Originally posted by jddwoods Thank you, this is very much appreciated and useful information. I never found the focus breathing to be an issue at all. When I have the lens zoomed all the way out at 300 mm, I am shooting birds at a distance and almost always at infinity focus. Less than 300 mm, I just zoom to the point I want and don't mind what the focal length is.
I suspect your usage and mine would be fairly typical with xx-300 lenses. I guess someone will tell us if we are missing something.
I can only think of one situation that I might encounter in practice where it would (theoretically) be worth me taking off the PLM and using the screw-driven version instead. That would be one the @mikesbike referred to: where I could use the DA-L at 135-190mm to gain two-thirds of a stop advantage in aperture (f4.5 v f5.6) for the same FOV (which might, if the subject is quite close, mean the FOV for the PLM in the low 200s). (Let's put aside the fact that in using the DA-L I'd give up QS, WR and HD coatings - the screw-driven WR version would have all those.) An example would be indoor sport, or action photography of some other kind, or low-light wildlife close by, where the faster aperture could really matter - for example by pushing up the shutter speed, or lowering the ISO, by the equivalent of two-thirds of a stop. The camera's AF system might also be able to focus better at f4.5 than at f5.6, although of course I would have slower and noisier AF. (I haven't done any comparison to see whether the IQ would be as good.) The importance of this might depend on which body was being used.