The problem comes when using these lenses wide open, as the original poster is interested in doing. Very few SLR lenses are sharp across the entire image area at wide apertures, and light falloff can sometimes be quite noticeable. What's the sense of paying for fast glass if the first couple of apertures don't yield good results. Of course, if one's only interested in the center portion of the frame, one may argue that the results are acceptable.
For example, there's a very thorough test of the A28/2.0 by Joachim Hein http://phred.org/pentax/lensgal/a28_2/a28_2.html and the quality of the images are clearly inferior until f5.6 is reached. Some of Fred Wasti's tests confirm the generalization re: light falloff and sharpness of even some "legendary lenses" from Pentax. I've seen similar results from Zeiss, Tokina, Nikon, and Zuiko glass. If your objective is just to capture an image in low light, all these lenses will work, and will get you through times of darkness better than slower lenses. But, if the objective is to capture a high quality image, then these lenses may well be dismal failures at wider apertures. All lenses, even Leica lenses, suffer from lower quality at wide apertures, but recent Leica glass suffers less than any SLR lenses I've come across. This means that, although expensive, you actually get more of what you're paying for, as the lenses are more useable when used wide open. Of course, there are some dogs in the Leica kennel as well <g>. "Paul F. Stregevsky" wrote: > > No doubt, Pentax's fast glass is often out of reach to someone on a budget. > My advice is to seriously consider Konica. They made an outstanding 85/1.8 > and various fine, fast wide angles that can be had for a fraction of the > Pentax price. Ditto for third-party lenses in Konica mount, such as the > outstanding Vivitar Series 1 135/2.3. > > You can also get a Pentax SLR and equip it with sharp third-party lenses. > All the 90mm macros are very sharp, though admittedly the fastest is no > faster than f/2.5. There are no readily available third-party K-mount > 35/2s; Vivitar made a fine 35/1.9 but I've seen only one specimen in K > mount in four years. At f/2, the sharpest Pentax 35/2 is probably the FA > (autofocus), followed by the original, scarce K (SMC). Each goes for about > $200 to $250 used. > > For a fast 28 for less than $150, go for the Vivitar 28/2 Close Focus (55mm > filter). > > However, as Shel recently pointed out, the drawback to using third-party > lenses is that they yield different color casts, their flare resistance is > usually not up to Pentax's gold standard, and they sometime focus the > "wrong way." -- Shel Belinkoff mailto:[EMAIL PROTECTED] http://home.earthlink.net/~belinkoff/ - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
