IQ of repaired M-Rokkor f2.8/28mm

[kuuan]

My copy of the M-Rokkor f2.8/28mm had the dreaded 'white spot issue' in an advanced state, they not only appeared around the outer rim, which is said not to impact IQ,
but the full surface of the front lens was effected and photos taken had an overall soft look


Minolta M-Rokkor f2.8/28mm by Andreas, on Flickr

so I decided to try to fix it and polished the rear of the front lens. Now the lens looks like this ( actually a bit better again, I later repainted the black, outer rim once more )

Now images look sharper but since polishing must have removed the coating that had gone bad the lens now very easily 'glows' and it handles highlights, specially against dark, high contrast areas rather badly.

a few typical samples ( taken on Sony A7 )

Nha Trang by Andreas, on Flickr

typical problem of a tree against the sky

cementery by Andreas, on Flickr

if there are no strong highlights there is little problem

Khai Doan Pagoda by Andreas, on Flickr


Untitled by Andreas, on Flickr

sure it looses contrast easily and it's use is somewhat limited

picnic by Andreas, on Flickr

and I had to invest more of my limited editing skills than usual to make these look like this, added 'clarity' in Lightroom, something I usually don't.
to see full size choose 'view all sizes' after clicking on the image and the 'download' arrow at the lower, right corner of the page. If required I may add 100% crops and more samples, see all photos taken with this lens here: https://www.flickr.com/photos/kuuan/albums/72157644175227413

in spite of it's obvious flaws still I rather like the images, let's say the 'vintage look of them'. What do you think? Am I not able to 'accept defeat' and they actually are simply too bad?
grateful for any opinion, cheers, andreas

 

[Richard G]

The last one looks OK. The others, even opened larger in Flickr, look fuzzy. I am not seeing this in your 90mm M Rokkor shots. I couldn't live with that 28 the way it is.

 

[kuuan]

The last one looks OK. The others, even opened larger in Flickr, look fuzzy. I am not seeing this in your 90mm M Rokkor shots. I couldn't live with that 28 the way it is.

thank you for your feedback Richard. On a short trip this last week during which all these samples had been taken I had taken the 3 M-Rokkor with me, curious how happy or unhappy I'd be with this 28mm. I discovered that I very much like the focal lengths of the M-Rokkor set and using it as a traveling set.
Hm..I am afraid you are stating the obvious that I am reluctant to accept. Still I will continue using this lens, in spite of it's obvious faults somehow I like the images it gives me. And I am not ready to forge out the money to buy another to make the set complete, or any other 28mm RF lens yet. I am looking into having the effected lens re-coated.

Still curious how others see the images this lens produces


Untitled by Andreas, on Flickr


Po Nagar Cham ruins, Nha Trang by Andreas, on Flickr

and with a difficult background

traditional weaving by Andreas, on Flickr

 

[raid]

I used my Rokkor a few days ago on the E-P2. It has white spots since many years. I will try to post some photos today,

 

[raid]

This one is from a few years ago.

 

[Bille]

Is this a photoshop filter on the glass or why does it look pixelated?
Either way, you created a sort of soft focus lens. https://c1.staticflickr.com/9/8019/7434679150_df5aa68ebf_b.jpg

 

[raid]

Something is not right with your images. Could it be a mismatch with the SONY camera? Did you move the glass elements and then did not place them back correctly in place? This lens has a reputation for being "nearly as good as the 28mm Elmarit".

 

[kuuan]

thank you Raid for your samples, looking forward in seeing more! It seems that your's also glows but just a very little bit, what do you think?

Is this a photoshop filter on the glass or why does it look pixelated?
Either way, you created a sort of soft focus lens. https://c1.staticflickr.com/9/8019/7434679150_df5aa68ebf_b.jpg

no, no filter. I am not sure why it looks like this. Possibly due to my repainting the outer black rim, not very well yet when this pic was taken, now it looks a bit better.

hm..I guess you are right. kind of a soft focus lens now, with added difficulties with highlights. That would mean that having it re-coated wouldn't really help all that much, right? Or at least that I would have to try to polish it better before considering re-coating.

 

[kuuan]

Something is not right with your images. Could it be a mismatch with the SONY camera? Did you move the glass elements and then did not place them back correctly in place? This lens has a reputation for being "nearly as good as the 28mm Elmarit".

Raid sure something is not right. As mentioned the white spots had been all over and I had found the images to be too soft. So I had decided to try to repair it, had the front lens separated ( which with this lens is all but easy ), found that the back of it was 'etched' all across, it must have been the coating that had been corrupted. So I polished that off. I also had taken off the black paint around the rim ( it having become flaky is what is causing the white spots around the outer rim ) and repainted that later. It's the painted surfaces that go into the housing, difference of thickness of the paint or it's un-evenness could be responsible for a slight misalignment.

 

[Highway 61]

Depending on how harsh your polishing compound was, you may have etched the lens too much and in a random way. The lens curvature might not be what it had to any longer. So the lens now performs as if it had a plastic front element, poorly machined.

Just think of a spheric metal surface which you will randomly "clean" with some abrasive paper and you get the idea.

This is why polishing a lens must be extremely carefully done with a gauge having the very same curvature as the lens you're working on :

http://www.nicorep.fr/uk/polissage.htm

As an aside, you also damaged the slots of the front retaining ring with your spanner wrench.

 

[kuuan]

Depending on how harsh your polishing compound was, you may have etched the lens too much and in a random way. The lens curvature might not be what it had to any longer. So the lens now performs as if it had a plastic front element, poorly machined.

Just think of a spheric metal surface which you will randomly "clean" with some abrasive paper and you get the idea.

This is why polishing a lens must be extremely carefully done with a gauge having the very same curvature as the lens you're working on :

http://www.nicorep.fr/uk/polissage.htm

As an aside, you also damaged the slots of the front retaining ring with your spanner wrench.

of course my polishing is not comparable with professional work done with precision tools. First I had tried for hours by hand and metal polishes and that had not done anything. In the end I had used cerium oxide and even a kind of tremel tool. This had slowly decreased the existing etching. By the way the existing etching slowly decreased I had not thought that the glass could have become much uneven, actually I have been thinking that only the corrupted coating was taken off and not more than that. But of course I don't know for sure resp. expect that a technician could or would teach me otherwise.
Oh, the lost paint of the slots of the retaining ring I don't mind even a bit. Considering that I must have opened and closed the lens, trying it out again and again in various states, at least 20 times there is little damage. Just like the dust it can be seen much more pronounced on the photo than with free eyes and it easily could be painted over.

 

[raid]

I would try to save the lens by Don Goldberg.
I will upload newly taken images with my lens very soon. My posted images are old scans of low quality jpg images.

 

[raid]

M8 and Rokkor

 

[kermaier]

I had an M-Rokkor 28/2.8 that was initially clear, but developed a fine misting of spots across the entire rear surface of the front element. The result was a total flare-out across the frame of images with a light source in the picture. I sent it to John Van Stelten at FocalPoint, who was able to remove the front element (as you've noted, no easy feat) and clean it up. Afterwards, it performed as well as it did originally. While this service was not inexpensive, I feel it was worth it. (I eventually sold that lens, but missed it so much I bought another.)

Here's a shot, post-cleaning, just for fun:

Epson R-D1s @ ISO 400 with M-Rokkor 28/2.8 at f/2.8

BTW, I had a Canon 50/1.2 that had the coating of one surface of the rear element badly etched by fungus. John at FocalPoint polished away the damaged coating, but we decided to leave it uncoated. The rationale was that there are 10 coated surfaces in that lens, so leaving an internal one uncoated would result in at most a 10% drop in contrast, On the other hand, recoating that surface would entail separating the two glass elements of the cemented couplet, recoating the one surface, and recementing the couplet -- a very pricey proposition. IIRC, the front element of the M-Rokkor 28/2.8 is also a cemented couplet, and thus not straightforward to recoat.


::Ari

 

[edinator]

I think the glow is actually due to the very small scratches introduced by the polishing. I would know since I tried the same thing with this lense. I think you have to go over it with a finer polishing compound.

 

[Highway 61]

I think the glow is actually due to the very small scratches introduced by the polishing. I would know since I tried the same thing with this lense. I think you have to go over it with a finer polishing compound.

+1.

To the OP : if cerium oxyde has been used, now the lens surface has lost its original curvature radius, and it has an erratic finish too, like the old tiles roof of your country house (if you can get a 40x lupe and look at the lens surface from an oblique angle and with the proper lighting, this will be quite scary I reckon).

A professional re-polishing will now be most difficult to achieve, because you cannot endlessly remove some material off the surface of an optical diopter, and probably at the same cost (if not more expensive) as if the untouched lens had been directly sent out to someone having the tools and the skills to professionally re-polish lenses.

This is why, in another thread, I warned RFFers about that DIY lenses polishing job someone suggested out. Metal or gel coat polishes won't be of any help ; cerium oxyde, when used at home, was it at hand or with a motorized tool, will cause more harm than benefits, because you cannot control what you are doing to the lens surface field curvature and radius.

Fixing damaged lens surfaces is probably the only thing the amateur repairer, even when gifted with many skills, shouldn't try out himself.

 

[raid]

Does this include using the Blue Magic Metal Cream to improve the front glass as some people have been recommending here?

 

[Highway 61]

Does this include using the Blue Magic Metal Cream to improve the front glass as some people have been recommending here?

The "Blue Magic Metal Cream" will be of no effect on improving the condition of your lens front (rear) elements surfaces.

The only thing it will do is nastily leave some white residues behind - i.e. between the front (rear) element retaining ring and the glass surface edge. Those will eventually migrate and lay on the rear side of the element you've applied that cream on. Very funny isn't it.

A scratched lens must be sent out to a pro cameras and lenses repairer being qualified for re-polishing the lenses and who will use cerium oxyde powder polishing compound combined with the proper tools respecting the lens curvature radius.

Not all of them are. I can quote only three : Focal Point in the USA, Nicorep in France, Arax in the Ukraine.

The good and responsible repairer is the one who may tell you : "Sorry Sir, I can't re-polish your lens because it's not a common one and I don't have the matching hemispheric gauge for the defective element in my workshop, so I'll send you back as is".

A dirty lens can be cleaned with small amounts of isopropylic alcohol and cotton swabs (with taking the utmost care about not letting the alcohol get behind the element you're cleaning).

For old, dried-up grease, goo, glue, whatever sticking to the lens surface and not wanting to be cleaned out with alcohol, you can use a bit of acetone. It will not harm the coatings.

But, in most cases, isopropylic alcohol will do it.

If your lens front/rear element remains matte and hazy after this, it's because it's scratched (the infamous "cleaning marks", you know).

If so, back to step 1 above.

End of the story.

 

[raid]

These are good tips. Thanks. I have never attempted to repair or to adjust any of my lenses. Ever.

 

[ferider]

I have a 28 Rokkor that I bought from Gabor who had white spots cleaned by Wil van Manen (who also modified the mount to bring up 28mm framelines). You can still see the faintest of marks in the coating, but the lens is now a stunning performer. Slightly different color rendering than - say - my v3 Elmarit, but the "sharpest" 28 I own when used on my 240. It's a great lens when fixed by a pro.

Roland.