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05-18-2014, 10:31 PM   #16
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I did a bit more looking into using steel wool to clean coatings off the lens elements.

From several patent applications, steel wool APPEARS to have a knoop hardness between 120 and 180.

MgF2 is a more common modern coating. It has a knoop hardness of 415. It is harder that steel wool. Modern coatings will wear down the steel wool.

Modern optical glass has knoop hardness values between 450 and 610. This also is harder than steel wool!

If something is hard enough to remove modern coatings, it will remove glass.

If I need to wear down steel wool, I know what to use.

It looks like I need to investigate chemical not abrasive means to remove the coating. Is there a safe solvent? Maybe I should try to find an old uncoated M42 lens.

I got the optical glass and MgF2 hardness values from Bob Atkins web site: Photographic Lens and Filter Cleaning

p.s. I've used steel wool for 40 years to clean kitchen glassware (tumblers, Pyrex, wine glasses) without leaving a mark. I have also used it on window panes without consequences.

---------- Post added 05-18-14 at 10:34 PM ----------

Anyone know of a good 50mm-ish M42 lens for me to check out?

Thanks

05-18-2014, 11:36 PM   #17
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QuoteOriginally posted by lmd91343 Quote
Anyone know of a good 50mm-ish M42 lens for me to check out?
Try a fungus infected lens. fungus is often on coating (organic???) and by removing fungus you remove the coating.
You could get a lens at almost the shipping cost.

Seb
05-19-2014, 05:30 AM   #18
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You might be better off just buying an El-Nikkor 80 f/5.6 (chrome ring version) instead. Good UV transmission.

-Johan
05-19-2014, 08:25 AM   #19
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QuoteOriginally posted by lmd91343 Quote
I need to investigate chemical not abrasive means to remove the coating. Is there a safe solvent?
Diluted nitric acid should do the trick, there are potentially 9 different coatings on each surface - each with their own chemical composition so you will want something that is able to chew through all of them in one hit.

QuoteOriginally posted by lmd91343 Quote
I've used steel wool for 40 years to clean kitchen glassware (tumblers, Pyrex, wine glasses) without leaving a mark. I have also used it on window panes without consequences.
But if you examine the surfaces under 5X magnification you will see the negative effects of the steel wool.

05-19-2014, 09:12 AM   #20
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a far easier way to have a good lens for UV photography is to use cheap and barely coated lenses ! For cheap !

The industar 50, a 50mm f3.5 lens can do the trick. or a Helios 44M a good 58mm f2.

As stated before, the SENSOR will be the main thing BLOCKING UV.

So no need to grind anything because al your work will be more or less useless because of the UV filter that is in front of the sensor.

I suggest you to get an old DSLR for very cheap like a Ist-D for example; with very weak UV filter on the sensor.
05-19-2014, 09:51 AM   #21
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QuoteOriginally posted by lmd91343 Quote
Anyone know of a good 50mm-ish M42 lens for me to check out?
Here's a cheap one,
with very little glass (Cooke triplet),
quite sharp at f/8:

E. Ludwig Meritar 50/2.9 Lens Reviews - Miscellaneous Lenses - Pentax Lens Review Database
05-19-2014, 03:19 PM   #22
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QuoteOriginally posted by aurele Quote
I suggest you to get an old DSLR for very cheap like a Ist-D for example; with very weak UV filter on the sensor.
Doesn't the ist-d have a CCD filter? CCDs because of their thick EPI layer and deep pixel wells are better for IR - CMOS sensors that always tend to have a thinner EPI layers are better for UV.
05-19-2014, 03:53 PM   #23
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QuoteOriginally posted by Digitalis Quote
Doesn't the ist-d have a CCD filter? CCDs because of their thick EPI layer and deep pixel wells are better for IR - CMOS sensors that always tend to have a thinner EPI layers are better for UV.
I completely rely on your better knowledge about this than me. So i guess you are right.
An old Cmos DSLR is what you need then

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