DPReview.com is closing April 10th - Find out more

Strange issue: Canon EF 70-200mm f/4 L IS USM acts as 85-250mm. How?

Started 8 months ago | Discussions thread
Sittatunga Veteran Member • Posts: 5,413
Re: focus breathing

Nightly wrote:

Alright. Will try it soon, whenever I get a chance for it.

The relationship between focal length and angle of view only holds good at infinity. A simple mathematical thin 200mm lens focussed to give a ¼ life size image will have to be 250mm from the sensor, and the focussed distance from subject to sensor (the only consistent way you can measure focussed distance with different camera lenses) will be 1250mm. That simple 200mm lens will have the same angle of view at 1250mm focussed distance as a 250mm lens focussed on infinity, so there is considerable focus breathing at that sort of distance with a unit focussing lens.

To avoid focus breathing and to keep the same angle of view as they focus, lenses have to zoom to a shorter focal length when focussing closer.

Post (hide subjects) Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow