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Lens glass fluorescence

Fluorescence
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#1 Cadmium

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Posted 23 June 2017 - 06:50

Something I generally don't see mentioned about lenses, and something I only recently started thinking about is the lens glass fluorescence.
Line up a few or more lenses on a table, and shine your 365nm torch on them and notice the difference in how some fluoresce more than others.
Now of course the UV 365nm light would need to shine on them perhaps to make this a problem,
and if you have a 420nm longpass filter or the like on your lens, then that would prevent the lens glass from fluorescing,
but this is something to be aware of and think about with your lenses.
Perhaps some people shoot UVIVF with stock cameras with no lens filter, and you may want to shine the UV 365nm light on your stock lens to see how much it fluoresces.
I typically use a Schott GG420 longpass filter for my UVIVF shots, although I know that filter fluoresces when UV 365nm light is shined on it, it doesn't fluoresce with the way I aim the light and usually don't have a near background or much that reflects UV back at the lens. Point being, I guess if I can do that with no problems, then the lens glass fluorescing would probably not be a problem either.
Just thought I would mention this aspect though.

Examples:
Kuribayashi 35mm f/3.5 doesn't fluoresce.
Kyoei 80mm doesn't fluoresce.
Nikon 18-55mm VR does fluoresce.
Kyoei 250mm does fluoresce.
Etc...
Some of the lenses that transmit UV deeply and well actually fluoresce (not the ones I have listed, but some other I noticed do).
So it is something to check for.

#2 nfoto

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Posted 23 June 2017 - 08:57

Shining a narrow-beamed UV torch into a lens can be quite illustrative. Some lenses appear like they are densely fogged over and typically this occurs at the surface of a lens element, not necessarily the front one. The "fog" often looks brownish, at least with my Nichia torch. Other lenses can be crystal clear or at worst show the (few, hopefully) internal dust specks.

I think there is a correlation between the degree of "fogginess" and the usefulness for UV photography, but haven't gathered data points systematically though. My standard UV lenses (Coastal 60/4, UV-Nikkor 105) do not show any fogging. The Noflexar 35/3.5 shows some weak traces and the Tamron 21/4.5 is fogging slightly only inside of the rear group. Like Steve, I saw no fogging on my Kyoei 35/3.5.
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#3 Øivind Tøien

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Posted 23 June 2017 - 09:45

Ouch, I wish I had not tried that... Just about all of my Nikon lenses in the pre-AI/AI/AIS show that brownish, sometimes milk like fog you describe above. Some newer lenses have less of that in the front group, then usually with a weak green shimmering instead (for instance the zoom lens for the AW1).The rear group has it on almost all. It also looked like the diaphragm lit up in some of them, but less sure about that. The only lens that was almost clear is my 50mm f/2.8 Cassarit, which incidentally is supposed to be half good for UV as I understand.

Edit: Second thought: How intense is UV say when shooting into the sun compared to what the 365nm flashlight provides at that close range?

Edited by Øivind Tøien, 23 June 2017 - 12:59.

Øivind

#4 Cadmium

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Posted 24 June 2017 - 00:18

Hmm, that is an interesting thought. I was only thinking about UVIVF shots, but if the UV passing through a UV-only filter fluoresces the lens producing visual range light, then that visual light is getting to the sensor mixed with UV.
Something to think about...

#5 OlDoinyo

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Posted 24 June 2017 - 03:54

With luck, any visible fluorescence in the optical train will reach the sensor as a uniform background or "fog" which can be subtracted out to get the net UV image. If this is not true, the situation is of course more complicated.

#6 Cadmium

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Posted 24 June 2017 - 04:23

Of course, rear mounting UV-only filters might be one way around lens glass fluorescence for UV-only.
But 420nm longpass filters to block UV would need to be on the front of the lens to keep the lens glass from fluorescing for UVIVF.
Also consider that the lens glass might also be fluorescing above the visible range, in the IR range, which can also be excited by 365nm UV...
I have not tested that yet, but easy enough to do with a full spectrum camera and IR longpass filter on the lens.

I have looked at a lot of my lenses, and the ones that have clear non-fluorescing glass are these (so far):
Kuri 35mm
Petri 35mm (the one Bjorn found)
Kyoei 80mm
Kuri 105mm

All the rest seem to exhibit some degree of lens glass fluorescence, which can range from a mild milky white, a strong milky white, to cloudy brown.
All of which can be described as 'cloudy', or 'foggy'.
Also, you may see fluorescence coming from the visually black paint inside a lens.

Some other examples:
Kuri 135mm, Kuri 180mm, Kyoei 250mm, Kuri 500mm all show varying degrees of milky cloudy foggy white fluorescence. Kuri 180mm and Kuri 250mm being the strongest.
ALL my enlarger lenses (mostly a lot of El-Nikkor) show some of the same, mostly mild, even the 80mm, with the Focotar-2 50mm showing very little.
Both Nikkor 18/4 and Bushnell (Tamron) 21/4.5 show brown fluorescence. Q 105mm and Q 200mm, brown.

My Petri/Lentar long lens collection, all milky white or brown, varying amounts.
So... not many lenses that have non fluorescing glass.

Edited by Cadmium, 24 June 2017 - 08:40.


#7 Shane

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Posted 24 June 2017 - 20:51

if you dig deep you will find earlier discussions on this issue but it is always a good refresher for newcomers.

With older lenses it can also be the optical coupler used between lens elements, which in some cases is canada balsam oil.

#8 Cadmium

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Posted 26 June 2017 - 06:19

A small comparison group.
Attached Image: Lens_Fluorescence_800h.jpg

#9 Øivind Tøien

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Posted 26 June 2017 - 11:02

A friend's 24mm f/2.0 AIS, one can barely see the aperture.

UVIVF front:

Posted Image


UVIVF Rear:

Posted Image


Cassarit 50mm f/2.8 visible light:

Posted Image


UVIVF front:

Posted Image


UVIVF rear:

Posted Image


In these last two it looks to be clear sight to the aperture from both ends.

Edited by Øivind Tøien, 26 June 2017 - 11:08.

Øivind

#10 nfoto

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Posted 26 June 2017 - 13:59

The 24/2 Nikkor is not very suitable for UV - hardly a surprise ?

Occasionally one stumbles across a lens that delivers outstandingly sharp images in UV, despite not having a "deep" UV response at all. Such a lens is the Nikkor 85/1.4 AIS that in a direct UV shoot-out compared very favourably against the UV-Nikkor 105. That is, in terms of image sharpness, not in UV response as such.
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#11 Andrea B.

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Posted 28 June 2017 - 12:55

I will put a reminder about lens fluorescence into the Lens Sticky.

The fluorescence I'm thinking must be from coatings or glues mostly?

I have a list of lens glass types, but there's nothing about possible fluorescence.
We should look that up.
Lens Glass Types: Approximate Transmission Ranges

Schott has a very good technical PDF full of info about their optical glass fluorescence but it references the glass by Schott ID and there is no correlation in the PDF to what kind of glass.
TIE-36: Fluorescence of optical glass - Schott AG


The Properties of Optical Glass
Editors: Bach, Hans, Neuroth, Norbert (Eds.)
from the Schott series on glass and glass ceramics
Springer 2004
There are used copies for $300-350 if you really really want to learn about this. (!!)
  • Chapter 3: Optical Quality
    Section 3.2: Colouration, Solarization and Fluorescence
  • Chapter 8: Selected Applications
    Section 8.3: Ultraviolet-Transmitting Glasses
    Section 8.4: Infrared-Transmitting Glasses
These screen shots are publicly available via Amazon's Look Inside feature.
Due copyright recognition is provided just above by the book listing.
These are just little intro paragraphs. There is a LOT of info in the sections.
unfortunately I cannot access Section 3.2 in its entirety to see what there is about fluorescence.

Attached Image: Screen Shot 2017-06-28 at 9.25.33 AM.jpg

Attached Image: Screen Shot 2017-06-28 at 9.25.42 AM.jpg
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#12 Cadmium

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Posted 28 June 2017 - 22:14

Yes, I think it is mostly due to adhesives. Some of these lenses above may not have any glued elements.
However, some adhesives are designed for low fluorescence.
Note an old test of two cheap clear diopter close up lenses (probably BK7 glass) at left.
These are glued together with two separate drops of two types of modern optical adhesives, these are separated by non glued glass areas, none can be differentiated in the photo. Norland #63 and Normand #88.

#13 OlDoinyo

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Posted 05 July 2017 - 18:07


Occasionally one stumbles across a lens that delivers outstandingly sharp images in UV, despite not having a "deep" UV response at all. Such a lens is the Nikkor 85/1.4 AIS that in a direct UV shoot-out compared very favourably against the UV-Nikkor 105. That is, in terms of image sharpness, not in UV response as such.《

Narrow bandpass can actually increase sharpness, just by decreasing the scope for CA.

#14 Hornblende

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Posted 28 December 2017 - 17:48

My Carl Zeiss Jena 50mm f/2.8, the orange glow comming from the front element was quite spectacular with my (UV-protected) naked eyes. What is also spectacular is the quantity of dust my lens collects, I should be more careful with my equipement :unsure:
Attached Image: IMG_0313 2.jpg

#15 Andrea B.

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Posted 29 December 2017 - 04:47

Wow! That is really strong orange. I do wonder what is fluorescing there?
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#16 Andy Perrin

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Posted 29 December 2017 - 05:59

I don’t know, but that lens looks like it’s about to ask Dave Bowman what he thinks he is doing.

#17 Hornblende

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Posted 29 December 2017 - 15:19

Andrea: I don't know, could be trace elements present in the glass?

Andy: :lol: :lol: :lol: like Cadmium's avatar!

Edited by Hornblende, 29 December 2017 - 15:20.


#18 Shane

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Posted 29 December 2017 - 18:22

I have actually tested a significant amount of optical adhesives and optical oils actually for a fractured filled emerald project. Table 1 in the following article may be of interest.
https://www.gia.edu/...ling-Substances

Keep in mind that many of these are modern optical adhesives and may not have existed at the time a lens was manufactured.

The other possibility is rare earth elements.

Edited by Shane, 29 December 2017 - 18:24.


#19 Hornblende

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Posted 29 December 2017 - 20:02

I own an old russian lens wich contains trace amount of Thorium in the glass, I will test its fluorescence once I get back home from holiday.

#20 Cadmium

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Posted 30 December 2017 - 00:40

View PostAndy Perrin, on 29 December 2017 - 05:59, said:

I don’t know, but that lens looks like it’s about to ask Dave Bowman what he thinks he is doing.

View PostHornblende, on 29 December 2017 - 15:19, said:

Andy: :lol: :lol: :lol: like Cadmium's avatar!

https://youtu.be/UgkyrW2NiwM

Edited by Cadmium, 02 January 2018 - 02:31.