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UV/IR Thermal or Xray Photography Humans happen to use visible light naturally but now we can go beyond the usual wavelengths we appreciate, to find out more about our world and ourselves.

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  #1  
Old August 12th, 2018, 05:33 PM
Reed Curry Reed Curry is offline
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Default Black-eyed Susan with a twist

I shot this Black-eyed Susan while testing a lens. Instead of setting the in-camera white balance against a PTFE disc, I set it to the entire frame. I like the camera's UV interpretation of the honey guide.




Last edited by Asher Kelman; September 22nd, 2018 at 08:31 AM.
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  #2  
Old August 12th, 2018, 07:49 PM
Asher Kelman Asher Kelman is offline
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Quote:
Originally Posted by Reed Curry View Post
I shot this Black-eyed Susan while testing a lens. Instead of setting the in-camera white balance against a PTFE disc, I set it to the entire frame. I like the camera's UV interpretation of the honey guide.

Explain to me how sufficient UV light gets into the camera! Do you have a special quartz optic?

Asher
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  #3  
Old August 12th, 2018, 08:42 PM
Reed Curry Reed Curry is offline
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Asher,
The lens is a Steinheil Caesar S 50mm 1:2.8 ca. 1956. The Cassars are triplets known to be good in UV transmission to about 320nm. The camera is a Lumix GF1, ISO 400, 1second, f11. The filter is a UVROptics SEU. Gen2, a new design. Independent tests show the Gen2 to be one stop faster than other filters tested.

(Disclaimer: I make the filters and have some understandable bias. Hence, independent tests.)
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Old August 13th, 2018, 12:30 AM
Asher Kelman Asher Kelman is offline
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Hmm, I have to check! I may have that lens!

Tell us about your UV filter production, seems interesting and useful!

Asher
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Old August 13th, 2018, 09:51 AM
Reed Curry Reed Curry is offline
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Asher,

The new UV Bandpass filter from UVROptics uses a sandwich of IR absorbent glass between two dichroic filters. A good overview of the filter may be found at SEU Gen2 Description.

For years I have been working on a UV bandpass filter that would be fast, sharp, and would capture the wavelengths from 370-400nm that the Schott UG11-based filters miss. The SEU Gen2 is that filter.

Andrea G. Blum of ultravioletphotography.com ran eleven different tests on the SEU Gen2. See Test Summary. I enjoyed some of Andrea's conclusions:
  • Exposures times under the SEU Gen2 are faster than with other well-known UV-pass filters, all other factors being equal, because the filter's highest transmission rate, between 60-73%, is in the 370-400 nm range where sunlight provides the most UVA. This aids outdoor UV captures under hazy or overcast conditions when there is less UV reaching ground level.
  • The SEU Gen2's 70-73% transmission between 380-400 nm is very useful for non-specialist, UV-capable lenses many of which do not reach past 370 nm or so.
  • The SEU Gen2 nicely preserves the sharpness and detail offered by the lens in use. It is impressive on a lens like the UV-Nikkor 105/4.5 (rig on tripod, remote shutter triggering). I was not able to fully explore monochrome comparisons, but I really liked the Black & White conversions from the SEU Gen2.
  • There is no Visible or IR leakage in photos made under a UV-cutting longpass filter stacked over the SEU Gen2 and given the same exposure as the UV-only frame. There is a very good transmitance chart on the product page showing the out-of-band blocking.
  • The SEU Gen2 is well made. Protective screw-on caps are included in the purchase and should be used for storage to protect the mirrored surfaces.

Thanks.

Regards,
Reed
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Old August 13th, 2018, 10:20 AM
Asher Kelman Asher Kelman is offline
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Thanks for the info. I found that site, but I am unfamiliar with her work.

Is there somewhere a list of non specialist lenses suitable for your filters?

Also, do you similarly design IR filters. For landscape that should cut the haze.

Asher
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Old August 13th, 2018, 12:49 PM
Reed Curry Reed Curry is offline
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Asher,

For a list of UV-capable lenses see uv-capable-lenses/

I don't construct IR filters, sorry.

regards,
Reed
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  #8  
Old August 15th, 2018, 01:52 AM
Dr Klaus Schmitt Dr Klaus Schmitt is offline
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From Mr Curry's site...the SEU Gen2 diabatic transmission graph showing some deep blue / violet leakage.

No leakage would be if transmission stays below 1E-03 (OD3), or even better 1E-04 (OD4) by current experience using converted digital cameras.



Another measurement from Dr Jonathan Crowther, note the area above 400nm



Nevertheless an interesting filter for the 380-400nm range (which by current ICC standards is not even considered UV; their UV definition starts <380nm) for scientific photography (sunscreen testing for skin protection etc comes to mind).

Certainly a plus to have it for the ambitious reflected UV photographer who know how and when to use it...
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Old August 15th, 2018, 11:15 AM
Reed Curry Reed Curry is offline
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While it is true that there is some violet "leakage" inherent in the SEU Gen2 filter, the actual occurrence of violet intrusion is a moot point. So let us moot:

The summary of the discussion regarding testing of the SEU Gen2 contained the following observation:
"The SEU Gen2's small passage of violet light (.2% between 400-406 nm) does not affect the UV capture. We already know this from using other UV-pass filters having a minor passage of violet light. Light around both sides of 400nm, say approximately 390-410 nm, is recorded similarly by our cameras."

To illustrate this point, let us examine the popular stack of Schott filters, the UG1 (1.0mm) and the S8612 (1.5mm). Below is the diabatic graph of that stack:



Please note the "deep blue / violet leakage" of that stack. This "leak" of the violet is more significant, that is, greater than 1% through 411nm, in the Schott stack than in the SEU Gen2, which is only greater than 1% transmission through 404nm. What is interesting is that the UG1/S8612 is used by Klaus himself and Klaus calls the result a "UV image". See http://photographyoftheinvisibleworl...4mm-quatz.html

The world of UV photography has historically, and continues to this day, to accord UVA to the range 320nm to 400nm. Many of the finest UV photos have been taken with the BaaderU filter which has a range to 400nm. Klaus has displayed many of his own UV photographs taken with his "workhorse" filter, the BaaderU. Thus, it seems strange to read about the ICC's interests.

One opinion, biased, of course. YMMV
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  #10  
Old September 9th, 2018, 09:49 PM
Steve Clay Steve Clay is offline
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The typical 'UV only' filter cuts off transmission above 400nm, removing visual and IR.

In this post I am going to use the term 'blue' when referring to the 400nm to 500nm range,
instead of using the term 'violet' which is 380nm to 450nm.

The UG1 1mm + S8612 1.5mm stack is not a 'UV only' filter stack, that formula of thickness is designed specifically to transmit some blue light above 400nm.
That stack design would NOT be a "popular" or typical formula used for 'UV only' filters, simply because it is not UV only.
So if anyone wants to make a UV only stack then you would design the thickness of the U glass to be thick enough to cut off 400nm+ transmission at or below about OD3 on the graph.
So you would need at least 2mm thick for UG1 (or U-360) or about 1.5mm of UG11 (or U-340).
U-360 2mm is my personal pick for such a stack, because it cuts of 400nm+ transmission slightly better than UG1, yet delivers a slightly better exposure time than does a UG11 version.
UG11 (or U-340) is good if you want to cut off even lower than 400nm, but will require slightly more exposure time. U-360 and UG1 are also much less expensive than UG11.
The U-360 stack will also have a white balance closer to the Baader U than does the UG11 (or U-340) stack version, however all of those should look almost identical when optimally white balanced.
The main reason I like U-360 2mm is because I prefer the results I get with it. It is more efficient than UG1 at transmitting UV, has the best exposure time, and I prefer the color balance.

The UG1 1mm stack shown above is not a popular stack, and would not be used by anyone who wants to shoot UV only photos (320nm to 400nm range).

The SEU is not what I would call a UV only filter. It clearly has some visual blue above 400nm.
There is nothing 'wrong' with that, but it is not typical of what someone would use to shoot UV only photos because of the blue.
The blue content of the SEU also changes the white balance of the shot.
Here is a link to Sparticle bandpass tests performed by Dr Jonathan Crowther showing transmission range and white balance of several filters including the SEU.
As you can see, the SEU has a strong 400nm+ blue light content, which shifts the optimized white balance dramatically from the other two filters.
http://www.ultravioletphotography.co...post__p__22919

Again, there is nothing 'wrong' with the SEU, but it is not what I would define as a UV-only filter, and a UG1 1mm stack is not at all a "popular", typical, or normal, stack to use, because it leaks blue, and is misleading in this context.
If you plan to build a UV only stack, then don't use UG1 1mm thick, use 2mm instead,
unless you specifically want to construct a UV+Blue filter.
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  #11  
Old September 22nd, 2018, 08:24 AM
Dr Klaus Schmitt Dr Klaus Schmitt is offline
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I have to agree with Steve, expecially if ones takes into account the much higher sensitivity a sensor has for violet and blue as compared to UV, which leads to an overproportional (as this is a nonlinear process) enhancement of any such violet or blue in the resulting image. Hence why this is usually called "leakage".
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Old September 22nd, 2018, 08:37 AM
Asher Kelman Asher Kelman is offline
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Quote:
Originally Posted by Reed Curry View Post
I shot this Black-eyed Susan while testing a lens. Instead of setting the in-camera white balance against a PTFE disc, I set it to the entire frame. I like the camera's UV interpretation of the honey guide.





Thanks Reed for the interesting picture that initiated this discussion. Thanks Steve and Klaus for expanding on Reedís useful information on UV filters.

Altogether, you guys have added a major resource for us. I will now start from the top the thread and reread.

I am please to see such a rich discussion and attention to science as well art!

Asher
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