Pacific Black Duck by RobGeraghty, on Flickr

[RobG]

Rob, focus breathing occurs with some lenses when focusing at closer distances where the effective focus length of the lens is reduced. I don't fully understand the mechanics of it, but my DA*60-250 when zoomed to 250mm has about the same field of view as a 135-140mm lens when focused on an object within the first 20 - 25 feet. With the teleconverter on, it increases somewhat, but it is still not even close to what the field of view should be from a 250mm lens. I have a Sigma 70-200mm lens that when zoomed to 200mm and focused an object 20 feet away, the object will appear significantly larger than my 60-250 zoomed to 250mm. This has no effect on IQ or ability to focus whatsoever. The 60-250 has had several posts about this on PF, but I have not seen anything posted about the 150-450 lens. An interesting test would be if you took your 55-300, your 150-450, and your 300, set the zooms to 300mm and take photos from each of them at an object at different distances from 10 feet - 30 feet. If the zooms have wider fields of view than the 300mm, then they have some degree of focus breathing (I assume that a fixed focal length lens is not subject to focus breathing, although I am not sure). I have to say that I was disappointed with my 60-250 when I found this out since I take a lot of photos with it within fairly short distances.

OK, most of my use of the long end of telephoto or zoom lenses is at longer distances, so I don't think I've had any circumstances where this is a concern. You might want to check this article;

I never heard of Focus Breathing (Shift) before - Not a Pentax consideration?: Pentax SLR Talk Forum: Digital Photography Review

[ToddK]

Thanks for the link Rob.