M42-PK adapters - some personal experiences


Link Posted 07/08/2012 - 11:51
The M42 lens thread is a metric thread, 42 mm diameter with a non-standard 1 mm pitch. It was first used as a lens mount by Zeiss in 1949 - see wikipedia. It was widely used by Pentacon, Praktica, Ricoh, etc as well as by Asahi Pentax. Many third party lens makers also marketed good lenses with what was, for a time, the standard screw mount.

Questions and answers about fitting screw-mount lenses to recent Pentax cameras come up regularly in these forums. To be specific, most people want to fit lenses, such as the Takumar ones from the 1960s and 70s or third-party ones, to camera bodies that have one or other of the K-series bayonet mounts. Examples of some of these postings are (most recent first): June 2012, May 2012, April 2011, January 2011, July 2010, Sept 2007 and others.

I was in this position when my wife bought me my first K-mount Pentax (K-x) for Christmas 2010. We both had several old M42 screw-mount lenses in our Spotmatic kits. I now have 3 different makes of flush-fitting ("infinity focus") M42-PK adapter, and here are my impressions. I begin with the most reliable:

I believe that this is a genuine Pentax accessory. I bought it on eBay a little over a year ago and was very lucky to get it for only 7.50 including postage. Genuine Pentax adapters usually fetch more on eBay. SRS list them new for almost 65 and used ones normally fetch 20 or more. Some are engraved ASAHI PENTAX but the SRS catalogue item looks like this photo.

This one is made of well-chromed brass and weighs 10 g, including the retaining spring. The M42 thread goes all the way through, with no inner flange at the bottom (what looks like a flange in this photo is the first turn of the 42mm thread). The quality of machining is better than on either of the other two that I have bought. All our old M42 lenses, by Pentax, Tamron and Soligor work perfectly with this mount - but only as 'dumb' manual ones of course.

The spring works perfectly, releasing easily with just a fingernail and one does not need a tool to remove the adapter from the camera.


I had earlier bought this used one, which looks mechanically almost identical:

It had been marketed by Jessop's as an "M42 Pentax-K Body Mount Adapter":

Like the Pentax one, it is well made in brass, with good chromium plating. It weighs 10-11 g, just a trifle more than the Pentax. The machining seemed almost as good as the Pentax and, as the retaining spring seemed OK, I tried it in the K-x. M42 lenses worked fine in manual mode, but when I came to remove the adapter it did not come out easily like the Pentax one did. I needed the demounting tool (supplied in the box, as above) and even then it took a bit of fiddling, plus a small screwdriver to depress the spring, before it released and could be taken off the camera body. I decided that I did not need the retaining spring for my semi-sedentary kind of photography, so I removed it. Without the spring the Jessops adapter fits snugly enough for me not to worry about it and lens accidentally falling off the camera. It can be removed easily - so perhaps not to be recommended if you want to carry an adapted camera slung on your back while rock climbing.


The adapter which I like least of all is the first one I bought, for only 4.70 plus postage. It was marketed by Kood, complete with a demounting tool:

This Kood pattern (and I think that there are others) is machined from a light alloy, weighing only 4-5 grams. The M42 thread does not go right to the bottom: there is an inside flange at the sensor-end that pushes the Takumar diaphragm pin in, so that a Pentax lens is always stopped down to whatever stop is set on the aperture ring. Some forum members have noticed this, and have not minded. I found it very inconvenient. The black finish on mine seems well applied, but I remain a bit nervous of it.

A dangerous feature of this particular Kood adapter is that the demounting slots are cut a little further in towards the centre than on the Pentax and Jessops ones. A few M42 lenses have other small pins which might pop up into these deeper slots. I had a 28mm SMC Takumar which had a tiny sprung pin next to the mounting thread. This pin would pop up into one of the slots as it was screwed into this adapter, and then it was impossible to unscrew lens from adapter unless one could get at the camera-face of the adapter to push the pin in. As with the other brands, the Kood one has a retaining spring and one cannot remove adapter from camera unless you can get at the spring, which is impossible with a lens in place. Thus, a combination of the adapter with a lens that has a pin fouling a slot, and a spring that cannot be accessed, is a dreadful predicament.

When I bought this secondhand adapter the retaining spring showed signs of damage. Heeding advice that I had already read on this forum, I got a local watchmaker to remove the spring before I even attempted to fit it to the camera. I shall keep the Kood as a reserve, but am unlikely ever to use it. Other members of the forum have Kood adapters, maybe slightly different from this one, and have been able to use them without problems. Therefore I must not condemn them all: just be careful when you come to use one.

I have no comments at all about the flanged adapters, which seem not to have removal problems. They inevitably move the seating face of the lens a fraction of a millimetre forward from its intended seating face on the camera body. This prevents most lenses from being focussed at infinity. This does not matter for close-up or macro work. A member has recently had this experience: link

I know that many members of this forum have and use various brands of M42-PK adapters. Any other comments or advice?

A few of my photographs in flickr.
Lizars 1910 "Challenge" quarter-plate camera; and some more recent stuff.
Last Edited by OldTaffy on 07/08/2012 - 12:00


Link Posted 07/08/2012 - 12:15
Only the generalised comment that we can avoid most problems by simply using Pentax-made accessories.

That's not to say we shouldn't experiment with other things, but carefully and at our own risk. One thing is sure, I would never use anything that required forcing or bodging to work.
Best regards, John


Link Posted 07/08/2012 - 12:25
Good write up The only thing I would add to that is:
Only Pentax know what tolerances they work to on their bodies and what tolerance
they can afford to allow on a converter.

The worst I've ever come across with 3rd party stuff was with a
German made Novoflex Bellows.... the lens thread was so undersized
that nothing would screw into it..... possibly there was another
1mm pitch thread that was just under 42mm? Novoflex stuff
is usually spot on and expensive.
Half Man... Half Pentax ... Half Cucumber

Pentax K-1 + K-5 and some other stuff

Last Edited by Algernon on 07/08/2012 - 12:26


Link Posted 07/08/2012 - 12:52
I have one Pentax adapter and one Chinese adapter. Both fit and work exactly the same, but as I keep them on the M42 lenses I use most I have removed the small spring from each as I find it a pain to dismount from the camera in order to use a modern lens.

I also have a Chinese flanged adapter which can be demounted by pressing the release button but as this type invariably cause a loss of infinity I have it permamently fitted to my old M42 bellows.

In conclusion I've found the cheaper adapters the equal of the very expensive Pentax one I bought and whilst there is the chance that I could drop a lens as it's not retained by the spring I am happy with what I've got. I suppose removing the spring is a botch (by the way bodging is a reputable skill - turning wood) but it's equally applied to both versions to work the way I want.



Link Posted 07/08/2012 - 12:54
I suspect the Novoflex 42mm thread you had was a T2 thread which is 42mm with a 0.75mm pitch. It's quite common and can easily be confused with M42.

As far as the tolerances for mount adapters, M42is an international standard, with known tolerances & as long as the K mount fits securely it will be fine. The important tolerance for mounting lenses is the flange distance, which is not relevant here as the K mount was designed to have the same flange distance as M42. M42 lenses fit flush with the body, any change in this (flanged adapters) will effect the lenses focusing, normally making infinity focus impossible.
Pentax:K5ii, K7, K100D, DA18-55, DA10-17, DA55-300, DA50-200, F100-300, F50, DA35 AL, 4* M50, 2* M135, Helicoid extension, Tak 300 f4 (& 6 film bodies)
3rd Party: Bigmos (Sigma 150-500mm OS HSM),2* 28mm, 100mm macro, 28-200 zoom, 35-80 zoom, 80-200 zoom, 80-210 zoom, 300mm M42, 600 mirror, 1000-4000 scope, 50mm M42, enlarger lenses, Sony & micro 4/3 cameras with various PK mounts, Zenit E...
Far to many tele-converters, adapters, project parts & extension tubes etc.

.[size=11:].Flickr WPF Panoramio


Link Posted 07/08/2012 - 13:45
petrochemist wrote:
I suspect the Novoflex 42mm thread you had was a T2 thread which is 42mm with a 0.75mm pitch. It's quite common and can easily be confused with M42.

No it's definitely 1mm pitch x 41.2 to 41.3mm.... Never thought about it before, but 1 5/8" is 41.275 so it's possibly that

The camera end screws loosely into a camera, but tightens up
OK and if I remove the lens end and screw it onto the camera
end it's a really nice fit. Just seems strange that considering
Novoflex did their own M42 lenses that they would make two
products that were so close but that's German Engineering
for you

I've fitted an M42 plate on the lens end.
Half Man... Half Pentax ... Half Cucumber

Pentax K-1 + K-5 and some other stuff



Link Posted 08/08/2012 - 11:37
Nice post, thanks. The Kood is useful when lenses are auto only. I'm currently trying to modify one of those lenses and could save the time if I had one of those Kood ones. On the other hand, I only trust the original Pentax one
Pentax K10D + Vivitar 55/2.8 macro + Super Takumar 55/1.8 + SuperMultiCoated Takumar 85/1.8 + SuperMultiCoated Takumar 135/3.5 + SuperMultiCoated Takumar 200/4 + Super Takumar 300/4
Pentax K100D + DA18-55ALII + DA55-300
Pentax K5 + FA31Ltd + M50/1.7 + DFA100WR + M120/2.8 (+ DA18-55WR at occasion)


Link Posted 20/11/2013 - 19:24
Thank you OldTaffy for this, you've just enabled me to find out the provenance of the adapter I've bought. It's identical to the Jessops one. It's fiddly but it works. After fiddling with it there were lots of new specs of I don't know what on the mirror. So I am relegating it to my Ricoh KR-10 and will try not to remove/refit it too often. Tomorrow my LX arrives, and I've just ordered a real Pentax adapter for it. No way will I sully it with anything inferior! Luckily I found an adapter for 'only' 30 at Etsy. The ones on ebay today are 40 plus.


Link Posted 20/11/2013 - 20:21
I bought a genuine Pentax one from 'Clarky' on this forum - it's been great as was the sale/purchase/delivery etc

Well done for providing this information as it should help those looking to use m42 lenses
K10D, K5 plus plenty of clueless enthusiasm.

My Flickr site link


Link Posted 20/11/2013 - 20:45
I agree entirely with Frogherder's post (Bernard), my experience of the Chinese ones I have is that they fit exactly the same as the Pentax one does. I too have removed the spring and have them fitted permanently to all of my M42 lenses, thus turning them into bayonet mount lenses. I've never had any issues with any of the following:

- screw thread not correct
- wobbling / loose fitting
- sticking in lens mount

I'm sure there may be issues with some of the copies, but I haven't experienced this.

Congratulations to Old Taffy for a really excellent write-up, one of the most informative and helpful on the Forum in ages.


Nicola's Apartments, Kassiopi, Corfu

Some cameras, some lenses, some bits 'n' bobs


Link Posted 25/10/2017 - 12:08
I know this is an old thread but just had a "personal panic" with one of these adapters in trying to remove the bellows (ASAHI) managed to get a scalpel point into the slot to release the spring. As this outfit is for in house use I'll remove the spring and keep fingers crossed. Couldn't unscrew the bellows from the mount because of the protusion where the pop up flash goes



Link Posted 25/10/2017 - 12:39
Stan you need to try an Extension Tube between the bellows and the camera.

I've got a couple of genuine Pentax adapters and a Chinese one. The Chinese one stinks of SOY SAUCE

Half Man... Half Pentax ... Half Cucumber

Pentax K-1 + K-5 and some other stuff

Last Edited by Algernon on 25/10/2017 - 12:40


Link Posted 26/10/2017 - 08:48
Algernon wrote:
Stan you need to try an Extension Tube between the bellows and the camera.

I've got a couple of genuine Pentax adapters and a Chinese one. The Chinese one stinks of SOY SAUCE


I wish I was clever like you Algi, maybe an age thing so I have lots to learn I've got a set of extension tubes but no Soy Sauce. Will it work just as well with Lea and Perrins Worcestershire sauce.



Link Posted 26/10/2017 - 10:25
Lancashire Sauce is the BEST!!!

Comes from Upper Ramsbottom


Half Man... Half Pentax ... Half Cucumber

Pentax K-1 + K-5 and some other stuff

Last Edited by Algernon on 26/10/2017 - 10:28


Link Posted 27/10/2017 - 00:16
Doesn't do your adapters a lot of good though.
Both the *istDS and the K5 are incurably addicted to old glass

My page on Photocrowd - link
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