Filtering a very patient tiger lily.

[Guest]

Out of curiosity, I set about comparing some combinations of my UV, IR, and VIS filters, looking to recreate some images I've been able to make in the past - and possibly find some ways to improve upon my methods (in anticipation of getting my new full spectrum camera back soon). Since this tiger lily was readily available, and seems to present as such a good model, I took it in and set it up for what I thought might just be a few test shots. Instead, this happened...

 

I wanted to capture one UV image, and wound up taking four. All were taken under 2 x F40T12-BLB for overhead illumination (fully pre-warmed for minimal IR contamination).

 

Next, since I had the UV bulbs running, I figured I would grab a UVIVF image. Or three (all taken under the same illumination as above).

 

Then, in a darkened room, filter out that Cyan light with a Hoya R72 - and behold the otherworldly beauty of its cyan-induced-infrared-fluorescence (this is quickly becoming my favorite kind of imaging):

 

How far into IR does this fluorescence extend? I tried the next shot with a Tiffen87 IR filter to push the bottom end up a bit, and while it was a bit lower exposure, it was clearly still there - and with a slightly different flavor (which I also like):

 

I did also try this through an Xnite 1000b IR filter, but there was practically no IR up there.

 

My guess is it has something to do with the lack of spectral distribution in the white LED. Either way, it was fun to be able to build the image from three separate colors up into one VIS image.

[Cadmium]

Mark, Nice shots.

I can no longer find the XDP filter on MaxMax' website, I can only find the 330 filter, and the UVR filter.

The XDP should be UG1 (U-360) glass, or was at one time, and B+W 403 is UG1 also.

The 330 looks somewhat like UG11 or U-340.

The UVR looks like UG5 or U-330.

I know this doesn't exactly correlate with your tests, but given graphs and test I have done, this is what I think.

Your tests are un-stacked (no IR suppressing filters)?

[Guest]

I did not stack or use any IR suppression filters anywhere. I did let the UV bulbs warm up for an extended period though, so there would be the least IR contamination potential (see my post here on IR emission from these bulbs: http://www.ultraviol...lb-ir-emission/). I understand it only takes a small amount of IR to contaminate an image, but I think they still produced decent images, even unfiltered (as compared to the ZRR0340; which generally doesn't need to be stacked) (XDP transmission profile example is here: https://farm4.static...a65a3b749_o.jpg, from https://www.flickr.c...57625481501672/).

[Andy Perrin]

Yeah, I mean if there's negligible IR in the spectrum of the light source then these probably aren't IR-contaminated, I would think? Certainly the flower centers look plenty dark, although that depends on processing and all the rest of it.

[Cadmium]

(XDP transmission profile example is here: https://farm4.static...a65a3b749_o.jpg, from https://www.flickr.c...57625481501672/).

 

Hi Mark, All your tests are great.

My intent was focused on the types of glass.

Your graph link for XDP transmission shows 360nm type U-glass, so not UG11 or U-340.

Here is my list of U-glass:

Schott UG1 (or Hoya U-360) = B+W 403, Xnite XDP

Schott UG11 (or Hoya U-340) = Xnite 330

Schott UG5 (or Hoya U-330) = Xnite UVR

 

As usual, a complimentary free graph:

[Andrea B.]

Your Hemerocallis in its many versions is quite lovely. I have enjoyed the experiments. It is very cool to see something new & interesting with the cyan LED results. Thanks!!

 

**********

 

The Hoya 72 passes a certain amount of red light and so we need to be sure that visible high red is excluded in order to properly claim cyan-induced infrared fluorescence. Please understand that I'm not saying that you have not captured that. But proper fluorescence photography demands both excitation (light source) and barrier (lens) filtration. If dual filtration is not used, then results are qualified. I do of course note that you are careful about mentioning that your UV source is warmed up to reduce IR output. "-) When fluorescence is captured in laboratory settings, very specific narrowband filtration is used. That is, of course, prohibitively expensive for us who enjoy this kind of experimental photography. But I'm wondering if an IR-pass somwhere in between the Hoya 72 and the Tiffen 87 might be useful here? What do you think?

[ADDED LATER: That Tiffen 87 might not be an 870 nm?? Just realized I wasn't sure of its cut on wavelength.]

 

Yes, it is true that white LEDs are too narrowband to give a natural colour representation. Most (all?) LEDs are like that.

 

Did you ever see any of the very old "color" photographs made before colour film was invented? The photographer used a red, green and blue filter to make 3 separate B&W photographs - later combined (I don't recall how) in the darkroom. I bet those guys would have loved to have had red, green & blue LEDs for that!!

 

So, where are you purchasing all your LEDs? Do you have a favorite online shop you can recommend?

[Guest]

@Cadmium: Thank you for the charts! (I just can't get enough of them). I do also have an Xnite 330, but I haven't been able to use it for a long time now, because it has developed some kind of film on it. I was able to remove this film with a sapphire polish once, but it has since returned - and I'm long out of that polish. I'm guessing this is related to humidity, hydration of the glass surface, or something along those lines. Do you know of another way I can clear up my filter so I can use it again? Something cheaper and easier to get than sapphire paste, hopefully.

 

@Andrea: Just to note, these IR fluorescence images were not made with the UV source - so the warm up/IR contamination/etc from that source doesn't apply here (I used only the cyan LED for the IR fluorescence shots). I'm sure the R72 images are composed of some far-red light. And IR. That's why I moved up to the Tiffen 87, since that doesn't really start open up until around 750 nM, compared the to the R72 which starts at about at 700 nM. As for the excitation barrier - I opted not to filter the source (cyan LED) because this LED should be roughly monochromatic (it is not a mixed/pulsed output), so I figured it was safe to assume that none of its output was getting into the camera (I can do a quick test for this too - I'll just add it to my list of things to look into :) ). For now, I'm going to keep tinkering with what I have to see if I can actually get a decent, full resolution, low-noise IR fluorescence image. I just need more [excitation] light! I don't have any preferred vendors for LEDs, though it may just be time to find one...

[OlDoinyo]

Some inexpensive "white" LEDs are actually pseudowhite: they contain just two components, usually yellow and cyan, mixed in such proportion that they stimulate all three visual channels equally and so give the impression of white light. But this does some very odd things to the color appearance of illuminated objects--for example, nothing can really look red or deep blue, because the necessary wavelengths are just not there.

[Cadmium]

@Cadmium: Thank you for the charts! (I just can't get enough of them). I do also have an Xnite 330, but I haven't been able to use it for a long time now, because it has developed some kind of film on it. I was able to remove this film with a sapphire polish once, but it has since returned - and I'm long out of that polish. I'm guessing this is related to humidity, hydration of the glass surface, or something along those lines. Do you know of another way I can clear up my filter so I can use it again? Something cheaper and easier to get than sapphire paste, hopefully.

 

Unscrew the retaining ring from the frame ring, take the glass out, clean it with hydrogen peroxide (household strength, like about ~3%~), I like to use PEC Pads for that.

If that doesn't' remove the gunk, then try cerium oxide mixed with water, and use microfiber cloth to polish the surface. Be clean, don't get anything mixed in with the cerium oxide slurry, like some inadvertent minute metal or abrasive.

Cerium oxide can polish your (uncoated) filters clean from oxidation before it becomes too strong to remove, if it gets too bad you will not be able to remove it with cerium oxide, so preventative maintenance can make your filters last a long time (don't use on coated filters).

It is wise to store your filters in sealed containers, with desiccant, especially for such glass as UG11 (U-340), UG1 (U-360), UG5 (U-330), S8612, BG39, etc..

[JCDowdy]

Do you know of another way I can clear up my filter so I can use it again? Something cheaper and easier to get than sapphire paste, hopefully.

 

Before resorting to cerium oxide I would try plain white toothpaste with a little water and a clean fingertip. If it is not to bad sometimes this works on UG-11 Xe-arc lamp filters.