Dialing to infinity ... on a kit lens?

batmura · Dec 5, 2012

I have been doing some more reading and every once in a while I read people "dial to infinity" but I can't really say I get what it means and why they do it. I also read that an 18-55mm kit lens won't allow the user to do it, so one has to choose a focus point or let the camera autofocus on something before switching back to manual mode in order to leave the focus point setting undisturbed.

Can anyone fill me in on this or provide me with a link?

KmH · Dec 5, 2012

Because most people today rely exclusively on auto focus and to help keep costs down, many of today's lenses (particularly consumer grade or 'kit' lenses) do not have a focus distance scale.

Infinity focus is used to ensure the most distant parts of a scene are in focus.

However that is really a notional concept, because the further from the camera an object is, the more atmosphere is between the camera and the object, the more movement of that atmosphere, and the softer the focus of distant objects will be.

When the astronauts were on the Moon, they were not able to determine long distances accurately, because there was no atmosphere to add blur with increasing distance which is a subtle visual cue humans depend on to gauge distance.

Many lenses that do have a focus distance scale don't accurately indicate the 'infinity' focus adjustment and/or are able to focus past 'infinity'.

So what you can do is pick a distant object and manually focus on it as best you can. Another issue because of auto focus is that today's cameras don't have any manually focusing aids like a split prism focusing screen.

All of that points to the fact that though the increasing use of automated camera features, like auto focus, opens the world of photography to more people, it comes at the eventual cost of losing many helpful features.

Older lenses not only had focus distance scales on them, they had DoF and hyperfocus scales on them too. Focus rings had slower gearing so very fine, manual adjustments to focus could be made.

In other words, be careful what you wish for.

scorpion_tyr · Dec 6, 2012

You can manually focus it to infinity by simply turning the focus ring to focus farther away until it stops, and then turn it back just a hair. Or more accurately just auto focus on something in the distance, say a cloud or something should be far enough. If it's at night focus on a far away street light or the moon. After you have the auto focus, just switch it to manual without touchig the focusing ring. I do this all the time when getting lightning shots. The camera should focus just fine even at night as long as you put the focus point right over even the smallest, furthest, light as long as its bright.