Can anyone tell me if it is possible to mount a large format lens that is in a helical focus mount on the Pentax 67?If Alpa does this with their 12SW camera why wouldn`t it be possible with the Pentax?

-- Mike Sellers (msellers1@email.msn.com), December 17, 2000

Answers

Not sure if what you ask is possible. If I were to consider using LF lenses on the P67, I would buy a used Auto Bellows and replace the front lens mount with a 4x5 lens board. Focusing would be via the rail. SR

-- Steve Rasmussen (srasmuss@flash.net), January 02, 2001.

Its certainly possible but depends on focal length and infinity focus requirements. Plus you need a mount converter of some sort. Is it really worth it? How many lenses do you have? I have described the restrictions for focal length elsewhere but in case you didn't see it here goes. I'm assuming you require infinity focus as any LF lens with helicals is bound to be a wide angle used for landscapes. The minimum focal length of the lens you wish to convert is restricted by the distance between the film plane and whatever mount the lens has. In order to achieve infinity focus this distance must at least equal the focal length of the lens. Now consider that for the P67 the film to lens mount distance is already 89mm or so. So this alone would restrict the min focal length to 89mm. However you still need some type of lens mount adapter which adds to this distance. Also depending on lens design the "built in helicals" may be at the back of the lens and also contribute to this distance. So probably only lenses >120mm could be converted. On the other end the amount of helical extension you get will affect magnification. For 1:1 magnification you need the lens to be twice the focal length from the film plane. The helicals will give nowhere near this kind of extension but at least you can use extension tubes. Remember how you need wide angle bellows for wide angle lenses in LF, and the wide angle restriction is how much you can squeeze the bellows? Well think of the P67 body plus mount adapter as a fixed bellows which cannot be squeezed and hence restrict wide angles. Heck just buy an LF camera.

-- M.B. (mbarroca@americasm01.nt.com), January 02, 2001.