Why does the screw-mount exist?

[Max Power]

Seriously 😛

I was thinking about this this morning. A week or so ago, a friend gave me a Praktica SLR. It uses the M42 screw-mount. I also own a few FSU RFs and a 50/1.5 Nokton for my R3A.

I find that screw-mount lenses are a bit of a PITA to mount. You have to line them up just right or you risk counter-threading them which could damage the mount. They are also IMO longer to mount and dismount.

So, my question: why did/do some manufacturers bother with a screw-mount setup over a bayonet mount? Were bayonet mounts harder to engineer and manufacture a century ago? Or is it simply a case of nobody really coming up with the idea of a bayonet mount in time to beat screw-mounts? Is there something inherently 'better' about a screw-mount which I don't understand?

Inquiring minds want to know 😀

Cheers,
Kent

 

[Gabriel M.A.]

I think for the same reason Diesel engines were harder to engineer centuries ago, they came up with the steam engine. That's why rudimentary things come up first.

There are few cases where it's the other way around. But they didn't "come up with the M42 mount" just because they didn't want to think about bayonet mounts. Simplicity is often best.

 

[ErnestoJL]

IMO It was easy to manufacture in 1948, and also easy to change lens with a little bit of care.

Bayonet mounts OTOH are expensive as they require several machining operations to finish one, some other tiny pieces for the locking device, and it means increased manufacturing costs. An M42 mount just requires a screw and a nut and no locks. Besides, lens position isn´t critical, as the only linkage needed was the iris actuating pin (it can be operational within +/- >15 deg. from center)

At the time K VEB Pentacon started to make SLRs with this mount, the only other SLR in the market was the Exakta which used an internal bayonet with an external odd looking lock and it wasn´t copied or adopted for other manufacturers but Topcon, years later. They needed this arrangement because the automatic iris actuator was in the lens, not in the camera and it should be placed in the right place.

Screw mounts died when lens position accuracy was a must (electrical or mechanical connection/linkage between lens and body).

Today with cheap plastic bodies, a bayonet mount isn´t a price issue.

Ernesto

 

[oftheherd]

I really don't know. However, I suspect it has to do with the fact bayonet mounts hadn't been thought up yet, or somebody held a patend or something. On the other hand, things had been getting screwed together for a long time.

I always find it interesting that folks say screw mounts are harder than bayonet mounts. I learned how to do it by setting the lens on the camera and screwing counter clockwise until I could feel it seat. Also by learning quickly not to force it if I was wrong and it hadn't seated.

I can mount a screw mounted lens by feel, without looking. I cannot do that with my Yashica/Contax mounts. Maybe they are just different and more difficult than any other bayonet mount. They are the only ones I have experience with.

Try mounting those screw mount lenses you have that way, with your eyes closed, then try it with your bayonet mount. Of course, it you don't need that skill it makes no difference. However, I used to do a lot of available light photography.

 

[ywenz]

Screw-mount viewfinder sucks too. How do ya shoot with those thangs?

 

[Solinar]

Screw mounts aren't for wimps or whiners - There are other systems that will and can save us from our own incompetence. - Fors example: Why don't all cameras have motorized, automat film loading? The list is endless. 🙄

 

[XAos]

It's pretty simple really. Threads are one of the simple fundamental methods of fastening. Bayonet mounts are an improvement that people thought of after futzing with screw mount lenses. Sometimes the ideal solution doesn't present itself until you've been annoying by something long enough.

 

[Jocko]

Another important thing to remember is that neither the M39 or M42 screw were ever patented. Bayonet mounts always were. An "open" universal standard can pay huge commercial dividends, enlarging markets and reducing unit prices as many manufacturers compete with compatible products. This is often decisive, particularly at a point when technologies are establishing themselves - for example in terms of the battles over railway gauges in the mid-1800s or Microsoft v Apple in the 80s and 90s, when "closed" but arguably superior systems lost out to "open" rivals - as with the Leica screw and the Contax Bayonet (respectively 1930 and 1932).

Cheers, Ian

 

[FrankS]

Back in the day, folks were thrilled enough to be able to change lenses at all, and weren't worried about a few rotations of a lens to mount it. After the thrill of interchangeable lenses wore off, other folks began to think of ways to make it easier/faster.

 

[Kim Coxon]

The most common existing mount at the time they were introduced was the LTM M39. It could just have been an extension of that. It has also proved to be the "universal" SLR mount and will even fit most DSLR's with an adapter in the same way that M39 is the "universal" RF mount.

Kim

 

[John]

Interrupted bayonet threads were used on the big copper diving helmets in the 1800's. Breech loading cannon also used them. For cameras it was likely what Frank said; 🙂

Back in the day, folks were thrilled enough to be able to change lenses at all, and weren't worried about a few rotations of a lens to mount it. After the thrill of interchangeable lenses wore off, other folks began to think of ways to make it easier/faster.

 

[flashover]

the "screw mount" works much better then the "glue mount method"

 

[Andy K]

The other advantage of the screw mount is you are not limited to one manufacturer's lenses. With patented bayonet mounts you are restricted in lens choice.

 

[Max Power]

Apart from the answers which are either insulting or opaque, some interesting hypotheses; it makes sense from an engineering/manufacturing and evolutionary POV that screw-mounts were first adopted.

oftheherd; your technique is precisely the one that I've applied to getting the lenses on; I find that it usually works and avoids cross-threading.

Kent

 

[FrankS]

Insulting? Huh?

 

[bmattock]

One additional thing - I was considering this, and my first idea for a response was sarcastic - like 'duh, why did they live in caves and not build modern houses?' But then I realized that from some points of view, it makes sense to ask the question.

And furthermore, there is another concept that hasn't been explored - backward compatibility and customer demand. Once the screwmount had been introduced and 'accepted' more or less by consumers, there was a demand that it not change on them and make their rather substantial investments (at the time) valueless for use with the next round of SLRs. This was one of the first cases that I can think of where consumers demanded 'backward compatibility.' And so the M42 mount probably lived a lot longer than it otherwise would have - having been eclipsed in popularity by more capable bayonet mounts that offered the ability to not have to manually stop down to shoot or take meter readings, etc.

Best Regards,

Bill Mattocks

 

[Gabriel M.A.]

Insulting? Wow. Every day I learn new things about insultingness.

 

[FrankS]

My only guess onthe "insulting" remark is that Max P did not get flashover's humour in post #12.

Bill, the original question was why screwmount and not bayonet mount initially.

 

[Kim Coxon]

I think he is refering to ywenz's remark in post 5. I must admit that it doesn't add much to the conversation.

Kim

My only guess onthe "insulting" remark is that Max P did not get flashover's humour in post #12.

 

[Gabriel M.A.]

http://dictionary.reference.com/search?q=insulting

I don't see how any of this is insulting. I see a natural conversation between friends happening...