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

[raid]

He is in the Netherlands. Is he that good?

 

[kermaier]

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.

My most recent example came to me with clear glass, thankfully. (I don't know if a previous owner had it cleaned at some point; or if it's one of the lenses that Minolta supposedly remedied at the factory in the years after initial release; or if it's just not developed the condition yet, but will sometime in the future.) I had DAG totally trick it out by modifing the mount to bring up the 28/90 framelines, milling the flange for 6-bit coding (coded as an Elmarit v4) and replacing the original focus tab with a 35/2 Summicron v4 style tab. Worked great on my M9-P, and also on the M240 (loaner I'm using while the former is in the shop for sensor replacement). I'm not sure it's sharper than my CV 28/3.5 Skopar, but it's definitely close, and I love the way it renders OOF backgrounds wide open.

 

[Palaeoboy]

.... the front element of the M-Rokkor 28/2.8 is also a cemented couplet, and thus not straightforward to recoat.

Actually its not, its a single element with no close partners. But the way the lens cells of these Minoltas lenses is designed they are Blo*dy hard to get apart!

I'm not sure it's sharper than my CV 28/3.5 Skopar, but it's definitely close, .....

Centre sharpness is about the same with both of these compact 28s but the edge distortion of the Skopar is quite severe. You just dont notice it until you do a side by side comparison with a Rokkor. The trouble with the Rokkor is finding a good one. Exposing the lens to excessive heat brings on the formation of the crystals that appear as the dreaded white spots.

 

[kuuan]

Raid your samples look great!

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.

haha, you have been there!
right! I am quite positive that finer polish would improve the lens further!
finer polishes would be, quote from tips I had received elsewhere: "chromium oxide (ingriedient in the paste you can buy for stropping straight razors or as pigment for oil-based dyes, naturally ~0,3-1µm) or better diamond lapping spray/paste (0,5µm/0,25µm) instead of Cer(IV)oxide (~1µm), both are finer and diamond is by far most effective"
With all the great info gathered in this thread I shall try to contact the services mentioned to get their opinions before attempting more, finer polish, myself

+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)...

thank you very much for all the good info!
I strongly suppose that my polishing has not removed substance from the glass, or hardly any if at all, actually I think that I have not yet removed the 'crystals' that have covered the whole surface entirely yet.

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.)

this is most encouraging! my lens had behaved like your's, had been unusable, by now it is much improved. I have high hopes that it still can be fixed further.

Now that I learned about the FocalPoint, and:

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

2 more services that might be able to polish the lens professionally I will contact them for help resp. quotes before attempting more polishing myself

.. the front element of the M-Rokkor 28/2.8 is also a cemented couplet, and thus not straightforward to recoat.

Actually its not, its a single element with no close partners. But the way the lens cells of these Minoltas lenses is designed they are Blo*dy hard to get apart!

Palaeoboy is right, it's a single element. In case a Pro will finish the work I have some hope that costs might be somewhat lowered because the difficult work of opening the lens already is done.
with all the collected info regarding polishing you also mention re-coating! Do you know, and if so could you please add the name of services that do re-coating?

There also was mention of Wil van Manen. I had contact him regarding repair of my lens and had received most friendly replies and help from both him and his partner Cathy Kuiper. For me a service located in Europe will be best and I shall inquire again. The contact for Nicorep in France can be seen in a link provided, here it is: nicorep@wanadoo.fr ( edit: tried to write to Mr. Marc at nicorep but the mail had been returned as undeliverable, it says it's an invalid address )
the email address of Wil van Manen: kamera-service@ziggo.nl hopefully we get contact info for Arax too. For those in the Americas, here the website of Focalpoint: http://www.focalpointlens.com/fp_intro.html

cheers and thank you all again for all the great input! I believe that you made this thread the very one on the whole net with the most comprehensive information regarding repair of the M-Rokkor f2.8/28m!
- with bonus added important information regarding polishing in general and related Pro services.


Untitled by Andreas, on Flickr

 

[astro8]

I'm not sure you have perfecty seated the front element.

I removed and cleaned the front element on a 28 Rokkor as it was almost opaque and useless for taking photos. I used acetone and then acrylic laquer thinner. I had to really scrub the element to remove the white haze and spots.

My first test shots were like yours. The more I tightened the front ring to seat the element, the sharper my test shots became. I'm very pleased with it now. Some images in my rff gallery... Look at the car shots and some others. I'm on my phone now so hard to post pics...

 

[kuuan]

I'm not sure you have perfecty seated the front element.

I removed and cleaned the front element on a 28 Rokkor as it was almost opaque and useless for taking photos. I used acetone and then acrylic laquer thinner. I had to really scrub the element to remove the white haze and spots.

My first test shots were like yours. The more I tightened the front ring to seat the element, the sharper my test shots became. I'm very pleased with it now. Some images in my rff gallery... Look at the car shots and some others. I'm on my phone now so hard to post pics...

thank you very much for that Greg! The photo of the car looks great, and perfect IQ from the lens!
This is a very important point and to know that your self polished lens first had given results like mine and that now it is performing that very well is very encouraging!
I just tightened the ring and first test shots seem to show some further improvement. As mentioned I am sure that the thickness of the applied paint will play a role. I will see if I can make the paint thinner, possibly using different paint, to make the front element make fit a tad lower again.

 

[Highway 61]

For me a service located in Europe will be best and I shall inquire again. The contact for Nicorep in France can be seen in a link provided, here it is: nicorep@wanadoo.fr ( edit: tried to write to Mr. Marc at nicorep but the mail had been returned as undeliverable, it says it's an invalid address )

Here is Marc Nicolas' newer email address : contact@nicorep.fr

Unfortunately he forgot to mention this on the English pages of his website (we'll forgive him) which still mention his obsolete email address.

I have had two RF lenses (a Leitz and a Nikkor) repolished by him ; he did a perfect job, and the turnaround time was 2 weeks.

 

[kuuan]

Here is Marc Nicolas' newer email address : contact@nicorep.fr...

thank you very much, I already resent my mail to him

...
as I am in Vietnam now and it will be some months before I go to Europe it would take a while before I send my lens to a repair service, if I will. no worries, no hurry, it already has taken over one and a half year to get that far

 

[raid]

Raid your samples look great!

Thanks. This is the same lens that I once may have sold to Ari, but he discovered in it some white spots, and it made the lens unacceptable to him. They are few spots even today, which is several years later. I am unsure if it is worth it to me to have the lens cleaned at a high expense and at a risk of changing it optically (other than the clarity from spots).

 

[kuuan]

Thanks. This is the same lens that I once may have sold to Ari, but he discovered in it some white spots, and it made the lens unacceptable to him. They are few spots even today, which is several years later. I am unsure if it is worth it to me to have the lens cleaned at a high expense and at a risk of changing it optically (other than the clarity from spots).

in case you don't notice a degradation I would just leave it as it is, it looks a flawless performer.
and I would care not to have it stored in a hot place, as that could, I read, be a reason for it to deteriorate

 

[raid]

I store my lenses in a cool place, with a dehumidifier unit (not too powerful) to keep fungus also away from them.

 

[kuuan]

wha, envy

 

[kermaier]

I store my lenses in a cool place, with a dehumidifier unit (not too powerful) to keep fungus also away from them.

Nice! I once looked into getting a dry-box for my lenses, but finally decided that the NJ climate didn't warrant it.
::Ari

 

[kuuan]

keeping the lenses I carry, and it's quite a number, in the hot and often very humid places I frequent, e.g. Bali and Saigon, is a permanent challenge. In Bali one way silica products are available, in Vietnam I struggle with silica gel balls I had brought along and which I re-charge in a microwave

an update regarding my mails to Mr. Will van Manen and Mr. Marc at Nicorep:
Once again very fast I had received another extremely friendly and informative answer from Mr. Wil van Manen. He had gone through this thread and says that he strongly believs that I have not yet altered the curve of the lens. He recommends more fine polishing and gave me detailed tips on how to proceed I have not yet received an answer from Nicorep.

 

[raid]

Nice! I once looked into getting a dry-box for my lenses, but finally decided that the NJ climate didn't warrant it.
::Ari

I have lived in Pensacola since 28 years, and I have not seen any fungus on any of my (many) lenses.

Humidity levels in NJ are not low, Ari.


Average relative humidity (%) for Atlantic City, New Jersey
Daily Morning Afternoon
70 January 77 59
69 February 78 58
67 March 77 55
66 April 76 54
71 May 78 57
73 June 81 58
74 July 83 59
76 August 86 61
76 September 87 61
75 October 87 59
73 November 83 61
71 December 78 61
72 Annual 81 59





Average relative humidity (%) for Newark, New Jersey
Daily Morning Afternoon
65 January 73 57
63 February 72 54
60 March 69 50
58 April 66 47
62 May 70 50
63 June 70 51
63 July 72 51
66 August 75 54
68 September 78 55
66 October 78 53
67 November 76 57
67 December 74 59
64 Annual 73 53

 

[kermaier]

I have lived in Pensacola since 28 years, and I have not seen any fungus on any of my (many) lenses.

Humidity levels in NJ are not low, Ari.

Hmm, nothing like hard data, eh?
How's that compare to Pensacola?

 

[edinator]

He recommends more fine polishing and gave me detailed tips on how to proceed I have not yet received an answer from Nicorep.

Care to share? I may try to look for those polishing compounds you mentioned above as well. Another important aspect of polishing is what you actually use to polish. If the polishing head is soft, it won't be as effective since the polishing compound won't have constant, strong pressure against the lense.

 

[kuuan]

Care to share? I may try to look for those polishing compounds you mentioned above as well. Another important aspect of polishing is what you actually use to polish. If the polishing head is soft, it won't be as effective since the polishing compound won't have constant, strong pressure against the lense.

ok, I have bothered Mr. Will enough and instead of asking him if he minds me if I shared what he had written I just will send it to you via PM. In case more need to know I think I should ask Mr. Will first,
cheers

 

[Trius]

This has been a VERY nice informative and helpful thread - 28mm lenses, lens repair, polishing, resources - wow.