Minolta Auto Tele Rokkor PF 100mm F2.0 – History, Disassembly, Cleaning & Impressions

[Velectron]

[SIZE=+2]Minolta Auto Tele Rokkor PF 100mm F2.0 – History, Disassembly, Cleaning and Impressions[/SIZE]


Recently, I have the very good fortune of acquiring a complete set of an extremely rare vintage Minolta Auto Tele Rokkor PF 100mm F2.0 lens. From the patchy sources of information that I found, this lens was introduced on 25[SUP]th[/SUP] Feb 1961 for the Minolta SR series manual cameras. Featuring 6 elements in 5 groups, with 7 aperture blades, this lens weighs 425g and is pretty compact for a fast portrait lens, about the size of your Sony 18-55mm kit lens. This lens was updated in 1966 with an MC tab for the Minolta SRT series. Production of this lens ended in 1968 due to the difficulty and high costs involved in making this lens. Accordingly, there were not many copies of this lens made, contributing to their rarity. The successor to this lens was the Minolta MC Rokkor PF 100mm F2.5, which is another legendary portrait lens. Minolta never made another 100mm F2.0 lens until 1987 where the Minolta AF 100mm F2.0 was introduced, which is a completely different lens to the Rokkor 100mm F2.0.


The Minolta Auto Tele Rokkor PF 100mm F2.0 Package. If you look carefully at the box, you would find that the lens formula description was actually printed wrongly. It should be PF and not FP. I wonder if this printing error actually makes it even more valuable, much like printing errors in stamps and dollar notes. I have never seen another intact box for this lens so I have no idea if this error was widespread or just for a limited number of lenses.

The lens itself. Click-stops are all single stop, no half-stops.

Lens Schematics

A piece of Minolta history

Unfortunately, this wonderful lens has a lot of oil gumming up the aperture blades when I got it. The aperture control ring was unable to open and close the lens diaphragm properly.

 

[Velectron]

Well, I can’t just let this wonderful lens sit down there, unable to be used, right? What you are going to see next is probably the first photo-documented disassembly instructions in the world for this rare lens (and I am not kidding!)

First of all, set the lens to infinity and then loosen the 3 set screws holding the silver ring to the mount of the lens. After the screws are loosened, the silver ring could then be lifted up.

Next, turn the aperture ring to F2.8. This would expose the 4 screws that holds the lens mount. Remove the 4 screws.

There are another 3 small black screws below the aperture ring that needs to be removed

Once the 3 small screws are removed, the lens mount could now be lifted up.

You will see a silver ring with 8 small holes inside the lens. Four are through-holes and the rest are threaded (for the 4 screws securing the lens mount). Be careful not to turn this ring as this ring is used to adjust the infinity focus. Turning the focusing ring at this point in time would also cause this ring to turn, so it is best to immobilize the focusing ring and this silver with tape. I made the mistake of shifting this ring and it costs me a whole afternoon and one night to figure out and adjust back the infinity focus. Turning this ring would actually change the depth that the lens mount part would sit into the lens, much like the function of metal shims often found below the mount of AF lenses. This is the first time I encountered this kind of mechanism for adjusting infinity focus. The other MC/MD lenses I came across use a different mechanism to adjust focus.

 

[Velectron]

The rear glass elements are next unscrewed to provide access to the aperture blades.

With the rear elements removed, there is now a “pothole” to access and clean the aperture blades. By right, it would be best to remove the whole aperture assembly for cleaning, but that would require further disassembly of the front lens group. My belief in lens servicing is that the lens elements should be disturbed as little as possible so I opted not to disassemble further. Anyway, this pothole is sufficient enough for me to clean the blades using alcohol and some cotton swabs. Interestingly, the aperture blades of this lens are made from some smooth uncoated grey metal, not the usual black-coated (or anodized) blades seen on the MC/MD lenses.

An afternoon and now the lens is good to go! Mounted on the Minolta XD-11, it does really look beautiful and impressive.

 

[Velectron]

So how does this lens perform? Well, I haven’t use it a lot yet but initial impression is that it is reasonably sharp wide open, with a very shallow DOF and very smooth bokeh blur. Some others who had this lens described it as a “Bokeh Monster” with a bokeh similar to the legendary Minolta MC Rokkor PG 58mm F1.2. The lens is supposedly ideal for black & white photography.

Since I do not own a NEX or other mirrorless cameras yet, I can’t use it to its full potential. The MC-MA adapter with glass I had is pretty crap with only a central 5-10% that is sharp when the lens is used wide open. I removed the glass from the adapter and thus could only use it for close-up shots. Do pardon the quality of the snapshots here, they were just quick shots taken in a hurry and do not do due justice to this fine lens. All were taken handheld wide open in pretty flat dim lighting, with some slight enhancements in PS.


A series of snapshots taken at 4 different aperture openings. Focus is on the word “Minolta” on the camera.

 

[Velectron]

Some other random subjects…..

Note the very shallow DOF….

 

[Velectron]

My usual model, who wasn’t very cooperative today. Add an extremely shallow DOF to a fast moving model who cannot keep still and keeps wanting to go beyond your limited focusing range or MFD, and you would have a Mission-Near-Impossible. Didn’t really get the focus or composition right here but it is the best out of the others I had to junk…better luck next time I hope!

I hope you enjoyed this article! Any inputs would be welcome

I do hope that more people would come forward and share their experiences, either pictures or their equipment and add more human touch and vibrance to the forum.

 

[sje4182]

Great article and nice shots....especially ur model - can TFCD?

 

[Velectron]

TFCD? You sure? She is shy and often uncooperative. But if you are good with children, and have a way with them, you are most welcome to try. If you are truly game for it, just pm me to discuss further. Haha

 

[albertri]

Wow bro very nice find and great write up. Got skill in opening lens is really good. I don't have the patience lolz

 

[Ben Ang]

i want!!... haha. congrats on the find! i din even know it existed.. you should be able to convert it to EOS mount reversibly... shouldn't hit the 5D mirror either.

 

[nsalman]

Bravo. Nice read.

 

[Velectron]

i want!!... haha. congrats on the find! i din even know it existed.. you should be able to convert it to EOS mount reversibly... shouldn't hit the 5D mirror either.

Bro Ben,

I am using Sony, not Canon

Dun think I would want to convert it. Several parts had to be custom machined for it because of the way the lens mount is used to lock several other parts of the lens. But it is of course do-able because I just recently saw one converted to Sony mount on sale. I don't think I want to monkey around with a rare lens like this. Oops I think I just did that with this article!...haha :bsmilie: Will probably use it with a future mirrorless camera that I have yet to purchase.

However, I am thinking of converting the successor to this lens, the Minolta MC Rokkor 100mm F2.5. It doesn't seem too difficult but I would need some advice from you (will pm you later)

 

[Velectron]

Wow bro very nice find and great write up. Got skill in opening lens is really good. I don't have the patience lolz

Bravo. Nice read.

Thank you

 

[albertri]

Thank you

I'm also planning to get a mirror less system or the A77 as mentioned when we last met

 

[Ghostfit]

I do hope that more people would come forward and share their experiences, either pictures or their equipment and add more human touch and vibrance to the forum.

Thanks for a really inspiring article on lens cleaning, Bro ! :thumbsup:

Now I'm stroked to see if I can snap some shots and post similar articles on other minolta AF lens. :think:

 

[Velectron]

Thanks for a really inspiring article on lens cleaning, Bro ! :thumbsup:

Now I'm stroked to see if I can snap some shots and post similar articles on other minolta AF lens. :think:

Thanks Bro Ghostfit! Sure would love to see your articles!

 

[mattbellphoto]

First of all, thank you for making this thread. It's the best info I've found on this particular lens and its inner workings online.

Now for my problem/question...

A friend of mine bought one of these for super cheap, but its focus was very chunky and difficult. And I offered to fix it..

I followed your directions, opened the lens, found, and corrected the problem (A missing screw). But now I cannot get it reassembled correctly..

Two mistakes I believe I made: I marked the silver ring that controls the infinity focus thinking that could reset it if I moved it (which inevitably, I did). I also unscrewed the focus ring completely from the rest of the lens.

When I get it put back together in a way that seems to fit based on the lens markings and the marking I previously made, the f-stop markings end up aligned on the opposite side of the lens and nothing turns correctly.. And I cannot figure out what to do now.

Do you have any idea how I can get everything aligned correctly? How did you fix the silver ring that controls the infinity focus once you moved it?

 

[Velectron]

Thank you for your compliments.

I am sorry to hear what happened. You seemed to have dismantled the lens further than I did so there are things I can't advise you on. Removing the focusing ring is a tricky affair if there are multiple helicoid threads and starting points for the threads. Unless you remembered or marked how the threads on the focusing ring match those on the lens, it is going to be a long process of trial and error to see which is the correct thread.

As for setting the silver ring that controls infinity focus, you would need a NEX or M4/3 camera with the appropriate adapter. Again, its trial and error - move the ring 1/4 of a turn each time, put the mount back and check focus at infinity. There is only 1 way that the mount part would fit correctly onto the lens - the aperture linkage must connect with that inside the lens and the holes for the 3 set screws must match.