JimBuchanan
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 p.1 #1 · FS: Minolta Rokkor 58mm EOS conversion kit | |
I have EOS conversion kits for the Minolta Rokkor 58mm lenses at a price of US $69, shipped in the CON-US. Outside US, please email for shipping.
We use a lot of the Rokkor 58s on our digital EOS cameras, and these surplus kits are being offered to help photographers put these fast Rokkor lenses back into service.
The kits are for the MC 58/1.2 and MC58/1.4 lenses only, as they are the only Rokkor lenses, that I am aware of, with simple backs that have no aperture mechanics.
They are made to be as turn key as possible. Unscrew the 4 long screws on the Minolta back, remove the Minolta flange and spacer, place the new custom spacer and EF flange in place noting the Canon locking pin position, and replace/tighten the 4 original screws.
This conversion kit is not meant to be sanded or filed for infinity adjustment, as the EOS flange is inset into the spacer and together they form the new face that mates with the camera mount.
Infinity focus will be close, but due to all the variables, one will have to fine tune infinity with the lens focus screws. Instructions are here:
http://farm4.static.flickr.com/3454/3254448076_cd5a9f0f8c_o.jpg
Infinity adjustment of the Rokkor 58/1.2 lens
After the lens is converted to EOS, and mounted on an EOS camera, the lens ID ring should be removed. It unscrews counter clockwise, looking at the front of the lens, and is shown below hanging on the end of the lens barrel.
The all metal focus ring of the earlier models are the same construction, and the front edge will unscrew CCW from the focus grip.
http://farm4.static.flickr.com/3122/3167932053_00c6bcfb4e.jpg
There are several methods of removal. Latex medical gloves will give the hands a better grip. A rubber wrench as shown below will help, also. The nice thing about this lens, is that one is not working with an ID ring so close to the front element glass as to do any harm to the glass.
http://farm4.static.flickr.com/3113/3108187420_6f715e6cab.jpg
Once the ID ring is removed, the 4 infinity adjustment screws are accessible around the front element assembly:
http://farm2.static.flickr.com/1277/3168762560_d65eec0d08.jpg
Although, there may be several techniques to do this, I find the following works for me, and is very exacting. It requires one to have a computer to view 100% crops on, AND have a tripod setup close enough to view a geometric object several miles away.
The 4 infinity adjustment screws lock the focus ring to the lens helicoid. If you unscrew all 4 screws, the focus ring should move freely and independently from the helicoid.
I find a distant telephone pole or other geometric object several miles away and place it center frame. It’s easiest to use a tripod and set the camera lens wide open, 2 second delay and mirror lockup, aperture priority.
I take a shot with the lens focus ring turned all the way to the infinity stop, Then, take a 2nd shot after turning the focus ring back toward near, a very, very small amount, and a 3rd shot back just a bit more. I then remove the card from the camera & plug into the computer, import & view at 100%, and compare the 3 frames I’ve shot.
There will be 1 of 3 scenarios. Exact, perfect focus. If you think you have perfect focus, then the job is done and lets go take pictures. But, if you want to see if that infinity object can get any sharper, then go to next scenario.
#2 scenario where the 2nd and 3rd frame get progressively more out of focus and your not sure 1st frame is perfect. Turn the lens all the way to the infinity stop and loosen all 4 screws until the focus ring moves freely, and back the ring about half way toward the 30ft mark and tighten just 2 of the screws. Now you can turn the focus ring/helicoid more toward infinity. Continue take a frame and compare, until you find that point the distant object gets no sharper. Once the sharpest frame is found, then loosen the 2 tight screws, move the focus ring to the infinity stop, tighten all 4 screws and replace the lens ID ring.
#3 scenario where the object gets more sharp as you go from frame 1, to 2, to 3. This means you started at past infinity, and should continue to move the lens ring a micro amount, shoot a frame, compare, until you find that point the distant object gets no sharper. Once the sharpest frame is found, then loosen the 4 screws, move the focus ring to the infinity stop, tighten all 4 screws and replace the lens ID ring.
Note: There is a tolerance where the lens can be moved 2 or 3 “micro amounts” and there will be no difference in center infinity sharpness. If your technique is good enough, its possible to find the short side of this tolerance and bring nearer distances more into focus, thereby increasing depth of field at the infinity setting.
Another Note: I have found that an "Industrial Sharpie" marker will blacken the inner exposed back from reflections in the mirror box, and could help with image quality.
ADDITIONAL INFORMATION
The Rokkor 58/1.2, like most other prime lenses, have one single assembly of elements that move as a group and do not change their relationship with any other part of the lens assembly. Exceptions to this would be floating element designs like the Zeiss ZF 50/2.0 makro, Canon FD 50L, Leica M 50/1.4 ASPH, a host of higher quality wide angles, etc.
In the case of the Rokkor 58/1.2, and countless lens designs like it, there is one and only one lens position that produces a sharp focused infinity photo, which happens to be the closest position to the sensor, and therefore could cause mirror interference issues. To be clear, regardless of method of positioning the lens assembly for infinity focus, the position will be the same. The end result can be achieved by sanding a spacer down in thickness to reduce the optical path in the case of Minolta lenses on EOS, or use my parts. It makes no difference, except for the quality, geometric accuracy, cleanliness, and appearance of my kit.
Now, if a 5D/Rokkor 58 shooter is only interested in mid-range or close range portraits, then the lens can sacrifice infinity for mirror clearance, as the lens assembly doesn't need to be as close to the mirror. I've heard descriptions of same like this, "Infinity focus needs f/4.0". In this case, the lens simply doesn't reach infinity focus and the fact is masked by the depth of field, stopped down to f/4.0 in this case. That statement is really subjective at best.
With all the variance reported in 5D camera mirror clearances, the likely scenario is filing the lens housing, filing the 5D mirror, or both, and the possible sacrifice of infinity focus altogether.
As far as I am concerned, these last options are the shooters choice, as there are so many variables.
Please reply, or send me a PM with questions or comments.
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. Is it too late to get the conversion kit?
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