Infinity focus on kit lenses

WelliesNBrellas

In the advice I've been reading about capturing fireworks, the recommendation repeats to manually focus at infinity. Where on the kit lenses is infinity? There are no infinity marks on either the standard 18-55mm or 55-200mm kit lens. How do I know where to set the focus?

bruto

Infinity should be the furthest focus at the stop, but actually some lenses these days, especially plastic zooms, may focus a bit past infinity, which is likely to be worse than falling a bit short. Depth of field this side of the focus point is shallower than depth on the back side, and focusing past infinity can leave everything a bit off.

If you can find a focusable object at a distance, you're best off focusing on that. If you focus at or beyond a distance approximating your focal length, you're pretty safe for getting infinity within your depth of field. The further the better.

WelliesNBrellas

Thanks, Bruto! I'll try out your advice during daylight hours to see where things fall into focus best. You've given me a good starting point, thank you!

bruto

Playing a bit just a while go with my 18-55mm kit lens, I find it focuses rather far past infinity, and if you crank it manually to the stop, it's definitely blurry at infinity. It's really pretty sloppy. Once upon a time, manual lenses which were made of all metal generally tended to have a proper infinity stop, and one could just crank it to the stop in the dark. No more.

If you don't worry too much about making a mark on the lens, you might consider auto focusing on a cloud during the day, and marking that on the lens as the infinity point. If you then manually focus to that point, or a gnat's eyebrow closer, you're pretty sure to hit proper infinity when AF is not available.