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Regrinding badly scratched front lens of M plan 20x ELWD?
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viktor j nilsson



Joined: 01 Mar 2013
Posts: 60
Location: Lund, Sweden

PostPosted: Mon Feb 05, 2018 6:22 am    Post subject: Reply with quote

Finally had time to do some test stacks.

EDIT: Note that these pictures are taken with three different lenses. First the Nikon E Acrhromat 10x 0.25, then the damaged M Plan 20x ELWD, and finally a fairly nice BD Plan 40x ELWD.

EDIT 2: Note that these are taken with the damaged 20x ELWD shown in my original post. No polishing.


First, I'll just put the pictures here to make sure everything looks as it should. Comments in next post.

First, the full frames, resized in Photoshop:


Nikon E Achromat 10x 0.25


Nikon M Plan 20x ELWD


Nikon BD Plan 40x ELWD




Second, 100% crops (1024 x 1024 px):



E Achromat 10x 100% crop


M Plan 20x ELWD 100% crop


BD Plan 40x ELWD 100% crop


Last edited by viktor j nilsson on Mon Feb 05, 2018 12:27 pm; edited 2 times in total
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enricosavazzi



Joined: 21 Nov 2009
Posts: 1072
Location: Stockholm, Sweden

PostPosted: Mon Feb 05, 2018 6:27 am    Post subject: Reply with quote

I was skeptical about the idea, but the proof is in the pudding. Well done!

I guess this particular lens has old-style coatings, which are softer and relatively easy to remove (also accidentally). As a rule, modern multicoatings are much harder than the glass, which makes removing the coating mechanically without damaging the glass problematic.
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viktor j nilsson



Joined: 01 Mar 2013
Posts: 60
Location: Lund, Sweden

PostPosted: Mon Feb 05, 2018 6:37 am    Post subject: Reply with quote

The pictures are totally unaltered except for resizing.

Actually, the 20x doesn't look as bad as I had expected.

However, compared to the 40x, its contrast is certainly very low. But the IQ is a quite a bit more uniform over the frame than I had expected.

When I've tried the 20x objective earlier, I had used an adapter (cheap extension tubes + home-made aluminum dovetail adapter) that had no flocking material at all. Before I took these photos, I carefully covered everything with Doodlebug flocking paper. Maybe flocking is especially important when the front lens is damaged?
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viktor j nilsson



Joined: 01 Mar 2013
Posts: 60
Location: Lund, Sweden

PostPosted: Mon Feb 05, 2018 6:41 am    Post subject: Reply with quote

enricosavazzi wrote:
I was skeptical about the idea, but the proof is in the pudding. Well done!

I guess this particular lens has old-style coatings, which are softer and relatively easy to remove (also accidentally). As a rule, modern multicoatings are much harder than the glass, which makes removing the coating mechanically without damaging the glass problematic.



I should have been clearer: I still haven't done anything with the lens yet! These are the "before" pictures. So this is the picture produced by the 20x ELWD with a sand blasted front lens. I really thought that it would look much worse than this.

I mainly produced these to have something to compare with IF I went ahead and polished the lens. However, after seeing the picture produced by the 20x, I am starting to hesitate if it is going to be worth it.
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viktor j nilsson



Joined: 01 Mar 2013
Posts: 60
Location: Lund, Sweden

PostPosted: Mon Feb 05, 2018 6:46 am    Post subject: Reply with quote

To give you an idea of what I had expected, this is a stack that a friend shot with the 20x ELWD a few weeks ago:


Resized, almost full frame


100% crop

Could cleaning the lens a bit more and adding flocking to the adapter really make such a difference?
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viktor j nilsson



Joined: 01 Mar 2013
Posts: 60
Location: Lund, Sweden

PostPosted: Mon Feb 05, 2018 6:58 am    Post subject: Reply with quote

Actually, I realized that I could sort of answer how much an impact the flocking had myself since I also shot a stack of the same subject before I added the flocking material. (I forgot that I did this!).


Full frames without and with flocking:


20x ELWD no flocking


20x ELWD with flocking


And 100% crops without and with flocking:


100% without flocking



100% with flocking
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neurodoc



Joined: 29 Aug 2012
Posts: 57

PostPosted: Mon Feb 05, 2018 1:34 pm    Post subject: Reply with quote

You could try making a lap by mixing up some Jett Ballistic Fixturing Material(this is a plastic that is softened in hot water, molded into shape while soft, and allowed to set up hard). You can get it in jeweler supply houses, like Otto Frei). This sets up much harder than waxand would give you a fairly accurate negative surface to use as a formed lap while you polish the lens. It just might do the trick.
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viktor j nilsson



Joined: 01 Mar 2013
Posts: 60
Location: Lund, Sweden

PostPosted: Thu Jun 21, 2018 11:55 pm    Post subject: Reply with quote

I finally found time to give this a try. I tried making a pitch lap out of colophonium and beeswax. It melted together nicely. Streched a piece of cling wrap over the front lens and poured it on. It flowed very slowly and formed a moldable blob on top of the lens. After it has started to settle, I gave it a slight push to press it tight against the lens.

Making a lap was harder than I thought.
Sometimes I tried to take it off too soon and it got deformed in the process.
Sometimes there were bubbles.
Once I tried to shave off some excess material on the sides and it cracked.

After about ten attempts, I still hadn't been able to make a good pitch lap. I started to feel dispirited.

At that point I got the terrible idea that the lap would only make it worse. How badly deformed can a lens get if I only polish away an ever so slight amount of material? I thought. What if I just polish it with cerium oxide on my finger?

The answer is: it can get really bad.

I had thought that it only needed a very slight polish since the pits looked to shallow. Like, 10-15 minutes. But it soon became clear that the pits on the surface were deeper than I thought. Polishing of course widened the sides of the holes, so at first, the more I polished, the worse it looked. It was too late now, I just had to keep going. An hour went, still far from reaching the bottom of the pits. An hour more, still just widening the pits. An hour more, one more. My finger started to hurt. It became increasingly clear that I had made a huge mistake.

After six hours, I could start to see the surface looking flatter (rather than full of craters). After nine hours, the front lens looked pristine. I was ready to clean it up and put it on the microscope.

The result was... horrendous. A mush. Vaseline on the lens level bad. I had ruined it. I can post pictures later, but it was so demoralizing I just couldn't get myself to even do a test stack.

Anyone has a decent 20x objective to spare for a decent price?
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