• Ultraviolet Photography
  •  

Am I getting an image at 303nm?

14 replies to this topic

#1 Bernard Foot

    Bernard Foot

  • Members+G
  • 402 posts
  • Location: UK

Posted 21 November 2020 - 14:48

Following a discussion in this topic - https://www.ultravio...various-lenses/ - I thought I’d see if I could get an image at around the 300nm mark.

I think I am able to get an image at around the 303nm mark, but before I get too excited I’d be interested in other members’ opinions as to whether I really am getting an image at that wavelength, or whether there could be some type of contamination.

The kit used was:
  • Sony A6000 full-spectrum conversion
  • Simple plano-convex lens made from UV-grade Fused Silica (at about f/3.7)
  • 303BP10 filter from Omega Optical
  • 4 x WS560 cheap-from-China flashguns (de-lensed)
The main problems were likely to be:
  • Lack of illumination provided by the flashguns (as indicated in that other post). Stuff on the internet indicates that a Xenon tube would provide illumination to well below 300nm, but the lower wavelength limit could be severely restricted depending on the material the tube was made from.
  • The high transmission of the filter at 800nm (see below). All I had available that might block this was a U340 + ZWB1, plus ZWB1 filters over the flashguns – but IR leakage has to remain a real threat.
Attached Image: 303nm Filter Spectrum.jpg

The target was a piece of paper with “UV Only” written on it using an ink that was transparent to IR and “UV + IR” in an ink that would show up in both UV and IR. (Unfortunately I didn’t have an ink that would show up in IR but not UV). A “normal” IR shot using an R72 filter looks like this:

Attached Image: R72 Refocussed.JPG

The image I got using the 303BP10 + U340 + ZWB1 was this:

Attached Image: 303+ZWB1+U340 .JPG

Was this really a UV image? Yes – using a Hoya UV(0) filter completely destroyed the image.

Is there any visible leakage? No – as shown by the Hoya UV(0).

Was there any IR leakage? I don’t think so – the “UV only” writing should have been a lighter grey or not visible at all if there was an IR component to the image. More importantly, the Hoya UV(0) would have allowed any IR through, but the blank image from that filter indicated there was no IR present. Similarly, adding an R72 filter killed the image completely. It was also noticeable that significant re-focussing was needed between the UV the IR images shown above – indicating that the UV image did not have an IR component. (In fact the helicoid I was using did not have enough travel to get the IR image in focus.)

Was there leakage from other parts of the UV range? I don’t think so. Switching from the UVFS lens to a Cassar S lens (at f/2.8) killed the image – this is as expected, as the Cassar S transmits down to about only 315nm. Adding a 345BP20 or 380BP25 filter completely killed the image. Adding a 315BP25 filter did provide a dimmed image, but this would be expected as the transmission curves of the 303BP10 and 315BP25 filters overlap (see images below).

Attached Image: 303+ZWB1+U340 + 315.JPG

Attached Image: 303nm vs 315nm.jpg
Bernard Foot

#2 Stefano

    Member

  • Members(+)
  • 1,183 posts
  • Location: Italy

Posted 21 November 2020 - 15:35

Well, judging from what you said, I would say you got to 303 nm. You tested UVA, visibile and IR leakages and found nothing.

#3 colinbm

    Member

  • Members+G
  • 2,056 posts
  • Location: Australia

Posted 21 November 2020 - 16:29

Good on you Bernard.

#4 Andy Perrin

    Member

  • Members+G
  • 3,444 posts
  • Location: United States

Posted 21 November 2020 - 17:34

Definitely seems plausible. Can you do a UVA and UVB comparison of something like glass that we know usually darkens, like Jonathan did with that vase awhile ago?

#5 Bernard Foot

    Bernard Foot

  • Members+G
  • 402 posts
  • Location: UK

Posted 21 November 2020 - 18:17

View PostAndy Perrin, on 21 November 2020 - 17:34, said:

Can you do a UVA and UVB comparison of something like glass that we know usually darkens, like Jonathan did with that vase awhile ago?

I'll give that a go tomorrow - right now I've wound down for the day with a couple of glasses of wine - so not the best time to carry out highly precise, scientific experiments ...
Bernard Foot

#6 dabateman

    Da Bateman

  • Members+G
  • 2,213 posts
  • Location: Maryland

Posted 21 November 2020 - 18:28

Looks like you have all the controls in place.
I have the exact same 303bp filter and its good when you block it as you have done. It has the most 303nm transmission. My other 300bp10 filter only lets through about 10% at most.

The advantage I have found with using the single element lenses is one of there biggest disadvantages. That being that you need to refocus for each wavelength. This is good in that my 50mm BICX needs to move at least 6 inches back to get IR in focus. So it helps to isolate the UV signature.

You can get affordable continuous 302nm source lamps. Even the ExoTerra UVB bulbs will output some 302nm.

#7 Bernard Foot

    Bernard Foot

  • Members+G
  • 402 posts
  • Location: UK

Posted 21 November 2020 - 18:35

View Postdabateman, on 21 November 2020 - 18:28, said:


You can get affordable continuous 302nm source lamps. Even the ExoTerra UVB bulbs will output some 302nm.

I have an Exo Terra, and I will try using this. From what I remember, it is good at around 300 nm but it has quite a high IR footprint too.
Bernard Foot

#8 dabateman

    Da Bateman

  • Members+G
  • 2,213 posts
  • Location: Maryland

Posted 21 November 2020 - 20:51

View PostBernard Foot, on 21 November 2020 - 18:35, said:



I have an Exo Terra, and I will try using this. From what I remember, it is good at around 300 nm but it has quite a high IR footprint too.

Yes but for the ExoTerra its 708nm if I remember correctly. The filter hits just above 780nm. The flashes I think would have much less at 303nm and much more light at 800nm+.

But be careful with them. That light is still very dangerous. But you can get it really close to the subject as its not hot.

Edited by dabateman, 21 November 2020 - 20:52.


#9 JMC

    Member

  • Members+G
  • 1,150 posts
  • Location: London, UK

Posted Yesterday, 13:47

Bernard, it looks like you are getting a 303nm image. If you view the RAW file in Darktable or whatever RAW file viewer you have, without giving it any white balance, what colour is it? When I have tried doing 313nm imaging with my cameras with the Bayer filter still attached (a Canon and a Sony) when using a UV lens, I get a very strong green colour cast. I guess this is because of all 3 of the Bayer filters, the green has a slightly more transmission at that wavelength and dominates the image. Be interesting to know if you get a similar effect.
Jonathan M. Crowther

http://jmcscientificconsulting.com

#10 Bernard Foot

    Bernard Foot

  • Members+G
  • 402 posts
  • Location: UK

Posted Yesterday, 17:31

Hi, Jonathan.

Yes, I get green, as I do with the 315BP20 filter. Here is a shot with no profile and no WB set:

Attached Image: 303+ZWB1+U340 No WB No Profile LoRes.jpg

BTW - I also tried to get a shot in daylight. Here is what I got - straight out of the camera, set to give monochrome JPEGs. The image is very faint, and increasing the exposure just made it lighter without getting any more detail. This would be in keeping with the amount of 303 nm light in daylight being close to zero. And a 315 nm shot for comparison. In fact, if you look closely at the 303nm image you can see signs of IR contamination - light foliage, some other objects coming out light rather than dark, clouds standing out against the sky, and obvious focus shift - so there may be no UV component at all in this shot.

Here is the shot taken through the 303BP10 + U340 + ZWB1 (f/11, 30 sec., ISO 500):

Attached Image: Sun Winter 303 U340 ZWB1 LoRes.jpg

Here for comparison is a shot taken just 15 nm or so away, through a 315BP20 + U340 + ZWB1 (f/11, 20 sec., ISO 400):

Attached Image: Sun Winter 315 U340 ZWB1 LoRes.jpg

Edited by Bernard Foot, Yesterday, 17:36.

Bernard Foot

#11 Stefano

    Member

  • Members(+)
  • 1,183 posts
  • Location: Italy

Posted Yesterday, 17:54

Seeing the world in UVB always fascinates me.

In your 303 nm image you have for sure no visible light leaks (the OD anywhere between 400 and say 650 nm should be crazy high), you may have a weak point in the 700-800 nm region (where U-340 and ZWB1 leak a bit) since you may be getting some of your filter spike leak in the 760-800s. You may also have some UV leakage, but this wouldn't make things much lighter than normal, especially foliage (even if UVB is absorbed more in general than UVA by most materials, but not by foliage).

To catch 303 nm light in sunlight you have to have a strong filter, blocked really well, and we all know it isn't easy, but your camera/sensor are for sure capable of that.

#12 Andrea B.

    Desert Dancer

  • Owner-Administrator
  • 8,047 posts
  • Location: USA

Posted Yesterday, 18:33

Bernard, did you make the image in a dark room (or dark closet) to prevent IR contamination from ambient light?
I also don't think you are getting IR contamination, but a dark room adds another "filter" to the experiment.
Andrea G. Blum
Often found hanging out with flowers & bees.

#13 Bernard Foot

    Bernard Foot

  • Members+G
  • 402 posts
  • Location: UK

Posted Yesterday, 21:38

Andrea - no, it wasn't a dark room. Perhaps I'll retry with a properly dark room. But as I was using flash, the shutter speed was 1/200 sec so I can't believe there would be enough ambient IR getting through the 303B10 + U340 + ZWB1 to record any kind of image.
Bernard Foot

#14 Bernard Foot

    Bernard Foot

  • Members+G
  • 402 posts
  • Location: UK

Posted Yesterday, 22:51

Stefano - I'm sure the leak is in the IR where the U340 and ZWB1 have their secondary transmission peaks.
Bernard Foot

#15 Stefano

    Member

  • Members(+)
  • 1,183 posts
  • Location: Italy

Posted Yesterday, 23:11

Did you use every piece of U-340 and ZWB1 you have around? I think yes, but if not, you need to put as much glass as you can.

Also, are there other filters you have which can help you? If you have an Omega 330WB80, it cuts IR and also significantly reduces UV at 300 nm, but at least it should work.

A Baader U won't work. An Invisible Vision 308 nm filter should work, but I think you don't have one.