[Scott_the_Artist]

I'm wondering if there is any advantage in the use of a Takumar prime lens with a Pentax dSLR as opposed to use with another brand like Cannon or Nikon. For that matter, do Pentax dSLR's (like my k20d) work better with m42 screw mounts in general than other brand dSLR's?

If they don't work better with the old m42's, do Pentax cameras really have an edge in reverse compatibility with older lenses? Are K-mount primes superior and cheaper than primes in other brands?

[Just1MoreDave]

Canon is compatible with just about everything except the Canon FD lenses. That's because the Canon mount has one of the shortest distances from mount to sensor (registration distance). If the registration distance is larger than what the lens was built for, it can't focus to infinity. Some lenses can be adjusted for this, most can't. Canon full-frame cameras have some trouble with lenses that protrude far into the mount; APS-C cameras rarely have trouble.

Pentax adopted the M42 registration distance for the K mount, so M42 lenses work well on Pentaxes. Contax/Yashica did the same. The Nikon registration distance is slightly larger than the M42 spec, so Nikons have trouble with M42 lenses.

Besides having the lens fit and focus through its range, you also have to use the meter and maybe get an indication of focus. That works pretty well on the Pentax cameras, but there are some complaints about accuracy. I don't know about Canon here.

You can't really make a blanket statement about all K-mount lenses. The SMC coating was a huge advantage in the 70s but other manufacturers worked on the problem and became at least competitive. Prices don't always reflect quality - sometimes rarity drives up prices for lenses that aren't superior. K-mount lenses do work a lot better on K-mount DSLRs.

[Scott_the_Artist]

Wow, that was pretty thorough. Thanks.

Dave nailed it... The Canons have the most options for old lenses. Not just M42 but many others can adapt onto the Canon.

I have a lot of old M42 lenses I really like, and I have almost switched to Nikon a couple of times, but my m42's need a glass adaptor on the Nikons to deal with the reg distance issue or else you lose infinity focus.

But the Pentax does have good m42 backwards compatability, and another thing it has going for it over the Canon is that the lenses are all SR stabilized. For the longer m42 lenses it is very helpful. I just shot a series of family snaps with the 200mm F4 and they are sharp, thanks to the SR.
It has been discussed on here that the new K7 with its improved Live View, actually helps focus and especially metering with the M42 glass.

[Mike Cash]

I believe that the Canon bodies also require a special M42 adapter for the focus confirmation feature to work. A friend of mine here in town uses Takumars on his Canon and at first had the adapter which does not provide focus confirmation. He changed and reports that he is getting much better shots. He still has the stock focus screen, which as we all know is hard to use for manual focus (even on Pentax).

[stevebrot]

Yep, Canon is the cross-brand compatibility king...unless you include the micro 4/3rds bodies in the equation. You can mount almost any thing onto them.

Steve

[Jasvox]

If you already have a K20D, you're going to find little, if any difference by changing to a Canon with regards to the performance of your screw mount lenses. The only thing I would factor if I was just starting out is...do I already have a good Pentax body (such as yours) or am I looking at other brands since I have nothing already. Maybe the Canons appeal to you more or maybe you are already eying the switch?

I'd explore the possibilities of your K20D with the screw-mounts, I think you will be happy.

Jason

[Scott_the_Artist]

I have absolutely no intentions to switch brands! I just got a k20d as my first DSLR and I'm very happy with it. I over researched to make my decision and I'm convinced beyond a shadow of a doubt that Pentax is my brand. Unless the company stops trying to compete with Nikon and Canon, I'll be a Pentax guy for a long, long time.

I love Pentax primes and I love the high quality results for such a better price. I'm convinced that Pentax gives you the best value for your dollar. If I'm ever rich, maybe one day I'll consider over-spending for a Canon due to their apparent compatibility with other lenses, but at that point I still can't see myself getting out of Pentax, I'd just own two brands.

The reason for my question is curiosity. Also, I may consider loaning lenses to my friends who unfortunately shoot with Canon and Nikon. I guess the takumars I have/have on the way wouldn't work out so well for my Nikon friends. Too bad for them.

[noblepa]

The registration distance on Nikon's F-mount is about 1mm longer than that on the Pentax. This means that, without optics in the adapter, an M42 lens on a Nikon camera won't focus to infinity. That's fine, if you only want to use it for macro shots.

There are such adapters, but, like teleconverters, they degrade the image a little.

Nikon dslrs won't even meter properly with some of their own F-mount lense, so I can't imagine that they'd do much better with someone else's M42 lenses.

My brother has a D200. We were discussing this and I pointed out that my K10d can accept any Pentax lens ever made and thousands of other brands. He responded, "Yes, but why would you want to?". He can't even use most of the lenses from his Nikon F on his sD200, without paying someone $50 per lens to machine the mount.