Purpose of Infinity Locks?

What are these annoying devices used for? I suppose they do make lens mounting

easier? What is the reason for them?

On a Leica, or a technical field camera? I've only used them on the latter, makes moving the front standard to the infinity position quick and easy. What would they do on a 35mm camera with helicoid focusing? Perhaps for use with a bellows?

They were of use with the LTM bodies holding the lens immobile, in the locked position while

unscrewing the lens. They were carried over to the early M mount lenses--first two versions

of the 50 Summicron and the first version of the 35 Summicron and the 35 Summaron.

Oops, I was thinking of an infinity stop.

On the thread mount lenses, you can unscrew them without turning the focusing helix all the way to minimum focus. Notice that it's only done on the relatively short focal lengths. For example, on the Summaron, 35mm, the lock is the only thing you can hold onto to focus at all as there is no focusing ring to hold.

I found the infinity lock on that 'cron made it easier to get the lens on and off the camera, since there is little to grip on the mount side of the lens. Much more useful on the LTM Elmarit that I had once, though.

A key point is preserving the focusing mount of the lens, by providing a wrenching point for your thumb. For the lenses with non-rotating fronts, the mechanical parts that keep the front from rotating, while still being able to slide in and out, are not very robust. They are small bits of metal, and they are quite long on the longer focal length lenses, making them all the frailer. We're talking 2 to 3mm wide, and maybe 1 to 2mm thick! They are secured by very small screws, to boot.

 

The Canon rangefinder manuals make it quite explicit that the normal and wide angle lenses are only to be torqued using the infinity lock, and that the telephotos are to be torgued only using the knurl at the base of the lens.

 

Yes, the ones on the 35mm and 50mm Elmars aren't really all that important, since there's a stop stud for close focus, so you won't strain anything without the lock. But it's a nuisance putting away the lens when it comes off the camera at close focus, especially with the 35mm Elmar which won't fit in its bakelite case except when focused at infinity.

 

I find it sad how many lenses are found with them missing, removed and lost in some drawer years ago. But it is a matter of taste to some degree.

 

You also see some where folks have just bent the focusing tab such that the infinity lock doesn't engage. Doesn't loose the part, but not cleanly reversible either. But, hey, these are just tools, ultimately.

I think that it was on the first Leicas to make it easier to collapse and extend the lens. Then it was continued on later non-collapsible lenses to help when they screwed the lenses off and on. I know that I grew up with it, and miss it if it ain't there.

Strange, I prefer the infinity lock and miss it on lenses where it has been omitted. It is the only complaint I can think of concerning my Summicron C. If you don't like it is hardly a major issue to disable it. I suppose we all need something to gripe about! It is curious that the Contax also featured an infinity lock which was much more complicated and I have not heard a whisper of complaint from Contax aficianados.

Contax owner responds: I dislike the infinity lock on my contax iiia / sonnar 50 combo.

"I know that I grew up with it, and miss it if it ain't there."

 

Me, too.

I should have said that I like it on my Leicas but it is a PITA on my Contax and Kiev. As much as I admire the old Contax system, I just can't get used to dodging the RF window with my right hand. The Contax grip just doesn't work for me!

I'm with you guys about the infinity lock on my Contax IIa. The lock on Leica lenses is a natural (ergonomic) function, while the Contax always seems to "stick" and take an extra thought/motion.

"They were of use with the LTM bodies holding the lens immobile, in the locked position while unscrewing the lens. They were carried over to the early M mount lenses--first two versions of the 50 Summicron and the first version of the 35 Summicron and the 35 Summaron."

 

For a short while I had the very first model 28 Elmarit and it had an infinity lock built into the finger scallop. AFAIK that lens was never made for LTM.

On collapsible lenses such as the older model 50mm f2.8 Elmarit you must set the aperture before focusing. The reason is because the front portion of the lens will move while setting the aperture, particularly if the aperture ring is the slightest bit stiff. Perhaps one of the reasons for the infinity lock is to facilitate setting of the aperture.

 

An old trick someone taught me years ago is after each shot (on any lens)to return the focusing ring to infinity. That way for the next shot (and each shot) you are starting the focusing from the same position each time. For beginners who don't employ this technique finding the proper focus sometimes involves going back and forth with the focusing ring not really knowing if they are starting from a greater or closer distance from the subject. The technique makes focusing faster. I have no idea if this is what Leitz had in mind by installing infinity locks on some lenses, but it's a thought.

 

Cheers,

 

Dennis

I had wondered the same until I bought an LTM camera - then figured it out just from learning to use the camera. I'm gratified to find out that I was right!

The lock is great for aerial photography! The less you have to worry about when you are in a hurry, the better. Locking the focus at infinity is one less degree of freedom in the system. Many experienced photographers would put some masking tape to fix lenses at infinity if there was not a built-in lock.