The M 40mm lens

I have just been reading or re-reading some of John Riley's well-researched articles on the K-mount. One thing that struck me was his description of the M 40mm as "stellar".
In my collection I have one of these and it has never impressed me. So I took a look at "another forum" where they have user reviews of almost all Pentax lenses, and was surprised at the wide variety of opinions expressed. Many people give it 9 or 10 out of 10, whilst others don't recommend it at all.
Now I know that you have to take some of these reviews with a pinch of salt, but I cannot recall another lens which attracted such diverse opinions. And I can only conclude, unless somebody has a better explanation, that a large number of these lenses weren't made as well as they might have been.
The lens appeared in 1977, at a time when Pentax was rushing to put out a whole new range of bodies and lenses. Unlike the original K series lenses, which were mainly just Takumars with a bayonet mount, nearly every M lens required a completely new construction, if not always a completely new optical design. So it would not be surprising if some corners were cut.

Interesting take. I’ve seen some mixed reviews too, typically because the image quality is less ‘sharp’ wide open than other lenses, which is fairly moot in my opinion.

I’ve been tempted for a long while to pick one up to go on a film camera, but recently splurging on a Voigtlander Ultron 40mm f/2 put a nice stop to that.

There is a limitation to testing older lenses. We only have one sample, the lenses are maybe 40 or 50 years old and we have no idea how they have been treated in that time. So, where possible, conclusions can include reference to how the new lenses behaved on our new film cameras many years ago, and, more relevant now, how they behave with digital sensors. Lenses being of varying performance may relate these days very heavily on how they have been looked after.

As for the 40mm, it was a lovely lens on my ME Super and MX bodies, and, perhaps a coincidence, the DA APS-C format 40mm is a lovely lens as well.

Of course what matters most of all is how your copy behaves on your camera.

Is this the pancake lens?
It was the first lens I had with my K1000. I was happy with it but had to sell in part exchange for a new Pentax camera with built in self focus (can't remember whic) and missed it.

I am not for a moment suggesting your assessment of the lenses you have used is wrong. One thing to remember, of course, is that a lens can never be better than it was meant to be, but, thanks to ill-treatment or poor construction, it can always be worse.

But even when I bought the lens (having lusted after it for years) I recall that it wasn't uniformly admired.

Anyway, I am going to give it a go while the light is good and see hw it performs on a K1.

And to answer Walkeja, yes, this is the famous pancake lens. And it works best on a Super-A.

Well, I gave it a quick test, and I have to say it's not half as bad as I thought. It's perhaps not as contrasty as some lenses, but I have put a photo into the gallery that has had almost no post-processing and is as punchy as one could wish.
The reason for the lack of PP is that I am struggling to come to terms not only with a new (to me) very complicated camera, but also a not particularly intuitive RAW convertor.
I am not quite sure why I wrote this lens off all those years ago, but it may be because I had just purchased a *Ist D, and it didn't really inspire me on APS-C. You seldom hear people weeping because they lack a 60mm lens, which in effect was what it was.
Until now.

Glad you like your lens with your new camera, the image posted really is punchy.

I rather like it on my MX or ME Super when I want a small and pocketable film camera. It always feels/looks a bit too small on the K-3iii.

The M 40/2.8 was released in 1976, the same year as the MX and ME. The trend at the time was for smaller 35mm cameras such as the Olympus OM 1 and 2, and the MX/ME were direct competitors.

I believe the rationale behind the M 40/2.8 was to make it as small and light as possible to keep with the trend.

They certainly succeeded. It was almost half the weight of any comparable 35-50mm lens at the time, and much smaller. Compromises necessary in the design meant it was never going to outperform similar 50/35mm lenses in the sharpness stakes, but it is no slouch either.

I acquired one for my collection about 15 years ago, complete with resident dead spider inside ( speedily evicted). I don't think I have ever used it on film.