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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, 06:33 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 09:31 AM.
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  #2  
Old August 12th, 2018, 08:49 PM
Asher Kelman Asher Kelman is online now
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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, 09:42 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, 01:30 AM
Asher Kelman Asher Kelman is online now
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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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  #5  
Old August 13th, 2018, 10:51 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, 11:20 AM
Asher Kelman Asher Kelman is online now
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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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  #7  
Old August 13th, 2018, 01:49 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, 02:52 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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  #9  
Old August 15th, 2018, 12:15 PM
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, 10:49 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, 09:24 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, 09:37 AM
Asher Kelman Asher Kelman is online now
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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 Reed’s 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 pleased to see such a rich discussion and attention to science as well art!

Asher
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Last edited by Asher Kelman; September 25th, 2018 at 02:02 PM.
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Old September 25th, 2018, 01:34 PM
Reed Curry Reed Curry is offline
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Hello Steve and Klaus,

Steve, why do you wish to call violet, blue? Do you have ultra-blue filters?

Is a "UV only" filter the most desirable attribute of a UV-Pass filter? I propose that it is more important to capture the maximum range of the solar UV that is available to the ecosystem at sea-level. I mention this on my website:

"Which UV wavelengths are significant?"

"All of the UV wavelengths that a camera sensor can interpret are significant. The perfect broadband UV-bandpass filter, therefore is that filter which best replicates the effect of air in the UV wavelengths while providing deep blockage of all other wavelengths.


"In striving for the best approximation of air transmission, UVROptics has enlisted the aid of optical engineers well-versed in dichroic filter design. Only the dichroic type of filter permits the steep drop in transmission necessary for our latest efforts. The usual broadband UV bandpass filter uses ionic glass, such as the Schott UG11, to define the UV transmission parameters. Inevitably, this glass presents a Bell curve of the transmission with the peak between 350nm and 365nm, and the lowest points of transmission near 320nm and 400nm. The result looks like the chart to the left. With this curve, the filter is missing the best of the critical wavelengths of 370nm-400nm.

The SEU Gen2, on the other hand, has its dichroic coatings placed upon clear Borofloat glass, ensuring that the filter is not limited by UG-type glass in order to define the UV transmission.

"The SEU Gen2 offers optimum transmission of the 370nm-400nm wavelengths. These wavelengths contain most of the UVA available in solar radiation; i.e, natural sunlight. As you can see from the illustration to the left, the amount of ultraviolet light in sunlight diminishes rapidly as the wavelengths get shorter. Using this high end of the UV wavelengths results in greatly reduced exposure time, making UV video photography practical. The SEU Gen2 transmission curve is a superb replication of the natural UVA available to the photographer at sea level."

from uvroptics.com

The question we can ask is "Do I want an optimum representation of the most prevalent UV photons, or will I settle for capturing only those UV wavelengths that ionic glass technology permits?" I determined that I wished to capture the natural curve of UV wavelengths.

However, reducing the possibility of some violet photons being captured is part of our ongoing R&D.

Regards,
Reed
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Old September 25th, 2018, 02:31 PM
Reed Curry Reed Curry is offline
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BTW, just as a point of interest and a matter of full disclosure:

Steve Clay, are you the Steve Clay Smeed of Eugene, OR, who sells UV filters under the name of UVIRoptics? If you are, you might wish to discuss with the forum the transmission curve of your MoonU, a UV-Pass filter that seems to provide a lot of violet "leakage".



Thanks.

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Old September 26th, 2018, 12:09 PM
Dr Klaus Schmitt Dr Klaus Schmitt is offline
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Uuuuhh Asher, I had forewarned you, its is starting....
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Old September 26th, 2018, 12:35 PM
Reed Curry Reed Curry is offline
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Klaus,

What is starting? This sounds ominous. Is there a new disease affecting Rudbeckia?
Please share your warning with the forum.

Thanks.

Regards,
Reed
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Old September 26th, 2018, 01:29 PM
Asher Kelman Asher Kelman is online now
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Quote:
Originally Posted by Reed Curry View Post
Klaus,

What is starting? This sounds ominous. Is there a new disease affecting Rudbeckia?
Please share your warning with the forum.

Thanks.

Regards,
Reed
I really enjoy details about your flowers and the filters you use or might design.Allow me to discuss OPF philosophy on exactness and truth! One can jump to the last few sentences, below, 🐝 🐝 to get the same drift of the matter!

In all this, we must be careful not to appear to cast aspersions on other folks commercial business unless there is:

1. A danger to other folks cameras or commerce
2. There is a danger to health

If it is a photographic course, I will intervene is I believe that the folk running it don’t seem to have the qualifications to run it. I will also intervene is folk sell gear that appears to be overpriced or of questionable provenance.

Apart from that we have a strict attitude of not “taking the bread of anyone else’s table”. So one has to be careful about seeming to “expose” flaws in equipment that others are normally selling. Sometimes, like an attachment for color balance, we did intervene with our own careful scientific analysis to the best of our capability as it was seriously flawed!

Here, I no longer have an optical bench and instrumentation to either confirm or refute claims of leakage of particular light that a filter should exclude according to its specifications.

So there is a conundrum: while we want to learn about gear that we can leverage, we don’t have a mechanism at hand to check all claims specifications.

Wherever we can, we all want folk to be comfortable offering and selling the items that they feel are useful and can depend on towards making a living. If anyone feels that someone else is offering for sale here some device that is simply “not capable of doing the job at hand”, no matter the specifications, (if it effects us enough), we’ll attempt to find the truth of the matter, (within cost restraints).

Otherwise, we ask whether the gap between “expected” and “measured” makes the product of limited benefit in our photography. (Remember as scientists, we will likely need to be more stringent, as I do, check the spectrum referenced to international standards)

As photographers, however, if it works reasonably for the artistic purpose at hand, then, we must refrain of appearing to be disparaging.

🐝 🐝 I think that the following distinction can be understood.

For science “”Good enough”, Isn’t!”

For art, one can paint with “fingers dipped in ink” or use a fine “camel-hair” brush. The same choices apply to photography.

I believe that Klaus is rightly sensitive to your “leakage” critique of another person’s UV filter, being “out of place” in the practical choices of art.

For his own recognized academic work, he’ll be as relentless as you are here, in examining the measured spectrum of light allowed, as can be devised, given his budget.

After all, we might not need that degree of thoroughness in filters for artistic effect or IR filters for peering through haze?

If clarification is needed to purchase a filter for my own work, such as a rare decamirad filter, and there is some specification oddity, I will always address the matter privately, first.

I assure you we are thrilled to have folk as knowledgeable as the three of you here and we will learn a lot!

I hope this answers your question and satisfies you.

Keep up on the pictures!

Asher
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Old September 26th, 2018, 05:18 PM
Steve Clay Steve Clay is offline
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Unlike the LUV U and the La La U, the Moon U was specifically designed to transmit UV + a small amount of Blue, just like the graph shows, and was not listed as a 'UV-only' filter, but specifically as a UV+Blue type filter.
I have nothing against your filter, but because of the blue content and how the ratio of such figures into the rest of the transmission, it is not what I consider a UV-only filter or UV pass filter, and people who want a UV only filter should be aware of that fact, and that is why I posted the link to the Sparticle bandpass tests above, illustrating not only the brightness ratio of blue light to UV light, but also illustrating the overall white balance breakdown.

Your other filters are UV only I think, but I would not call the SEU a UV only filter. It has a strong ratio of blue (400nm+) transmission, so much so that the 400nm+ blue BP filters of the Sparticle test are very bright compared to the other UV range BP filter.

I mean nothing against your filter, only accuracy.

Here again is the Sparticle comparison of three UV filters.
I believe these are all 10nm wide bandpass filters, rear illuminated.
Top row L to R, 303nm, 321nm, 341nm
Middle row L to R, 355nm, 364nm, 382nm
Bottom row L to R, 396nm, 404nm, 405nm
http://www.ultravioletphotography.co...post__p__22919
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Old September 26th, 2018, 07:34 PM
Steve Clay Steve Clay is offline
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Here is a Sparticle test comparing Baader U, LUV U, La La U, and Moon U.


Here they all share the same WB:


The main thing you will see is the difference in the blue/violet color of the Moon U.
The Moon U blue is a bit bluer than the violet of the other three filter shots, and a slightly faster exposure time.

Baader U f/11 2.5s


LUV U f/11 3s


La La U f/11 2.5s


Moon U f/11 2s
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Old September 26th, 2018, 07:44 PM
Steve Clay Steve Clay is offline
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All 4 close up:
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Old September 26th, 2018, 07:52 PM
Asher Kelman Asher Kelman is online now
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Steve,

Can you explain why the filter is being used in these 4 pictures? What needs to be shown that the filters help show?

Asher
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Old September 26th, 2018, 08:02 PM
Steve Clay Steve Clay is offline
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Primarily it illustrates how similar the white balance is between those 4 filters,
with the exception of the Moon U, which is slightly more blue and has slightly faster exposure.
An intentional trade off between exposure time and UV only accuracy, if you will, or a preference in color perhaps for some.

The Sparticle bandpass tests show the UV depth, and the amount of blue (above 400nm).
I use the word blue to describe the 400nm to 500nm range, technically the blue above 400nm that is transmitted by the Moon U is violet, but since violet is the range from 380nm to 450nm, I tend not to use that, sense it become a little confusing when discussing the 400nm threshold.
Typically, we think of UV only or UV pass filters as blocking everything above 400nm.
Since UV 380nm to 400nm is technically part of the violet range, so even if the filter cuts off clean at 400nm, it still has violet in it... so I use the word blue, or 400nm+. There are a lot of things you could call it.
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Old September 26th, 2018, 10:24 PM
Asher Kelman Asher Kelman is online now
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Steve,

But why are these various different “UV” filters used? Artistic photography, multispectral analysis of crops, archaeology, military intelligence or what?

Asher
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Old September 26th, 2018, 11:12 PM
Steve Clay Steve Clay is offline
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Hi Asher, Well that is perhaps a separate discussion, because there are more uses than I am maybe aware of, and I see a few UV photographers here on your site...
Often flowers are shot in UV to see other patterns that are not seen in the visual or IR spectrum.
The classic flower would be the Rudbeckia, which has a different pattern in UV, however there are a few Rudbeckia variations that show the pattern in visual these days.

UV photography should not be confused with fluorescence photography, which some people might think of as 'black light' photography, or more technically UVIVF (UV induced visual fluorescence).

In this topic you have three people, each of which sell their own versions of UV filters.

And then there are UV+Blue, and UV+Blue+Green, and UV+...

Probably the old 'industry standard' UV-Only filter, the Baader U, which is the UV-A range, and that is the range that almost all older UV capable lenses will transmit, 320nm and above.
Unless you have a very special lens, then any UV filter that transmits below the 320nm to 400nm range is truncated by the lens, and doesn't reach its potential range.
There are more expensive special lenses that transmit all the way down into UV-B and UV-C, but since our camera sensors don't reach that far it is pretty much pointless, but those lenses at least transmit down to 320nm on a flat curve, but 7 grand gets pricey, the Kuri 35mm I use works well for me, and there are other such lenses.
Most newer lenses however will not transmit UV well, and they may cut off UV at about 360nm or even 370/380/390nm... and with very weak amplitude.
The lens is the big bottleneck with UV photography, and a very important important item in the mix.
The camera of course needs to be converted to full spectrum, removing the BG internal glass replacing it with clear UV transmitting glass, and various places can do that, usually costing $300 to $450, depending on model, company, etc..
The two main places in the US are MaxMax and LifePixel, and some on eBay also.
Full spectrum conversions, which can be used for UV and IR, and returned to visual with BG filters.
Often used for astronomy also.

UV can be used for people's faces, landscapes, medical skin analysis, forensics, like I said before - flowers, plants, animals, insects...
UV is just the other end of the spectrum from IR, not quite as easy, because the sensor is not as sensitive to UV as it is to IR even when converted, so usually we need to use longer exposures with a tripod if we want UV pics with low ISO and less noise...

I come from the artistic perspective, even though I get kind of technical with all this, my tendency is to admire the art in everything photographic, but of course that can involve a lot of technical things.

Here is a UV photo of a red barn with white trim using a UV-only filter, probably a Baader U at that date. My favorite filter is the La La U, it looks the same as the Baader U when using a shared white balance, and has the same exposure time, at least with my Kuri 35mm, and much less expensive.

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Old September 27th, 2018, 02:02 PM
Reed Curry Reed Curry is offline
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Steve,

You wrote:
"I mean nothing against your filter, only accuracy.

"Here again is the Sparticle comparison of three UV filters.
I believe these are all 10nm wide bandpass filters, rear illuminated.
Top row L to R, 303nm, 321nm, 341nm
Middle row L to R, 355nm, 364nm, 382nm
Bottom row L to R, 396nm, 404nm, 405nm"
Let us look at the matter of accuracy. The Sparticle is inherently inaccurate. For example, you say a Sparticle filter is 405nm. However, that is the CWL (center wavelength) and if it is 10nm wide, that width is at the FWHM (full width half maximum). The FWHM of a filter with 48% CWL transmission would be at 24% transmission. So, such a 405nm filter (CWL) would have 24% transmission at 400nm! It would probably also have a possible +2nm/-2nm on the FWHM AND +2/-2 on the CWL. So, a 405NM filter might be a 403nm CWL and have transmission all the way down to 395nm. Below is an illustration of one such. Some of its properties are:

405nm CWL, 12.5mm Dia., 10nm FWHM, Interference Filter
Center Wavelength CWL (nm):
405.00
Center Wavelength CWL Tolerance (nm):
±2
Full Width-Half Max FWHM (nm):
10.00
Full Width-Half Max FWHM Tolerance (nm):
±2



Thus, the Sparticle test does not mean that the SEU Gen2 is exhibiting transmission at 405nm, the transmission may be in the 395nm-400nm range. As the SEU Gen2 has its peak transmission at 392nm, the likelihood that the light transmitted is less than or equal to 400nm is greater than the light being 405nm.

That does not seem like a concern for accuracy.

There is no blue content. Some violet transmission is possible, but no blue. We have seven colors in the spectrum, it is grossly inaccurate to call 401nm "blue".

Are you certain your disparaging of the SEU Gen2 is in the interests of accuracy?

Thank you.

Regards,
Reed
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