cogitech
Offline
Buy and Sell: On
Registered: Apr 20, 2005
Total Posts: 6342
Country: Canada
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 Minolta Rokkor-X 45/2 EOS Conversion | |
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:
back:
front:
side:
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.
Here's what it looks like by default:
I simply turned back till it nearly stopped (this took some friggin' about, to get it just right). Then it looked like:
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):
Then I simply screwed the element assembly
...back into the barrel helicoid as far as I could and stopped where things looked aligned
then re-installed the guide bar (which had to be shaved as well, to allow the helicoid to move back so much further
The final steps are to set the aperture shim in place...
and then install the mount (here I used a NikonF-EOS adapter, because it is so thin):
...and take some test shots:
Wide open:
100%
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.
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