster, the 85mm being f/2 and the others f/2.8 or f/3.5. They also focused closer, but where the zoom scores is in concentrating all those focal lengths into one useful package.

Starting at the front of the lens, we have a built in sliding lens hood, which is very convenient, but not really long enough to be very significant. Within this is the 49mm filter thread, which shows how slim the barrels of these lenses are. For flare control we rely on the SMC (Super Multi Coated) coatings, Pentax being the first of the manufacturers to make a real push into this valuable new technology. To put this in perspective, at this stage many Olympus OM lenses were actually still coated conventionally.

The wide zoom/focus ring is a trombone action. It is pushed/pulled for zooming and rotated for focusing. This demands a high degree of precision in manufacture and this sample is as new, with a superb, super-silky action that is typical of Pentax M series lenses and a positive tactile pleasure in its own right. There will be zoom creep when the lens is carried, but zooming does not alter the length of the lens barrel, so it is not much of a problem. Focus is held well and it appears this is a parfocal zoom – that is, it holds its focus even after zooming. A slight disadvantage over prime lenses in the range is that the front element rotates, so using graduated and polarising will be more difficult. The distance scale is clearly marked in feet and metres. Focusing is down to 1.2m (4 feet), closer than the 1.6m (5.2 feet) of the similar Olympus OM lens. It compares very well with the minimum distance of the 120mm and longer lenses that it covers, as they focus down to 4 feet for the 120mm and 5 feet in the case of the 135mm and 150mm.

Smc Pentax M 75 150mm F4 Old Vs NewThe aperture ring is firm and smooth and has full stop détentes between f/4 and f/5.6 and f/22 and f/32, the rest being in half stop steps. There is no “A” on the aperture ring, so the camera cannot control the aperture. The high quality stainless steel K mount is also devoid of any electronic contacts, so operation of the lens has to be manual. This entails setting the desired aperture on the lens, setting the camera mode to M and pressing the green button on the camera. This sets the shutter speed and hence the exposure. When the shutter release is pressed, the lens is stopped down to the taking aperture selected and the image captured. It works, it's simple and becomes fast enough with a little practice.

Optical construction is 12 elements in 9 groups, slightly simpler than the 15/11 of the Olympus 75-150mm f/4 lens. I mention the Olympus particularly as these lenses were both at the start of this new revolution and a comparison throws up interesting differences and similarities. It is also worth noting that Pentax opt to gives us an f/32 setting, whereas Olympus stop at f/22.

It has to be said that the quality of finish on the lens is really beautiful, as is the super-smooth handling. Focusing is extremely easy on the K-1, snapping in and out precisely either using the viewfinder or Live View. Ergonomically, it is pure silk, but of course, the essential question is how does it perform, so let's see how we did with the technical tests.

Smc Pentax M 75 150mm F4 Rear Oblique View

SMC Pentax-M 75-150mm f/4 Zoom Performance

At 75mm, central sharpness is very good all the way through from f/4 to f/22, and still good at f/32. Thus the inclusion of that smallest aperture may be vindicated. The edges are also very good from f/4 to f/22 and good at f/32. The evenness of sharpness from edge to edge is remarkable.

At 100mm, centrally sharpness is very good from f/4 to f/11, good at f/16 and f/22 and fair at f/32. The edges are good at f/4, crisping up and becoming very good from f/5.6 to f/11. This drops to being just fair from f/16 to f/32.

At 150mm, the centre is very good from f/4 to f/8, good at f/11 and fair from f/16 to f/32. The edges are good at f/4, very good at f/5.6 and fair from f/11 to f/32. Whilst this is true at test chart distances, it's reasonable to point out that sharpness at longer ranges is actually very much better.

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 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) at 75mm is extremely well controlled, both centre and edge. Very impressive. At 100mm, the centre is just as well corrected, the edges less so, but still keeping CA to within around 1 pixel. At 150mm the centre is still under one half of a pixel, but the edges show around 2 pixels. This is all an excellent result and better than many modern zoom lenses. In any event further corrections can be made in software.

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.

Bokeh, the quality of the out of focus areas in an image, is very pleasant, although the sharp edges of the diaphragm blades will show up as highlights with hexagonal shapes. This can be avoided when the lens is wide open as at that point the diaphragm is perfectly circular – this setting works very well for portraits at 150mm, with a sharp core and softer outer field.

This may be an early SMC coating, but Pentax's 7-layer multi-coating is highly effective. Even with the tiny lens hood, flare is not a problem.

Pentax M series lenses are “compact” lenses in the Pentax range and as such we might expect some vignetting. In fact, at 75mm and f/4 corner darkening is just -1 stop. This reduces on stopping down to f/5.6 and remains around -0.7 stops. At 100mm we have -1 stop at f/4, about half a stop throughout the rest of the range. At 150mm, we have around -1 stop throughout the aperture range. This is actually a very satisfactory performance.

The lens has characteristics that can be worked with. At longer distances, images are crisp and sharp. Closer, the edge performance at 150mm is the weakest point, but the centre is very good to f/8 and this lends itself well to portraiture. It is a case of knowing our lens and working to its strengths. For the highest optical quality, 75mm and 100mm offer extremely good results centre and edge, in the latter case at mid apertures, in the case of 75mm at virtually all settings apart from f/32.

Smc Pentax M 75 150mm F4 Top View Closest Focus

Value For Money

Based on what I paid for this lens, the SMC Pentax-M 75-150mm f/4 lens could cost as little as £20, there's clearly scope for picking up a quality zoom lens that may be unfashionable and overlooked. If you can find one at this sort of price and in this condition, just buy it, and maybe spend a little more if needs be.

It is likely that there will be few chances like this, but even at a higher price it could still be a good lens to invest in. It will certainly offer some nicely balanced qualities and the opportunity to have some fun.

SMC Pentax-M 75-150mm f/4 Zoom Verdict

It is easy to see why these 75-150mm lenses caught the imagination when new, offering previously unattainable quality levels in a relatively compact package. Olympus were first off the mark, Pentax and others soon followed. The Pentax offering is a gorgeously made lens, a real tactile pleasure to use, but that could equally be said of most of the SMC Pentax-M lens range.

The lens is very strong at 75mm and although this fades as we zoom in, it still retains a high level of attainment , particularly centrally and at wider apertures. At 150mm and f/4 it could be usefully exploited as a very fine portrait lens, with a sharp central core and a nice soft effect towards the edges.

Performance is also better at longer distances. The state of lens design at the time offers us today a very usable and interesting optic with plenty of potential for good photography. If you can find a good copy then well worth buying.

M Series Lenses:


SMC Pentax-M 75-150mm f/4 Zoom Pros

  • A high level of sharpness
  • Well controlled distortion
  • Low CA
  • Modest vignetting
  • Gorgeously smooth engineering
  • Parfocal zoom
  • Constant f/no when zooming
  • Excellent flare resistance
  • Modest cost

SMC Pentax-M 75-150mm f/4 Zoom Cons

  • No weather sealing
  • Technical performance drops at 150mm

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

John Riley

My specialised interest in Pentax started from the first moment I looked through the viewfinder of my first Spotmatic, the SP1000. That gorgeous clarity, sharply defined within a pure black frame is my definitive way to view the world and make images. Pentax is a superb example of a range of manufactured tools that is both the path to creativity and also a gem of engineering elegance and excellence in its own right.

Biography Profile John Riley Photography

Asahi SMC Pentax-M 75-150mm f/4 Zoom Specifications

Lens Mounts Pentax K
Focal Length 75mm - 150mm
Angle of View No Data
Max Aperture f/4
Min Aperture f/32
Filter Size 49mm
Stabilised No
35mm equivalent No Data
Internal focusing No Data
Maximum magnification No Data
Min Focus 120cm
Blades 6
Elements 12
Groups 9
Box Contents
Box Contents No Data
Weight 465g
Height No Data

Posted 26/06/2019 - 00:12 Link
Super review John
Posted 07/07/2019 - 21:18 Link
Thanks, I find these reviews so interesting
George Lazarette
Posted 15/04/2024 - 16:33 Link
I bought one of these lenses round about 1982 or 83 and remember how impressed I was when the first slides were developed. It has always surprised me that they now sell for so little. They are so cheap that you can afford to buy several.
Keywords: Charming, polite, and generally agreeable.

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