re older Leitz lenses:

[Dante221]

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Hello All!

Forgive the noob question: What was the purpose of the button on

some of the Summicron 50mm lenses that "locked" the focus at

infinity?

Thanks for your patience!

Dante

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[bill]

Welcome Dante

 

It does exactly what you have said. It locks the lens at infinity so that you do not put strain on the focussing helicoid when changing lenses.

 

Regards,

 

Bill

 

Sent from another Galaxy

[earleygallery]

The focus lock button is rather curious. As Bill says, it makes changing lenses easier/safer as the focus ring is locked and can be gripped when changing lenses.

 

However, the earliest fixed lens Leicas also had this feature.....I think it was also to hold the lens in place when extending or collapsing a lens (such as was fitted to those cameras, and the later Elmar 5cm etc).

 

Also the button doubles as a focussing tab.

 

So the infinity lock as served several purposes!