For my second lens conversion, I sure picked a difficult one. The cost of this lens is extremely low ($5 or $10), and I was attracted by the possibility of having a nice 45mm pancake lens that is a full stop faster than the typical 45/2.8 pancakes. I figured I couldn't lose, even if I ended up throwing it in the garbage. (I don't think I will, now.)
This is a particularly challenging conversion because essential parts of the aperture mechanism are built onto the under-side of the original mount. Hence, ripping the mount off and replacing it is not a great option.
Instead, I proceeded to take a hack saw and cut everything off right at the base of the mount. I then used a file to even it out as best I could (I still need to find a better way to make it completely uniform).
Here's what the "aperture shim" ends up looking like:
But, alas, I knew I would have an infinity focus issue, because I was unable to reduce this shim enough to gain the .5mm register difference plus the adapter thickness. I needed to get 1mm or so from somewhere else. So, I took the whole lens apart and moved the barrel portion of the focusing helicoid back further.
Not a huge difference, but this combined with an infinity focus adjustment all the way as far as I could go seems to have made a big difference. The only problem with tweaking these two things back this far is that the focus ring also needs to be shaved down so it can sit back further. Here's how much I had to take off (actually, I overshot it a bit and I plan to buy another $5 lens and redo this part. Here it is in its original position to show how much it needs to go back):
I plan to find a way to make the shim completely flat, which should get me perfect infinity (not far to go at all, now) and also it will mitigate the "tilt" lens effect I'm getting (see close shot).
Once I get it all perfectly flat, I'll paint the innards and edges flat black, but leave the mount as it is.
I think I have figured out how to get the "aperture shim" perfectly flat, though. I plan to take the whole lens apart again, and then attach the shim to the lens barrel (leaving the element assembly out) and then basically use the barrel as a handle as I rub the shim back and forth on a piece of sandpaper. I used a similar method with the shim on the Rokkor 58/1.2 and it worked perfectly. I tried to do this with the "aperture shim" alone, but there just isn't enough to hold onto to do a proper job of it (without also sanding my knuckles and/or finger tips/nails).
What you need is a small lathe and some aluminum pie jaws, you can bore them out to the exact outside diameter of your "shim", since the pie jaws are cut in the lathe you will be able to hold a part perfectly flat. Also since you will have full contact on the circumference of the "shim" you can easily take a 80 Deg. tool to face the part. your shim will be parallel/flat and as thin as you need it to be.
You know, so you can fill the lens conversion orders from here....
But on a budget side, you can probably rig something up with a belt sander and a holder that will make sure the part has parallel contact with the belt sander.
Pushing it against the flat surface of the belt sander should get you some okish homegrown flatness, better than manually scratching a file over it at least.
The shim is nearly as thin as it can get already. I'm not sure I would risk using a power tool on it right now. The side profile shot is misleading. That is not the thickness of the whole shim. As you can see on the bottom shot, the aperture mechanism is inset into the bottom of the adapter. The "pegs" that hold the levers and springs are embedded into the thinnest part of the shim. If I go too thin, those pegs will simply fall out and I'll have to start from scratch. Therefore, I will proceed with the manual sanding method I mentioned earlier. Much more control is afforded by this method and it is possible to get very flat results as long as the sandpaper is laid out on a perfectly flat surface and the shim is turned often during the process. This worked extremely well for my 58/1.2 shim. It takes time and effort, but I enjoy it.
No lens conversion orders yet, but I can't say it hasn't occurred to me to convert a bunch of these Minoltas and sell them... the 58/1.2, in particular.
cogitech wrote:
No lens conversion orders yet, but I can't say it hasn't occurred to me to convert a bunch of these Minoltas and sell them... the 58/1.2, in particular.
