SMC Pentax 55mm f/1.8 Lens Review

John Riley reviews the Pentax 55mm f/1.8 manual focus K mount lens from the 1970s. Is this relatively inexpensive easily adapted lens worth buying? John puts it to test providing MTF & CA charts, sample photos and his verdict.

Posted: 23/07/2024 - 07:48

Handling and Features
Performance
Verdict
Specification

The year 1975 brought with it the Pentax K mount, developed jointly with Zeiss and originally intended to be a universal bayonet mount in the same way that the previous 42mm screw thread had served for many years. New lens designs needed wider lens mounts and speed of operation became more and more critical, especially for professional photographers. The first K bayonet lenses are mostly the same as the screw thread SMC Takumars that preceded them, so large numbers of new lenses had to appear very quickly to accompany the new K series cameras.

We now look at one of the most popular standard lenses that would have been sold with many thousands of camera bodies as a kit. However, this precedes by decades any concept of a "kit lens" that is cheap and cheerful, and indeed sometimes not so cheerful. Standard lenses set the standard for camera systems and would hopefully impress the user and lead to the purchase of many more lenses from the same marque. The upshot today is that there are now huge numbers of standard lenses available second hand, so the question is how do they behave on current digital cameras? To find out, we couple up a virtually mint SMC Pentax 55mm f/1.8 with the 36MP Pentax K-1, so let's see how it all works out.

SMC Pentax 55mm f/1.8 Handling and Features

There is a natural progression in the Pentax 55mm f/1.8 lenses, through the screw thread era to the first bayonet lenses to the M series and beyond. The coatings change but the 6 elements in 5 groups configuration works consistently well and survives intact. In fact the 55mm f/2 lenses are identical apart from a baffle to reduce the aperture and obviously a differently marked aperture ring. Thus was the lower cost version created for the SP1000 (screw thread) and K1000 (K bayonet) cameras. There are size and cosmetic differences, and the Pentax K 55mm f/1.8 starts to gain the aesthetics of the M series that follows, with similar marking styles and a similar focusing ring grip design. The silky smooth focusing is there in its full glory, still the same tactile pleasure to be enjoyed. The lens is slightly larger than the screw thread ones, but still compact, weighing in at a svelte 221g and measuring just 63mm x 39mm.

First then, our tour of the lens. No lens hood is provided, but there is a conventional 52mm filter thread. The K standard lenses adopt the slightly larger 52mm filter thread, whereas the norm for the screw thread lenses that came before and the M series lenses that came after is 49mm. The focusing ring offers a good solid grip and the design carries forwards into the later M series. Focusing is down to 45cm (1.5 feet) for a maximum magnification of 0.17x, the same still being true today from the latest new 50mm compact lenses.

The cut out for the focusing scale is much wider than previously, showing feet in blue and metres in yellow. There is an IR correction mark at the f/4 point on the DOF scale, indicating the amount of focusing correction needed for Infra-red light. The wider cut out makes full use of what is a very usable depth of field scale. There is a small plastic nodule on the lens barrel and this can be aligned with the lens release lever to make positioning the lens by feel to be much easier. Thus changing lenses in dark conditions is facilitated.

Optical construction is 6 elements in 5 groups, with no special glasses used. The diaphragm comprises 6 blades. The SMC (Super-Multi-Coated) coatings are highly effective and remain so to this day. The diaphragm comprises 6 blades, the norm for its day, and the hexagon shaped aperture can be clearly seen in the bokeh of the images produced.

The aperture ring is nicely engineered, with a smooth action and click stops at half stop intervals. The initial settings are f/1.8 - f/2 - f/2.8 and there is one full stop interval between f/16 and f/22.

The basic K mount is beautifully manufactured in stainless steel and the tolerances are so good that even this old lens (made from 1975-1977) still mounts into place smoothly. There are good reasons for changing to a bayonet mount. The lens throat is 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.

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 50mm lens. The alternative is 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 for a 50mm lens will be around 75mm. However, the full potential of the lens may well be best enjoyed on the full frame K-1.

The standard lens for any format is deemed to be roughly the measurement of the diagonal of the format. So, for full frame that would equate to 43mm. There is only one 43mm lens, the SMC Pentax or HD Pentax 43mm f/1.9 Limited, but traditionally lenses have been a little longer, at 50mm, 55mm or even 58mm. The basic reason is that it is easiest to design high quality fast lenses at focal lengths slightly longer than the standard lens. This may not apply in the same way with current lenses, which seem determined to defy the laws of Optics, although we know they don't, but they do have some cutting edge designs. Given the high quality, the standard lens also acepts add ons to it design with better grace than most, so filters, close up lenses, bellows, teleconverters and any optical accessories can be used with potentially better success.

Using vintage lenses is a fascinating area of photographic discovery, seeing whether or not the sometimes awesome reputations still hold true when faced with digital sensors. The handling aspects will always be less convenient, but the SMC Pentax 55mm f/1.8 handles easily and distinctly better than many of its contemporaries, who were making quite large, clunky designs in the mid 1970s. It also has an enviable reputation as a lens with the magic "pixie dust" status, that indefinable but obviuous fine quality that we know when we see it. Having passed the handling test with flying colours, let's see now if we can find the magic in its optical performance.

SMC PENTAX 55mm f/1.8 Sample Photos

SMC Pentax 55mm f/1.8 Performance

Central sharpness is Very good from f/1.8 right through to f/16, rising to excellent at f/4 and f/5.6. It is still good at f/22. The edges are very, very close in terms of figures and hence also very good from f/1.8 to f/16, also rising to excellent at f/4 and f/5.6. Again, f/22 remains good. No complainits at all then regarding sharpness, a great result.

SMC PENTAX 55mm f/1.8 MTF Charts

CA (Chromatic Aberration) is kept very well controlled, better than many zoom lenses are today and equalling many primes. There is a bit of colour fringing at the edges at wide apertures, but it is not really an issue with most subjects. Another great result.

SMC PENTAX 55mm f/1.8 Chromatic Aberration Charts

Distortion measures -1.03% barrel, which is well within what would be expected of a standard lens.

Bokeh is the smoothness of the out of focus areas in an image, and in its day was not something often discussed, not having acquired the name yet. At some point collective wisdom decided that round diaphragms looked better than hexagonal ones, a matter perhaps of aesthetic fashion, so bokeh won't be the ultra-smooth type, but it is actually quite attractive. Inevitably a subjective issue.

SMC PENTAX 55mm f/1.8 Aperture Range

The SMC coating has improved over the years, but is very satisfactory and in the 1970s was ahead of many of its competitors. Rather than creating artefacts, very severe lighting causes a slight loss of contrast and a haziness. This is very minimal though, and flare is actually very well subdued.

Vignetting starts off at -1.5 stops, but by f/5.6 is a very mild -0.6 stops. Impressive, especially for such a compact lens.

Value for Money

Two samples of this lens were used, the first being kindly loaned by geordie01 for the K Series article and the second for this review, purchased from eBay for £50. Both lenses were identical in their smooth handling, neither had any faults, and the eBay purchase, used for the technical tests, delivered excellent results. All in all, £50 well spent and a good price to aim for if the lens is in impeccable condition.

SMC Pentax 55mm f/1.8 Verdict

Pentax standard lenses are excellent, the design being relatively unchanged over the years and still available today, albeit in the f/1.4 version. It is arguable that the slower lens, such as this K series 55mm f/1.8 or the later 50mm f/1.7 designs, actually has better pictorial qualities than the f/1.4, although the f/1.4 is grittier and perhaps more suited to reportage and street photography. The lens reviewed here is actually rather special, and should well please photographers looking for a more pictorial rendition, such as landscapes, portraits, architecture and travel. Although these are wonderfully vague descriptive terms, lenses can be like that, and the same sort of language applies to our assessment of bokeh. In all these senses, the SMC Pentax 55mm f/1.8 is a lens with a fine character that is subtly different to the later M series and could tip the balance and make the K lens quite a desirable optic.

In terms of pure technical results the figures and graphs speak for themselves and we have a lens with a very high, very even edge to edge performance and again a result that makes it highly desirable. The downside is that there is no AF, but if that is OK with the photographer then this is a great lens and is Highly Recommended.

davidwozhere davidwozhere

3448 posts
10 years
Slap in the middle of England

Posted 24/07/2024 - 00:24 Link

A well presented article with lots to learn from (how many of us know it all?) This may well have been a near mint example of a K mount version; my own is a shockingly battered M42 version that confirms my idea that, if the glass is good then it got battered through repeated use, simply because it is a good lens. It can stand shoulder to shoulder with this 'new' one and produce results exactly as John describes. I am surprised at the comment, ".... the later 50mm f/1.7 designs, actually has better pictorial qualities than the f/1.4...." because I would not even put the two lenses in the same IQ category, the 1.8/55 having oodles of pixie dust across its range and the 1.7/50 being simply a competent, sharp image producer.
There are dozens of cheap Takumar 1.8/55s on Ebay so don't be afraid to buy one. You won't be disappointed, especially with the bokeh. It really isn't necessary to blow £50+ unless you are after a collector's copy.
Thank you for producing this critique John and for the wonderful collection of images that has accompanied it.

Both the *istDS and the K5 are incurably addicted to old glass

My page on Photocrowd

HarmanNielsen HarmanNielsen

1 years

Posted 01/08/2024 - 15:16 Link

davidwozhere wrote:
This may well have been a near mint example of a K mount version; my own is a shockingly battered M42 version that confirms my idea that, if the glass is good then it got battered through repeated use, simply because it is a good lens. It can stand shoulder to shoulder with this 'new' one and produce results exactly as John describes.

I own both, the K version and the Takumar and I think there really is a difference between these two lenses: the Takumar favours greens and blues, whereas the K version produces deep reds as well, resulting in warmer tones overall, and the Takumar draws even more delicately than the K, in my opinion.

Edited by HarmanNielsen: 01/08/2024 - 15:23

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