[boriscleto]

Pentax did have older users in mind (clearly, with the exact register distance and total diameter of screw mounts in mind when designing the K...and providing an OEM adapter for peanuts [anyone care to look up a genuine Canon FD to EOS adapter price and availability?

Not to mention that the FD to EOS adapter only works with a few telephoto lenses and requires optical correction to work at infinity focus.

[Lowell Goudge]

Not to mention that the FD to EOS adapter only works with a few telephoto lenses and requires optical correction to work at infinity focus.

Or that it was only offered to a few select pros

[Laurentiu Cristofor]

People shouldn't get so defensive. The Pentax backward compatibility story is better than that of other brands, but this doesn't mean it couldn't be even better.

Even if the M42 adapter was removable using the lens release button (I, too, wish it were), why would Pentax take the time and money to do it when they could just design a big nut instead?

They could have put the nut on the inside of the mount - it's not a big deal.

And in the end, the adapter would stay in the mount regardless of whether or not it was the design they went with, or tooled the initial K design differently to use the lens release button.

It doesn't matter that it would stay in the mount - the issue is how easy it is to get it out and switch to using another lens. It is ironic to move away from a screwmount because it's not an effective lens changing solution and then offer a backward compatibility solution that maintains all the drawbacks of the original mount when you could have done a tiny bit of change and make the use of old lenses even better (for those that can afford an adapter per lens). It's either poor engineering or denotes a lack of interest - my bet is on the latter.

Screwing and unscrewing lenses on an adapter also has the drawback of getting fine metallic dust on the sensor, besides the inconvenience in changing lenses.

My biggest gripe is that the lens is "loose" when the body of the lens doesn't contact the metal camera mount. They should have changed that, IMO.

The ability of the adapter to rely on a proper locking mechanism would have fixed this aspect too.

actually, Asahi Optical probably assumed that most people would prefer to use one adapter on a camera body for several m42 lenses rather than paying the equivalent of $31 per adapter. Once the adapter is installed, adding and removing a Takumar is the same as on a m42 Asahi body.

This doesn't make much sense. Nobody forces users to buy more adapters if they just want to use one and continue with the screwmount mounting way. A Canon adapter (let's drop the AF/SR aspects for now) allows you to mount 10 lenses on the same adapter or also mount the adapters permanently on lenses. The Canon story is better from a mechanical perspective - their adapters cover the contacts and lock into the proper lens locking mechanism. It's ironic, but it's what it is. We can try to hit back with our AF/SR advantage, but note that even for AF, we can only use center point, while Canon enables use of *all* AF points when using a chipped adapter. That kind of compensates the lack of SR for those that rely on AF confirmation. It's pretty much a tie. Who cares about FD lenses - no one else can use those and the introduction of the EF mount is what made Canon in what they are - they were right to drop the FD mount.

My guess is that the ability to effectively mount/unmount M42 lenses was just not a design goal for the K-mount.

[Blue]

. . .

My guess is that the ability to effectively mount/unmount M42 lenses was just not a design goal for the K-mount.

once installed, it is just as easy to change Takumar lenses on a K2 as it is a Spotmatic F.

[Blue]

I'm sure it was a slip, but the EOS registration is slightly longer than FD I know you know what's going on

That's also how Canon EOS cams have a heck of a lot of adapters and adapters with flanges--the register is still shorter than other systems (OM, F mount, K mount, Leica R, etc). Putting lenses with shorter register distances than the body is where infinity focus is lost

Yeah, I was typing too fast. I actually have an authentic fd to eos adapter for the FD 50/3.5 Macro lens and FD bellows. They have no optics in them and of course do not go to infinity but the bellows wouldn't anyway and it isn't really an issue for macro. I also have the rare Adaptall-2 EOS-M mount. All that was for the A2 and 10s (I still have the latter).

[pacerr]

My guess is that the ability to effectively mount/unmount M42 lenses was just not a design goal for the K-mount.

An' my guess is that's true.

It was 1972-73, folks! -- design goals were being developed for the next generation of Pentax lenses which were introduced in 1975. The KA2 lens mount wasn't even a glimmer in the designers' eye; the capabilities of the FA lenses and body types were as yet undefined and largely unforeseen. (Which desktop computer and wireless phone did you have then?)

The immediate design goals for the K-mount were to:

- increase the mount diameter to allow electric AE contacts, "faster" lenses and eventually some sort of connection for a mechanical auto focus mechanism.

- convert from the linear diameter aperture adjustment mechanism to an area-rule aperture scheme to accommodate the needs of simple, open aperture, matrix metering.

- design a mount with more precise indexing than the M42 thread mount was capable of to satisfy the requirements of items 1 and 2. (That the bayonet was quicker to mount was a nice touch too.)

The diameter of the existing M42 mount simply did not provide the dimensions needed. Other manufacturers faced with the same challenge mostly chose to completely abandon compatibility with legacy lenses in the interest of simplicity and cost.

The fact that Pentax ended up with a mount with the same registration distance that allowed the older lenses to be mechanically adapted within its diameter is a plus.

Providing an M42 > PK adapter was a marketing tool that allowed pro/business users worldwide (and a much smaller pool then of "wealthy amateurs" who could afford a LOT of lenses) to spread the cost of transitioning to the new lenses and bodies over a much longer period of time.

Employees in 1975 didn't envision that a consumer market population would be calling Pentax Corp. devious, bumbling, incompetent conspirators on an internet forum today because they couldn't use cheap, 40-year old lenses on digital SLR bodies and had no way to define such a feature.

Consider this: even if there was a magic adapter to somehow convert an old Super Takumar 50mm/1.4 into a virtual DA auto-focus lens there'd still be the mechanical issue of linear vs. area rule aperture operation and its effect on exposure to contend with. Or were they supposed to have anticipated a software program to translate that effect too?

Pentax DID make it easy to use legacy M42 glass though. It's called M mode. It's just not as convenient as with a ol' Spotmatic 'cause that silly, damn internal flash bump hides the aperture ring. That's my only gripe.

H2

[m42man]

...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...

Why are you critcising Pentax when you've obviously got yourself a cheap, badly designed third-party adapter? Pentax were very careful to design their adapter so that it's dead easy to remove from the camera without any tools. And you don't insert a real Pentax adapter into the camera, you first screw it onto the M42 lens, and then mount on the camera. Nothing inconvenient about it at all.

...My biggest gripe is that the lens is "loose" when the body of the lens doesn't contact the metal camera mount. They should have changed that, IMO.

It's not possible to mount rigidly those lenses (of Eastern European and Soviet origin) which have a raised "lip" on their base without compromising the ease of disassembly (above). But why would Pentax bend over backwards to accommodate lenses which were intended only to fit Praktica and Zenit cameras?

[RioRico]

Screwing and unscrewing lenses on an adapter also has the drawback of getting fine metallic dust on the sensor, besides the inconvenience in changing lenses.

Aim the camera down when (un)screwing lenses. Metallic dust usually doesn't fall *up*.

I won't echo all the other points that have already been made well. I will echo that the Pentax adapter was/is an elegant solution that has functioned for 35+ years. That period has seen an ongoing revolution in imaging, and data-handling and -consumption, and economics; the demise of many formerly-leading camera makers; changes far beyond the scope of the design engineers' brief. I call that DAMN GOOD ENGINEERING.

Now I can eBay twenty bucks to an account in China and get five clone adapters shipped to me; and I remove the f*cking screw and clip from each, and tighten them onto another 5 lenses, some pre-WW2; and they WORK on a camera they were never designed for. A little diddling with lens mounts and/or adapters, and I can use an even wider universe of seemingly-incompatible lenses. Life is good!

[Jüri]

I think you have missed the point of the OP question and of my response. Jüri rightfully pointed out that the way the M42 adapter locks inside the K-mount could have been better if Pentax would have designed the K-mount lens locking mechanism differently. The adapter cannot be anything else than what it is, once the K-mount is set in stone, so no one is knocking that. It is the K mount that should have been designed to allow an M42 adapter to lock inside the mount the same way that K-mount lenses lock onto the mount.

Pentax could have gone two ways:

1) Keep their current style of lens locking mechanism, but shorten the register distance, so that adapters would look like those that lose infinity focus but lock on the mount like lenses do - of course, with a shorter registration distance, they would no longer lose infinity focus anymore. This would basically offer the mechanical adaptability that Canon EF mount offers today. But this would also imply that you would have to redesign a lens line for the new registration distance, which is costly.

2) Keep the same registration distance, but make the lens to mount locking mechanism such that an adapter that fits inside the mount can use it too - this means the lock would have to be inside the mount - this is a fairly trivial mechanical feat to accomplish.

The question is - why did they not do 2? On second thought, I assume backward compatibility was a secondary goal in the design of the mount - as long as some story could be provided (the one we have today), no one spent resources to polish it.

Thanks a lot for your thorough and relevant responses. Most others don't seem to understand what my question was. I was not asking "What do you think about using M42 lenses with Pentax adapter?".

Pentax has done a great job designing it's cameras to work with old lenses and it's defenitely superior to other DSLR brands in that aspect. However, they could have made it even easier simply by putting the lens locking mechanism inside the mount. "Why didn't they do it?" is what I was asking.

I would conclude that Pentax probably had backward compatibility in mind, but it wasn't so relevant back in 70's, so they just didn't think it though.

Strange how devensive people get when asking a simple question about Pentax. It's probably just a Pentax user thing.

[xjjohnno]

Juri, I think you'll find the same defensiveness in other Brand forums as well. The only M42 lenses that are an issue are those with the aperture pin but no auto/manual switch so I'd have to say they got it pretty near right when they designed their adapter. Adding a little flange to depress that pin would have made all the difference.

[Lowell Goudge]

However, they could have made it even easier simply by putting the lens locking mechanism inside the mount. "Why didn't they do it?" is what I was asking.

In looking at the limited supply of different mounts I have sitting around, the pentax locking approach is like nikonn's.

Minolta;s MD is internal as you imply pentax should have done, canon at the time had a breach mount


In fact, with any kind of foresight, the best approach would be to shorten the regester distance by 0.8-1.0mm and use a flanged adaptor.

it is too bad they didn;t, and I suspect that the screw mount adaptor, as others have mentioned, was to convert a new body to screw mount, and not to convert screw mounts to bayonett.

Personally, and this may sound defensive of pentax, but is not intended that way, of you want to shoot M42 lenses a lot, then just leave the adaptor in one body. It's what I do.

I don't trade in cameras, I keep them as back ups and / or for other uses. One of which is MF lenses, where I have also mounted a split image focusing screen.

my adaptor can remain in a body for weeks at a time.

The other option, and I have conisdered that too, is to put a flanged adaptor on each of my M42 lenses (after all they are only $5 each in volume, and readjust the focus to account for the change. to me, that risks the value of the lens so I have not done it

[TaoMaas]

I have an old Yashica camera. It has a yashica/contax mount...

That's not an old Yashica. The old Yashicas used the M42 mount...no adapter needed.

[pacerr]

Why did Pentax make using M42 lenses so awkward?

For the same reason automotive engineers didn't make it possible to "repair" a modern ignition distributor system with a paper clip and a matchbook cover (as was actually possible in pre-computer days) or provide for the convenient attachment of horseshoes as spare tires. The ability to do so was logically incompatible with the design goals, concepts and materials available at the time. There was no practical reason to provide an adapter to use OLD TECHNOLOGY except to reduce the cost of transition for users.

Adding a lens lock mechanism (which the M42 doesn't use) for an imprecise screw thread is practically incompatible with the bayonet mount system without modifying each lenses in some manner as well. The flanged adapters do provide a safety locking notch but not the precision indexing required for the KA-mount functions.

It makes as much sense to ask why Pentax didn't provide for the use of tiny Polaroid film clips or sheet film in place of the digital sensors for those in a nostalgic mood. (Although no doubt someone could figure out how to expose film by pressing it against the LCD window. Hmmm, now there's a rainy day project!)

It would be like trying to adapt an ol' Smith Corona manual typewriter and a black & white TV set so they can be used along with and/or in place of your computer monitor and keyboard! An interesting challenge but unnecessary.

H2

[Blue]

For the same reason automotive engineers didn't make it possible to "repair" a modern ignition distributor system with a paper clip and a matchbook cover (as was actually possible in pre-computer days) or provide for the convenient attachment of horseshoes as spare tires. The ability to do so was logically incompatible with the design goals, concepts and materials available at the time. There was no practical reason to provide an adapter to use OLD TECHNOLOGY except to reduce the cost of transition for users.

Adding a lens lock mechanism (which the M42 doesn't use) for an imprecise screw thread is practically incompatible with the bayonet mount system without modifying each lenses in some manner as well. The flanged adapters do provide a safety locking notch but not the precision indexing required for the KA-mount functions.

It makes as much sense to ask why Pentax didn't provide for the use of tiny Polaroid film clips or sheet film in place of the digital sensors for those in a nostalgic mood. (Although no doubt someone could figure out how to expose film by pressing it against the LCD window. Hmmm, now there's a rainy day project!)

It would be like trying to adapt an ol' Smith Corona manual typewriter and a black & white TV set so they can be used along with and/or in place of your computer monitor and keyboard! An interesting challenge but unnecessary.

H2

Its no more awkward screwing a Takumar on a K2 than screwing them onto a Spotmatic F or SV. That's the whole point. A person that bought a K2 in 1975 (that's the release date of K, not 73) probably had several Takumars. The adapter adapts the body to screw mount, not the lens to K-mount.

On a separate note, some makers didn't have an a-m switch on their lens such as the Mamiya SX line of m42 lenses. When they adopted a bayonet type mount, they had to come up with a inner ring to press the pin in order for their sx to be used on their newer bodies. Pentax never had this problem with their Taks.

[Lowell Goudge]

Adding a lens lock mechanism (which the M42 doesn't use) for an imprecise screw thread is practically incompatible with the bayonet mount system without modifying each lenses in some manner as well. The flanged adapters do provide a safety locking notch but not the precision indexing required for the KA-mount functions.

Note, that the pentax M42 mount in its final generation did require precise rotational orientation, specifically for the Spotmatic F and ES II which had open aperture metering achieved by the same aperture reading lever as the origonal K mount. As I said in an earlier post. if that was the limit of technical requirements then we would still be using screw mounts.
As for the precision of the flanged adaptor, its locking is just as accurate as any pentax lens.

but the remainder of your post is correct.

the compatibility was offered for ease of transition. the new mount has, when you consider how far cameras and lenses have progressed served pentax well.