John Riley reviews the Pentax 135mm f/2.5 telephoto K Series lens with a bonus comparison with the Takumar (Bayonet) 135mm f/2.5 - John provides sample photos, MTF & CA charts along with his verdict on both lenses.
Posted: 10/09/2024 - 05:26
Handling and Features
Performance
Verdict
Specification
The main thrust of this review is the SMC Pentax 135mm f/2.5, but as a damaged copy of the Takumar (Bayonet) 135mm f/2.5 has become available at the same time, some interesting comparisons can be made. The Pentax is a 6 element design manufactured from 1975-1985 and the Takumar (Bayonet) is a 4 element budget version manufactured from 1980-1988. Both are finished to an equal quality level, so any differences are under the skin, apart from a difference in cost. Unfortunately the Takumar lens has a faulty aperture mechanism so will not stop down reliably to any particular value. However, some resolution details could be teased out of it, although not reliably enough to present as the usual graph. The SMC Pentax lens is in beautiful condition, so all the usual measurements can be confidently made. Thus armed with the two lenses, let's couple them up to the full frame 36MP Pentax K-1 and see where it leads us.
Many thanks to PU member womble for the loan of the SMC Pentax 135mm f/2.5 lens along with the other recently reviewed SMC Pentax 28mm f/2 and SMC Pentax 85mm f/1.8 lenses too.
SMC Pentax 135mm f/2.5 Handling and Features
Why 135mm is well understood, and dates back to the Leica rangefinder cameras. 135mm is the longest focal length that can be reliably used with Leica rangefinder focusing. Anything longer, then SLR/DSLR focusing is more accurate. Composition is also easier, remaining full frame rather than a rapidly reducing bright line viewfinder as seen on rangefinder cameras.
The lens weighs in at a relatively heavy 495g (as measured without hood or caps), considering its modest dimensions of 68mm x 86mm. There is no built in lens hood, unlike most Pentax lenses of 120mm or longer, but there is a snap-on plastic hood available as an optional extra. This hood is allocated for three lenses, 135mm f/2.5, 200mm f/4 and 85-210mm f/4.5. There is no doubt that a clip on hood is more convenient than a screw thread one, but despite this some users of this lens prefer to use the screw-in metal hood intended for the Takumar screw thread lenses. The filter thread is 58mm.
The wide manual focus ring is a beautiful bit of engineering and we should expect any Pentax lens from this era to have that gorgeous tactile experience of an ultra-smooth action, with just the right amount of resistance. The quality of finish extends to the distance scale, found within the cut-out section that is the style of this era. Engravings are high quality, in blue for feet and yellow for metres. There is an infra-red correction mark, indicated by a red line on the useful depth of field scale.
Focusing is down to 1.5m, or 5 feet, for a maximum magnification of 0.11x. Although this is not particularly close, it is a vast improvement on SLR lenses of the 1950s, which could have a close limit of up to 13 feet. With the longer focal length, manual focusing is easier, but more demanding considering the reduced depth of field. The key to really accurate DSLR manual focusing is to use Live View with magnification.
The aperture ring is the usual slick standard, with firm but nicely judged click stops at f/2.5, f/2.8, f/4 and then half stop intervals until a final full one stop interval between f/22 and f/32.
Optical construction is 6 elements in 6 groups, with a diaphragm comprising 8 blades. SMC coating is well established as a highly effective solution to flare.
Finally we have the plain K mount, 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, in which case the “35mm equivalent” field of view for a 135mm lens will be around 202.5mm.
135mm is a very versatile focal length, bringing in portraiture, landscape, close sports, flower portraits and many other subjects. Like this reviewer, some may find it too long and prefer the 100mm as a short telephoto, but the choice is there and for most 135mm has been the go to short telephoto for the past 60 years or longer.
The Takumar (Bayonet) budget lens is interesting, and handles just as well and as smoothly as the full priced Pentax. It even has a couple of advantages, focusing closer to 1.2m (4 feet) for 0.15x magnification and having a built in lens hood. A table summarising the differences sums up the comparison between the two.
| SMC Pentax 135/2.5 | Takumar (Bayonet) 135/2.5 | |
| Coatings | SMC | non-SMC |
| Elements/groups | 6/6 | 4/4 |
| Diaphragm blades | 8 | 8 |
| Filter thread | 58mm | 52mm |
| Closest focus | 1.5m (5 feet) | 1.2m (4 feet) |
| Magnification | 0.11x | 0.15x |
| Weight (measured) | 495g | 388g |
| Size | 68x86mm | 64x79mm |
Pentax SMC Pentax 135mm f/2.5 Sample Photos
SMC Pentax 135mm f/2.5 Performance
First, the SMC Pentax 135mm f/2.5:
Central sharpness is very good all the way from f/2.5 to f/8, steadily tailing off after that to good at f/11 and f/16 and just fair at f/22 and f/32. The edges are very good from f/2.5 through to f/5.6, good at f/8 and fair thereafter from f/11 to f/32. This is a lens that is at its very best between f/2.5 and f/8.
Pentax SMC Pentax 135mm f/2.5 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 generally kept under one half of a pixel. The edges are less well corrected and will show themselves up in severe cases, such as tree branches against bright sky. Correction in software is a possibility, but to be fair most images do not really show the CA to any significant degree.
Pentax SMC Pentax 135mm f/2.5 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 +1.18% pincushion, which is acceptable and better than some modern zoom lenses.
Bokeh is a delight, very smooth and no doubt aided by the longer focal length and the 8 bladed aperture.
Pentax SMC Pentax 135mm f/2.5 Aperture range
Flare is well controlled, with no real sign of artefacts being created, but with a slight overall loss of contrast. In general use, flare is not evident.
Vignetting is modest wide open and when stopped down almost reduced to zero.
| Aperture | Vignetting |
| f/2.5 | -1.1 |
| f/2.8 | -0.7 |
| f/4 | -0.3 |
| f/5.6 | -0.3 |
| f/8 | -0.3 |
| f/11 | -0.3 |
| f/16 | -0.3 |
| f/22 | -0.3 |
| f/32 | -0.3 |
Looking at the budget Takumar (Bayonet) 135mm f/2.5 lens, the faulty diaphragm of the sample available means that it's not possible to be very specific about sharpness, but suffice it to say that it can equal the SMC Pentax version at mid-apertures but is very weak at the edges when wide open. In terms of CA and vignetting it is not far behind its more expensive sibling and it does have the built in lenshood, which is a useful feature. In terms of flare, the severe flare test shots made show the image is totally wiped out in a mass of white artefacts, so the coatings do make a very significant difference. However, at the right price not to be completely dismissed and perhaps with potential for portraiture.
Value for Money
The SMC Pentax 135mm f/2.5 can be found at Buy-it-now prices of £130-£150 on eBay, and that seems very fair value. The budget Takumar (Bayonet) 135mm f/2.5 at around £40-£50 Buy-it-now also seems very fair value.
Both lenses have their advantages and disadvantages, with the trade-off being between higher quality for the SMC Pentax version, and not much less quality for the Takumar (Bayonet) version (except for the flare) at a much lower price.
SMC Pentax 135mm f/2.5 Verdict
There is no denying that 135mm is a very popular choice for a short telephoto, although as mentioned this reviewer finds this too long and prefers the 100mm. Both the fast f/2.5 lenses though do have merit, and both match up very well with current DSLR cameras. It is a shame that the closest focusing distance is 1.5m (5 feet) for the SMC Pentax, which is not particularly close, although still close enough for a fairly tight head and shoulders portrait.
Quality is better at wider apertures with the SMC Pentax version and this is really the one of choice, but the Takumar (bayonet) version catches up when stopped down and could be a very useful alternative, especially if cost is a major factor.
The SMC Pentax 135mm f/2.5 can be recommended. The budget Takumar (Bayonet) lens not so much, but it does still have some possibilities.
SMC Pentax 135mm f/2.5 Pros
- Very good sharpness at wider apertures
- Low central CA
- Almost no vignetting
- Modest pincushion distortion
- Super handling
- High quality of construction
- Good flare resistance
SMC Pentax 135mm f/2.5 Cons
- Obvious edge CA
- Could do with closer focusing
Takumar (Bayonet) 135mm f/2.5 Pros
- Lower cost
- Closer focusing
- Built in lenshood
Takumar (Bayonet) 135mm f/2.5 Cons
- Very prone to flare
- Poor edge sharpness at wider apertures
Further reading - Pentax K Series - The Original K Mount
Pentax SMC Pentax 135mm f/2.5 Specifications
| Manufacturer | Pentax | |
| General | ||
| Lens Mounts | ||
| Lens | ||
| Focal Length | 135mm | |
| Angle of View | No Data | |
| Max Aperture | f/2.5 | |
| Min Aperture | f/32 | |
| Filter Size | 58mm | |
| Stabilised | No | |
| 35mm equivalent | 135mm | |
| Internal focusing | No | |
| Maximum magnification | 0.11x | |
| Focusing | ||
| Min Focus | 150cm | |
| Construction | ||
| Blades | 8 | |
| Elements | 6 | |
| Groups | 6 | |
| Box Contents | ||
| Box Contents | No Data | |
| Dimensions | ||
| Weight | 495g | |
| Height | 86mm | |
Members photos with related tags: 135mm
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