SMC Pentax-F 50mm f/1.7 Lens Review

Fast, sharp 50mm F 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: 10/02/2025 - 13:30

Handling and Features
Performance
Verdict
Specification

The F series has already been covered as an overview, but here we have an excellent sample of the SMC Pentax-F 50mm f/1.7, one of the lenses most likely to be offered with the first autofocus bodies. In production from 1987-1991, before being superceded by the FA version, the "humble" first AF 50mm lens was from a time when the quality of the "kit lens" was no different to any lens in the lineup, the concept of a cheap and cheerful zoom being a long way off yet. The previous lineage of 50mm lenses performs to a very high standard, so is anything lost in the first AF offering? Let's have a close look at the lens and its performance, from a modern viewpoint with the 36MP Pentax K-1 full frame digital body.

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

Let's start with a big Thank You to PU member womble (Kris) for the loan of the lens. These reviews would not be possible without such generosity and it is very much appreciated.

Despite this being an AF lens, in terms of bulk it is very little different to the SMC Pentax-M 50mm f/1.7 or the SMC Pentax-A 50mm f/1.7 lenses that came before it. Slightly larger maybe, but at 65mm x 31mm and weighing in at a modest 205g it could hardly be described as a burden.

Starting our usual tour of the lens at the front, there is no bayonet fit for a lens hood, just the standard 49mm filter thread. Specific hoods have always been part of the Pentax range, and this lens is no exception. Even with the excellent SMC (Super Multi Coated) coating a hood can be a sensible idea, if only to protect the front of the lens from impact damage, and Pentax offered round screw-in and rectangular spring type clip on designs. The rectangular clip on type was used in this review and is by far the most convenient. Of course any screw in filter for standard 50/55mm lenses can also be used.

The small plastic button that tells us by touch where the lens needs to be positioned for insertion into the camera bayonet mount is still there, but not a white or yellow blob of plastic (as before for the M and A series) but a much reduced small black one, downplayed and on its way to being quietly retired on future lenses.

There is a very thin manual focusing ring which must have seemed rather strange at first, having less friction than previous lenses. Obviously as an AF lens less friction was advantageous as the whole unit moves to focus and has to be driven by the motor in the camera. However, although lighter in action than manual focus lenses, enough feel is left in the movement to make it viable. Focusing is down to 45cm, for a maximum magnification of 0.15x, all just as the previous manual focus lenses. AF/MF is selected on the camera. The AF is fast, accurate and very noisy as it is screw driven from the camera. However, in many environments this may not matter too much, although if it does then we can always switch to MF to be more discreet.

There is a distance scale in feet and metres under a rather more prominent than previously clear plastic window, plus a slight redesign of the depth of field scale which works rather well. There is an IR correction mark intended to indicate the shift in focus point necessary when using IR film. This would be rather slick with digital if the lens had Quick Shift, but that is another feature that will have to wait for the future.

Optical construction is the same 6 elements in 5 groups and as we shall see from the technical results, all indications are that this design is the same as all the previous 50mm f/1.7 lenses, going back to the M and A series. The diaphragm comprises 6 blades with no attempt to make them curved as the fashion for round apertures has not yet arrived.

The aperture ring does not feel quite as slick as the M lenses, but rather more like the potentially notchy feel of some of the A series. However, it works just fine with its half stop detentes (click stops), the exception being a full stop interval between f/16 and f/22, in common with most Pentax lenses. A button lock enables the A setting to be locked in so the aperture can be controlled by the camera.

SMC PENTAX-F 50mm f/1.7 Sample Photos

Finally we have the high quality steel mount and can see the added electronic contacts. Now the lens and camera are starting to talk to each other in more ways that before. Many things will follow from this, but for now we have small beginnings. Using the SMC Pentax-F 50mm f/1.7 lens is a great experience in simplicity. Without the ability to zoom we have to use our feet to create the best composition. Working around a subject there is a wonderful sense of freedom from technology, with the electronics just doing what it is told out of sight. If this sense of freedom to creativity is to be fully realised we do need a high quality lens to go with it, so let's see now how the technical tests stack up.

SMC Pentax-F 50mm f/1.7 Performance

Central sharpness is very good from f/1.7 to f/4, excellent from f/5.6 to f/11 and very good at f/16 and f/22. The edges are fair at f/1.7, good at f/2, very good at f/2.8 and f/4, excellent from f/5.6 to f/11 and very good at f/16 and f/22. In summary, from f/2.8 right through to f/22 the lens is a great perfformer both centre and edge. The only weakness in terms of sharpness is the edges at f/1.7 to f/2, especially close up. In this respect it follows the same pattern as the previously tested SMC Pentax-M 50mm f/1.7 which pretty much clinches the received wisdom that the optical design of the two lenses is the same.

SMC PENTAX-F 50mm f/1.7 MTF Charts

CA (Chromatic Aberration) is centrally very well controlled, and apart from a little more at wider apertures at the edges the lens as a whole is not particularly prone to colour fringing.

SMC PENTAX-F 50mm f/1.7 Chromatic Aberration Charts

Distortion measures -0.90% barrel, pretty much the norm for this design of 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. It was only recognised in the broader terms of expecting more out of focus background with a telephoto lens than with a standard lens. Lack of curved diaphragm blades there may be, but the Pentax 50mm f/1.7 design is capable of some gorgeous bokeh. This is definitely true of the lens under review. Beautiful.

SMC PENTAX-F 50mm f/1.7 Aperture Range

Flare is not a problem in general shooting, but artefacts can be generated with strong light sources in the frame. Considering that currently a 50mm f/1.4 lens has been introduced as a "Classic" version complete with traditional flare as just described, then maybe there are plenty of such lenses available second hand at a fraction of the cost, such as this one.

Vignetting is pretty obvious wide open, but has cleared up to a modest level by f/2.8.

Aperture	Vignetting
f/1.7	-2.1
f/2	-1.9
f/2.8	-1.1
f/4	-0.8
f/5.6	-0.8
f/8	-0.8
f/11	-0.8
f/16	-0.8
f/22	-1.1

Value for Money

Looking at the usual places such as eBay, there are some, but not many compared to the other series, F series lenses. They vary in price quite a bit, the 50mm f/1.7 from perhaps £50 to £150. It can be unfortunate that users and collectors tend to compete and as a consequence prices can become inflated, but a good example of the lens will serve very well if it can be found at a price that the buyer feels is acceptable. That's a definition of a good deal - a price the seller is willing to sell for that the buyer finds acceptable.

SMC Pentax-F 50mm f/1.7 Verdict

The lens works just like all other Pentax lenses of its day, so no surprises there. The finish, quality of construction, superb handling, they are all there. At the right price, fantastic. What is especially true is that given the lens, a gorgeous day and just using the one lens gives a wonderful sense of freedom from the contraints of bulk. At some point perhaps we only had a 50mm lens, and then felt obliged or felt the need to add wide angles, telephotos, filters, close up devices, flash guns, and bigger and bigger bags to carry it all in.

Accepting that for some purposes specific lenses are needed, for general shooting a 50mm lens can go a long way towards fulfilling what is necessary. The feet act as substitute for zooming and the experience is worth repeating at intervals if only for its sense of liberating our creativity. Then the results...and the SMC Pentax-F 50mm f/1.7 is just a superb lens pictorially. It has terrific punch, clean crisp contrast, gorgeous bokeh and even the edge weakness wide open can be utilised creatively.

In conclusion, inexpensive, very classy and an Editor's Choice.

Specifications: SMC PENTAX-F 50mm f/1.7
General
Focal Type	Standard
Lens Mounts	Pentax K SMC-F
Availability
Year announced	1987
Discontinued	No
Dimensions
Diameter	65mm
Height	31mm
Weight	205g
Construction
Groups	5
Elements	6
Blades	6
Lens
Stabilised	No
Filter Size	49mm
Min Aperture	f/22
Max Aperture	f/1.7
Angle of View	47°
Focal Length	50mm
Focusing
Macro	No
Min Focus	45cm
Focusing Type	Automatic, Manual

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

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