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Fast lens de-yellowing without a UV lamp
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PostPosted: Mon Nov 17, 2014 6:38 pm    Post subject: Fast lens de-yellowing without a UV lamp Reply with quote

Recently I bought a Minolta MC 2.5/28 lens from fellow forum member Tervueren (thanks again John!). Smile
One of the internal elements was 'yellowed' so I started researching both on this forum and on the web in general for a solution. I always thought that UV light was required either from a lamp or from exposure to the sun to bleach the lens until I came across an article on YouTube from an American photographer with a different solution. He used a LED lamp from IKEA (Model JANSJO). I must admit I was a bit skeptical, but as the lamp only cost 10 I thought I would give it a go and if it didn't work I would still have a worklamp I could use.

Here is a photo of my set-up. I lined a bowl with silver foil, placed the lens face down with aperture wide open and positioned the lamp just above it. As it is an LED lamp it doesn't generate any heat so the lamp was as close to the rear element as I could position it.



I left it like this for 72 hours or three days if you prefer. The result is amazing! The 'yellowing' has practically gone.
I don't understand the science behind this because I always thought UV light was required, but if someone can explain it I would be very interested to know.

Below is a photo of the lens taken by Tervueren before I bought it.



This photo is the same one altered by me to show what the lens looks like now to my eyes (I'll update this thread with a proper shot of the cured lens as soon as I can).



PostPosted: Mon Nov 17, 2014 7:40 pm    Post subject: Reply with quote

Can not work, it is not profesional work like this Wink
Click here to see on Ebay
OK, he/she wrote that is is home build, so your setup will work likely as well.

But his/her list of yellowing / radioactive lenses is quite good, worth saving that list Smile


PostPosted: Mon Nov 17, 2014 9:35 pm    Post subject: Reply with quote

Excellent! I've read about that Ikea lamp before and had thoughts to buy one. I would use the same setup except that I would put the lens on a mirror. Don't know if it would work any faster though...

Btw, I think the LED is emitting UV-light.


PostPosted: Tue Nov 18, 2014 10:44 am    Post subject: Reply with quote

My wife's nail dryer UV lamp does this job for me. Wink


PostPosted: Tue Nov 18, 2014 4:02 pm    Post subject: Reply with quote

I never knew such a thing existed, I shall have to get my wife to buy one. Laughing

http://www.amazon.co.uk/LEVIPOWER-EDITION--Quality-Professional-Approved/dp/B00M4SXO36/ref=sr_1_192?ie=UTF8&qid=1416326382&sr=8-192&keywords=nail+dryer

this looks like ideal, she could get both hands in, if it's not full of old lenses, and the bottom slides off, so it could easily be placed on top of a bigger box, with even more lenses! Shocked


PostPosted: Tue Nov 18, 2014 6:05 pm    Post subject: Reply with quote

dan_ wrote:
My wife's nail dryer UV lamp does this job for me. Wink


So it does work? I was wondering if it would but never could find a definitive answer. Which kind does she have - one lamp or multi?


PostPosted: Wed Nov 19, 2014 1:05 pm    Post subject: Reply with quote

It is a 4 lamps unit. I have only used it twice because I don't have so many yellowed lenses. I let the lenses in for ~ 1 week and clearly noticed an improvement.


PostPosted: Thu Nov 20, 2014 2:26 pm    Post subject: Reply with quote

Wow, a week?! I expected you'd say overnight and not a trace of yellow.


PostPosted: Thu Dec 24, 2015 5:15 am    Post subject: Reply with quote

DigiChromeEd

Good solution, thanks for sharing!


PostPosted: Thu Dec 24, 2015 8:14 pm    Post subject: Reply with quote

I wonder if the heat produced by the lamp highly increases the deyellowing-speed.
Because the UV-exposure caused by such a lamp (these kind of LED's are producing only a very little UV light as far as I know) within a week should be much lower than one summer day of direct sun I guess. But these lamps are getting warm


PostPosted: Fri Dec 25, 2015 9:19 pm    Post subject: Reply with quote

Can someone provide some argumented reason why "UV" would be able to clean such a yellowed element ?
I have been professsionally involved in lots of spectro-photometric equipment and I've never know that "glass" is letting any UV pass through .. In fact the cut-off frequencies are around 400-380 nm .. which is anything but UV ... so please explain this IMHO sort of witchcraft ?


PostPosted: Fri Dec 25, 2015 9:45 pm    Post subject: Reply with quote

From this it seems that it is not exactly the UV light that is needed, but probably just enough "energy"?


PostPosted: Sat Dec 26, 2015 12:33 am    Post subject: Reply with quote

+1 blende8

@ForenSeil, I don't think that led puts out much power -- less than one watt -- not much heat at all...

Perhaps proper wavelength is inside blue color...this would make sense because the blue sky radiates a lot of UV too, but it is the blue color that cures the glass (or in this case maybe coating).


PostPosted: Sat Dec 26, 2015 1:22 pm    Post subject: Reply with quote

I doubt that it has anything to do with blue sky radiating UV ... The "blue" in the sky is caused by light scattering due to the Rayleigh and/or Tyndall effects ... mabe the blue wavelengths in visible light have enough energy to clean up the "yellowing" ?
Fact is that orange-yellow is the "complementary" color of "blue". is the strong absorption (energy) of the "blue" light the cause of clearing the "yellow" ?


PostPosted: Sun Dec 27, 2015 2:45 am    Post subject: Reply with quote

Rigel wrote:
I doubt that it has anything to do with blue sky radiating UV ... The "blue" in the sky is caused by light scattering due to the Rayleigh and/or Tyndall effects ... mabe the blue wavelengths in visible light have enough energy to clean up the "yellowing" ?
Fact is that orange-yellow is the "complementary" color of "blue". is the strong absorption (energy) of the "blue" light the cause of clearing the "yellow" ?


Very Happy Brilliant! Could light of the proper blue wavelength, such as some octave of the orange-yellow wavelength of thorium, re-energize the degraded thorium to clear? Now if there is a blue led "just opposite" the orange-yellow of thorium...


PostPosted: Sun Dec 27, 2015 10:24 am    Post subject: Reply with quote

UV photons have more energy than any visible wavelengths.

Total energy is not too relevant, in chemical reactions. It's the energy of the photon that's important. If the photon has enough energy to get the reaction over the threshold it can proceed, if not the energy is no help.
It's a bit like climbing over a wall, a small jump doesn't let you reach the top & you fall back, another small jump won't help, but one bigger jump can.

Glass does block UV but it's not total. At longer UV wavelengths you can get over 50% of the UV transmitted through a typical lens. A couple of the photographic lenses I've measured transmit about 1% right down at 300nm (that's nearly half wave down through the non vacuum UV region by ~180mn air absorbs UV pretty quickly).


PostPosted: Sun Dec 27, 2015 10:38 am    Post subject: Reply with quote

@DConvert: That may all be correct, but the above LED lamp does not emit UV light.
LEDs are especially low of UV.


PostPosted: Sun Dec 27, 2015 11:43 am    Post subject: Reply with quote

DConvert wrote:
..
Glass does block UV but it's not total. At longer UV wavelengths you can get over 50% of the UV transmitted through a typical lens. A couple of the photographic lenses I've measured transmit about 1% right down at 300nm (that's nearly half wave down through the non vacuum UV region by ~180mn air absorbs UV pretty quickly).


That may cutting short through the bends Wink

I have my doubts about that 50% transmission figure, I've never seen this happen and it would have saved us a lot of money in not having to buy expensive analysis cells. Very Happy The caveat is that it is unknown which combinations of "glass"(es) are used in lenses. Searching spectral transmission graphs for all types of glass show all sorts of curves .. some "special glass" types even have a 10% transmission at 300 nm while others have a steep cut-off showing 0% transmission at 390-400 nm ...
but let's assume that lens glass has the beneficial 1% transmission factor at 300nm Smile (which I've never seen listed in any spectro-photometric equipment tech specs.) call me sceptic. Very Happy


PostPosted: Mon Dec 28, 2015 12:07 am    Post subject: Reply with quote

Rigel wrote:
DConvert wrote:
..
Glass does block UV but it's not total. At longer UV wavelengths you can get over 50% of the UV transmitted through a typical lens. A couple of the photographic lenses I've measured transmit about 1% right down at 300nm (that's nearly half way down through the non vacuum UV region by ~180mn air absorbs UV pretty quickly).


That may cutting short through the bends Wink

I have my doubts about that 50% transmission figure, I've never seen this happen and it would have saved us a lot of money in not having to buy expensive analysis cells. Very Happy The caveat is that it is unknown which combinations of "glass"(es) are used in lenses. Searching spectral transmission graphs for all types of glass show all sorts of curves .. some "special glass" types even have a 10% transmission at 300 nm while others have a steep cut-off showing 0% transmission at 390-400 nm ...
but let's assume that lens glass has the beneficial 1% transmission factor at 300nm Smile (which I've never seen listed in any spectro-photometric equipment tech specs.) call me sceptic. Very Happy


The data I measured can be found at http://global-infrared.freeforums.net/thread/80/lens-transmission-wavelength-repost-forum. It was measured on a reasonably high grade UV/vis spectrometer (a Perkin Elmer Lambda 35) but without the aid of an integrating sphere or any special alignment aids. This poor alignment probably being responsible for the low overall transmission seen in the wider angle lenses.

The lenses that gave best UV transmission tended to have less glass & no fancy coatings. The 80mm El-Nikkor having been brought specifically because of on-lines reports that it was usable for UV, but the 35mm c mount also proved to have reasonable transmission.

It's not difficult to find 'special glasses' with no significant UV transmission, quite a few of them don't transmit blue either!

As far as LEDs go I've never tried measuring the UV emissions, but I do know that many white LEDs achieve their relatively broad spectrum light by means of a phosphor that is exited by the LEDs emitted wavelength.
The LED lamps lighting the room I'm in at the moment have a good broad emission spectra & incidentally do emit some IR (I've photographed it through a diffraction grating with & without a 720nm filter - Unlike tungsten lights the IR emitted is considerably weaker than the visible.


PostPosted: Mon Dec 28, 2015 8:22 am    Post subject: Reply with quote

DConvert wrote:
Rigel wrote:
DConvert wrote:
..
Glass does block UV but it's not total. At longer UV wavelengths you can get over 50% of the UV transmitted through a typical lens. A couple of the photographic lenses I've measured transmit about 1% right down at 300nm (that's nearly half way down through the non vacuum UV region by ~180mn air absorbs UV pretty quickly).


That may cutting short through the bends Wink

I have my doubts about that 50% transmission figure, I've never seen this happen and it would have saved us a lot of money in not having to buy expensive analysis cells. Very Happy The caveat is that it is unknown which combinations of "glass"(es) are used in lenses. Searching spectral transmission graphs for all types of glass show all sorts of curves .. some "special glass" types even have a 10% transmission at 300 nm while others have a steep cut-off showing 0% transmission at 390-400 nm ...
but let's assume that lens glass has the beneficial 1% transmission factor at 300nm Smile (which I've never seen listed in any spectro-photometric equipment tech specs.) call me sceptic. Very Happy


The data I measured can be found at http://global-infrared.freeforums.net/thread/80/lens-transmission-wavelength-repost-forum. It was measured on a reasonably high grade UV/vis spectrometer (a Perkin Elmer Lambda 35) but without the aid of an integrating sphere or any special alignment aids. This poor alignment probably being responsible for the low overall transmission seen in the wider angle lenses.

The lenses that gave best UV transmission tended to have less glass & no fancy coatings. The 80mm El-Nikkor having been brought specifically because of on-lines reports that it was usable for UV, but the 35mm c mount also proved to have reasonable transmission.

It's not difficult to find 'special glasses' with no significant UV transmission, quite a few of them don't transmit blue either!

As far as LEDs go I've never tried measuring the UV emissions, but I do know that many white LEDs achieve their relatively broad spectrum light by means of a phosphor that is exited by the LEDs emitted wavelength.
The LED lamps lighting the room I'm in at the moment have a good broad emission spectra & incidentally do emit some IR (I've photographed it through a diffraction grating with & without a 720nm filter - Unlike tungsten lights the IR emitted is considerably weaker than the visible.


If you're interested in UV transmitting lenses, have a look at my Blog http://uvir.eu


PostPosted: Mon Dec 28, 2015 10:04 am    Post subject: Reply with quote

That is an extremely interesting blog !! (some pages missing ? list of UV lenses ?) ... but you will have to admit, this is hardly the daily setup of any John Doe that spends his/her spare time with photography ! Very Happy


PostPosted: Mon Dec 28, 2015 10:49 am    Post subject: Reply with quote

kds315* wrote:

If you're interested in UV transmitting lenses, have a look at my Blog http://uvir.eu


An excellent blog Klaus, and the reason I'd found the El-Nikkor.
My photographic funds are quite limited, but working with spectroscopy has distinct advantages.

Sometime I'll get my old K100d out & have another go as it seems to have more UV response than my converted camera! I might also try a single elements quartz lens.


PostPosted: Mon Dec 28, 2015 12:19 pm    Post subject: Reply with quote

DConvert wrote:
kds315* wrote:

If you're interested in UV transmitting lenses, have a look at my Blog http://uvir.eu


An excellent blog Klaus, and the reason I'd found the El-Nikkor.
My photographic funds are quite limited, but working with spectroscopy has distinct advantages.

Sometime I'll get my old K100d out & have another go as it seems to have more UV response than my converted camera! I might also try a single elements quartz lens.


Yep, that 5.6/80mm (and 105mm) older chrome/black EL-Nikkor is one of the best + affordable UV lenses!

Glad you liked it! Wink


PostPosted: Mon Dec 28, 2015 5:20 pm    Post subject: Reply with quote

Since starting this thread I have come across this article on the web which may be of interest:

https://mbphotox.wordpress.com/2015/09/25/removing-the-color-cast-in-radioactive-lenses-results/


PostPosted: Mon Dec 28, 2015 5:48 pm    Post subject: Reply with quote

I hope you all know this classic?

http://web.aanet.com.au/bayling/repair.html
(Not for the faint of heart.)