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05-18-2014, 12:26 PM   #1
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Are the lens elements all glass?

I wish to remove the coatings from a Pentax A 50mm f2.0. Are all the elements glass?

I would use steel wool to remove the coatings. Obviously, steel wool should not be used on plastic.

I would like to try UV photography. I understand modern lens coatings and lens cement block some UV. This lens does not have cemented elements exposing all ten surfaces for coating removal.



Thank you!

05-18-2014, 12:34 PM   #2
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QuoteOriginally posted by lmd91343 Quote
I wish to remove the coatings from a Pentax A 50mm f2.0. Are all the elements glass?

I would use steel wool to remove the coatings. Obviously, steel wool should not be used on plastic.

I would like to try UV photography. I understand modern lens coatings and lens cement block some UV. This lens does not have cemented elements exposing all ten surfaces for coating removal.

Thank you!
The lens elements are all glass, but using steel wool would render the lens useless for every type of photography.
Glass probably blocks more UV than the coatings, you need lenses made of special types of glass for UV to pass, like quartz and fluorite.

And then there is also the sensor protective glass to worry about...
05-18-2014, 12:43 PM   #3
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I understand that some types of glass block some UV. But much much still gets thru. I don't understand why using steel wool would render the lens unusable for photography. The removed coatings will increase both veiling and direct flare, decreasing contrast. It would be like a 1950 lens.

I understand that the UV focusing will be slightly different than visible light. But I would rather play around with a $5 lens and a couple of filters before I buy $4.5K UV lens
05-18-2014, 12:50 PM   #4
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I imagine that steel wool is extremely course compared with the special polishing compounds used on optical glass. You'd likely just end up with a very cloudy looking lens.

Edit: Doh! I thought the OP was talking about IR


Last edited by Swift1; 05-18-2014 at 01:24 PM.
05-18-2014, 01:01 PM   #5
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Steel wool would scratch the glass. I have heard of people removing coating before. I think they used solvent based methods - which on glass should be OK.
05-18-2014, 01:03 PM   #6
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DSLR UV photography can work with some "regular" lenses if you only want the longer UV-A spectrum (350-400nm).

Suggested reading:

All You Ever Wanted to Know About UV and IR Photography

I suggest you read the whole article but here are the relevant pages:
All About Digital UV and IR. Page 3: Can Digital Capture UV images?
All About Digital UV and IR. Page 4: How Digital Differs From film
All About Digital UV and IR. Page 6: Filters for UV
All About Digital UV and IR. Page 7: Which Lenses?

The author suggests using an abrasive cream to remove the coatings and buying models of lenses (the "budget" lines) that have less elements and more fragile coatings. I would not use toothpaste - too abrasive. Supposedly the aluminum in SPF 40 or higher sun screens will work as an abrasive and not damage optical glass. Just be prepared to spend a lot of time buffing the coating off.
05-18-2014, 01:04 PM   #7
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QuoteOriginally posted by lmd91343 Quote
I would like to try UV photography. I understand modern lens coatings and lens cement block some UV.
I believe the sensor's poor sensitivity in the UV-band is far more significant than smc coatings. But you might want to try something like this(???):

Photography in the Ultraviolet spectrum

I have no personal experiences, but it does make sense to me that you would need a UV-bandpass filter - and a bright UV-light source.
05-18-2014, 02:07 PM   #8
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I've used 0000 steel wool on chrome and it did not scratch it. I've never used it on glass, but have heard of people using it on vehicle windshields without a problem. If you stay in one spot and really rub hard it may affect it. Most use it with denatured alcohol and make sure there are no particles or rust trapped in it.

I am not an expert, and YMMV.

05-18-2014, 02:47 PM   #9
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Glass is harder that steel. Glass is more brittle, but harder. In a previous life I cleaned VERY expensive, custom blown lab glass with steel wool.

---------- Post added 05-18-14 at 02:55 PM ----------

QuoteOriginally posted by Not a Number Quote
DSLR UV photography can work with some "regular" lenses if you only want the longer UV-A spectrum (350-400nm).

Suggested reading:

All You Ever Wanted to Know About UV and IR Photography

I suggest you read the whole article but here are the relevant pages:
All About Digital UV and IR. Page 3: Can Digital Capture UV images?
All About Digital UV and IR. Page 4: How Digital Differs From film
All About Digital UV and IR. Page 6: Filters for UV
All About Digital UV and IR. Page 7: Which Lenses?

The author suggests using an abrasive cream to remove the coatings and buying models of lenses (the "budget" lines) that have less elements and more fragile coatings. I would not use toothpaste - too abrasive. Supposedly the aluminum in SPF 40 or higher sun screens will work as an abrasive and not damage optical glass. Just be prepared to spend a lot of time buffing the coating off.
Those are the best web pages I have found in my searching. It is good to know that I am not the only one.

Page 7 is what led me to my lens choice. My problem/question still remains. Both abrasive creams and steel wool will scratch plastic.

Thanks!

---------- Post added 05-18-14 at 03:15 PM ----------

QuoteOriginally posted by Stone G. Quote
I believe the sensor's poor sensitivity in the UV-band is far more significant than smc coatings. But you might want to try something like this(???):

Photography in the Ultraviolet spectrum

I have no personal experiences, but it does make sense to me that you would need a UV-bandpass filter - and a bright UV-light source.
I can assume that the sensitivity of the sensor to UV behind the sensor filter is small. Therefore I need to make the lens as efficient as possible.
I plan to do mostly outdoor work. I hope sunlight will work with long exposures.

I would be using the B+W 403 and Tiffen hot filters on the lens. The 403 blocks the visible, lets the UV pass along with a little IR. The hot filter will block the remaining IR.

I could not find any material about how sensitive the K5 and K20 sensors are. Digital UV photography has been done with Nikon and Canon cameras. There are firms that will replace the sensor filter with one that will pass UV. I have read that long exposures will be required.
05-18-2014, 03:32 PM   #10
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FWIW jewelers rouge (ferric oxide) is used to remove fine scratches and to put the final polish on glass.

I've removed the coating on old eyeglass lenses (polycarbonate) using sunscreen containing aluminum silicates. This did not seem to affect the surface of the lens optically.
05-18-2014, 03:50 PM   #11
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QuoteOriginally posted by bluestringer Quote
I've never used it on glass, but have heard of people using it on vehicle windshields without a problem
QuoteOriginally posted by lmd91343 Quote
In a previous life I cleaned VERY expensive, custom blown lab glass with steel wool.
True, but both lab glass and car windshields are made of tempered glass. I used to work at a body shop. Steel wool is fine to clean grease pencil and stuff off of windshields and windows, but not the mirrors, which are not tempered. I'm pretty sure optical glass isn't tempered, either, so steel wool will scratch it.
05-18-2014, 04:11 PM   #12
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QuoteOriginally posted by lmd91343 Quote
I wish to remove the coatings from a Pentax A 50mm f2.0. Are all the elements glass?
Yes, but there are different types of glass used in this lens.

QuoteOriginally posted by lmd91343 Quote
I would use steel wool to remove the coatings. Obviously, steel wool should not be used on plastic.
For the love of god, do not do this. Crown glasses used in older lenses contain lead which make the glass somewhat softer and easier to shape, this property is why lead crystal glass is commonly used for ornate glassware. Some of the elements in the 50mm f/2.0 have high concentrations of lead in them and would be quite easy to damage them with steel wool. Personally If I wanted to remove the coatings from a lens I would strip it down clean the lens elements sonically and place the elements in an acid bath to remove the coatings and re-polish the elements with a suitable polishing compound afterward, ferric oxide would be an effective (albeit messy) way of doing it.

QuoteOriginally posted by lmd91343 Quote
Glass is harder that steel. Glass is more brittle, but harder. In a previous life I cleaned VERY expensive, custom blown lab glass with steel wool.
Lab glassware is constructed to high standards using tempered borosilicate glass that is harder than steel and less prone to fracture under temperate extremes and is resistant to abrasion. I have used fuming aqua regia to clean glassware without the surface getting etched but the materials are far from indestructible - Frisky perchlorates if mishandled, can pulverize lab glass back into sand in a fraction of a second.

Last edited by Digitalis; 05-18-2014 at 09:22 PM.
05-18-2014, 08:14 PM   #13
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A variety of opinion some of which I disagree with.


Lens elements are made of either glass or plastic. Lenses cannot be ground aspherically so any aspherical elements are cast plastic, a technique pioneered by canon in the 1970s. The front element is almost invariably glass but I don't know about all lenses manufactured. Its conceivable but unlikely that a lens exists with a plastic front element.


All surfaces in your lens will be coated so removing the coating from just the first surface is somewhat pointless. Most of the surfaces will be still coated after you have finished.


Optical glass is softer than window glass and easily damaged, wire wool will I imagine render the lens at worst unable to pass light other than totally diffuse and therefore unable to resolve any kind of image. Coatings are bonded to the element and will be difficult to remove and any removal is unlikely to be uniform or complete.


Lenses on cameras had no coatings at all for over 100 years, and I don't see any issues with any of the images they created, so a lens without coatings is perfectly useable.


I have a lens that has no coatings at all, its my best lens and my go-to lens for most work due to the beauty of the images it can produce.


I would agree that a lens without coatings can be unusable if it has a high number of glass surfaces. An uncoated glass surface loses 15% of light due to reflection, a coating cuts this to less than 1%.


Modern lenses with more than 15 elements would be unusable without coatings.


In the days of coating-less lenses 4 elements were the maximum that could be used. The Planar 6 element lens was designed in 1892 and was abandoned as useless until coatings could be applied to it in 1935. The Tessar however was a 4 element design, and was successful without coatings.


I agree, don't do it.

Last edited by Imageman; 05-18-2014 at 08:59 PM.
05-18-2014, 08:56 PM   #14
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It would be simpler to start with a lens with single or not very durable coatings. My guess would be something Russian but I don't know a lot about those lenses. Trying to polish the SMC off ten lens surfaces might get pretty old.
05-18-2014, 09:13 PM   #15
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QuoteOriginally posted by Imageman Quote
Lenses cannot be ground aspherically so any aspherical elements are cast plastic, a technique pioneered by canon in the 1970s.
Incorrect, solid ground glass aspherical elements have been mass produced since the 1950's*. Other manufacturers have found ways to make asperic molds and use them to shape heated glass blanks**. Also some manufacturers use plastics with aspherical shapes and by bonding them to solid glass lenses allow for a similar degree of correction**. The most prominent early photographic lens featuring a solid glass aspherical element was the Leica noctilux-M 50mm f/1.2 ASPH that was introduced in 1963.

* Though it has been said that aspherical lenses had been developed and created in limited numbers during the 1600's in order to improve the optical performance of telescopes.
** The Pentax FA31mm f/1.8 ASPH Limited uses a glass molded Aspheric in its construction.
***The DA- HD 15mm f/4 ASPH Limited uses a bonded Aspheric in its construction.

Last edited by Digitalis; 05-18-2014 at 09:19 PM.
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