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06-25-2021, 10:37 PM - 6 Likes   #1
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In Praise of the Lowly Flanged M42 Adapter

Prevailing wisdom on this site and elsewhere in the Pentaverse is that using or even recommending other than the official "genuine" Pentax-brand M42 adapter is so very much unacceptable and that a flanged adapter is at best a cheap, but crippled, alternative to the will and intent of the Wisdom of Asahi.

Despite the objections of the many, I would suggest that quality flanged adapters have a purpose and deserve respect for the very legitimate roles they may perform. For the purpose of understanding, it is probably good to know what is meant by a flanged adapter. Here is a set of bullet points:

What is a flanged m42 adapter?
  • Allows use of an M42 (Praktica/Pentax, 24x1mm) screw-mount lens with a Pentax-K body.
  • Engages the K=mount using both bayonet tangs and a flange that covers the body mount face such that the flange snugs securely to the mount face when fully engaged.
  • Cutouts and contours are provided to engage the mount's release pin, aperture ring coupler, and centering guides
  • Due to the presence of the flange, it is not possible for the adapter to provide proper flange focal distance (45.46mm) for the M42 lens flange, thus compromising infinity focus.
  • For comparison the genuine Pentax in-mount adapter see: Reviews | Pentax Mount Adapter K
  • Looks similar to the photo below


From Fotodiox product page (LINK)

Common Uses:
  • As an inexpensive (often below $10 USD) and reliable* alternative to the genuine Pentax and other in-mount adapters.
  • For lenses where the M42 lens' mount face has inadequate diameter to engage the body's mount flange. While not a problem with Asahi-Pentax lenses, such designs are common across a wide swath of German and Soviet designs.
  • To avoid light leaks at the adapter with some narrow diameter mount face M42 lenses, including some Pentax models.
  • When use of the body K-mount retention pin is desirable for easy attachment and removal of lens + adapter as a unit.
  • When slight standoff from the mirror box is desirable to avoid interference.
  • For use with M42 bellows.extension tubes, or M42 macro lenses where infinity focus is not a central concern.

Considerations when purchasing:
  • Prices range from under $10 USD to under $30 USD with the more expensive models using heavier gauge metal.
  • Finish (black anodized vs. bright alloy) is mostly a matter of preference, though the anodized adapters will present less bright to the mirror box.
  • Compatibility is broad, with most M42 lenses being fully compatible with the adapter.** The exceptions being those with proprietary projections that might interfere with the lens seating onto the flange and those not having provision for manual aperture.
  • Flange thickness varies with the lighter weight versions at about 1mm and the beefer versions at about twice that. The thinner the flange, the further distance you can focus.
  • A knurled edge on the flange may come in handy, though is not essential.


Usage:
Despite flanged M42 adapters being extremely simple, some aspects of usage are not very obvious. The list below should help.
  • Basic usage goes like this:
    1. Spin the adapter onto the lens with the adapter flange facing the lens mount flange. There is no need to apply force to hold it in place; friction will do. Torquing the lens onto the adapter is counter-productive.
    2. Align the index mark (usually a red or orange dot) with the index on the camera mount and twist into place (about 1/6 turn), as with any K-mount lens. The mount's retention pin will engage the slot cut into the adapter to lock it in place
    3. Confirm that the lens aperture is set for manual operation and take photos using full manual technique.
    4. To remove, press the lens release lever/button for the K-mount and rotate the lens + adapter off the camera the same as with any K-mount lens. It is this last that confuses many folk since the expectation is that the lens will simply spin off. Strangely, this probably will not happen.
  • Removing the adapter from the lens consists of putting a K-mount end cap on the adapter and twisting counter-clockwise. It should spin right off.
  • The biggest challenge will be to remember to have the lens wide open for focus and to stop down manually for metering and/or to take a photo.
  • When mounted, the adapter itself will always be at the same orientation to the body, courtesy of the retention pin. The position of the lens is another matter. Very few M42 lenses line up with their focus index mark to high noon, not even when attached to a proper M42 body. With adapters, the same is true. When the lens does not line up true, it is not an indication of a faulty adapter or lens. If this bothers you, therapy might help.
  • Friction is generally enough to keep the lens from rotating out of the adapter when focusing or changing the aperture. If additional tightening is needed, do so very gently. Eventually, there will come a need to remove the adapter and best not to make it too difficult.
  • Pairing adapters with K-mount end-caps for storage is a practical habit that allows for easy lens transfer in the field without fumbling with an assortment of caps.
  • There is a strong case for having an adapter for each lens it is used with and maybe even storing the adapter on the lens.
  • Don't agonize over the loss of infinity focus too much. There is no modification to the adapter that will make it right and any modification to the lens may compromise its utility for M42 film photography.
  • Added: In regards to flange thickness and maximum focus distance, much depends on focal length and where the infinity stop is set on the lens. For example, I own a couple of the Fotodiox adapters pictured above. The flange thickness is only 1mm, though that is enough to trim maximum distance to less than 2 meters with my S-M-C Takumar 28/3.5, down from about 50 meters using the non-flanged genuine Pentax adapter. The effect is much less severe with normal and telephoto focal lengths. A reasonable take-away might be to avoid pairing flanged adapters with short focal lengths unless doing close-up work.

I hope this is useful!


Steve

* Most (all?) third-party adapters that are visually similar to the genuine Pentax have design or quality issues that compromise their utility, the most blaring being a tendency to become stuck in the camera body.

** A larger issue than lens-to-adapter compatibility might be lenses that present mirror box and mirror clearance issues.


Last edited by stevebrot; 06-26-2021 at 04:20 PM. Reason: Added note regarding flange thickness and maximum distance
06-25-2021, 11:00 PM - 2 Likes   #2
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The main usage I have with a flanged adapter is with my M42 bellows. When the bellows are used with the genuine Pentax adapter it does not snug up against the mount on the body. So there is a bit of rotational play of the camera body relative to the bellows. While not serious it complicates focus stacking or animations from time-lapse serious should the camera move.

With the flanged adapter snug to the bellows and locked to the K-mount lock pin the play isn't there.
06-25-2021, 11:36 PM   #3
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I have found them useful where ifinity focus is not necessary. They do help with some narrow diameter M42 mounts.

Last edited by PJ1; 06-27-2021 at 02:03 PM. Reason: typo
06-26-2021, 12:17 AM   #4
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I've used flanged adaptors both to semi-permanently modify M42 bellows for use on K-mount cameras, (the bulge on the prism-housing on modern DSLR's prevents some bellows being screwed on), also to replace the mount on Praktica-bayonet lenses for use on my Pentaxes. The later Pentacon lenses (apparently) have the same optical formulas as their earlier Meyer Optik and Zeiss Jena equivalents, often with superior coatings, but the bayonet-mount versions are often available somewhat cheaper than the M42 originals.
One point to note :- many/most (cheaper?) flanged adaptors do not activate the aperture pin on M42 lenses, so in the event of an a/m switch not being available, other provision will need to be made if wishing to use the lens at other than wide open.

06-26-2021, 02:37 AM   #5
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Good tutorial Steve. I’ve never used one simply because of the stuck lens warnings and having to use a removal tool on some of them. It’s nice to see the positive side also.
06-26-2021, 04:10 AM - 1 Like   #6
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QuoteOriginally posted by kypfer Quote
I've used flanged adaptors both to semi-permanently modify M42 bellows for use on K-mount cameras, (the bulge on the prism-housing on modern DSLR's prevents some bellows being screwed on) <snip>
To prevent this, I have an 11mm extension tube between the adapter and the bellows, which also gives a slightly larger image on the sensor.
06-26-2021, 06:28 AM   #7
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QuoteOriginally posted by stevebrot Quote
Prevailing wisdom on this site and elsewhere in the Pentaverse is that using or even recommending other than the official "genuine" Pentax-brand M42 adapter is so very much unacceptable and that a flanged adapter is at best a cheap, but crippled, alternative to the will and intent of the Wisdom of Asahi.

Despite the objections of the many, I would suggest that quality flanged adapters have a purpose and deserve respect for the very legitimate roles they may perform. For the purpose of understanding, it is probably good to know what is meant by a flanged adapter. Here is a set of bullet points:

What is a flanged m42 adapter?
  • Allows use of an M42 (Praktica/Pentax, 24x1mm) screw-mount lens with a Pentax-K body.
  • Engages the K=mount using both bayonet tangs and a flange that covers the body mount face such that the flange snugs securely to the mount face when fully engaged.
  • Cutouts and contours are provided to engage the mount's release pin, aperture ring coupler, and centering guides
  • Due to the presence of the flange, it is not possible for the adapter to provide proper flange focal distance (45.46mm) for the M42 lens flange, thus compromising infinity focus.
  • For comparison the genuine Pentax in-mount adapter see: Reviews | Pentax Mount Adapter K
  • Looks similar to the photo below


From Fotodiox product page (LINK)
Common Uses:
  • As an inexpensive (often below $10 USD) and reliable* alternative to the genuine Pentax and other in-mount adapters.
  • For lenses where the M42 lens' mount face has inadequate diameter to engage the body's mount flange. While not a problem with Asahi-Pentax lenses, such designs are common across a wide swath of German and Soviet designs.
  • To avoid light leaks at the adapter with some narrow diameter mount face M42 lenses, including some Pentax models.
  • When use of the body K-mount retention pin is desirable for easy attachment and removal of lens + adapter as a unit.
  • When slight standoff from the mirror box is desirable to avoid interference.
  • For use with M42 bellows.extension tubes, or M42 macro lenses where infinity focus is not a central concern.

Considerations when purchasing:
  • Prices range from under $10 USD to under $30 USD with the more expensive models using heavier gauge metal.
  • Finish (black anodized vs. bright alloy) is mostly a matter of preference, though the anodized adapters will present less bright to the mirror box.
  • Compatibility is broad, with most M42 lenses being fully compatible with the adapter.** The exceptions being those with proprietary projections that might interfere with the lens seating onto the flange and those not having provision for manual aperture.
  • Flange thickness varies with the lighter weight versions at about 1mm and the beefer versions at about twice that. The thinner the flange, the further distance you can focus.
  • A knurled edge on the flange may come in handy, though is not essential.


Usage:
Despite flanged M42 adapters being extremely simple, some aspects of usage are not very obvious. The list below should help.
  • Basic usage goes like this:
    1. Spin the adapter onto the lens with the adapter flange facing the lens mount flange. There is no need to apply force to hold it in place; friction will do. Torquing the lens onto the adapter is counter-productive.
    2. Align the index mark (usually a red or orange dot) with the index on the camera mount and twist into place (about 1/6 turn), as with any K-mount lens. The mount's retention pin will engage the slot cut into the adapter to lock it in place
    3. Confirm that the lens aperture is set for manual operation and take photos using full manual technique.
    4. To remove, press the lens release lever/button for the K-mount and rotate the lens + adapter off the camera the same as with any K-mount lens. It is this last that confuses many folk since the expectation is that the lens will simply spin off. Strangely, this probably will not happen.
  • Removing the adapter from the lens consists of putting a K-mount end cap on the adapter and twisting counter-clockwise. It should spin right off.
  • The biggest challenge will be to remember to have the lens wide open for focus and to stop down manually for metering and/or to take a photo.
  • When mounted, the adapter itself will always be at the same orientation to the body, courtesy of the retention pin. The position of the lens is another matter. Very few M42 lenses line up with their focus index mark to high noon, not even when attached to a proper M42 body. With adapters, the same is true. When the lens does not line up true, it is not an indication of a faulty adapter or lens. If this bothers you, therapy might help.
  • Friction is generally enough to keep the lens from rotating out of the adapter when focusing or changing the aperture. If additional tightening is needed, do so very gently. Eventually, there will come a need to remove the adapter and best not to make it too difficult.
  • Pairing adapters with K-mount end-caps for storage is a practical habit that allows for easy lens transfer in the field without fumbling with an assortment of caps.
  • There is a strong case for having an adapter for each lens it is used with and maybe even storing the adapter on the lens.
  • Don't agonize over the loss of infinity focus too much. There is no modification to the adapter that will make it right and any modification to the lens will compromise its utility for M42 film photography.

I hope this is useful!


Steve

* Most (all?) third-party adapters that are visually similar to the genuine Pentax have design or quality issues that compromise their utility, the most blaring being a tendency to become stuck in the camera body.

** A larger issue than lens-to-adapter compatibility might be lenses that present mirror box and mirror clearance issues.

Good write up Steve . Thanks. I use the flanged ones mostly on Bellows and have one on one of my Macros that I just leave there. They definitely are lot Cheaper cost than the Pentax Official M42 adapter.



as a side note I do use the 3rd party knock offs that are visually Similar to the Genuine Pentax ones also, but I remove the side screw locking mechanism and it works great ( no sticking) as long as I am careful when focusing..I haven't dropped a lens yet at least.


al

06-26-2021, 08:30 AM   #8
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QuoteOriginally posted by ramseybuckeye Quote
Good tutorial Steve. Iíve never used one simply because of the stuck lens warnings and having to use a removal tool on some of them. Itís nice to see the positive side also.
Those warnings are actually not for a flanged adapter (which won't get stuck and don't come with a tool), but for third-party non-genuine (non-Pentax branded) non-flanged m42-K adapters. Those have a spring in them that should be immediately removed before use in order to keep from getting stuck and preserve your sanity. (So actually ALL three of these types of adapters have their place for a person that uses a lot of m42 lenses on K-mounts, and none of them really is a danger -- you just need to remove that spring with the one type and it works as a friction fit.)
06-26-2021, 08:37 AM   #9
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I propose a motion in praise of using those cheap non-flange adapters with the lock spring removed!

They are cheap enough to use semi-permanently, one for each M42 lens.
Just screw them on and attach like any K mount lens, retains infinity.
Bonus points for drilling/filing and small hole/slot so it even locks in place like a proper K lens.

06-26-2021, 09:37 AM   #10
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QuoteOriginally posted by kypfer Quote
One point to note :- many/most (cheaper?) flanged adaptors do not activate the aperture pin on M42 lenses, so in the event of an a/m switch not being available, other provision will need to be made if wishing to use the lens at other than wide open.
You would be correct. I am pretty sure that the Kipon in-mount adapter is the only M42-K adapter that provides this feature.


Steve
06-26-2021, 09:46 AM   #11
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QuoteOriginally posted by ramseybuckeye Quote
Good tutorial Steve. Iíve never used one simply because of the stuck lens warnings and having to use a removal tool on some of them. Itís nice to see the positive side also.
The stuck adapter warnings are for non-Pentax versions of the other type of adapter, where adapter fits fully with the mount opening (no flange) and where it must be removed separate from the lens.

I did not provide emphasis, but one of the nicer aspects of using a flanged adapter is the ease of attachment and removal. Since the adapter engages the K-mount in a manner similar to a K-mount lens, there is no need for the lock spring used by in-mount types and nothing to jam.


Steve
06-26-2021, 01:56 PM   #12
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Thanks for voicing the unmentionable, Steve. There is at least one excuse for removing the flange though.

Twenty years ago when eBay was flooded with cheap, off-brand M42 lenses removing the flange provided a very inexpensive adapter that could be 'glued' to those lenses for convenience. A little judicious fiddling with spacing even allowed focusing to 'infinity and beyond' -- should one choose to go way out there.

With considerable wasted effort one could even lathe-turn the adapter to exact M42 specs -- just to prove it could be done you understand. (Oh, the hours . . . )

Besides, what percentage of images are actually shot with infinity as the intended point of focus? For some strange reason I've never been able to confirm my infinity focused shots were actually in focus. Every time I got close . . .

The flip side is that the flange offered an extra bit of close focus and with TTL focusing and a little attention to DoF tables $10 worth of lens plus adapter covered 99% of my interest in those lenses. Somewhere 'round here I've still got a couple of nice old third party lenses with those 'circumcised' flanges super-glued to 'em. With ring or bellows . . .

The truth is, we owe Pentax thanks for maintaining the limitations of the original lens mount diameter which allows use of the legacy M42 and PK mount lenses while every other manufacturer either abandoned their earlier mounts to transition to AF and AE lenses or went out of business. (Really; think about the timing.)

Pentax still bears that burden today. What they got for it though was body-based anti-shake mode for ALL lenses. And Sigma and Tamron had to respect the new, limited Pentax-market for universal lenses with big-market sales.

This would be a good time for a resurrection of interest in older lenses for the newer digital-only folks.


More #2
06-26-2021, 03:25 PM   #13
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QuoteOriginally posted by pacerr Quote
Besides, what percentage of images are actually shot with infinity as the intended point of focus? For some strange reason I've never been able to confirm my infinity focused shots were actually in focus. Every time I got close . . .
This the point that is often missed. There have been a few recent threads with forum members complaining bitterly about vintage wide-angle lenses being collimated from the factory with the infinity stops at fairly modest distances, say 50 meters. Two factors at work here that should temper the angst; 1) a 28mm lens at f/2.8 will realize the hyperfocal at 8 meters on 24x36mm FF and 14 meters on APS-C, 2) focus precision with most wide angles simply sucks due to short focus throw with less than 20į of arc between 1 meter and ∞ for block focus primes, even with fairly flat helicoid pitch.

With the possible exception of astro, one might reasonably ask if a photo of a technically OOF toy poodle from a 24mm lens which focus stop is set at 50 meters will look different on a 16x20" print viewed at 20" then if the focus stop had been set to 100 meters. It will be tiny on both.

\ rant


Steve

Last edited by stevebrot; 06-26-2021 at 03:55 PM. Reason: Put the right numbers in
06-26-2021, 03:51 PM - 1 Like   #14
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On shorter focal length lenses, the flange can cause well more than loss of just "infinity" and you won't be able to get crisp shots of something like a house from across the street. On a telephoto, it matters less unless you are shooting the moon or something. So while we may sing songs to our flanged adapters...still, look for the one with the thinnest flange.
06-26-2021, 04:17 PM   #15
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QuoteOriginally posted by vonBaloney Quote
On shorter focal length lenses, the flange can cause well more than loss of just "infinity" and you won't be able to get crisp shots of something like a house from across the street. On a telephoto, it matters less unless you are shooting the moon or something. So while we may sing songs to our flanged adapters...still, look for the one with the thinnest flange.
Thanks for this comment. While you were typing it, I was adding a note to the original post on the matter of flange thickness and the price paid. I purposefully purchased the Fotodiox pictured above because of its thin flange and black anodized finish. With my S-M-C Takumar 28/3.5 the maximum focus distance goes from ~50 meters to ~2 meters when a 1mm thick flange is present. Even at f/8, DOF only covers to about 2.5 meters.

A good practice might be to avoid shorter focal lengths with flanged adapters unless doing close-up work.

Note: To better understand the impact of the flange, consider that the full axial travel of the S-M-C 28/3.5 when focusing from infinity to MFD is only 3mm.


Steve

Last edited by stevebrot; 06-26-2021 at 04:32 PM. Reason: Completeness
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