I'm looking for data on the optimum f-stops for best sharpness for the 75mm and 105mm lenses, so if I don't need to stop down excessively for DOF or set the shutter speed to avoid shake, I can at least optimize for sharpness. Anyone done any testing?

-- Mark Brown (mark@enri.go.jp), March 29, 2000

Answers

I haven't done any test charts for the 75 or 105 like I've done for the 300 and 600. I've used the 75 and 105 for 12 years now and can give you a subjective opinion. The 75 is by far the sharpest of the two. It has a huge sweet spot; f/22 to f/5.6. I would say that f/11 is its sharpest but be aware that this lens does not vary much in performance with aperture. The 105 is known to vary in performance from one lens to the next, with some claiming the lens is junk at most apertures. Mine is the Takumar and can say that it is a sharp lens. The sweet spot for mine is from f/16 to f/5.6. Its sharpest stop, I would say is f/11. The 105 has a nine blade diaphragm while the 75 has an eight blade. Compare with Hassy. BTW, the 45 and 150mm are very sharp wide open. SR

-- Steve Rasmussen (srasmuss@flash.net), March 29, 2000.

I have seen official and unofficial test results for both lenses. The 75 is the clearly the better of the two lenses, and both lenses are of excellent quality. I believe the 75mm is the only lens in the Pentax line to receive an "EXC" rating at every aperature, center and corners, by Modern Photography. Also, the 75mm was listed as "10" lens in Japanese trade magazines (the only other P67 lens to receive this mark was the revamped 55mm f4). The 75mm is in some ways the most overlooked lens in the line; it is very, very sharp, and one of the cheapest lenses on the used market. You really can't go wrong with this lens. The only way to improve it would have been to get it down to 77 or 67mm filters, or to drop it down to a 2.8 lens - but both options might be either impossible or just too costly.

-- Miles Stoddard (p67shooter@yahoo.co.uk), September 04, 2001.