I have a Mamiya/Sekor 55mm F1.4 lens, an early version with chrome tip and chrome f stop rings. The aperture blades were sticky so I took it apart (carefully I thought). I cleaned and solved the sticky aperture but now I find it impossible to get the focus threads (helix) re-aligned in the correct spot! I tried several ways but to no avail. No apparent index mark (?). I'm perplexed. Any one have experience with this problem? The lens is otherwise easy to take apart and put back together. I know, I did it at least 12 times! Almost had it right but then the main aperture pin popped out of its alignment when I focused it back and forth. I also noted it would not focus at infinity after these attempts to get it right. I need help. Thank You!!!

-- Gary A. Turner (turnergande@earthlink.net), August 27, 2002

Answers

Hi Gary,

Well I've never done one of these lenses specifically but I'm trying to gently teach myself camera repair so I'll share what little I know.

Basically you should try to avoid ever taking the focussing helicoid apart if possible (which I suspect you now know), but if you must do so (to clean the threads and regrease them for example), IT IS ESSENTIAL that you mark the position at which the threads finally disengage, if you are not to avoid hours of boring trial and error work. Using a chinagraph (wax) coloured pencil is a good idea, as the mark is very clear but can be rubbed off afterwards. It is also important to note where the focus was set as the lens comes apart, because frequently the helical threads are on a ring which itself can rotate within the barrel, unless held with grubscrews of some type (check that these are tight as you put the lens back together).

In addition, the lens barrel may have a lug of some sort on its inside which has to engage with a slot on the element group, in order to stop the group rotating during focus. Frequently the lug will only engage or disengage from the slot with the focussing ring on the lens barrel in a certain position before you engage the helical threads (infinity or minimum focus for example). Without this lug engagement the lens will not focus properly.

Also watch whether you've put the lens elements in the right way round if youve taken them out for cleaning. I once had to rebuild a lens five times before I got this right!! Again mark with a wax pencil or a spirit marker that can be wiped off.

Now in terms if getting the damn thing back together, the key thing is to try and work methodically, taking notes as you go (it really is boring, but very satisfying once it works).

The most important thing is to really examine how the whole focussing mechanism is constructed, and which things rotate and which don't. Use of a digital camera can be very helpful, believe me!

Setting the focussing ring to say minimum focus (or maximumum, as you please), make a note on the barrel of where you think the element group should end up when you've interted it (has it got marks which correspond with the focussing ring?) Try and work out how much of a turn the helical threads provide as they bite and then, work backwards from this to a theoretical starting position for the barrel and element group.

Now marking the position at each attempt on the barrel, go round the whole lens helical threads one at a time until the element group is in the right position when fully inserted. Check the inside for lugs or similar (see above), and make sure that the various linkages all work properly.

If you find that the whole structure doesn't work, then remove the element group, after marking the biting position, and set the focussing mount to the other extreme. Now repeat.

Obviously the more 'starts' the helical mount has on it, the harder it is. 6 or 7 starts are common, but I have heard of 12 starts !!!

Anyway, I hope this makes some kind of sense and is useful, any problems please come back to me.

Regards,

Luke

-- Luke Albanese (luke.albanese@dol.ie), September 14, 2002.