That plastic dome on lenses. What does it do?

[Hamster]

On a lot of SLR lenses, there is a small plastic dome near the lens mount. For instance, the red dome on Minolta and Leica lenses, white dome on Pentax Lenses or blue dome on Zeiss.

I have read somewhere that it is referred to as a "finger point". Is there any functional value to this dome? I always thought it was there for marketing purposes only.

 

[Lee L]

On Zeiss and Leica it aligns with the lens mounting release lever on the body, allowing you to mount the lens by feel, matching up a finger or thumb on the lens dot with a finger or thumb on the camera body. You can change lenses in the dark or without looking (as in keeping an eye on your subject). If you learn to use your equipment correctly, the raised dot is highly utilitarian. If not, it's considered an affectation.

I'm not saying the other brands don't work the same way, I haven't used them.

Lee

 

[Anscojohn]

On a lot of SLR lenses, there is a small plastic dome near the lens mount. For instance, the red dome on Minolta and Leica lenses, white dome on Pentax Lenses or blue dome on Zeiss.

I have read somewhere that it is referred to as a "finger point". Is there any functional value to this dome? I always thought it was there for marketing purposes only.

******
It allows matching up the bayonet mount by feel when changing lenses.