This article compares three "normal" prime lenses, each being classics of the film-era: a fast Pentax 50mm f/1.2, the distinctive Pentax 43mm Limited f/1.9, and the Contax Carl Zeiss Planar 50 f/1.4. I'll shoot some photos and describe the characteristics of the lenses themselves. This will not be a formal test, but nonetheless I will adopt a reasonable methodology. No doubt photographs of human models would be more appealing, but I don't have any handy!
The lenses
Each lens will be named using their official designation (using lens markings). Then some salient features will be described.
The "SMC Pentax 1:1.2 50mm" comes from the first line of lenses that Asahi Pentax created for their K-mount SLRs, after migrating from the Takumar branding. This line is commonly called "Pentax K" to mark them distinct from the following M and A series. But they are not inscribed in any way to designate the "Pentax-K" status. It's simply a handy moniker. The Pentax-K 50/1.2 was produced from 1975 to 1984 in two versions which differ only in their inscription. I have the later version.
The Pentax-K 50/1.2 is 49mm in length, weighs 385g, and takes a 52mm filter. The lens is manual focus with an aperture ring featuring half-stops from f/1.2 to f/22. These include an unmarked detent for f/1.7 between 1.2 and 2. Operation is completely manual, using stop-down metering.
This lens was not updated in the subsequent M line, but did receive a refresh as the "SMC Pentax-A 1:1.2 50mm" (produced 1984 to 2004). The main reason was to facilitate an aperture coupling... the "A" standing for automatic. Pentax produced many other manual 50mm primes over the years, including f/1.4, f/1.7, and f/2 variants. Many are highly regarded.
The "SMC Pentax-FA 1:1.9 43mm Limited" is the first of three lenses branded "Limited" by Pentax, though these were not actually produced in fixed numbers. The focal length was chosen to be the perfect normal for full-frame (135 film). This lens is a tiny jewel, only 27mm in depth and barely noticeable at 155g. It has a custom screw-on metal hood and a lovely felt-lined slide-on cap. Overall the presentation is fantastic, which accounts for the high retail price. Produced between 1997 and 2021, it's now been replaced with an HD version that is fundamentally the same. So this lens is still in production for the digital era. Automatic exposure and auto-focus are enabled on appropriate Pentax cameras.
The "Carl Zeiss Planar 1,4/50 T*" was produced starting 1975 for Contax SLR cameras that use the Contax-Yashica mount. It is 41mm in length and weighs 290g, so falls halfway between the Pentax extremes in form factor. Like many in the Contax Zeiss line, this lens was introduced in an original AE version (made in Germany) and subsequently released in an updated MM version (made in Japan). I have the latter, distinguished by a green aperture marking at the minimum aperture. Note that this is only f/16. The lens does not stop down further.
There are two main differences between the versions. First, MM implemented aperture coupling, allowing shutter-priority on Contax bodies. This has no relevance today when operated through a dumb adapter. Second, AE lenses have a distinct ninja star shaped bokeh at certain apertures. People either enjoy this as a sign of character, or find the prominent background shapes intrusive.
The three lenses have a lot in common. All are built on the classic Double-Gauss design with an extra element at the rear, hence 7 elements in 6 groups. All three have identical 45cm close focus distance.
Method
Photos were taken on the Lumix S5 in RAW using Natural style. With IBIS off, the camera was mounted on a tripod. In order to maintain a workable shutter speed, I changed the ISO between some shots but never above 4000. The lenses were used via mount adapters, so operation was completely manual. Appropriate metal hoods reduced glare.
The RAW files were developed in Affinity Photo 2. I would normally enhance clarity and exposure during development, but for the sake of a level playing field I omitted this step. Real-world images will look much better!
I took a 1000 pixel square section of each image and arranged these into a grid for ease of comparison. You can click through an image here to see it in full size.
Image 1: close focus
The first image is of fruit, shot at a distance of 48cm, so just past the close focus distance. Colours are rendered quite similarly by the lenses. The different field of view of the 43mm focal length is apparent.
The Pentax-K 50/1.2 has a distinct glow wide open that remains prominent at f/2, but is almost gone by f/2.8. The texture of the fruit is now distinct. From here stopping down mostly only adds depth of field to the sharp central image. However, when viewing the full image it's obvious that improvements to clarity and contrast continue to f/11.
The Zeiss Planar 50/1.4 has a similar glow wide open and seems to resolve detail equally. At f/2.8 and f/4 detail seems similar, but the Zeiss might have a tiny bit more contrast.
The wide open image from the Pentax 43/1.9 is as clear as the other lenses at f/2. Perhaps there's even a tad less glow, though this could be down to the difference in FOV. Stopped down, this lens maintains parity with the others.
Here I will make an editorial comment about the reputation of the Limited 43mm, which is oddly divided. Many photographers rate it as one of the best normals ever made. Back in the day, Amateur Photographer magazine made this lens their normal reference. But other users will claim that it's too soft, especially wide open. This latter claim is not validated by my experience, nor the current test. Perhaps it is the price that puts some people off the lens, which is understandable. Or perhaps difficulties in focusing at such an aperture lead some to conclude the fault is in their equipment.
In conclusion, the first image perhaps fails to distinguish meaningfully between the lenses, which all look more similar than different. Only the wide-open performance differs to any significant degree.
Image 2: medium focus
The second shot is of a clothes line about 2m from the camera, with a hedgerow another 2m behind that. Such vegetation presents something of a torture test. Here each lens rendered a very different image.
The Pentax-K 50/1.2 is soft wide open but the focal point is reasonable at f/2, crisping up with each subsequent shot. The bokeh is nice and smooth, gaining contrast as stopped down. But even at f/8 the hedge is blurred. Something unexpected can be seen by examining the blue pole. It is under-saturated and lacks detail.
The Zeiss Planar 50/1.4 has quite a different bokeh, with more obvious circles and a brighter rendering overall. The blue pole is crisp by f/2.8 which is a much better achievement than either Pentax lens. At f/8 the busy background is more blurred than the 50/1.2 but also more distracting, since it has more highlights and is overall brighter. This could have been a result of changing light conditions during the shoot. Admittedly this test did not account for all variables.
The Pentax 43/1.9 also does a good job smoothing out the background. Of the three, I prefer this rendering, since it does not call attention to itself. At f/8 the background is a lot clearer than the 50mm lenses, a more pronounced effect than I would have expected for the 7mm difference in focal length. The background is not distracting, despite the visible detail. The vegetation looks more natural and pleasant than the other lenses.
Image 3: distant focus
For the third shot I focused on the tops of trees 5m distant. But this time the crop is taken from the extreme bottom-right corner of the frame. Since this area was quite dark, I brightened the exposure by a constant amount. Note that this is a 4:3 aspect image, so if you were shooting a video aspect (say, 16:9) these extreme corners would be cropped out and the overall performance would be better.
The focal plane is not parallel to the hedge but at an angle, which is not ideal for judging, since the subject will be varying in distance to the camera. Nonetheless, the crop is only a small part of the image and so should not vary any more than the leaves themselves. (If I was shooting a wall I'd be sure to maintain a correct perspective.)
All lenses show the effect of vignetting up to f/2 with the Zeiss being less shadowed at f/2.8. But since vignetting is trivial to fix in development, I've never attached much significance to this issue.
The Pentax-K 50/1.2 image is clear by f/8 which is a good result. We can of course stop down further if further edge clarity was required. The Zeiss Planar 50/1.4 is almost as sharp at that same aperture. The FOV of the Pentax 43/1.9 makes it difficult to compare, since we are seeing a different part of the hedge. But again it seems similar.
Conclusions
In two of these photos the lenses were more similar than different, which is perhaps not surprising given their similar optical design and intended purpose. No doubt I could cook up scenarios to enhance any rendering deviations, but in real-world shooting one tries to play to a lens' strengths and not weaknesses.
In practice, I would stop each of these lenses down to f/2.8 to get optimal detail and contrast. However, if you are buying the Pentax-K 50/1.2 it's most likely because you want that glow effect. And truly this lens can deliver. By f/4 images are super crisp but can still have an appealing bokeh.
I have found the Pentax 43/1.9 to be more usable at f/2.8 than the Pentax-K 50/1.2 at that same aperture. But there is a further important difference that is not apparent in these shots. The Limited lens renders a very pleasing dimensionality that favours portraits. I've never seen that effect from its counterpart.
The Zeiss Planar is a newer addition to my arsenal, though I shot with it on film a few times back in the 1980s. It has a different look that calls a lot more attention to the bokeh. That's not really my style, since I prefer photographs of appealing subjects rather than photos of the effects of the photographic process itself. But for anyone obsessed with bokeh, this is an interesting lens.
I can say that I love this lens' appearance and haptics. In particular the aperture is easier to turn than Pentax lenses. I like the soft clicks. But 50mm is far from my favourite focal length, so only time will tell if the Planar makes itself useful.
In the meantime the compact and exquisite Limited 43mm remains the finest lens I've ever used.
Costs
The HD Pentax-FA 43mm is available brand new for €650. The older version bought used will only save you about €100. Be certain that the package includes the hood and lens cap, since these accessories are €100 on their own... if they are ever in stock. The package should also come with a lens bag.
The Pentax-K 50/1.2 can be found for around €350. The Zeiss Planar 50/1.4 MMJ version regularly sells for the same. Condition and the mood of the seller mean that prices fluctuate quite wildly.
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