I am not bowled over by GM on Amazon's review. For the record, we have a Sigma 120-400 zoom that we use for portable birding (if there is such a thing)
, and it functions very well and is very sharp....
I have also put many F, F*,FA,FA*,DA,and DA* lenses on K-5 and K-3. No issues beyond the lens' individual personalities.
I suggest the following technical remedies for GM...
See an optometrist...
Clean your glasses...
Eat carrots and spinach...
Look at your camera manuals under diopter....
Look through lenses, some may be cruddy inside, from using UW without a housing...
Remove greasy thumbprints from objective lenses and stacked "soft" focusing filters....
Clean objectives after each 50 shots of a barbecue grill cooking lamb...
Get an underwater housing, no actually one for each body with ALL of the attachments....
Buy at least 50 cheap Black & White color filters form each lens, with a complete set for each lens in case you need all bodies ready for inspection...
Prozac, Valium, or equivalent.....
Call your local sanitation department so you can file your review appropriately.......
Sell all of your Equipment, buy second tier Nikon and Canon glass, and repeat your review process many times....
Gee whiz...