Hi, I have finally did a small test of several filters on my CZJ 2.8/20 and found out, that due to extremely bulging front element, there can be problems with some brands of filters screwed on which touch/rub the front element.
Tested with cigarette paper, as it is the thinnest stuff I can find. Results: Pentax SMC L39 (UV) filter: !!! touches, quite a lot! The glass on this filter is very recessed. I stopped using it on the lens, even though the SMC is excellent on it. Hoya HMC SKY filter: safe noname yellow fitler, in silver rim: touches... but less than Pentax one BW polariser - safe (but vignettes quite some) ... Some of you may say, why use filters at all? Simply - damaging a 200-300 E lens is much much worse than damaging one 20 Euros filter... and I shoot a lot in rough environment. If you have other filters, please try them on, with the cig. paper and looking for obvious change of opacity of it. We could make a list of dangerous filters! And finally, although I have been using the Pentax UV filter (the dangerous one) on the lens for a long time, crewing and unscrewing it when using B&W/POL filters, there has been no damage to the glass nor coating, there were some marks which easily cleaned off with lens cleaning cloth. So even if you use a "dangerous" filter, it may not be a big issue. OTOH, it may :) Good light, Frantisek Vlcek - 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 .
