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UltravioletPhotography

Hello from the UK


JMC

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Hello everyone. I'm Jonathan, and I've been interested in photography for about 20 years now, both with work and in my spare time. I recently started on a new work project which involves UV imaging, so am definitely on a learning curve and am looking forward to spending some time on the forum. I'm working with sunscreens and using UV photography to understand how they behave when spread, and how this might impact their performance in use. I'm using a modified Nikon D810 for this, along with a Rayfact 105mm UV lens, and modified SB910 flashes (camera and flashes were done by Advanced Camera Services in the UK to convert them to UVA). I was so impressed by ACS that I had one of my Canon EOS 7d cameras and flash converted for my own personal use as well, as I fancy playing more with the UV imaging for landscape photography.
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Welcome to our peaceful yet interesting corner of the cyberspace :D

 

You for sure have a potentially powerful weapon for UV work at your disposal. The Rayfact UV 105 apart from minor cosmetic changes should perform as well as the legendary UV-Nikkor 105/4.5, a lens which a few of us have at our disposal (I have two at present, to give some redundancy and backup). I think many will be anxious to learn what the D810 modified could deliver in terms of UV imagery. I assume you only use the best and most efficient UV bandpass filters already?

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Hello Jonathan and Welcome to UVP. I hope you enjoy our website. We have samples of so many different kinds of reflected UV photography and will look forward to seeing some of your UV photographs added -- sun screened people and landscapes, both.

 

Please do let us make sure your filtration is good. We have a wealth of info about filtration.

Under UV/IR Techniques & Tests, please see the FILTERS board.

Also you can use the search tag: Filters

And there is a summary in this write-up: Sticky :: UV/Vis/IR Filters

 

I am happy to hear of your good recommendation for ACS and will add them to our Sticky :: UV Photography Intro, Cams, Mods, Lights, Links .

Update: I just looked and I already do have ACS listed.

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I'm working with sunscreens and using UV photography to understand how they behave when spread, and how this might impact their performance in use.

 

I have done this, we might consider collaboration.....

 

Welcome!!

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Thanks for the welcome. I'm working purely with the filters supplied by ACS. The camera sensor has been modified to be sensitive between 320nm and 390nm. The flash apparently emits between 295nm and 410nm. Although I must emphasise that this is based on info from ACS rather than any measurements of my own. At the moment my sunscreen work in in vitro, on thin plates used for SPF testing, however the eventual aim is to develop the technique for photoing people. I'm currently working on a method to better quantify the degree of UVA absorption and fine details of the morphology of the film. Hopefully once that's published I can share some of the photos (although to be honest they are not what you'd call fine art).
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Ah in-vitro sunscreen testing, an area I know well, I have actually published a bit on the subject.

 

No, the images are far from fine art. The art is in applying the sunscreen to the substrate!

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Because ACS did not provide you with a transmission chart for the filter they installed into your camera, do please be sure to test the filtration for Infrared leakage. This is a strike against ACS. I urge everyone to always demand transmission charts for their filters. Ideally a statement about the Optical Density should also be provided. There should never be any "secrets" about these filters! I feel strongly about this.

 

If the camera does leak some IR, then at least we know how to fix it here!!

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You've got me worried now Andrea. I just went out into the garden and did 3 test shots. The weather was slightly overcast, and not direct sunshine. So I have 3 images, also shot at 1/30s and ISO 1600 using my modified 7D and a 40mm EOS pancake lens. Shot were saved in camera as monochrome JPGs.

 

1. No filtration on the lens.

post-148-0-91550000-1496403156.jpg

 

2. B+W 403 filter held in front of the lens.

post-148-0-89639700-1496403091.jpg

 

3. B+W 092 filter held in front of the lens.

post-148-0-08402400-1496403049.jpg

 

I see some loss of brightness for the 403 filter as expected, but with the 092 the image is not completely black. It's very very dark, but not black (perhaps not so easy to see on here but I can see an image on my monitor). So do I have a problem with the ACS filter letting some non UV light in, or does the 092 let a very small amount of UV through?

 

EDIT - I've just gone out and done a set of photos at different exposures with the 092 filter. Very intriguing and I'll post when I have a few minutes. UV imaging really is a fascinating area :)

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Just a quick follow on. So I went out again and took a set of photos with different exposures, from 1/30s to 8s, while keeping the lens at f4 and the ISO at 1600, using the B+W 092 filter. Weather was slightly overcast, without direct light.

 

Base photo, no filter, 1/30s.

post-148-0-19086700-1496408124.jpg

 

092 filter, 1/30s.

post-148-0-54637500-1496408121.jpg

 

092 filter, 1/15s.

post-148-0-06633900-1496408120.jpg

 

092 filter, 1/8s.

post-148-0-46169400-1496408118.jpg

 

092 filter, 1/4s.

post-148-0-04412700-1496408112.jpg

 

092 filter, 1/2s.

post-148-0-37558800-1496408105.jpg

 

092 filter, 1s.

post-148-0-51654000-1496408099.jpg

 

092 filter, 2s.

post-148-0-05199700-1496408103.jpg

 

092 filter, 4s.

post-148-0-87567200-1496408108.jpg

 

092 filter, 8s.

post-148-0-77296900-1496408116.jpg

 

For the longer exposures, there does look to be more of an IR element to the image as the foliage becomes more white, as well as just the brightness of the image increasing. It looks to me that the brightness of the filtered image at about 1s, looks similar to that of the unfiltered image at 1/30s, but will the sensor have greater sensitivity to IR than UV anyway?

 

I'd be interested to know if this is an issue (and too much of an influence of IR in a supposedly UV camera) or not?

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You didn't mention the used aperture setting? But the exposure data otherwise indicates a very short exposure as far as pure UV is concerned. Or, restated, that some IR might be present.

 

EDIT: f/4 ? if the same as used later.

 

The digital sensors are inherently (much) more sensitive to IR than UV. That is why IR contamination through a leaking filter is so damaging for UV photography. One might easily end up with an IR image instead of one in UV.

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Hi there, yes aperture and ISO were kept constant for all the images (f4 and ISO1600 for everything). Looks like a small (hopefully very small) amount of IR getting through then. Atleast for my work use with the camera I am in an enclosed room with no sunlight, and a flash which also has one of their 'UV only' filter on it. I'll be getting a fibre optic spectrometer before too long too, so I can get the background spectra in the room. Hmm, I can see myself having a word with ACS about this too....
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The flash emits, if possible, even more IR-rich illumination than the sunlight ....

 

About the only thing a UV bandpass filter will do to a flash is cutting down its output in UV. Getting a satisfactory filtration in IR concomitantly is hardly possible. Thus one has to fall back to the camera or lens filtration to keep unwanted IR out.

 

For my studio work with UV, I use uncoated Xenon tubes (Broncolor flash heads) and rely on the Baader U (last generation) in the optical chain, usually in-camera, sometimes over the lens depending on the actual gear deployed.

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Looks like I need to that spectrometer as soon as possible.

 

Not really, what you need is a BaaderU and don't worry about it. :D

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Well the spectrometer is on order anyway (for this and other work as well). Don't get me wrong, I do appreciate the advice - I would never have considered IR leaks if I hadn't read about it on here. My imaging work is done in a nice dark room, I want to check the light source out first. Plus I'm cheap and don't want to go and ask for more money for a filter just yet. Am I right in thinking that even the Baader U leaks some (albeit small) amount of IR? One good thing about my current job is that i have access to a state of the art UV-vis spectrometer which I can use to check filters :)
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Any bandpass filter will have side lobes (or "leaks") in their spectral curve. The critical aspect is how far below the bandpass response these unwanted leaks are. OD 4 or better suffices for most purposes.

 

With strong enough incoming light of the "wrong" kind and long exposures, you can get unwanted response even with the best filters. As long as the bandpass response is good enough, having a subimage 6-12 stops below the base image is of little or no concern.

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One good thing about my current job is that i have access to a state of the art UV-vis spectrometer which I can use to check filters.

 

Fortunate, it is going to require a good bench grade spectrophotometer to measure OD 4 or better.

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It'll do 2 dp on transmission, however I get the feeling it'll need very long collection times to even try and get anything reliable or reproducible. I see fun times in the lab ahead :)
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The two most commonly occuring leaks in UV-pass filters are IR around 700-730nm and small amounts of violet around 400-410nm. Any little violet leak can usually be ignored. At most, a bit of violet leak will give a blue cast to the raw file. However, even smallish IR leaks are quite damaging to a UV file. So you need to block that IR.

 

Given that you already have an internal UV-pass filter inside your camera, it really is not necessary to put a BaaderU onto the lens. That will just make exposures much longer. Instead, I think one of the blue-green blockers might be the thing to use. BG glass passes UV + Visible light and blocks IR light. The hands down favorite here for IR blocking is Schott S8612 glass. (Which does not have a BG in its name!) A 52mm S8612 is not an expensive filter. The BaaderU is very expensive. With such an IR blocker, the exposure time might also increase but not by much.

 

Not knowing exactly what internal UV-pass filter that ACS gave you, it is difficult to know the correct thickness of S8612 glass to recommend to you. I would think that between 1.5 - 2.0 mm thickness would cut most of the IR. Via PM, I will send you a place to look for S8612 filters.

 

BTW, almost every filter will "leak" under strong enough illumination. The goal is to suppress the leak enough to suit your shooting conditions.

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Agree with the S8612. The BG filters are quite good too, but they do cut a little too much into the UV transmission for my liking.
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