Using Vintage M42, "K", "M" and "A" lenses on Pentax DSLR
1. Overview   2. M lenses.    3. M42 lenses

This is the first of three pages in which I try to provide a more comprehensive look at the ins and outs of using vintage lenses on Pentax DSLR's than is currently (AFAIK) available on the web. It is a particular Pentax USP that their cameras are backwards compatible with the array of vintage lenses, the K mount not having changed in its basic design since its inception in 1975. And because before then Pentax used the M42 mount, they kept the registration distance the same, so M42 lenses are also easy to mount with a simple non-optical adapter.
Only Nikon has something of a comparable backward compatability, the basic design of the F mount also not having changed since its inception (but see eg Ken Rockwell on lens compatibility on Nikon). All the other main manufacturers have, at some point, completely changed the lens mount, rendering earlier lenses unmountable.

The pics show K-bayonet mount and M42 screw mount prime (ie non-zoom) lenses that I use with my Pentax K-r DSLR. You can see the identical P-KM mount of the two Pentax SMC-M lenses on the left, a mount that is the same in all respects to the mount on eg a modern 18-55mm kit lens except for three: no electrical contacts, no autofocus connection and a second mechanical connection in a slot opposite the protruding aperture lever. The other three lenses are of the more ancient M42 screw-in mount: (L to R) Pentax Takumar 55mm f2; Russian made Helios "Carl Zeiss biotar" 58mm f2; Panagor 135mm f2.8. With these an adapter is required to mount the lens on the camera (see below).

I also have manual focus lenses K-mount with electrical contacts on the bayonet (and an "A" position on the aperture ring). Apart from the manual focus (and the need to do the setup detailed below) the operation of these is not really so different to modern autofocus (AF) pentax lenses. I also have a number of Tamron "Adaptall" lenses with interchangeable mounts, these are discussed on my adaptall page.

So why bother with these?
  1. Image quality and character. Many of these vintage lenses are really good and/or are quite distinctive.
  2. Fast apertures. The standard 18-55mm kit lens is f3.5 to 5.6 (f number increases - ie smaller aperture - as you zoom to 55mm). The SMC-M 50mm f1.4 is about four stops faster (as we say) than the 18-55mm kit lens at 50mm. Not only does this give more options and faster shutter speeds when the light isn't bright, it also gives more creative options - eg shallower depths of field to isolate a photographic subject (for more about fast fifties see this Pop_Photo article: "50mm f/1.4 lens: Photography's Magic Bullet")
  3. Cost. Typical used auction price (UK) for the 50mm f1.4 SMC is £50-80 - a fraction of the cost of a new lens (SMC-M 28mm: £30-50; Takumar 55mm:£20-80; Helios 58mm: £10-50; Panagor 135mm:£10-30).
In addition, I like the aesthetics of these metal 'n glass lenses; for me manual focus is familiar from owning a pentax 35mm ME-super slr since 1981 and so the AF/no AF is less of an issue.

Using the Lenses - Basic Setup

The first range of Pentax K-bayonet lenses that superceded the M42 lenses are referred to as "K" lenses (and marked "SMC PENTAX" on the nameplate). Their essentially similar successors were the "M" range (marked "SMC-M PENTAX"), and they were followed by the "A" lenses ("SMC-A PENTAX") with 'A' position on the aperture ring. The initial set up (Pentax K-r, other models are similar) to use all these lenses is the same.

  1. i. Dive into your camera set up menu and set "use aperture ring - permitted".
    This is usually the last page in the setup menu.
    ii. (depending on DSLR model - not necessary for K-r) Set "green button action" to "Tv shift".
    This is usually in the camera menu: page 4 on the K-r.
    iii. (depending on DSLR model - necessary for K30 for example, not necessary for K-r) Online advice says don't leave on "auto-ISO"; set to a specific number.
    2. This is readily done using the button labelled "ISO" on the 4-way controller.
  2. Change the focus setting switch to "MF" - manual focus*.
    *leave on AF for Catch-in (AKA trap) focus (need to set catch-in focus on in the setup menu).
  3. Use M (= manual) mode. Manually change the aperture using the aperture ring.
  4. Set lens focal length (for the shake reduction) - easily done by switching the camera off then on.
  5. Press the "green button" to meter. Use the E-dial to fine tune the shutter speed. Shoot!
    If the exposure of the image is not quite right, adjust and retake.
  6. For "A" lenses you also have the (preferred) option of putting the aperture ring onto the end position marked "A" and using Av, Tv, P automatic modes. Apertures will now be displayed - and set - on the camera and recorded in EXIF data.
  7. For M42 lenses, use an M42 adapter to attach the lens. For these lenses Av mode is also generally preferred - see below and page 3.

Additionally you can check out this thread on Pentax Forums, and this video. The specifics for a Pentax K10D are described by Robert Donovan, with big clear pics, on his blog. This post from dpreview.com is for the K100D.
The K30 menu is a little different see here

The ins and outs and differences between camera models, metering/compensation issues and why we refer to the "crippled K-AF mount" are the subject of page 2.

M42 lenses

For M42 lenses the picture is a bit more involved: an adapter is needed to mount the lens on the camera, and M42 lenses can have slightly different technical design that affects how they operate.

Hover to see page

Adapters

The pic shows my four M42 adapters, which are pretty representative. The shiny rimless one is an original made in Japan adapter cost £10 used (very similar to a genuine original pentax one). This video demonstrates its use. Next to it is a modern Chinese clone with key, cost £5 new. The Kipon (£5 used) is also a Chinese made rimless one but with an occasionally significant extra design feature of a rear inside flange. This depresses the small pin on the M42 mount (arrowed in pic above), the point of that is addressed by photographer Hin Man on his blog (see also my review). All the rimless adapters are placed in the cameras' bayonet mount in a similar way by lining up the usual red dot and rotating clockwise, using fingers or a key, till it clicks into position. All these three will be flush with the camera mount. The rimmed adapters are screwed onto the lens first, then the lens is mounted just like a normal PK mount lens.

Hover to see page
The black one is a cheap rimmed adapter cost £1.50 new. The most important thing to appreciate is that this and similar rimmed adapters push the lens a little further away from the camera mount than it should be. The effect of this is that the lens will (probably) no longer focus to infinity. How much the focussing zone will be affected will depend on the lens, and the aperture used. Pic shows the effect on my takumar 55mm at f2, infinity focus, and as you can see most of the image is out of focus! It is for this reason, that the rimless ones are preferred, although in practice it is worth considering whether the rimmed one will affect your photography. For close up pics with a macro lens, for example, the infinity focus issue is probably no reason not to use one (I can mention that with my M42 Vivitar 90mm lens the focus with a rimmed adapter extends to almost 10m - plenty for all macro and most portrait situations).
There are two details to be mentioned. This adapter doesn't have the little spring clips that the others have to hold the adapter + lens in place; it has a small hole in the flange that accomodates the cameras lens locking pin. This is more secure and less problematical than the clips. Secondly the painted nature of this particular mount means that there can be conducting/non-conducting mount issues as discussed on page 2, and in this article I wrote.

This thread on pentaxuser forums offers a photographers appreciation of the quality and usability of respective adapters. I can mention that there are many who would be cautious about the Chinese clones, however my experience is that they work OK but they are more fiddly and that the lens just doesn't quite line up correctly at 12 O'clock. Some photographers remove the little spring clips on the M42 adapter and leave it semi-permanently (screwed on tight or even with some glue) on the lens. Good way to go if you are regularly using a particular lens - mount/demount like a bayonet lens.

M42 designs

My M42 lenses in the pic above are of what I can call the main, and most common, variety. They all have a small auto-aperture pin (arrowed - basically relevant only to usage on a film camera of the era but CARE! I have occasionally noticed that the pin can catch on something when mounting the lens on the camera), and an A-M (auto-manual) switch (red dotted in the pic above). The effect of this switch on DSLR's, once you have set an aperture, is to flick the aperture from wide open (A) to your chosen aperture (M). I think most M42 users find this a useful, indeed important, feature.

Hover to see page
The other variants then are manual M42 lenses without the auto aperture pin (inconsequential); lenses without an A-M switch but with a pin (with which the Kipon and similar adapters could be useful); and lenses of the type in the pic left, often referred to as "preset" lenses.
This 200mm lens has no A-M switch, or indeed any aperture connection at the mount end. The aperture ring is near the front of the lens. To use a particular aperture press the ring down (it's spring loaded) and click it round to the desired f- number. The movement of the aperture ring will now be restricted from wide open to your selected f number. Standard technique is to focus wide open, then the ring can be spun smoothly into position just prior to depressing the shutter.
Many preset lenses have a two ring design, one ring is the limiter, the other, often labelled O-C for Open - Close, does the stopping down. I can mention in passing that lenses like these have a certain following amongst video photographers, because the aperture movement is "clickless".

Pentax Takumar lens "pin".

An extra small feature of my SMC Takumar lens is another very small pin (circled) that locks the A-M switch until it's depressed by screwing the lens into the mount. One important point is that with the Kipon adapter this pin catches: so if you have a Takumar or similar lens with this pin TEST IT with your adapter OFF the camera to check for this problem. If you don't you may find you are unable to remove the lens from the camera.
I shall mention also the existance of M42 mount lenses with electical contacts, specifically of Practica origin. This post on Pentax forums has a picture of an example, and describes a problem when using the lens on a Pentax K-r.

But overall, apart from the particular case of an automatic (with a pin) M42 lens without an A-M switch (see link below re: "modding"), there isn't any major difference in using the variant M42 lenses.

Using M42 lenses

The principal difference between using M42 and K-bayonet lenses is due to the protruding aperture lever (L in pic) on the P-KM mount lenses. On mounting the lens this lever is engaged and holds the aperture open, thus giving the advantages of open aperture focussing (= bright viewfinder and smallest depth of field). On pressing the green button, the camera closes the lens down to the selected aperture to meter.
Most often we use `M' = manual mode with P-KM mount lenses. Actually you can use `Av' = aperture priority mode! However the lens will be limited to wide open aperture only. Even if you change the aperture ring position, the lens won't stop down when you press the shutter when using the lens on a DSLR in Av mode (unlike my film ME-super see page 2).
With M42 lenses there is no connection to the lens aperture on a Pentax DSLR camera. The photographer has to do the stopping down manually, using the aperture ring and (if present) the A-M switch. This means that you can shoot away in `Av' aperture priority mode at whatever aperture you choose to set on the lens, and for me this is in principle the preferred mode, because it's quicker and the camera measures the exposure and sets the shutter speed at the moment of pressing the shutter.

T-mount: I shall mention in passing that t-mount (an early swappable mount system) lenses work the same as M42 lenses because the K-bayonet t-mounts also have no aperture lever.

It was my hit-and-miss learning to use P-KM and M42 lenses, with a lot of browsing the net, and my appreciation that the ideal of easy, problem-free usage of these lenses hasn't been realised by Pentax, that has prompted these pages. Page 3 is the discussion of using these lenses with specific reference to the metering, connectivity and inconsistency issues.

Samsung Cameras

Samsungs' initial move into DSLR cameras was a collaboration with Pentax. Their first models, the GX1S/L, GX10 and the GX20, were rebadged Pentax *1st DS/DL2, K10D and K20D respectively. They thus have the KAF3 mount and the same lens compatibility as the Pentax cameras. Since then Samsung have designed their own non-compatible camera mount and are pursuing mirrorless camera systems.

For the purposes of using these lenses these cameras can be regarded equivalently to the Pentaxes.

Useful Links/More Info

1Ricoh bought Pentax from Hoya in 2011. Pentax is continuing as a/the brand name for cameras.

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