Richard's use of the helix from the Olympus lens as shown in the 65mm 6x9 image is similar to mine.
Hmm I have a couple broken canon fd lenses sitting around.. what considerations are there in choosing a donor candidate for a helical?
Sorry no pics of during construction. I think the only bit that may have been of interest is in fiddling around trying to turn a standard 35mm lens into a usable focusing device for a completely different lens. I found it an attractive idea, although it required a fair bit of re-working, especially in forming a slot and maling a new slider for that slot that gave no play when focusing, and was tough enough to hold up with all the shutter cocking etc. I also found keeping the film and lens planes the same quite a challenge.
Also, I lost the slots which prevent it from turning hence my pin arrangement.
Yours looks neater than mine. Which lens did you use?
When I was looking for a suitable donor lens, the only one which looked like it would work.
Actually, my bigger Bronica ETRS lenses would have worked very well but I'm not sacrificing one of those!
It really needs to be a prime lens otherwise the zoom mechanism complicates things.
The diameter of the bore in the inner helix needs to be wide enough to take the rear elements of the lens you are using too.
Lenses such as my Schneider Super Angulon 65mm have quite large rear element assemblies. Almost as big as the front.
You also need to be able to mount a small circular lens board to the front of the helix. In that respect, my Minolta lens seems to have been designged for that very purpose!
Or you can spend £240 for the proper Schneider focusing mount.
Even though the 65sa is small, the 47sa is even smaller, and although olympus lenses are also small, there is about 2mm all round between the back element cluster and the helical inner. I did have doubts as to whether this would be a problem. I used 50mm 1.8 standard lenses, and if yours is anything like mine it needs the slot moving internally so it can be light tight. Incidentally to seal up the old slot in the helical I used some sticky back thick felt like stuff (b+q) that is supposed to prevent door handles banging against a wall or something. It is thicker than the thread is deep, so the felt lies jammed in the old slot, and takes on the profile of the thread, and is totally trustworthy even when the lens is fully extended. This was the only way I could figure out how to fill in the slot and make the helical and the old slot light tight.
I found mounting the new lens onto the helical required making new 'boards' - no probs if there are old ones kicking around.
Schneider have flange to film distances on their web site.
Richard. I have just bought an Olympus 50mm f1.8 lens on ebay for £2.75 so I will be trying the same conversion as you have done.
This lens has a faulty aperture mechanism so I'm not going to feel guilty about destroying a perfectly good lens.
I will wait until I get the lens and take it apart but if you don't mind, I may have some questions regarding the way you modified it - especially making a new slot.
My Minolta conversion needs an external pin and slider bracket assembly to prevent it from turning so your Olympus method would look neater.
I must admit making a new slot and the slider were the hardest parts especially as the slider with the lens cant be used. I had a 2 inch square of alluminium about 2mm thick that I knew to be dead square all round, and I cut 2 triangular pieces off 2 of the square corners. I forget the size, but they are about 3/4 inch high, 1/2 inch at the base, and the point at the top flattened off. These triangles happily sit on a machined ledge within the bore, and if memory serves me well, I put them in place inside, opposite where the lens slider is. What I suggest is you do a lot of staring at the components! (I did loads) because I found I had to completely ditch any metal on the moving helical that wasnt going to be used, because I reversed it, to give a square 'platform' to mount a lens panel onto. Also having 4 or 5 (cant remember) starts on the thread wont help either.
As for securing these triangles in the bore I used good old epoxy, and because I was essentially fastening something flat to a round, it meant epoxy could go round the back, and both triangles could be well and trully stuck in place. As a guide to the distance apart these triangles are, I decided to copy the olympus gap. If they are square and placed well they should end up giving a very decent slot for a slider, and for the slider I cut up some brass (off a picture frame plate) that was about 1.5mm thick, bent it to 90 degrees and filed away till the long part had a 'neck' with a wider bottom - very much like the one from the oly lens. The hardest part was to get it to 'slot width' at the bottom, without it having any play. This little slider was screwed into the holes left by the oly slider.
I have to say working it all out nearly drove me mad, but so far both focusing mounts are behaving well, and I have real faith in epoxy, as I cant see how any screws etc could have been used. Also near the end of all this I found there is a seperate threaded part to the lens (under the rubber ring) that made getting infinity dead easy.
I think whatever lens you use you are in for some fun!
Thanks for the explanation. Hopefully the lens will turn up tomorrow then I can take it apart and play with it for a day or two (and stare at it a lot!) before deciding what to do.
Was a square platform mounting area the only reason for reversing the helical?
If I kept the helical the correct way round and machined a flat surface to mount a lens board/disc to, would the existing slide still work or would it be in the way of the rear elements?
I know I could wait and answer these questions myself but I'm impatient!
I think you will find the slide is on the outside of the assembly, and as the slot runs through to the inside, it is open to the light so to speak. I pondered for ages trying to work out how to keep the slider as is, but realised it couldnt be made light tight, so inside it went, with the old slot being filled in with the felty stuff (its good) Also this move meant I could reverse the helical because the back had a better area to mount a lens plate onto, and it makes no difference. Its only the inner moving part that is reversed, the lens outer parts are the right way round because they offer 3 screw holes to fasten the whole thing onto the camera. I maybe cant make this too clear! (its hard with words and no pics) but the only part I chopped up was the inner moving helical, and as you will see apart from a few gaps to fill and make light tight the outer part with the focus ring needs little work apart from the new slot thingy. I'd be interested if you come up with a different solution to what is a pain in the arse to figure out!
I think you will run into similar problems as I had, with the slot/light tight issue, and the only way I could work round this was to put the slot in the dark, inside, with a reversed inner moving helical, and as I said it all works a treat.
Steve, the only thing in doubt here is wether your 65sa will fit the 'hole', as I mentioned the 47sa is smaller, and the 65 angulon posed no probs at all. If you have access to some metal removing machinery you may be in a good position. I only have a Dremmel.