I like 135mm lenses so naturally I acquired a few. Then of course, you have to wonder which ones are the best. The candidates, in the order I tested them:
SMC Pentax 135mm f2.5 - 58mm filter, 8 blades, minimum aperture f32, Minimum Focus Distance 1.5m, 510g. The lens uses the same six-element, six group formula introduced in the later models of Super-Multi-Coated Takumar 135/2.5s. It has a pretty good reputation, and not a bad price compared to the F or FA versions. The aperture ring clicks at f2.5, an unmarked stop and full and half-stops from f4-f22. It's the only prime lens here without a sliding hood.
Takumar Bayonet 135mm f2.5 - 52mm filter, 8 blades, minimum aperture f22, MFD 1.2m, 410g. The opposite of the SMC Pentax, this lens has only four elements, inferior coatings, and a poor reputation. The aperture ring clicks at f2.5, an unmarked stop and full and half-stops from f4-f22. Price varies a lot. What's it really worth?
Vivitar TX 135mm f2.5 - 58mm filter, 6 blades, minimum aperture f16, MFD 1.8m, 520g. TX lenses are an interesting bit of lens history, with an interchangeable mount system and lenses made by Tokina. This lens is about the same size as the SMC Pentax and well-constructed, except the aperture ring only clicks at f2.5 and full stops at f4-16. It made me curious about the TX line. It's more difficult to find this lens and the K or M42 TX adapter, while the M42-mount 135/2.8 Vivitar-Komine is very common. The lens itself might be cheap if it's sold with an unpopular TX mount. Is it worth the hunt?
Pentax-F 35-135mm f3.5-4.5 zoom - 58mm filter, 8 blades, minimum aperture f32, MFD 0.75m, 500g. This lens gets some attention today because its range is similar to the DA* 50-135/2.8. The range is probably why it wasn't popular on film, though there is a Pentax-A version too. It is the closest-focusing lens in the test because of a "macro" setting at 135mm. It has 16 elements in 12 groups, nearly a Pentax record. I used the A setting, not the aperture ring. I included it because of the DA similarity. Maybe I own a hidden gem.
Vivitar M42 135mm f2.8 - 55mm filter, 6 blades, minimum aperture f22, MFD 1.5m, 400g. The aperture ring clicks at all stops and half stops through f16. Many copies exist of this lens, and the price is often pretty low. It's made by Komine, a good maker of sleeper lenses. Will this test drive the price up?
Rikenon XR 135mm f2.8 - 55mm filter, 8 blades, minimum aperture f22, MFD 1.5m, 460g. I haven't heard much about this lens at all, but I was kind of encouraged by the 8-bladed aperture. Otherwise, construction ranks last in this group. It's adequate and focuses nicely, it just doesn't have as nice a mechanical feel. It also has clicks only on full stops. I might start a rumor about legendary sharpness!
Pentax-M 135mm f3.5 - 49mm filter, 8 blades, minimum aperture f32, MFD 1.5m, 300g. The aperture ring clicks at f3.5, an unmarked stop I think is f4 and full and half-stops from f5.6-f22. The M series was designed to be small, and this lens is the smallest of the group. It's also common and inexpensive. Does its performance match Pentax's reputation?
Weights are on my scale with both caps, TX mount or M42 adapter where appropriate. MFD is the smallest number marked on the lens.
Sharpness test - I have a brick wall so I waited for a clear day for consistent light. My *ist DS was mounted on a tripod about 10 feet from the wall. Distance is about portrait distance on film, probably what all these lenses were built for. I used the 2 second delay for all shots. I took a test shot with the SMC Pentax 135mm f2.5 at f8 to get a nice histogram, and used that exposure as a baseline for all the exposures. I also used the color temperature from this shot to set all the lenses to the same temperature in Adobe Camera RAW - obviously I took all the photos in RAW. I focused manually for all the lenses. I focused each lens, then adjusted apertures and shutter speeds for shots at the indicated apertures. I had to approximate or assume some apertures on lenses without stops or markings where I wanted to test (noted above). Since focus is so important for sharpness, I went through the group three times and chose the best-focused set of images to compare. (Even with a split-prism screen, my focus was not perfect every time.)
I created the sharpness composite images by choosing a set of the best focused images. Then I opened them in Adobe Camera RAW v3.7 and set the color temperature and tint to match the test image. I used Photoshop Elements 4.0 to copy sections from the center and upper right corner of each image, and pasted them into the composite image. I had to convert the images to 8 bit to add text labels produce a JPG composite.
For flare, I set up a flashlight so it was in the frame, and took a photo in the dark with the lenses wide open. I included a photo of this setup. I went to Denver Botanical Gardens for some comparisons of color, contrast and bokeh, and one distance shot. I used some Christmas lights to compare out-of-focus highlights.
I did some tests that I don’t show because the lenses were pretty equal. I tested for CA by shooting a high contrast object in bright sunlight at maximum aperture. The Pentax-F zoom was better at this but not much. It only opens to f4.5 and it’s not that sharp, so any advantage is masked. Distortion looks about the same too - it may vary by a small amount but not enough to make any difference.
Last edited by Just1MoreDave; 07-27-2009 at 09:42 PM.