Yesterday I bought a used 45mm at a very low price (from a shop). The reason for the low price was the condition it is in, the front lens is scratched. No deep scratches, but as if it always has been placed on the lens during its life. Probably the effect of the scratches will show when I use it in bright frontlight. I accepted this, because its price ($250 + swapping unused parts) was the only defendable reason (to my family) to buy this lens, already owning the perfect 55mm. Otherwise the lens looks fine, and undamaged (no fall-marks or strange dents). But at home I discovered another strange phenomenon: focussed at infinity (on the barrel) the image in the viewfinder is unsharp. To get a sharp image at infinity it has to be "turned out" and when the mark is at 1,5 m, the image at infinity gets sharp. To elaborate: the lens appears to be to close to the film. Does anyone has a clue about the cause? Again, the lens looks mechanically allright, compared to the general appearance with the pictures I have of this lens, I see no difference. I have a 3 months warrantee, and can bring it back without a problem, but I would like to keep it. It is usable when I want to accept that I have to focus "on sight" all the time and not be able to use DOF settings, as I am used to do with wide-angle lenses. Who can give a possible explanation? Should I keep it? (I donB4t have any results on film yet). BTW what is the function of the spring-steel ring, attached with to screws at the back of this lens? Filters? Peter

-- Peter Gooijer (rockrose@freeler.nl), October 28, 2000

Answers

The black spring-like sheet metal piece at the back of the lens is for gelatin filters. If you had a filter in place, that would be one reason for a changed focus. What I think is going on in your case is that you have a lens element that has moved. The lens has probably been dropped. If you want to keep it, you might consider using the thin extension tube.

-- Steve Rasmussen (srasmuss@flash.net), October 28, 2000.

You are right, Steve. It was an example of wishfull thinking, maybe I hoped someone would say all 45mm lenses are like this. But ofcourse before reading any answers I already knew there was something wrong optically. So I took a deep breath, a bright light, some little screwdrivers and... yes, I removed the black backplate. The back element was easy to remove. It consists of two rings screwed together, and behold, the most rear element was atached crooked, so it didnB4t reach the end of the thread. I screwed it back on in the right way, and hoorah!! now it is focussing ok. DONB4T DO SOMETHING LIKE THIS, IT IS BAD FOR YOUR HEART!! I visited www.pentax.de (all lenses with cross-sections) and there I found the function of the ring.

-- Peter Gooijer (rockrose@gironet.nl), October 29, 2000.