Originally posted by jatrax On the other hand if you really need f/1.8 then this is pretty much the only game in town.
Not the only one.
It's the only Pentax and maybe the best (optically), excluding adapted lenses, though there are a number of other options, even discarding leitaxed/adapted objectives.
I have a couple of them myself.
The best is the Soligor (Tokina) C/D P f/2 135mm, which is not exactly as fast, but has a nice bokeh, good overall rendering, and a build quality not far from the outstanding mechanics of Pentax-A Star lenses.
It's a very good portrait lens, and maybe it was also made in PK mount. I have the M42 version cause I found it at an affordable price. I don't think a PKA version was ever made.
The second is the Porst (Makinon) 1.8/135mm in PK mount. It's a decent performer, it's not rare, and it's rather easy to find it on Ebay. It's also the cheapest of the three.
The last is a Raynox Polaris 1.8/135mm in M42 screwmount. It's the oldest, it's not very sharp wide open, but I like the rendering. It has proven to be better than I expected.
None of them is very expensive, and all of them serve their purpose: thin DOF and blurred backgrounds.
Here is a picture with the optical designs of all the vintage f/1.8 135mm's that can be used on a Pentax DSLR camera.
The Zeiss could be adaptable using a Leitax mount. I don't remember which Zeiss are adaptable, and I have no idea if a lens similar to the one in the picture has been successfully adapted. Others on this forum know much better
Credit goes to whoever posted this interesting picture in the first place. Sorry, I have no track of the original URL/author.
This post is old, though after seeing it has been revived, I decided to share the little info I know, showing a few possible alternatives to either the old A* and the Sammy.
I believe the monumental A* has something more than the Samyang, and of course it's not sharpness wide open.
What the Pentax has for sure is a great build and the pleasure of handling (and shooting with) such a smooth, refined, beautiful objective.
I didn't buy it when i had the funds and the price was much lower, but I know very well how these lenses are, cause I have other three A Star's.
Leaving aside the collector's value and considerations about the build, a fair way to compare the Pentax to the Samyang would be to test the way they handle out of focus.
The Samyang wins hands down in sharpness, it's one of the most amazing (fast) 135mm's ever.
I also expect a better handling of both LaCA and LoCA.
What I don't know, and would like to see, is the performance of the Pentax on different focus planes of the image.
To do that, pictures have to be shot with bokeh in mind. Which generally means to leave the in-focus subject on one side, leave some blurred foreground if at all possible, and have different planes of progressive defocusing. The background should be distant, possibly with strong highlights.
I'm sure there are a number of photos of this kind shot with the Sammy. I remember I checked Flickr for examples of its bokeh.
Pictures shot with the A* are scarce, and I think I've seen none of them properly showing how it handles OOF rendering.
Until I see how it fares under this point of view I reserve my judgement.
From my personal experience I have understood that some over-hyped optics might cost a bit too much, but the rendition is definitely special... and not because they are sharp!
Some Meyer lenses, like the Trioplans and the Primoplan, are probably a little overpriced, though if you compare them with an humble Pentax-M 2/50mm and say that they should be cheaper because they are not as sharp.... well, I guess would be pointless to try to argue that photography is not mathematics