Minolta m-rokkor 28mm: The lens I sold but bought back again.

This is a legendary lens from Minolta and is the very best 28mm in Leica M mount. However the lens always suffered the coating degradation in the first lens element.  This problem may be caused by the anti-reflection black paint which leached out the chemical which attacked the coating.  I owned this lens before and it suffered an infamous white spot issue.  I sold it before it became too bad.

Last month I got a chance to buy a good copy of m-rokkor 28mm with a reasonable price. The lens is pretty clean and has no visible white spot on the first element.  Just a bit haze but it is not enough to cause any issue. Previous owner might want to clean the lens by himself but he couldn't remove the nameplate and in the end he scratched it.  It gave a lesson to everyone and you should have proper tools and skills to service your lenses. If you don't have 100% sure what you are doing,  leave it as is or let someone to do it for you.

To prevent the further degradation of the lens coating, the lens should be cleaned but it is a bit tricky to take the first element out  There is no screw-in retaining ring to hold the front element, instead it was hold by lens clement and tight-fitted to the casing .  To loss the front element the ring should be removed by a coping saw with very very fine blade. (Google it and you can find the procedure) or loss the clement by solvent. Then using a sucking cup to take the element out.  (And there is a small hole (air vent) behind the lens block and inserting a bamboo toothpick into the air vent can help to pop the element out). It is not a difficult process but it takes time to make it prefect.  The edge of the lens casing was smoothed out by #00 sandpaper and re-painted with solvent base matt black paint. If it was all done, the front lens block should look like new.

After re-lubricating all helicoids with lithium grease and cleaning the lens inside out, it is the time to test the lens. Let's go hiking.

The coating is really good, at least for this 38 years old lens

See the detail of the picture and resolution is pretty good (at f/4)

We cannot comment the colour accuracy by digital camera

All pictures were taken by Sony A7II with LM-EA7 Autofocus adapter. (Yes, it became an auto focus lens! ).  Aperture were set at f/4.  Corner performance is really good.  Please be noted that this lens is a retrofocus wide angle lens and not a traditional symmetrical lens design.  And it is the reason why this lens work so well with digital camera.

Remarks:  In the second attend to repaint the black paint on the side of the lens element,  all the haze was successfully removed and now the lens is in crystal clean condition.  I found the water base matt black paint for model kit is the best for repainting the lens element.