[Lowell Goudge]

Nope, you are missing the point again. The OP and my comments are about issues with adaptability of the M42 lenses specifically to K-mount. The OP would like a similar adaptability solution as he is getting on C/Y mount. I realize it may be tricky for you to detect the focus of the conversation given that several mounts are brought into discussion, but let me try to dispel your confusion - the focus is on the drawbacks of the K-mount that make adaptability of M42 lenses less convenient than on other mounts, like C/Y or Canon EF.

If I follow your arguments fully the ideal mount for a pentax camera would include a lens locking mechanism that engaged the bayonet directly not the flange and a throat large enough to allow for a tiny aperture pin mechanism in the M42 adaptor to actually allow for automatic aperture(I.e. Open aperture focusing) and if we are lucky an aperture ring coupling to allow for open aperture metering like the ES II

[Jüri]

If I follow your arguments fully the ideal mount for a pentax camera would include a lens locking mechanism that engaged the bayonet directly not the flange and a throat large enough to allow for a tiny aperture pin mechanism in the M42 adaptor to actually allow for automatic aperture(I.e. Open aperture focusing) and if we are lucky an aperture ring coupling to allow for open aperture metering like the ES II

Actually I think the best that Pentax could have done was to increase flange distance for new K-mount lenses for about 5mm or more. That would permit to use many different lenses using a respective adapter and without infinity focus issues. That's a whole different topic, though.

[RioRico]

Actually I think the best that Pentax could have done was to increase flange distance for new K-mount lenses for about 5mm. That would permit to use many different lenses using a respective adapter and without infinity focus issues. That's a whole different topic, though.

IMHO you have it backwards. Increasing FFD / register 5mm to ~51.5mm would make using 135/FF SLR lenses impossible -- no infinity focus. DECREASING the FFD to ~41.5mm would enable use of everything except Konica lenses. But Asahi was a lens company. It is one thing to enable your users to continue with their existing M42 lenses; it's quite another to cannibalize your sales by enabling all other brands. The elegant PK solution has succeeded for 35+ years. That ain't bad!

Some flange-focal distances:

40.5 mm Konica AR & F
42.0 mm Canon R & FL & FD
43.5 mm Fujica X-Fujinon
43.7 mm Minolta MC-MD
44.0 mm Canon EOS/EF/EFS
44.4 mm Praktica Bayonet
44.5 mm Minolta-Sony Alpha
44.7 mm Exakta bayonet
45.46 mm Pentax-Praktica, M42
45.5 mm Petri, Contax-Yashica
46.0 mm Olympus OM bayonet
46.5 mm Nikon F-mount
47.0 mm Leica R
50.7 mm Adaptall
55.0 mm T,T2,YS

[Blue]

Actually I think the best that Pentax could have done was to increase flange distance for new K-mount lenses for about 5mm or more. That would permit to use many different lenses using a respective adapter and without infinity focus issues. That's a whole different topic, though.

As I pointed out earlier, Canon didn't plan it that way, they just got lucky regarding adapters for other makes from various periods. Otherwise, they wouldn't have orphaned their own base followers with FD/FL lenses.

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Last edited by Blue; 07-17-2011 at 11:43 AM.

[Blue]

Nope, you are missing the point again. The OP and my comments are about issues with adaptability of the M42 lenses specifically to K-mount. The OP would like a similar adaptability solution as he is getting on C/Y mount. I realize it may be tricky for you to detect the focus of the conversation given that several mounts are brought into discussion, but let me try to dispel your confusion - the focus is on the drawbacks of the K-mount that make adaptability of M42 lenses less convenient than on other mounts, like C/Y or Canon EF.

Except canon didn't develop shit for m42 compatibility on their ef mount, they got lucky, hence their are people that have shaved the mirrors on full frame canon bodies to use various lenses. Lastly, the real issue that has been pointed out to you and the OP is that Pentax did not invent the m42 mount. It predated the Asahi Optical 'AP' by nearly 10 years. You also keep talking in circles about changing m42 lenses in the dark which really doesn't matter if the body is a 1949 Contax S or any of the other folks that followed suite when Asahi Optical showed Canon and Nikon what an SLR was supposed to look like and how it was supposed to function. The aperture pin is another issue and some manufactures made an adapter to deal with it because their lenses lacked a-m switches. Takumars of any series did not have this issue. So which is it, the aperture pin or changing m42 in the dark?

Furthermore, canon doesn't make a m42 adapter that I am aware of. Pentax kept the registration the same among the m37, m42 and k-mount bodies. That means the 3rd adapters like the ones used on Canon are problematic for use on K-mount bodies. The 3rd party adapters for canon actually add difference in the registration difference of the Pentax m42/K registration distance because of Canon having the shorter distance. I am looking at a 3rd party adapter, genuine Pentax m42 and genuine Mamiya m42 adapter at present. The Mamiya also had the same registration distance as Pentax because they also went from m42 to their own bayonet mount. Their SX series lacked an a-m switch so their adapter as a spring loaded band in side the threads to press the pin. The 3rd party canon adapter doesn't press the aperture pin, but the flange allows for it to lock and adds distance to adjust the registration.

Lets go back and look at what the OP said:

I have an old Yashica camera. It has a yashica/contax mount, so I have also aquired an M42 adapter. Using it is as easy as it could get. I just screw it on a M42 lens and get a y/c mount lens with infinity focus and no additonal glass. The adapter even pushes down that pin on automatic aperture lenses.

When I want to use M42 lenses with K-mount, I have to use a tool to insert a ring into the mount. The whole process is very inconvenient and takes time. And if i want to use the aperture on automatic M42 lenses, I need to disassemble the lens and find a way to fix the pin.

My question is why did Pentax make using M42 lenses on K-mount so difficult if it could be so much more convinient for many Pentax users.

Ah yes, the mechanism to push the Pin. Well as has been mention 20 times in this thread, non of the Takumars needed a device to push the aperture pins since they had an a-m switch. There is no glass needed in the genuine Pentax adapter nor any tool needed. M42 lenses have to be screwed onto the body regardless if it is a Zeiss body, Contax body, Mamiya body, Asahi body, Yashica Body, Chinon body, Ricoh body or the Papa Blue Smurf magic m42 body and the same goes with adapters for dSLR bodies. The caveat is to convert the lens to another mount.

[Blue]

IMHO you have it backwards. Increasing FFD / register 5mm to ~51.5mm would make using 135/FF SLR lenses impossible -- no infinity focus. DECREASING the FFD to ~41.5mm would enable use of everything except Konica lenses. But Asahi was a lens company. It is one thing to enable your users to continue with their existing M42 lenses; it's quite another to cannibalize your sales by enabling all other brands. The elegant PK solution has succeeded for 35+ years. That ain't bad!

Some flange-focal distances:

40.5 mm Konica AR & F
42.0 mm Canon R & FL & FD
43.5 mm Fujica X-Fujinon
43.7 mm Minolta MC-MD
44.0 mm Canon EOS/EF/EFS
44.4 mm Praktica Bayonet
44.5 mm Minolta-Sony Alpha
44.7 mm Exakta bayonet
45.46 mm Pentax-Praktica, M42
45.5 mm Petri, Contax-Yashica
46.0 mm Olympus OM bayonet
46.5 mm Nikon F-mount
47.0 mm Leica R
50.7 mm Adaptall
55.0 mm T,T2,YS

The now defunct Mamiya 135 system had the same registration as Pentax. They moved from m42 to 2 or 3 bayonet mounts of their own before dropping the 135 format in the early 80s.

[RioRico]

The now defunct Mamiya 135 system had the same registration as Pentax. They moved from m42 to 2 or 3 bayonet mounts of their own before dropping the 135 format in the early 80s.

Thanks, I haven't seen those. They must be more rare than those I listed!

[Laurentiu Cristofor]

If I follow your arguments fully the ideal mount for a pentax camera would include a lens locking mechanism that engaged the bayonet directly not the flange and a throat large enough to allow for a tiny aperture pin mechanism in the M42 adaptor to actually allow for automatic aperture(I.e. Open aperture focusing) and if we are lucky an aperture ring coupling to allow for open aperture metering like the ES II

I actually don't care much about the M42 aperture pin since most of the M42 lenses I have either have an A/M switch or have no aperture pin. The only point I was making is that it is not really possible to slap an adapter on an M42 lens and then mount it the same way you would mount a K lens. To put it in yet another way, the Pentax M42 adapter transforms the camera into a screwmount camera rather than transforming the M42 lens into a bayonet lens. It's more of a camera adapter than a lens adapter.

[newarts]

..... The only point I was making is that it is not really possible to slap an adapter on an M42 lens and then mount it the same way you would mount a K lens. .....

You can remove the spring from am m42-PK adapter, put it on the lens, then mount the lens like a K lens... I have a half dozen or more lenses modified in that manner.

I agree that the original adapter was designed to adapt the body to m42 lenses, but that doesn't mean you must use it that way.

[Laurentiu Cristofor]

You can remove the spring from am m42-PK adapter, put it on the lens, then mount the lens like a K lens... I have a half dozen or more lenses modified in that manner.

You must do this with the cheap adapters - the Pentax original one doesn't have enough friction to sit still inside the mount if you remove its spring (that's why you can remove it without any tool). And if you happen to have lenses with stiff focusing action, like I do, then this simply doesn't work. I managed to unmount an adapter when it had the spring on - imagine what would happen if it didn't.

[m42man]

Try three strategically placed "dots" of silicone sealer on the base of the lens to act as stabilizing "pillars". Set the lens base-down on waxed paper to level and setup the sealer. You may need to provide a "well" for the adapter and aperture pin to get a level base. Trim as needed.

A very thin rubber band or O-ring of the correct diameter may work with some "lipped" M42 lenses if it's compressible enough. Acts like the WR seal ring and stabilizes the mount as well.

I've used a rubber band between the adapter and the lens base to adjust the thread depth so as to rotate the aperture ring index to the 2 or 10-o'clock position for better visibility. The soft gasket still allows the lens base to seat on the camera properly for registration distance and provides a soft friction fit in the camera. Manual operation only of course.

H2

Thanks for the suggestions - these should be helpful to many owners of "awkward" M42 lenses. I must say I've already made up a couple of shims for my lenses, using the stiff(ish) clear plastic lids from some boxes of greetings cards, cut out using a pair of scissors. Obviously you have to use a material of the correct thickness, but I seem to have struck lucky here (they measure 230-280 microns, if I remember correctly).

...It's more of a camera adapter than a lens adapter.

Very nicely put, if I may say so!

[newarts]

You must do this with the cheap adapters - the Pentax original one doesn't have enough friction to sit still inside the mount if you remove its spring (that's why you can remove it without any tool). And if you happen to have lenses with stiff focusing action, like I do, then this simply doesn't work. I managed to unmount an adapter when it had the spring on - imagine what would happen if it didn't.

I've not had any particular difficulty with looseness with the original adapter - it may depend on the particular lens - ie if there is no flat lens base to speak of - then 3rd party adapters have problems too.

If friction isn't enough to hold the lens in place when focusing a solution is to notch the lens base so the locking pin engages; Pacerr posted a suggestion of placing a small pin in the lens base to engage the locking pin. I have also adjusted the angle of the adapter's flange to increase its friction with the mount (tap the trailing edges of the "ears" with a hammer.

I checked the dimensions of the 3rd party adapters I've purchased and found them to be very close to that of the original adapter.

One frightening failure mode for adapters with spring removed (including the original adapter) is over-rotation in the mount; if over-rotated it seems impossible to get the lens off at first. Fortunately it is possible by continuing to rotate the lens clockwise in the mount all the way back to the starting position - but it sure is frightening when it happens the first time.

[ryan s]

The authentic Pentax (and Asahi Optical) adapters don't require a tool, nor do the come with one nor have they ever.

Hence my use of the word "still" in the quoted post...

I'm not sure I described the problem very well. The "lip" I'm referring to is a slightly raised ring around the screw thread at the lens base, which means that the lens base, as a whole, isn't totally flat. This raised ring, on some lenses, makes contact with the surface of the adapter, but not the camera's mount. Since the genuine Pentax adapter is an intentionally loose fit in the camera mount (thus making it easy to remove without a tool), then the lens remains a loose fit when fitted to the camera. The only solution is to make up an annular shim, to bring the lens base height up to that of the raised ring.

On the subject of "defensive replies", I think the responses have been very polite and measured, when you consider that the opening post was highly critical of Pentax (the subject matter of all the forums on this website), on the basis of the shortcomings of a non-Pentax "counterfeit" item which has long been the subject of criticism (in this very forum).

There's a few threads on here about this subject (and I posted a vid on YouTube with various lenses).

What I meant earlier was this (now that I'm holding both an early and later version of the adapter as I type)...if you look at the camera mount itself, the bayonet flanges are sort of curved. If Pentax had made one of those flanges a bit longer then squared it off, I think it would have fit tightly without wobbling with the spring holding the tension. It would be a tight fit since the spring would prevent the lens from "backing up". I'm almost considering finding another camera mount just to square off a corner so the spring hits that point...

I still haven't gotten around to making a shim, though One of these days. I think I'll use metal, however, since I'm not sure about the gripping friction offered by any other material (my Mir-1 has a very damped focus ring).

I've not had any particular difficulty with looseness with the original adapter - it may depend on the particular lens - ie if there is no flat lens base to speak of - then 3rd party adapters have problems too.

If friction isn't enough to hold the lens in place when focusing a solution is to notch the lens base so the locking pin engages; Pacerr posted a suggestion of placing a small pin in the lens base to engage the locking pin. I have also adjusted the angle of the adapter's flange to increase its friction with the mount (tap the trailing edges of the "ears" with a hammer.

Now that I have a second original adapter, I'm wondering if I should molest my other one further; hammering the flange didn't solve it for me...

[Lowell Goudge]

Actually I think the best that Pentax could have done was to increase flange distance for new K-mount lenses for about 5mm or more. That would permit to use many different lenses using a respective adapter and without infinity focus issues. That's a whole different topic, though.

you mean reduce, don't you, so that you leave space for the adaptor, sort of like canon?

It would have been a good idea, but I think the issue there is complexity of the mirror arrangement and the swing, to clear the rear of the lens.

Considering a short regestry distance, this requires by default a larger mirror because it forces the mirror back and closer to the shutter, while at the same time reducing the room to swing the mirror.

Assuming in the long run, that technology offers us the possibility of EV cameras with the resolution we get today on reflex bodies (not a given at any rate) then this should be the objective of FF or ASP-C EVIL cameras. Make one that uses K mouont lenses as is with full compatibility, and adaptors for everything under the sun

[Laurentiu Cristofor]

I've not had any particular difficulty with looseness with the original adapter - it may depend on the particular lens - ie if there is no flat lens base to speak of - then 3rd party adapters have problems too.

The certain thing is that this is not an approach that simply "works". It may work for some lenses, but it won't work for others.

The notch solution requires a wide base - few of my M42 lenses have that.

In the end, these are hacks due to lack of a proper solution.

Very nicely put, if I may say so!

Thanks! You may even like the post! <hint>