What is this thing on my canon 50mm 1.4?

I just got my canon 50mm 1.4 and I'm trying to figure everything about this lens. Theres a distance indicator window on it but I've never worked with one of these before and have no idea why its there. Is it supposed to help me with something? How do I use it?

You can ignore it, it just shows you what distance you are focused at, and gives you an idea of the DOF at f/22 (place infinity on the right hand "22" and everything between the distance on the other "22" and infinity will be in the DOF (theoretically).

You don't need to pay any attention to this scale, unless you have a specific reason you want to. Just use it like any other lens.

It can help with manual focusing, pre-focusing, and hyper-focal computation. It's useful if you know what you can do with it, and have a use for it.

KirkS518 wrote in post #14834533
It can help with manual focusing, pre-focusing, and hyper-focal computation. It's useful if you know what you can do with it, and have a use for it.

Unfortunately, the scale as shown on that lens is pretty pitiful (as it is on most modern AF lenses). They do have room to have fitted another aperture mark in there, say f/8, which could have helped. As it is you only get f/22 and placing infinity on that mark will place roughly 2m on the other end. The throw on modern lenses is so small that using the scale (1.5m, 3m, infinity) for manual focusing or prefocusing is just too vague.

I am old school, so I can remember really using these markings back in the day, but that was on lenses with a much longer throw between near and far focus, with ALL the apertures marked, so you could decide on what aperture you needed for DOF using them, and set the HFD. But it just doesn't work well with modern lenses.

Oh, one thing that hasn't been mentioned, Evandot. You will also see a red dot there, that is for infra red focusing if you ever play with infra red photography. Focus as normal, then move whatever focus distance is shown against the regular mark slightly over so that it is against the red dot.

sandpiper wrote in post #14834553
...I am old school, so I can remember really using these markings back in the day

We also had to wait until we got our film developed to see the exact amount of depth of field we actually had (yes the DOF button on the cameras wasn't that useful back then either).

I think today all of my go to lenses have the distance indicator window and I have yet to use it like I did back in the day.......

What everyone else said essentially

Thanks guys if I get curious enough I'll look deeper into it but it seems like I wont really need it right now.