Minolta 58/1.2 AF Conversion with ROM Chip - Build

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:



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 to raise some funds for my impending wedding. 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's 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. It fits very nicely and is quite thicker than it looks. Really robust.





The chip installed actually reports a focal length of 60mm. Depending on which EV step you have selected, the camera will either show f/1.2(0.5EV step) or f/1.1(0.3EV step).











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



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



My Sony A700 has a Katzeye split image screen installed 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:

Pete's f/1.2 Mount Conversion thread

My previous f/1.2 thread

Arkku's 58/1.2 build thread

JamesLaoT's M42/ROM Chip sales thread



If you have any further questions about the lens and how it works, check out the massive FAQ I wrote on the ebay page for one of them.

Edited by Shaocaholica - 23 April 2012 at 20:24

Incredible work. I really like the A700 with this huge glass, and I think the ROM chip comes from a 85/1.4 lens, it is the smallest chip I have seen

Regards

Thanks for sharing your 1,2/58mm experiences.

Shaocaholica wrote: 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.

At least some camera bodies should support aperture values between "1.0" (0 Av) and either "64" (+12 Av) or "90" (+13 Av) in 1/4 EV, 1/2 EV or 1/3 EV steps according to the following table, which was compiled from various sources:

http://www.mi-fo.de/forum/index.php?showtopic=10426&view=findpost&p=122551

The internal representation is in 1/8 EV steps (binary values in the 5th column in the above-mentioned table).

Apertures displayed in 1/4EV steps (4th column) are only supported by the Minolta 9000 AF with Program Back Super 90 or Bulk Film Magazine EB-90, or by the Minolta 7000 AF with Program Back Super 70. Apertures given in 1/4EV steps follow some odd notation, where the aperture is given in 1 EV granularity (1st column) followed by a suffix 0, 1, 2 or 3 for +0/4EV, +1/4EV, +2/4EV or +3/4EV.

Apertures displayed in 1/3EV (3rd column) are supported by newer models (since the advent of the Dynax 9, IIRC).

The largest aperture value I have seen myself so far was "1.4" (PBS-90: "1.4_1") with my Minolta AF 1,4/50mm (in this case with a binary value of 25, not 24, as one would expect), the slowest aperture was "64" (PBS-90: "45_3") with my Minolta AF 3x-1x Macro Zoom (binary value 111, not 112). The largest value found in the Dynax 9 service manual and the Dynax 7D firmware is "1.0". The slowest value found in the Dynax 9 service manual is "64", in the Dynax 7D firmware it is "90".

Sometimes, aperture values are rounded for display, for example binary value 30 is displayed as "1.7" on the Dynax 9, not "1.8", as it should. The same goes for binary value 46 (shown as "3.5", not "3.6") and 50 (shown as "4.5" instead of "4.3") and 74 (shown as "13" instead of "12"). Since we don't have experiences with values faster than "1.4" yet, it is quite possible, that some of these values would be rounded in an odd fashion as well. This could explain the "1.1" display, assuming that all possible binary values have been tried already.
Still, at least on the Minolta 9000 AF with Program Back Super 90, it should be possible to tell apart apertures of "1.0", "1.1", "1.2" and "1.3". A true "1.2" aperture should be displayed as "1_2" (for 1 + 2/4EV corresponding with binary value 20), whereas a true aperture "1.1" should be displayed as "1_1" (for 1 + 1/4 EV, corresponding with binary value 18) instead.

Greetings,

Matthias

Edited by matthiaspaul - 01 April 2008 at 14:04

Super job on these conversions. The word "craftsmanship comes to mind.

rovhazman on dpreview gets the hero cookie for why f/1.2 worked on my camera.

Set exposure steps to 0.5 ev instead of 0.3 ev for f/1.2 to show up instead of f/1.1 and f/1.3.

I just verified this also works with my maxxum 9.

This post and its predecessor must be setting some records for viewing -- 25 out of 105 on the site when I wrote this were viewing it. The two posts have had a combined hit rate of 3000+ views.

A tribute to the thoroughness of your presentation Shao.

Shaocaholica wrote: Thanks for the explanation Matthias. Do you know why 58mm is also not a useable focal length?

http://www.mi-fo.de/forum/index.php?showtopic=4477&view=findpost&p=50472 [de]

In this posting your can find a table compiling a few values, I recorded when I had a closer examination of the Minolta 9000 AF flash protocol (almost 20 years ago. ;-) The focal length was non-lineary represented by a byte value, not a word or such. I had limited access to lenses in these days, so I recorded only these values:

35mm: 50 (32h)
50mm: 57 (39h)
70mm: 63 (3Fh) oder 64 (40h) with another lens
100mm: 72 (48h)
105mm: 73 (49h)
150mm: 81 (51h) or 82 (52h) with another lens
210mm: 89 (59h)

As you can see, there are at most six possible values between 50mm and 70mm. Focal lengths between 16mm and 600mm just won't fit into a byte value, no matter how hard you push. These were flash protocol values, but as discussed in this posting

http://www.mi-fo.de/forum/index.php?showtopic=14914&view=findpost&p=180793 [de]

we found the lens protocol values to be binary identical.

Still, it is possible, that Minolta has added new ROM data entries with a finer granularity in more recent lenses, I don't know.

Sidenote: The binary values mentioned in my other post are meant to be flash-protocol values, too. The actual ROM values are given in 1/8 EV as well, but are shifted by an offset of 7 (or 8?), as we discussed in the same posting.

I would be interested, what a PBS-90 would display for your converted 1,2/58mm marvel, "1_1" or "1_2"? If you ever get a chance to find out ... ;-)

Greetings,

Matthias

Edited by matthiaspaul - 08 April 2008 at 22:55