Originally posted by barbosas I can vouch for the M28/3.5, i consider it a little more sharper then the M28/2.8 i had, and more contrasty.
I have owned the K28/3.5 for many years, as well as the M28/2.8 version 1 for a few - I can't help with the others. The K version has more contrast and I think it is sharper. This discussion is academic, though, since both are great lenses (better than I can make them, anyway) and either would serve you very well.
If you really want the best 28 but money is an issue you might consider buying an M now, with a plan to upgrade to your top choice later. Consider any loss on the M lens (if it happens) as rental cost.
J Colwell's SPLOSdb (
SMC
Pentax
Lenses and
Other
Stuff
database) price and quality survey of 2004 rates the K28/3.5 and the M28/2 among the best Pentax lenses ever made. The M28/2.8 has an average rating and the A is very good. Although the prices are now stale, this is a great resource for Pentax lenses info and those of other makers for both M42 and K mounts, plus some accessories and LX information.
http://www.jcolwell.ca/_SPLOSdb/SPLOSdb.pdf
Price and availability are an issue.
Availability: The K lens is available in spurts on auction sites, but then not at all for weeks at a time; KEH will have one once in a while, then not for many weeks. The M is almost ubiquitous on auction sites and there are normally 2 or 3 for sale at KEH. The A 28 is about the same as the K - not easy to find at will.
Price: The K runs around $189 in KEH EXC condition; the M can be had for around $70 here and at auction, and around $110 at KEH in EXC condition. Add around 35% to that for the "A" version due to demand from digital users who want meter coupling without using the Green button. All seem to have been quite steady for several months - maybe the M is coming down into the 60's for a EXC rated item.
Caps: If you like your Pentax lenses to have authentic caps, don't forget the M front and back caps and the slightly different A caps (the rear cap has a lip to cover the electrical contacts) are about $10 value combined. The K version had an all-black, 52mm front cap - those are harder to find except at KEH, and are priced accordingly. Look for lenses that have the correct caps if you are fastidious (as am I) about your gear.
I've never scanned any of my film images from the manual lenses - only had a digital Pentax for a few months, but I've planned to get out tomorrow morning (weather permitting) and do some manual shooting in an architectural artwork park (rusty steel sculpture stuff) near me. If it works out I'll post some comparison images with my two 28's.