• Ultraviolet Photography
  •  

Strange Symbol Revealed In UV

Fluorescence UV Lens
11 replies to this topic

#1 Andy Broomé

    Invisible Light Enthusiast

  • Members
  • 109 posts
  • Location: Mississauga/Toronto, Ontario, Canada

Posted 31 July 2018 - 04:03

In my spare time, I am going through my collection of weird lenses to see if I can find some good candidates for UV photography. I have various "regular" lenses, along with enlargers and projector lenses in different and arcane mount/barrel sizes.

Using my Convoy S2+ flashlight, I have checked for "milky" lens elements in the front and rear. Then I shine the flashlight directly through the lens onto a reflective surface to roughly gauge the amount of transmission of each lens (I have no fancy equipment to measure the actual transmission, but even through my UV goggles I can see some clear winners).

All of the lenses render a brightish spot (surrounded by a darker area) on the reflective surface - some bigger, and some obviously brighter.

One weird projector lens, a "Bell KO-ON" 20-32mm f/1.5 zoom, gave me a particularly big spot. When I slowly pulled the flashlight away from the back of the lens, an odd symbol came into focus:

Attached Image: UV Lens Signature.png

So then I went back to my other lenses, and I noticed that they all had the same symbol, most of them smaller than the Bell KO-ON (even though some were almost as bright).

What is this symbol, and what purpose does it serve? Using a "regular" flashlight, this symbol does not appear.

#2 Andy Perrin

    Member

  • Members(+)
  • 1,641 posts
  • Location: United States

Posted 31 July 2018 - 04:56

If I'm right, you're going to laugh. I think that's the image of the LED chip in your Convoy!

ETA: Yep! LOOOOOL.
Attached Image: IMG_0555 small.jpg
Attached Image: IMG_0555 smaller.jpg

ETA2: It would be more fun to imagine an Illuminati-like organization stamping mysterious symbols in lenses to communicate SECRET MESSAGES in UV, though.

Edited by Andy Perrin, 31 July 2018 - 05:13.


#3 Jim Lloyd

    Member

  • Members(+)
  • 300 posts

Posted 31 July 2018 - 06:25

Presumably what you are seeing on the reflective surface is uv induced visible fluorescence otherwise you wouldn’t see it (even if you could see uv , wouldn’t get through the uv goggles). Probably the method still works though. I suppose you could use uv camera with known good lens to photograph the lens being tested . You could then remove the test lens and get an image of the flashlight so that you could quantify the transmission - maybe ? Just thinking aloud . I will have a play and see if I come to the same conclusions with this method compared to my recent sparticle tests

Edited by Jim Lloyd, 31 July 2018 - 08:31.


#4 UlfW

    Ulf W

  • Members(+)
  • 368 posts
  • Location: Sweden, Malmö

Posted 31 July 2018 - 08:36

View PostAndy Broomé, on 31 July 2018 - 04:03, said:

Using a "regular" flashlight, this symbol does not appear.
Most if not all power LEDs has patterns like this.
They are not exactly identical, but all have a channel-like pattern.
It is to distribute the current evenly over the LED-chip.
That helps to keep the light intensity and the local temperature even over the chip.

With some zoomable flashlights you can project that pattern in the most narrow setting of the zoom.
The edges of the pattern from a white light LED will have some coloured fringing due to differences in refraction for different wavelengths.
That phenomena is called dispersion.

Edited by UlfW, 31 July 2018 - 08:39.

Ulf Wilhelmson
Curious and trying to see the invisible.

#5 Andy Perrin

    Member

  • Members(+)
  • 1,641 posts
  • Location: United States

Posted 31 July 2018 - 13:20

View PostJim Lloyd, on 31 July 2018 - 06:25, said:

Presumably what you are seeing on the reflective surface is uv induced visible fluorescence otherwise you wouldn’t see it (even if you could see uv , wouldn’t get through the uv goggles). Probably the method still works though. I suppose you could use uv camera with known good lens to photograph the lens being tested . You could then remove the test lens and get an image of the flashlight so that you could quantify the transmission - maybe ? Just thinking aloud . I will have a play and see if I come to the same conclusions with this method compared to my recent sparticle tests

Jim, these LEDs have such a narrow band of output wavelengths that you’d only be testing transmission near whatever the flashlight’s peak wavelength is.

#6 UlfW

    Ulf W

  • Members(+)
  • 368 posts
  • Location: Sweden, Malmö

Posted 31 July 2018 - 15:51

View PostAndy Perrin, on 31 July 2018 - 13:20, said:

Jim, these LEDs have such a narrow band of output wavelengths that you’d only be testing transmission near whatever the flashlight’s peak wavelength is.
If using several types of LEDs more information could be available.

However there is a lot of problems to solve if any accuracy is needed.
The available types are few below 365nm.
The intensity varies with both with chip temperature and drive current.
The absolute wavelength of an individual LED is not very well specified and also varies with temperature.
Some LEDs I have seen (cheap Chinese) have casing materials that are fluorescent.
Most LEDs in the wavelength range 300nm-360nm cost around $100 per LED
Many of the LEDs for UV are surface mounted. They might be difficult to solder without correct equipment and experience.

Here is a link to what one big general component supplier has in stock of remaining alternative through hole mounted UV-LEDs:
https://www.digikey....k=1&pageSize=25

I think that a sparcticle solution is better. :) :) :)

Edited by UlfW, 31 July 2018 - 18:27.

Ulf Wilhelmson
Curious and trying to see the invisible.

#7 Andy Broomé

    Invisible Light Enthusiast

  • Members
  • 109 posts
  • Location: Mississauga/Toronto, Ontario, Canada

Posted 31 July 2018 - 17:23

View PostAndy Perrin, on 31 July 2018 - 04:56, said:

If I'm right, you're going to laugh. I think that's the image of the LED chip in your Convoy!

ETA: Yep! LOOOOOL.

ETA2: It would be more fun to imagine an Illuminati-like organization stamping mysterious symbols in lenses to communicate SECRET MESSAGES in UV, though.

Wow, don't I feel silly! :)

Easily explained then. Still, it's interesting how (I'm guessing) the rear element is reflecting the light back into the flashlight and then the flashlight's reflector is sending it back out again through the lens.

I suppose it's a similar effect to when the optometrist shines a bright light into my eye and I can see the silhouette of my eye's blood vessels.

Edited by Andy Broomé, 31 July 2018 - 19:50.


#8 Andy Perrin

    Member

  • Members(+)
  • 1,641 posts
  • Location: United States

Posted 31 July 2018 - 17:50

Maybe I'm misunderstanding what you're doing, but I thought you were just shining the light through the lens? Those are projector lenses, you said, so having them...project the light...does not seem that surprising?

#9 Jim Lloyd

    Member

  • Members(+)
  • 300 posts

Posted 31 July 2018 - 18:30

A quick test on few of my lenses using my WindFire 365 nm flashlight and I didn't feel I was getting any reliable information about the suitability of the lenses. I tried both looking at reflections when shining through the lens and looking at the torch (flashlight) with modified camera and visible blocking filter.

In my admittedly limited experience as a quick test of lenses with limited equipment, then I think photographing flowers is not bad. Particularly something like a dandelion which is false yellow in UV with UV absorbing centre.

#10 Andy Broomé

    Invisible Light Enthusiast

  • Members
  • 109 posts
  • Location: Mississauga/Toronto, Ontario, Canada

Posted 31 July 2018 - 19:12

View PostAndy Perrin, on 31 July 2018 - 17:50, said:

Maybe I'm misunderstanding what you're doing, but I thought you were just shining the light through the lens? Those are projector lenses, you said, so having them...project the light...does not seem that surprising?
That's what I'm doing, yes. With the flashlight right up against the rear element, this doesn't show. It's only when I pull the flashlight back that I'm getting the LED chip in focus.

I'm doing this with projection lenses, enlargers and conventional mount lenses.

#11 Andy Perrin

    Member

  • Members(+)
  • 1,641 posts
  • Location: United States

Posted 31 July 2018 - 19:34

Quote

With the flashlight right up against the rear element, this doesn't show.
Yes, if you hold the flashlight closer than the rear focal distance than it won't focus. G is your flashlight here.
Attached Image: Spimoptics_lensimaging.png

This one shows what happens when it's too close:
Attached Image: 154120_42201_68.jpg

Edited by Andy Perrin, 31 July 2018 - 20:30.


#12 dabateman

    Da Bateman

  • Members(+)
  • 338 posts
  • Location: Maryland

Posted 31 July 2018 - 19:58

@Jim,
Pedro has developed this method for lens test see this link.
https://photo.r4phot...otebook.nb.html