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First Light - I've just completed my first MD>MA conversi
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PostPosted: Wed Oct 28, 2009 11:39 pm    Post subject: First Light - I've just completed my first MD>MA conversi Reply with quote
It seemed to take forever, but I have finally converted my ROKKOR-PF 58mm f1.4 to MA mount.
I was encouraged by Arrku's flickr page (thanks Arrku!), but had to use a slightly different technique as the 1.4 contruction is different to the 1.2.
Here is my first daylight picture (taken at f9):

Here is a 100% corner crop:

Modifying the lends was certainly not for the faint of heart! At one point the barrel completely seperated from the housing and I had to just assemble and re-assemble the bits until I got it together correctly. Sadly, my final technique for the conversion was not reversable.
Having said that, I think it has correct infinnity focus (I worked out how to adjust the internal housing so that I did not need shims) and now I have a much better appreciation for lens construction!
For anyone thinking about doing this - it took me 5 nights of trial and error to rebuild the mount.


PostPosted: Sat Oct 31, 2009 1:02 am    Post subject: Reply with quote
Beautiful. I did my 50 1.4 MC to MA too and like you, took me a few night's work. Could have done it in an hour or so with the proper lathe machine but I did mine with just screw drivers, a small drill, vernier caliper and file. But I think my copy may be bad. Can you take some shots at 1.4 with brighter sunlight (at higher speed) and send to my e-mail vyywong@gmail.com? I could send you some of mine too. I will post one here at 1.4.



PostPosted: Sat Oct 31, 2009 2:47 am    Post subject: Reply with quote
Hi, I'm glad you found my Rokkor conversion page helpful. Since I get asked this quite frequently, can you describe how the f/1.4 differs from the f/1.2 with regard to conversion, e.g. what makes it irreversible?


PostPosted: Sat Oct 31, 2009 7:29 am    Post subject: Reply with quote
Hi Arkku,
For my conversion I removed the internal silver spacer ring, rotated the collar and reassembled - that's it (short version).
Now the long version...
I took off the mount and spring and bearings shot out - warning to anyone who want to preserve the original mount Sad
The next problem was the straight "pole" that contracts the diaphragm from the back of the lens. The pole was too close to the edge, so that when I placed the M42 convertor on top it touched. I tried to screw it off it with pliers but it did not come undone (although it did rotate).
To get access to bottom of the pole, I would have to take off the diaphragm lever, I know too well that touching that level *always* ends in tragedy, so I cut a notch in the pole with a hack saw (yes, I sawed my lens) and then bent it towards the centre at the cut.
I had a lot of difficulty reassembling the lens because I did not understand there was a rotation stop that meant you had to have the aluminium collar and the focusing barrel lined before screwing down the internal mount base.
Another problem I had was that I accidentally undid the barrel completely from the housing and it was quite hard to get threaded again. It doesn’t sound like a big deal, but that was my biggest problem. I suspected I could easily damage the threads so I was very careful to rethread. (ugg - I probably unscrewed the barrel 3 times by accident!)
Another problem was losing the small metal bearing that provides the click stops for the diagram. I ended up cutting the nib off a cheap 10 cent ball point pen and used that. The bearing is a little bit smaller than the original, but it has a more silky feel now - so I am pretty happy with that.
Interestingly, when the inner aluminium collar is fully extended, the focusing mechanism does not work when the inner base is screwed down. Trial and error solved this issue.
I don’t believe you can assemble the lens any other way but to remove the inner metal ring and cut the pole and maintain infinity focus. I still have to do a star test to confirm everything is perfect, but I am pretty happy with the result.


PostPosted: Sat Oct 31, 2009 12:48 pm    Post subject: Reply with quote
Arkku wrote:
Hi, I'm glad you found my Rokkor conversion page helpful. Since I get asked this quite frequently, can you describe how the f/1.4 differs from the f/1.2 with regard to conversion, e.g. what makes it irreversible?


Quote: "Here is the completed Minolta 58mm f/1.2 modification mounted on my Sony A100 DSLR. Originally the lens is for the Minolta MC mount, which can not adapted to the Minolta AF mount "passively", i.e. any adapter would need to have optical elements to maintain infinity focus (at the expense of image quality)."

But there is only 1mm difference between MC/MD and MA (The MA mount has a registration distance 1mm greater) so I would have thought that such a small difference should be simple to compensate for by simply adjusting the helicoid focus stops?


PostPosted: Sat Oct 31, 2009 1:36 pm    Post subject: Reply with quote
DSG, I agree with you that it *should not* be too hard - but wow, I find it pretty stressful!
here is my star test- Nice purple Star (not!)- This was 2 seconds at f1.4.

(No retouching)
None of the smaller stars were visible to my naked eye.


PostPosted: Sat Oct 31, 2009 6:17 pm    Post subject: Reply with quote
DSG wrote:

But there is only 1mm difference between MC/MD and MA (The MA mount has a registration distance 1mm greater) so I would have thought that such a small difference should be simple to compensate for by simply adjusting the helicoid focus stops?


It is, that's exactly what's done in the guide after the mount has been replaced. If you mean that one should be able to use an adapter on top of the original mount and then adjust focus on the lens, it's not possible because the minimum thickness I've seen for MC to MA adapter is about 7mm—the MC bayonet does not fit inside the MA mount. It's not at all like an M42 adapter.


PostPosted: Sat Oct 31, 2009 7:53 pm    Post subject: Reply with quote
I have a 50mm 1.7 md that I would like to convert, but the mount section holds the diaphragm ring. The only way to convert this would be to cut the mount section in half horizontally-I guess.


PostPosted: Sat Oct 31, 2009 10:19 pm    Post subject: Reply with quote
Arkku wrote:
Hi, I'm glad you found my Rokkor conversion page helpful. Since I get asked this quite frequently, can you describe how the f/1.4 differs from the f/1.2 with regard to conversion, e.g. what makes it irreversible?

Ohh, Arkku I forgot an important point, I had to reverse the location of the diaphragm guide. Originally it was screwed to the top of the fstop ring - I had to unscrew it and mount it to the bottom of the ring (in the same holes) as the guide came off the rail at the closest focus setting.
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