Filter leakage in reflected UV ultraviolet photography - How not to test a filter for leakage IV

Today about a method to test UV transmitting filters for leakage that should not be used. In priciple the idea seems to be straight forward and quite obvious: Shine a strong white light through an UV transmitting filter (a ionic colored LUV U2 will be used here) and if one (or a camera) "sees" something transmitted, that filter seems to leak. Well, let's have a look if that is really that easy....

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What my iPhone5 sees when shining a strong Cree white LED light through a LUV U2 filter:
 
So do I see leakage here? My iphone sees that as red, but I really see violet, so it either depends on the WB used or theremust be something else. It is basically all a matter of intensities, as the filter from what I know and have measured earlier has about OD4 suppression outside the UV range up to NIR, then using a very strong LED torch with an intensity of for instance 10.000 then gives 0.0001 (OD4) x 10000 = 1 and that can be easily recorded.

But let's see what my spectrometer system reveals about that same situation:
 
Obviously even that white CREE LED does emit some UV (peaks at 392nm) and there is some red between 650-710nm - that also explains why I see violet, as there is some UV + blue + red. (ignore the ripples, this is just noise caused by the very long integration time).

So what do we see now here in the next image: I have added to the experiment (using the same spectrometer settings) the Cree white LED light w/o that UV transmitting filter shining through 2x ND3 filters, equivalent to using 1x ND6 to reduce that enormous bright light to one my spectrometer can handle:
 
I needed two stacked neutral density ND3 filters (i.e. ND6) to reduce that intensity to a manageable level and to get about the same amount of count at around 670nm. So that means that this Cree LED is so intense, that it is even able to have that internal used phosphor (used to achieve the bright white light) emit some UV and some dark red!

Just to make that clear, ND6 means 1:1.000.000 reduction in intensity, so adjusting my previous example to real data now: if the UV transmitting filter suppresses OD4 (0.0001) and one uses a light with intensity 1.000.000 and shine it through that filter, one would still get 100 intensity counts (or simpler calculated OD6 – OD4 = OD2 equals a factor of 100). BUT in normal photography, one does not have that situation, so this really is irrelevant and renders such "test" useless.

Let me summarize:
I could not detect any IR leakage using the LUV U-2 filter as well as the spectrometric test did not show leakage up to 800nm in my earlier tests. So using a very strong LED torch of unknown properties to shine through such a filter, does not create a suitable and reliable testing method, nor do I recommend to use that. Neither do I recommend to look through such a filter pointing at the sun, as this creates an enormous risk for ones eyesight due to the high UV transmittance!!

I have previously written about filter leakage HERE.

Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos

[UV, FL] Roman Artifacts paint / glaze visibility

A study conducted for a friend using some excavated roman artifacts. The idea was to see, if deteriorated paint/lead glacing could be made visible after thousands of years, using these new high powered Nichia 4 dice UV LEDs (365nm + 385nm).

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1) Visible light shot: 


2) FL (385nm Nichia UV LED induced visible fluorescence): 


3) FL (365nm Nichia UV LED induced visible fluorescence): 


4) differential 1 - 2 


5) differential 1 - 3 


Interestingly enough, the induced fluorescence was quite different, although the LED emissions are just 20nm apart. A comparison was done to see, if a nearly monochromatic excitation using UV LEDs would provide a different result than a wide band filtered Xenon lamp (300-400nm) excitation, which was not the case (not shown here). 

Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos

Aster hybride meets Noflexar 35mm lens

Today few shots of an Aster hybride using the Noflexar 3.5/35mm lens and various filters.
No noticeable patterns, as expected though.

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visible light shot: 


UV shot (using Baader U-filter and Xenon flash): 


Butterfly vision shot (using my XBV2 filter): 


UV induced visible flourescence shot (using Baader UV/IR Cut filter and Nichia 365nm UV light): 


As boring as it might look like, this now is quite interesting (to me) as it shows UV induced IR fluorescence. Lights were all Nichia UV LED sources I could get hold of (to make sure not a bit of IR would be present), a B+W 092 cut filter (>65nm) in front of the lens and 30sec exposure in total darkness:
 


With the naked (but UV protected!!) eye quite a bit deep red fluorescence gets visible, but hard to ban that on a photo....

Same experiment but using a dark orange filter and same UV lighting setup in darkness (Nichia 4x 365nm LED using a front attached Baader U-filter to block any visible light!):



I have now found a reliable method to professionally infinity convert Noflexar 35mm lenses to Nikon mount - ask me if you need one!

Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos

Nichia UV LED torches for fluorescence photography

Well, since we're at it, let's have a look at UV induced visible fluorescence and how these UV LED torches perform there as compared to a Xenon flash.

Test done under identical conditions, ISO400, f5.6, 41mm quartz fluorite lens, except a Baader UV/IR blocking filter in front of the lens, ISO400, 15sec exposure.

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1) UV Led 390nm, Baader U-filtered ´


2) UV Led Nichia 365nm P6, no cut filter in front of taking lens 


3) UV Led Nichia 365nm P6, baader U-filtered, no cut filter in front of taking lens 


4) UV Led Nichia 365nm P6, Baader U-filtered, Baader cut filter in front of taking lens 


5) Xenon UV enhanced studio flash@400Ws filtered through Schott UG1, 3 shots, Baader cut filter in front of taking lens 


Here the Nichia really excells, since both the 390nm and 405 turned out to be of no use, since there is way too much visible light content (>400nm) in the output to be useful for stimulating visible fluorescence (the visible light content of the UV LED actually overlays the fluorescence, thus spoils the result). If the 390nm UV LED is filtered through a Baader U-filter, there is not enough UV left to stimulate fluorescence (#1)

#2 shows the result of using the Nichia LED w/o cut filter in front of the taking lens nor was the beam filtered. The little but noticeable visible light content of the LED beam plus the reflected UV both spoil the result.

#3 is an interesting result as the Nichia beam was Baader-U filtered and it even shows red and NIR stimulated chlorophyllum fluorescence (>650nm) as well as visible fluorescence. There might also be a reflected UV content, but that cannot be determined.

#4 shows the result of Nichia UV stimulated pure visible fluorescence (400-650nm), this is the result desired.

#5 shows the comparison shot if a Xenon flash is used to stimulated visible fluorescence. Since quite some UV is needed for that, three flashes had to be fired within 15sec open shutter. There is IR leakage from the Xenon flash, so this shows the advantage of the Nichia UV LED for stimulating visible fluorescence.


Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos

Rudbeckia hirta flower bottom up

This is again about a Rudbeckia hirta a flower but this time shot bottum up.

[click on image to see a large image]

UV LED lit showing visible NIR fluorescence 


butterfly vision image shot using Xenon light:




Visible image shot using Xenon light 



Visible stereo image (for crosseyed viewing)




Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos

[FL] Another Bouquet: Gerber Daisy, Hyacinth, Roses,...

Here a UV induced visible fluorescence shot of another flower bouquet using Nichia 365nm UV LED and a 400-700nm UV/IR Cut filter.

[click on image to see a larger one]

and here for comparison the white light (5600K LED) shot



closer to see more details...





Well and here as another comparison, what happens when a Xenon flash with UV filter is used to stimulate fluorescence.

UV Xenon flash, but that leads to IR + red contamination as may be seen here:



and here now using a BG filter to compensate for that



but in overall comparison, the Nichia UV LED wins hands down IMHO!


Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos

Fluorescence: Rudbeckia missouriensis using various light sources + filters

A quick series of tests done, showing the effects of various UV light sources + filters for UV stimulated visible fluorescence. Images just resized, straight from the cam.

[click on image to see a larger one]

0. Visible reference, 5600 Kelvin LED



1: Long wave UV lamp w. filtered mercury 2x 4 Watts lights ("blacklights"), 400-700nm dichroic cut filter on camera



2: Cree 385nm UV LED, 3 Watts, 400-700nm dichroic cut filter on camera (this LED leaks quite some blue light)




3: Cree 385nm UV LED, 3 Watts, filtered using 1.25" BaaderU-Filter , 400-700nm dichroic cut filter on camera



4: Nichia 385nm UV LED, 400-700nm dichroic cut filter on camera

5: Nichia 365nm UV LED, 400-700nm dichroic cut filter on camera

6: Nichia 365nm UV LED filtered using 1.25" BaaderU-Filter, 400-700nm dichroic cut filter on camera



7: High Power UV flash, filtered using Schott UG1, 400-700nm dichroic cut filter on camera



8: High Power UV flash, filtered using Schott UG1, Baader UV/IR cut filter on camera



9: High Power UV flash, filtered using Schott UG1, Schott BG38 + 400-700nm dichroic cut filter on camera



10: High Power UV flash, filtered using Schott UG1, 400-650nm dichroic cut filter on camera

Exposure times were between 15s (UV fluorescent lamp), 3-15s (UV LEDs) and 1/160s (Xenon flash), all shot using ISO400 and f11.

I did not try and make "the pattern" visible. The underlying assumption that the pattern using reflected UV and UV stimulated visible fluorescence should not be confused, since it is two completely different mechanisms and it might be just coincidential that both appear at the same time. It would be interesting to study that though, if these both are directly linked to each other (i.e. if the reflected UV pattern and the fluorescence pattern appear simultaneously and if so, why).

You may have noticed, that I tried to cut off the visible part of the exciting light source from about 395nm onwards using a 1.25" Baader U-filter in some of the tests. I wanted to see if that "leakage" of visble light (some blue usually) in the exciting light has an impact on the result - and quite obviously it has, with the exception of the Nichia 365nm UV LED, since that one has hardly any visible content. But still it makes a little, but noticeable difference.

The Xenon light source provides a continuous emission spectrum and using a UG1 like filter, I took out the UV part as exciting light. Now the question is, if the strong visible red in the results is a result of stimulated red+NIR fluorescence, or if it is caused by NIR leakage of the UG1 filter (i.e. reflected NIR). This is why I used three different  filters (BG38, Baader UV/IR cut and 400-650nm cut) to see the effect of them.

Here now the proof that IT IS indeed red/NIR leakage:

11: High Power UV flash, filtered using Schott UG1, 400-700nm dichroic cut filter on camera



12: High Power UV flash, filtered using Schott UG1 + UV passing IR blocking filter, 400-700nm dichroic cut filter on camera

Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos

Creeping Zinna, multispectral, UV induced fluorescence, reflected UV etc.

A walk over the local market not only brought some nice white "Lambertheimer" asperagus and new "Galatiner" potatoes home, nope, also a nice "Creeping Zinna" (Sanvitalia procumbens) plant made it to my balcony.

An ideal target to test out the UV enhanced High Power Xenon, the XUVIR "one shot" filter, the Xcut2 filter as well as the well known Baader U filter.

Equipment used was: Nikon D70 (unmodified), UV Nikkor 105mm lens @ ISO400, f11, 1/180sec.

[click on image to see a larger one]

VIS using XCUT2 filter (400-650nm):


UV using Baader U-filter (310-390nm):


XUVIR multispectral filter (300-1000nm), UV Flash:


XUVIR filter (300-1000nm), unfiltered flash for multispectral recording


UV induced fluorescence using XCUT2 filter (400-650nm), UV flash:


Sanvitalias UV pattern is actually not that easy to shoot. That may been seen if you have a look at the reflection spectra which I took, since the UV reflection of the petal tip (white line) is less than 10%, just a little bit more than the rest of the petal (teal line) which has hardly any UV reflection. At the same time the IR reflection is very high. So very careful filtering and a strong UV source is needed :


So, as you may see, a variety of results may be produced....and yes, the asparagus was delicious...

Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos

Filters for UV induced visible Fluorescence

Here now an overview and comparative test of filters for UV induced visible fluorescence, as an outcome of a recent test I made using a Phalaenopsis as a target. I was using for that test my newly developed High Power UV Flash with UV transmitting front filter to stimulate UV induced visible fluorescence.  As optics I used the X35 lens at f8, 1/160 exposure time and the various mentioned filters (but any good lens for visible photography would obviously do).

Just a reminder: The intention was to find a filter, which allows to record visible fluorescence in the 400-650nm range. Deep red or NIR flourescence >650nm is tricky to record, since it coincides with NIR (near infrared) transmitted from the flash, so it would be wiped out in the resulting images (IR leakage). To record that, either a NIR blocking but UV transmissive flash front filter has to be used (a bit tricky, but could be done by sandwiching a BG38 or BG40 filter in front of the UV transmissive flash filter), OR a excinting source like the Nichia 365nm UV LED has to be used, which emits no NIR/IR at all.

[click on image to see a larger version]

1. Schott BG38 filter, transmits UV, but filters out IR - NOT useful


2. Commercial noname IR Cut filter, obviously transmits UV, blocks IR - NOT useful


3. Omega UV cut, IR blocking filter (from 650nm onwards) - too much blue also cut off (missing blue)


4. Baader UV IR Cut filter - nice colors, but transmits to about 700nm, which creates an
issue with most UV transmissive flash filters, since NIR is transmitted (too bright reds)


5. Baader UV IR Cut filter + IR cut filter (from 650nm onwards) - nice and UV flash issue
also nicely covered; but needs two stacked filters


6. Xcut filter, UV + NIR cut, transmits ca 410-650nm - works nicely, the best, all in just one filter


7. Xcut2 filter, UV + NIR cut, transmits ca 400-650nm - works nicely, bit on the cold side with enhanced blue, all in just one filter


8. Tiffen Hotmirror - quite some UV bleed through - NOT useful
[identical to the Canon Hot Mirror Filter btw.]


9. B+W 489 IR blocking filter - quite some UV bleed through - NOT useful
[the B+W 486 digital UV IR cut filter cuts on at 370nm, so it will be about the same, NOT useful result]


10. Noname Hot Mirror Filter - quite some UV bleed through - NOT useful


...and just for the fun of it and for comparison....purely reflected UV...
Baader U-filter ("Venus") 310...390nm


Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos