Minolta 58/1.2 AF Conversion with ROM Chip - Build Log

Started Apr 1, 2008 | Discussions thread
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shaocaholica Contributing Member • Posts: 865
Minolta 58/1.2 AF Conversion with ROM Chip - Build Log

Well, I've waited way too long to do this write up but I've found a few spare minutes tonight and I've already got the pictures "processed" so I might as well. Before, I begin I would like to thank these members from Dyxum forums:

Hotwire - For bugging me about f/1.2s for the past year
Pete Ganzel - For doing all the initial research and offering his services

JamesLaoT - For supplying a ROM Chip small enough to fit in the limited space on the f/1.2
Arkku - For his initial work on the same lens

So a few months back I decided to get a f/1.2 and convert it to AF mount. Little did I know I would eventually end up with 5 of the things (one busted) and end up converting the remaining 4. Since then I've sold one at cost to Hotwire who followed this project with me from day -1. I've got another one on ebay:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=130207528822

to raise some funds for my impending wedding. Sorry for the blatant plug

Now I have just 2 left, a 50/1.2 (latest style) and a 58/1.2 (all metal). These I plan on keeping since they produce slightly different images.

Here are the 5 lenses I started this project with:

I managed to get these all at bargain prices just due to dumb luck I guess since every time I checked ebay or craigslist, a new one would pop up for a ridiculous price. Once I got 5 I stopped as it was getting out of hand. However, I did have to swap some parts around since some of them were damaged but in the end I ended up with 4 good lenses.

Here are some shots of the 58/1.2 MC Rokkor Rubber Ring Version after the modification

The aperture blades show some wear from rubbing against each other but it doesn't seem to affect anything.

This is an aftermarket square hood I got from fotodiox.com
http://www.fotodiox.com/shop/product_info.php?cPath=1_17_41&products_id=4118
It fits very nicely and is quite thicker than it looks. Really robust.

The chip installed actually reports an aperture of f/1.1 and a focal length of 60mm. While these figures are not exact, they were the only options from JamesLaoT and all the combined research into reverse engineering the lens ID codes. f/1.2 and 60mm are probably impossible and my guess is that Minolta never really intended or guessed they would need those exact figures for its AF lenses back in 1985.

Here it is on the Minolta 7 film where it works the same way.

Here are some quick sample photos

Here is the full sample gallery of various quick snaps I've taken with both the 50/1.2 and 58/1.2:
http://shaozhang.smugmug.com/gallery/4598419_HkpWc

After I got all the lenses, I opened them up and cleaned out all the accumulated dirt, sand and dust. I also removed all the old grease and applied fresh synthetic Nyogel grease. I then swapped some parts around so that all the worst parts ended up on one bum lens making the best use of all the best parts amongst the 4 other lenses. I let Pete keep the bum lens. I figure if anyone can use those optics it would be him. I then sent them off to Pete Ganzel so he could machine 4 matching mounts for them all with the proper registration distance without using any shims. While they were at Pete's, I also ordered 4 ROM chips from JamesLaoT on this forum. Once I got the chips and lenses back, I attached the ROM chips to the mounts which you can read more about in the gallery linked below:

Here is a full photo gallery of the build for the above lens:
http://shaozhang.smugmug.com/gallery/4630693_jPsbU

My Sony A700 has a Katzeye split image screen installed
http://www.katzeyeoptics.com/item--Sony-A700-Focusing-Screen--prod_A700.html

which helps in using this lens tremendously. However, with the chip installed, focus confirmation works as well although I find the split image screen is much faster to use and much more accurate.

The main benefit of the chip for me is the enabling of SSS on Sony DSLRs. On my A700, I now have a f/1.2 lens I can also use SSS with. This is an awesome low light combination that no other system has right now. Sure the Canonites have their 50/1.2L but that lens isn't IS and they don't have in body IS either.

Here are some related links:
http://www.pbase.com/pganzel/modification_of__58mm_f12_rokkor
http://www.dyxum.com/dforum/forum_posts.asp?TID=27049
http://www.dyxum.com/dforum/forum_posts.asp?TID=19601
http://www.dyxum.com/dforum/forum_posts.asp?TID=21894

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