EF-M 18-150 and manually focus on infinity

Sittatunga wrote:

RvL001 wrote:

Hi all,

Last week I tried to focus on some jet fighters doing a couple of fly by's. AF wasn't able to focus on them them as I couldn't catch the jets in the frame because I only saw OOF blur, which made it impossible for AF to focus.

So I tried to switch to MF, give the focus by wire ring a swirl to infinity and take the shot. I was unpleasantly surprised that by giving it a swirl, the lens actually focuses beyond infinity. After taking some test shots I found out that I have to give it a swirl and turn it back slightly. But not too much or it won't be infinity. And there's a, very fine line between closer than infinity, infinity and beyond infinity

Long story short, I missed the shot... Is this normal behavior for the focus by wire EF-M lenses?

This is normal behaviour for just about any AF lens. It's more noticeable with long lenses. It's mainly to do with the coefficients of thermal expansion for ABS, steel, aluminium, magnesium alloy, normal and UD glass all being very slightly different from each other. That means that lenses have to be made to focus beyond infinity at most temperatures in order to reach infinity at every temperature in their working range. Astrophotographers have to continually refocus their lenses as they change in temperature throughout the night just because of this.

Well, given a sufficient level of resolution and/or focal length, astronomy requires periodical refocusing whether your lens is MF or AF. When I was working on a large radio telescope way back when, we had to recalibrate as much as 3-4 times each night, and I assure you we did not have DPAF on that thing!

(We would recalibrate by simply focusing on a known object in the sky. I still remember getting a kick out of the one time we imaged Pluto just for the heck of it, using calibration as an excuse.)