Originally posted by Adam The effect is observable but moderate. The new lens can focus closer than the old one, at the expense of a bit of magnification. It's wider at 55mm and a bit shorter at 300mm.
Here are the values I calculated for actual focal length at MFD:
DA 55-300mm WR
MFD = 1400mm
Max reproduction ratio = .28
Focal length = 1400 mm / (.28 + (1/(.28)) + 2) = 239mm
DA 55-300mm PLM
MFD = 950mm
Max reproduction ratio = .3
Focal length = 950 mm / (.3 + (1/(.3)) + 2) = 169mm
The magnification difference at normal shooting distances for birds would be significant, IMO.
Read more at:
https://www.pentaxforums.com/forums/8-pentax-film-slr-discussion/334511-calcu...#ixzz4R8LB3cI7
---------- Post added 2016-11-26 at 11:48 ----------
Originally posted by Des @Adam, one aspect that would be interesting to check when doing the full review is whether, and if so to what extent, the PLM model is affected by focus breathing. One of the appealing qualities of the screw-drive 55-300 is that the magnification remains the same regardless of distance to subject: that is, 300mm means 300mm whether the subject is near or far. (As I understand it, this is an advantage of it not being an IF lens; and the flipside of having a relatively long MFD.)
I agree that actual focal length should be included in the review, but note that the screw drive DA 55-300mm is an IF lens and does suffer from focus breathing.