This answer to an earlier question of mine about manual focus lenses uses the term "focus throw". Exactly what does that mean? Why do manual focus lenses have more of it than auto focus lenses?

up vote 16 down vote accepted

The focus throw is simply how much you have to turn the focus ring when focusing, what's usually compared is how much you have to turn to get from closest focusing distance to infinity (or vice versa).

A manual lens generally have a longer focus throw, to enable you to do fine focus adjustments, while an auto-focus lens has a shorter focus throw so that it can focus faster.

  • Hope you don't mind my edit. – Karel Sep 8 '10 at 13:14
  • @Karel: No, you are so correct. :) – Guffa Sep 8 '10 at 13:26
  • Is it in fact from closest to infinity, or is it defined as rotation required to change focus a set amount? With the former definition, lenses that focus closer and have longer total rotation could have less fine-tuned precision than one that does not focus as close. Is there not a metric specifically for the latter? – Eruditass Sep 8 '10 at 13:52
  • @Eruditass: Yes, you are right that you can't make an exact comparsion across all lenses. Consider also that the focusing rings can have different diameters, so there is a difference between measuring turning angle and measuring distance along the diameter. :) – Guffa Sep 8 '10 at 13:58

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