Reviewed this time is the Pentax 85mm f/1.8 from the original K Series of lenses. With a focal length of 85mm typically ideal for portrait photography, John Riley put this vintage lens to test, providing sample photos along with MTF & CA charts.
Posted: 02/09/2024 - 15:01
Handling and Features
Performance
Verdict
Specification
The Pentax K 85mm f/1.8 lens is one of the first of the K bayonet lenses and was manufactured from 1975-1977, until superceded by the compact M series lenses. The K lens is slightly larger and yet could in itself be termed compact, especially compared to a typical current 85mm f/1.4 design. 85mm is the traditional "portrait lens", giving just a little more working distance to ensure good, flattering perspective. It is also in the area of focal lengths that are just longer than standard lens and the point at which manufacturers could produce the pinnacle of performance in their range. These lenses are highly sought after and can be relatively expensive. We have Pentax User member womble to thank for loaning this very fine sample. It looks great, but the key is how it responds to a digital sensor, so let's see how it behaves with the full frame 36MP Pentax K-1 DSLR.
SMC Pentax 85mm f/1.8 Handling and Features
As mentioned in the introduction, the lens is quite compact, measuring just 64mm x 56mm. It weighs in at a modest 331g. The hood is not with the lens, so we will have to rely on the SMC coating to reduce the chance of flare. There is a dedicated hood and this would be found in a quality leather case in its day., but would not have been supplied with the lens. There is a standard 52mm filter thread.
The wide manual focusing ring is as smooth as silk, a common feature of Pentax lenses of the era, which are arguably smoother than much more expensive marques. There is a very long focusing throw, so high accuracy is possible. As there are no focusing aids in DSLR viewfinders, the longer focal length does make it slightly easier than with a wide angle. For the most accurate focusing, then use of Live View and magnification (press the OK button to magnifiy the image and a light touch on the shutter release to revert to full frame) will really hit the spot. Closest focus is 85cm (2.75 feet), for a maximum magnification of 0.13x. There is the usual cut out for the distance scale, with beautifully engraved figures in blue (feet) and yellow (metres). There is also a depth of field scale, with the usual red marker for infra-red correction. The small white plastic bubble can be aligned with the lens release lever on the body to give a tactile way of placing the lens correctly in dim light to make mounting the lens easier.
Closest to the camera body is the aperture ring, with firm but slick click stops at f/1.8, f/2, f/2.8 and then at half stop intervals to f/16, with one final full stop interval to f/22.
Finally we have the plain K mount, originally with no electronic contacts. 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. Then when the shutter is released the lens will stop down to the appropriate aperture. 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 an 85mm lens will be around 127.5mm. This is still a short telephoto, and not far off the ubiquitous 135mm.
85mm lenses do tend to have a price premium, especially as they are faster than average, with f/2 or brighter apertures. There are also different approaches to their design, some having deliberately weaker performance at wider apertures, to make portraits kinder to the subject. Others have a design ethos where razor sharp images are there from the outset, something that is less flattering to skin. Hence the irony of buying a high class, ultra-sharp lens to put a softening filter in front of it. What sort of thinking is behind this lens we shall now look into as we consider the technical tests.
SMC PENTAX 85mm f/1.8 Sample Photos
SMC Pentax 85mm f/1.8 Performance
Central sharpness is very good from f/1.8 to f/2.8, excellent from f/4 to f/8, very good at f/11 and f/16 and still good at f/22. The edges are good at f/1.8, very good from f/2 right the way through to f/16 and good at f/22. The edge to edge variation is minimal, and the "very good" description is not far at all from nudging into the area that could be described as "excellent". This is a very satisfactory result, and although the sharpness is high, wide open at the edges there is a slight tapering off that might be used to advantage in portraiture.
SMC PENTAX 85mm f/1.8 MTF Charts
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.
Central CA is very well corrected. There is some CA at the edges, and the CA test shots do show under magnification some colour fringing. This is not severe though and correction could be made in software if desired. Most subjects do not really show this up.
SMC PENTAX 85mm f/1.8 Chromatic Aberration Charts
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 a miniscule -0.01% barrel, so we might as well say that the lens is perfectly rectilinear.
Bokeh is the smoothness of the out of focus areas in an image and this lens delivers beautifully. The bokeh is relaxed and ultra-smooth, just the thing to form a background to portraits or flower studies.
SMC PENTAX 85mm f/1.8 Aperture Range
In normal use, the SMC coating is still a great performer and there is no sign of flare. The extreme flare test shows some very faint artefacts and a slight veiling, but for all normal purposes flare is not a problem.
Vignetting is present, but at very acceptable levels.
Aperture | Vignetting |
f/1.8 | -1.8 |
f/2 | -1.3 |
f/2.8 | -1 |
f/4 | -1 |
f/5.6 | -1 |
f/8 | -1 |
f/11 | -1 |
f/16 | -0.9 |
f/22 | -0.9 |
Value for Money
The SMC Pentax 85mm f/1.8 is not a particularly common lens, but it is a great lens and will be highly sought after by both collectors and users. This can be a difficulty for users, but given the cost of current 85mm f/1.4 lenses then maybe easier to justify.
A mint example might be around the £300 mark, but bargains are always possible. VFM, as with all vintage lenses, really amounts to what the buyer is prepared to pay and the seller prepared to sell for.
SMC Pentax 85mm f/1.8 Verdict
Gorgeous, beautiful images and superb handling make a gem of a lens. This must be one of the high points in the original K series. In this reviewer's opinion, a far better 85mm than the SMC Pentax-M 85mm f/2 lens that followed it. The key with vintage lenses for users is of course how the lens handles and performs on digital cameras. We have seen wide angles flounder slightly with non-telecentric designs, but this is far less of a problem with the telephotos.
The lens under review is clearly an excellent example and most definitely Highly Recommended.
Further reading - Pentax K Series - The Original K Mount
SMC Pentax 85mm f/1.8 Pros
- Excellent sharpness
- Virtually no distortion
- Lovely smooth bokeh
- Low central CA
- Excellent flare resistance
- Smooth handling
SMC Pentax 85mm f/1.8 Cons
- Manual focus
- Stop down metering
- Rarity means higher price
Specifications: SMC PENTAX 85mm f/1.8 |
||||
General | ||||
Focal Type | Telephoto | |||
Availability | ||||
Year announced | 1975 | |||
Discontinued | Yes | |||
Dimensions | ||||
Diameter | 64mm | |||
Height | 56mm | |||
Weight | 331g | |||
Construction | ||||
Groups | 6 | |||
Elements | 6 | |||
Blades | 8 | |||
Lens | ||||
Maximum magnification | 0.13x | |||
Internal focusing | No | |||
35mm equivalent | 85mm | |||
Stabilised | No | |||
Filter Size | 52mm | |||
Min Aperture | f/22 | |||
Max Aperture | f/1.8 | |||
Focal Length | 85mm | |||
Focusing | ||||
Macro | No | |||
Min Focus | 85cm |
Members photos with related tags: portrait,woman
Fan of DA limited and old manual lenses
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7625 posts
16 years
Hertfordshire,
mostly.
I have the genuine hood somewhere but couldn't find it... ~sigh~
K.
It is an illusion that photos are made with the camera… they are made with the eye, heart and head. Henri Cartier-Bresson
Lots of film bodies, a couple of digital ones, too many lenses (mainly older glass) and a Horseman LE 5x4.