Q:

Is it possible to DIY adjust the focus ring distance scale of a lens?

I have a particular lens in mind, but is it generally possible to do this adjustment? Of course there are a lot of lenses that don't have any distance scale to begin with. Many lenses have the scale though. I'm mostly interested if there is a way to do this adjustment by myself.
To see the amount I'm in need of adjusting, I took five shots of stars with all else kept static but nudging the focus ring a little between each shot. What I found out from the photos is that best infinity focus (the stars!) was somewhere between positions 2 and 3. That's not even near the end of focus ring rotation.

Naturally, I'd start by checking if the shorter distances marked on the scale match any better, but first I just want to know if lenses with a distance scale are designed to allow for adjusting of the scale. And if this adjustment is possibly a DIY-level job.

A:

Part of the problem is that you are at infinity.  The reason that infinity is shown as a range is that it does not remain constant.  Environmental conditions can actually impact (fairly significantly) what the actual point you need to focus the lens on to be focused on a point infinitely far away.  The value that gives best results can change from one sitting to a next, which is why it is marked as a range of values.

