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Pentax Mount Adapter K (M42 Screwmount to K Mount) Review RSS Feed

Pentax Mount Adapter K (M42 Screwmount to K Mount)

Reviews Views Date of last review
12 54,221 Sun December 1, 2019
Recommended By Average Price Average User Rating
100% of reviewers $29.75 9.50
Pentax Mount Adapter K (M42 Screwmount to K Mount)

Pentax Mount Adapter K (M42 Screwmount to K Mount) Pentax Mount Adapter K (M42 Screwmount to K Mount)
Pentax Mount Adapter K (M42 Screwmount to K Mount)
Pentax Mount Adapter K (M42 Screwmount to K Mount)


This adapter allows the use of M42 screw mount lenses on Pentax Bayonet cameras (film and digital), in manual or Av exposure modes. You will have to stop the lens down manually to the shooting aperture since there is no linkage between the camera and a screw mount lens.

Installing the adapter in the mount can be fiddly. The easiest way to do it is to first screw the adapter onto a lens, then mount the lens (with adapter), and finally screw the lens out leaving the adapter in place on the camera.

This genuine Pentax adapter sits flush with the surface of the camera's bayonet which allows the M42 lens to focus to infinity. Third party adapters with a flange should be avoided - they prevent the lens from focusing to infinity.

Pentax Mount Adapter K (M42 Screw Mount to K Mount)
©, sharable with attribution
Image Format
Full-frame / 35mm film
Lens Mount
Pentax K
Light Loss
0 stops
0 elements, 0 groups
Mount Variant (Rear)
Mount Variant (Front)
M42 (Conventional)
Weather Sealing
Diam x Length
Production Years
(in production)
User reviews
This adapter allows for mounting M42 screw mount lenses on a K-mount camera.
The only exposure modes supported are M and Av with stop down metering, and Bulb.
The adapter has no provision for the camera stopping the aperture down.

Full-Frame Support
Price History:

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Sort Reviews by: Date | Author | Rating | Recommendation | Likes (Descending) Showing Reviews 1-12 of 12
Forum Member

Registered: March, 2011
Location: Ontario
Posts: 89

1 user found this helpful
Review Date: December 1, 2019 Recommended | Price: $15.00 | Rating: 10 

Pros: It does what it supposed to.
Cons: Cost makes no sense

It delivers 100% on what it is supposed to.

The price is just outrageous though, The $15 I paid for mine was outrageous. I'm thinking of sending mine to a machining company in China to get them duplicated so I can sell them for $10 and make $9.50 apiece. I'll be rich in no time.

But hey, if you need one, you need one. Market economics
amateur dirt farmer

Registered: December, 2014
Location: probably out in a field somewhere...
Posts: 35,735

1 user found this helpful
Review Date: November 26, 2018 Recommended | Price: $20.00 | Rating: 10 

Pros: proper fit, easy to remove (if needing to do so)
Cons: new prices can be prohibitive - look for a good, used copy

mine came in a bundle with a couple of other accessories and then sat in a box for a couple of years...

finally became confident enough to buy an M42 lens (Super Takumar 55mm f1.8) and tried it initially on one of my K-3 bodies....

liked it well enough to buy a dedicated-body to be my M42 DSLR and mounted this adapter on the camera, with the intent to never remove the adapter...

it does what it's intended to do perfectly: allow you to use M42 mount lenses on a K-mount body

a comment on current pricing - I noticed that B&H currently has them listed at $79.95, which seems ridiculously high.... check the Marketplace here, post a 'Wanted' ad, and look also on eBay for a good used copy....

used copies will still be higher than knock-offs, but you'll be getting an adapter that is designed for your camera and less likely to leave you with it stuck on the body...
Loyal Site Supportaxian

Registered: September, 2013
Location: Texas
Posts: 501

1 user found this helpful
Review Date: December 3, 2016 Recommended | Price: $45.00 | Rating: 10 

Pros: Precise.
Cons: none.

The real deal. Superior to cheap knock-offs. This is the one you want.
Loyal Site Supporter

Registered: July, 2010
Location: NW Ohio
Posts: 2,008

1 user found this helpful
Review Date: September 13, 2015 Recommended | Price: $30.00 | Rating: 10 

Pros: it works, it's high quality, worth the price for peace of mind
Cons: None

It does the job while providing peace of mind. What more can I say? It's a simple device but some of the most simple things can cause a lot of pain in time and money. This little gadget simply does what it was designed to do. I would not trust a non-Pentax adapter on my camera.
Forum Member

Registered: September, 2012
Location: Tokyo
Posts: 72

1 user found this helpful
Review Date: October 25, 2012 Recommended | Price: $12.00 | Rating: 10 

Pros: It works
Cons: Getting expensive

Does what it says. I have both the "Japan" labelled Pentax one and the "Philippines" labelled one. They seem to be identical. In Tokyo, only the Philippines labelled one is widely available, and costs upwards of $50 equivalent. The Japan labelled one I found in a dusty shop in Ginza, in a big cardboard box of bits and bobs. The shop asked for 1000 yen ( $12 ) which I happily paid.

I leave the clips on, it's no hardship to remove the adapter from the body.


Registered: April, 2011
Location: Lost in translation ...
Posts: 18,052

2 users found this helpful
Review Date: March 26, 2012 Recommended | Price: $25.00 | Rating: 9 

Pros: Works great, safest investment in the long run
Cons: None really - maybe see previous reviews


This was a no-brainner for me because I have no brain and I wanted a near "zero risk" mount my newly acquired Super-Tak 55/1.8 on the brand new K-5. Gladly paid a few bucks more for having a lot of security here ... what is it, "Penny wise and pound foolish"?

Just basiclly asked myself the following: "OK, so the adapter is going to cost about 25 bucks ... not the cheapest about town ... but, how much is it going to cost me in bank funds, lost time to repair and general (in)sanity if a cheaper adapter gets jammed on the K-5?" Again, a no-brainner for me without a brain.

Salut et bon courage, J Frog
Loyal Site Supporter

Registered: November, 2007
Location: Sparwood, BC, Canada
Posts: 12,382

1 user found this helpful
Review Date: January 26, 2012 Recommended | Price: $35.00 | Rating: 10 

Pros: The perfect M42 adapter
Cons: None that I know of

This is the only adapter that reliably does what it is supposed to do. I've had one since the mid 1970s when I bought my first K mount camera. It clicks in solidly. It allows infinity focus. My M42 lenses fit tightly. The adapter goes on off with a fingernail. I am too anal to not use the clip.

I am astonished at those who want to save $20 and buy a cheap adapter that may or may not be easy to install or remove, or might not even allow infinity focus.
Site Supporter

Registered: November, 2010
Location: California
Posts: 2,223

1 user found this helpful
Review Date: July 26, 2011 Recommended | Price: $45.00 | Rating: 10 

Pros: The best thing Pentax made to allow use of M42 lenses
Cons: Genuine Adapter is great, come copies are not. Bowers is good.

This adapter is the best thing since sliced bread. There are some cheap Chinese copies that can work, but no infinite. The Bower is well done and works fine. I had many problems trying to use M42 lenses and the adapters because I did not have instructions. However, when I bought the genuine Pentax / M42 adapter, it came with instructions and it works MARVELOUSLY. The truth is that I was then able to use my Bower adapter and found that it also works just fine. The main mistake: I was attaching the adapter to the lens, and that is not the correct way to do it. The adapter has to be attached to the camera, then the lens is screwed in and voila'. To remove the genuine adapter, you pinch the spring with a ballpoint pen and rotate and done. The Bower brings a tool to lose the spring and rotate at the same time, so it is indeed easier to use. Go and enjoy the M42 legacy lens. Here is a transcript of the instructions to install and remove the adapter:
1) Fit the adapter, matching the red dot of the adapter with the red dot of the body mount.
2) Turn the adapter clockwise until it stops (65 degrees) by using a ball-point pen or the like to lock it. Then screw-mount lenses can be used.
3) TO remove the adapter, push the spring with a ball-point pen and turn the adapter counter-clockwise until it stops.
Site Supporter

Registered: June, 2008
Location: Florida Hill Country
Posts: 17,377
Review Date: August 10, 2010 Recommended | Price: $30.00 | Rating: 9 

Pros: well made and precision fit

The genuine Pentax adapter can easily be removed with a finger nail. It allows infinity focus and is precision fit. The only improvement would be to have the inner ring to depress the auto aperture actuation pin like some other makers did such as Mamiya for auto aperture lenses that lack an A-M switch.
Veteran Member

Registered: June, 2008
Location: Limbo, California
Posts: 11,263

4 users found this helpful
Review Date: July 25, 2010 Recommended | Price: $45.00 | Rating: 8 

Pros: safe, vanilla
Cons: tedious, costly

Basically, three types of M42-PK (screwmount to K-mount) adapters exist.

1) The Official Pentax Adapter, reviewed here. Adapted lenses can focus to infinity.
2) Cheap clones of (1), sometimes bearing the Bower name. Variable quality.
3) Cheap flanged adapters, shiny or painted black. Safe, but lacking infinity focus.

If you have few and ordinary screwmount lenses, buy one or more OPA's (1). I own one. I use it when I want to use unadapted screwmount lenses all day. I've grown used to screwing and unscrewing and screwing and unscrewing...

If you have many screwmount lenses, buy some of (2). I own a couple dozen. Warning: REMOVE THE SCREW AND CLIP OR YOU WILL GO APESH!T!! The clip easily becomes stuck in the camera mount and is difficult / infuriating to remove. Stripped down, it's simple: firmly screw the adapter onto a lens, using the rear lens cap as a wrench. Leave it there. The lens now might as well be a K-mount; you might even forget the adapter is on.

For special cases, use (3). I own a half-dozen. The flange pushes the lens a bit away from the camera, so infinity focus is lost. I use them on teles and scopes that normally focus past infinity, and with macro, closeup, and portrait lenses where I don't care about infinity anyway. Shiny, or with the paint filed off in the appropriate place, (3) also allows Catch-In-Focus.

Every Pentaxian with screwmount lenses should own at least one Official Pentax Adapter (1) -- but don't limit yourself. I own ~70 screwmount lenses. I cannot afford OPA's for each of them.
Veteran Member

Registered: July, 2007
Location: Florida Gulfer
Posts: 3,054
Review Date: July 10, 2010 Recommended | Price: $35.00 | Rating: 9 

Pros: Works great with the M/42 glass
Cons: Tricky to remove adapter

Don't settle for any other adapter for your screw mount lenses. This is the best and only one you should spend your money on.
Veteran Member

Registered: January, 2008
Location: GTA, ON, Canada
Posts: 1,673

1 user found this helpful
Review Date: May 23, 2010 Recommended | Price: $20.00 | Rating: 9 

Pros: Allows use of legacy M42 lenses on K mount bodies
Cons: may wobble with lenses that have a narrow base, inconvenient to switch between K and M42 lenses

I have 3 of these genuine Pentax adaptors. One has the spring clip on it for days when I'm only shooting with M42 lenses, and I've removed the clips on the other 2 so that I can leave the adaptor on a lens and mount/dismount the lens as though it had a regular K mount.

One of my M42 lenses is wide enough that I've drilled a small hole in the base to engage the K mount locking pin. The rest are too narrow to use the locking pin on the body and I rely on friction between the body and the mount to keep them in place.
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