MINOLTA M-ROKKOR 28mm f/2.8 - White spots

Eric Rose · Jun 7, 2019

I was looking on eBay for a MINOLTA M-ROKKOR 28mm f/2.8 lens and I would say 80% of them have some really nasty looking white spots on the back side of the front element. What gives?

I have some older Minolta lenses that don't have this. Why just the M-Rokkor 28mm?

I suppose it can be fixed but it seems odd.

Eric

Andrew O'Neill · Jun 7, 2019

At photo dot net:

"I have examined many of these lenses and dont believe it to be a coating flaw. The problem is with the black paint used to coat the rim of the lens to reduce internal reflections. Basically crystals form from something leaching out of the paint. In a fair number of examples you will see the spots only evident on the rim of the front element. Because at the early stages it limits itself to the rim and not in the optical path and is why its reported it doesnt effect picture quality in alot of cases. However if the problem is allowed to continue there becomes so many crystals that they dislodge from the rim and get onto the rear of the front element where they then etch into the coating. Dan mentioned above that if the lens hasnt developed the spots its unlikely to happen, sorry but this is not so. I had one develop the spots last year. Not only that, it occurred in one outing where it was an incredibly hot day and thats when the spots appeared quite severely. This further supported the theory that the spots were crystals formed from leaching in the excessive heat.

Strange as the problem is, I have seen it occur in other lenses in an identical manner. One lens was the Zeiss M 15mm Hologon. So if you have a Rokkor 28 with just a few white spots round the rim my advice is to have the edges of the front element cleaned and repainted with a more suitable paint before it spreads".

Eric Rose · Jun 7, 2019

What a DRAG! I suppose you can do the repair yourself but I sure don't have the time to putz around with it. Just wondering why on earth Minolta would do something like that on only this lens. Geez.

AgX · Jun 7, 2019

Andrew, I know those reflective spots between lens rims and their non-reflection varnish, have seen them at many lenses. But in this case it does not look to me this way, more as spots all over the free lens(es) surface. (Erik himself described them to occur at the backside of the front lens element.)
This could be due to condensation staining.
But also cases of reflective spots between cemented lens elements not originating from the circumference have occured.

We would need better photos to be sure.

Eric Rose · Jun 7, 2019

AgX said:
Andrew, I know those reflective spots between lens rims and their non-reflection varnish. But in this case it does not look to me this way, more as spots all over the free lens(es) surface.
This could be due to condensation staining.
But also cases of reflective spots between cemented lens elements not originating from the rim have occured.

We would need better photos to be sure.

Just check eBay listing for these lenses. You will see lots of examples. Maybe one of them could give you more information.

Eric

AgX · Jun 7, 2019

Seeing rim-varnish artefacts at other samples, does not necessarily mean that the artefact at your sample is of the same kind.

Rim-varnish defects are rather easily to locate at those rims (the part of the lens-element located between both retaining rings).

AgX · Jun 7, 2019

By the way, I got lenses from a reputable manufacturer that have not got a varnish at all (or it disappeared...).

vicmortelmans · Sep 1, 2024

I had this lens lying on the shelf for years, showing hunderds of white dots behing the front element. Googling discussions like this, I was in fear it was a loss, but yesterday I fixed it!

Unscrew the front ring. Screw out the front element.

[edit]I sawed off the narrow 1mm wide front rim of the housing of the element, as was instructed on some other forum. Not sure if this was needed, though.[/edit]

Then holding it in a pair of plyers and heating it with a heat gun. Some tapping with the front lens downward, made it come out.

The dots appeared to be moisture! The lens must have had some water ingress in a previous life. It cleaned off perfectly.

I pushed the front lens back in place (no heat needed for this). I was a bit afraid that it might not be aligned perfectly anymore and the focus might be off, but some test pictures show it's quite all right!

Sometime one must have a bit of luck and a bit of daring

WeiW · Oct 13, 2024

probably ‘schneideritis’, if you google this term there are some examples. Should be fine.

JPD · Oct 14, 2024

WeiW said:
probably ‘schneideritis’, if you google this term there are some examples. Should be fine.

Dots on the glass isn't schneideritis.

MINOLTA M-ROKKOR 28mm f/2.8 - White spots

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