[jannking]

I am a total newbie to the DSLR and just bought a manual focus lens. After I tried it, really like it. Manual focus is not as bad as I expected. I noticed there is a white dot on the distance ring. It looks like a LED to me, but it is never got lit up. Very curious what is this for?

[Eagle_Friends]

what is the manual lens you are referring to?

[Ash]

It's not a LED, it's a cosmetic spot on many lenses that can act as a place to mark the spot on the lens without having to look (know by feel rather than sight.
It has little relevance to the lens function itself.

[JeffJS]

Do you mean the white bump looking thing at about 8 o'clock as you look at the front of the lens? It most certainly does have a purpose. In fact two IMO. One, it will give you something to grip when mounting and removing the lens so you aren't wrenching the aperture ring back and fourth. Two, you may notice that when you are putting the lens on the camera, it lines up with the release button you press to remove the lens from the camera body (kind of what Ash is referring to but explained more fully). But no, it never will light up.

[jannking]

Thanks for the information.

It's not a LED, it's a cosmetic spot on many lenses that can act as a place to mark the spot on the lens without having to look (know by feel rather than sight.
It has no other relevance to the lens function itself.

Yeah, that's what I was talking about though it is at about 11 o'clock after the lens is mounted on the camera. Just tried to mount the lens again and now I clearly get the idea what you guys are talking about.

Do you mean the white bump looking thing at about 8 o'clock as you look at the front of the lens? It most certainly does have a purpose. In fact two IMO. One, it will give you something to grip when mounting and removing the lens so you aren't wrenching the aperture ring back and fourth. Two, you may notice that when you are putting the lens on the camera, it lines up with the release button you press to remove the lens from the camera body (kind of what Ash is referring to but explained more fully). But no, it never will light up.

[calculator01]

My extremely old (1970's) Pentax how-to guide says the bump is there so you can mount lenses in the dark

[JeffJS]

My extremely old (1970's) Pentax how-to guide says the bump is there so you can mount lenses in the dark

Which I've always kind of wondered about. If it is too dark to see while installing the lens, what will the pictures taken with it look like (time exposures aside)? No ISO dials in the 1970s to let us shoot in no light conditions

[m42man]

Just to clarify: the bump was more relevant when used with the older 35mm bodies, when it actually did line up with the lens release lever. The lens release button on modern DSLRs isn't in quite the same place, so the bump shouldn't be used for alignment.

[Mike Cash]

Jeff, it sometimes happens that it is dark where you are but your subject is in the light.

[opfor]

Or if you use the change the lens in the bag method when you are somewhere dusty...:-P

[JeffJS]

Jeff, it sometimes happens that it is dark where you are but your subject is in the light.

Or if you use the change the lens in the bag method when you are somewhere dusty...:-P

I was kind of being sarcastic about it but I guess it doesn't always translate well. I've actually used the feature on a number of occasions when it's easier to line things up rather than look for the red dot on the mount. I notice as others have, they've stopped putting it on the lenses.

[jannking]

You are right about that. But I noticed there is a small bump on my K-r mount and it perfectly lines up with the white bump on the lens when you try to put on the lens.

Just to clarify: the bump was more relevant when used with the older 35mm bodies, when it actually did line up with the lens release lever. The lens release button on modern DSLRs isn't in quite the same place, so the bump shouldn't be used for alignment.