What tests can I do to determine the UV limit of my camera ?

[colinbm]

What tests can I do to determine the UV reach of my camera with a quartz lens ?
My present camera is converted to full spectrum with the Bayer CFA intact.
Soon early next year I plan to get a full spectrum camera with the Bayer CFA removed for mono photography.

[Andy Perrin]

I would suggest a diffraction grating test (like many have done on this board) using a light source that has a known line spectrum? The grating itself would have to pass up to UVC I suppose, though. 

[ulf]

14 minutes ago, Andy Perrin said:

I would suggest a diffraction grating test (like many have done on this board) using a light source that has a known line spectrum? The grating itself would have to pass up to UVC I suppose, though. 

Then (all?) transmission grating foils are unsuitable.

I use one sample to extrapolate when I say that.  ;-)

 

Long time ago I measured a sample of such foil and published the results here:

https://www.ultravioletphotography.com/content/index.php?/topic/2643-first-attempt-with-linear-filter-grating/#comment-19967

 

Half DVDs are not usable either as they are produced by Polycarbonate that cuts UV very early.

 

Spectrometers use reflection gratings and a suitable one might be found, but then the proper wavelength calibration has to be found.

The full setup can be a bit tricky to arrange and in worst case maybe different orders of diffraction might confuse the result.

 

[lonesome_dave]

Maybe a monochromator?  They use an internal reflection grating with no other optics in the path. You shine a broadband light in one slit and get only the wavelength you select out the other slit. I have a couple of them but mine are only calibrated down to 350nm.

[lukaszgryglicki]

I actually don't know limits of my camera :/

Seems like I can record mercury 253nm but not sure if leaks are not dominating :(

 

[dabateman]

You can buy a calibrated monochromator, but they are very expensive.  You just use your camera to see if you see the light. You also need the light, but a germacidal bulb might work.

 

https://www.newport.com/f/oriel-1_8m-hand-operated-monochromator

[colinbm]

Thanks for the suggestions.
I guess with the 260nm LED test I did was just getting the bottom right of the bell shape curve of the 260nm LED spectrum at about 280nm & that was enough to penetrate the glass flask.
I seem to be getting a better photo with the filtered 310 LED light.
I will post some photos next week with the 310 LED.

[lonesome_dave]

My monochromators are simpler models that can be had for a few hundred USD in the surplus market. I suppose you could swap in a different grating to get down into the 250nm range and then calibrate it with known spectra.

 

I like to use them for a quick check of laser lines when I don't want to fire up a spectrometer. Also good for educational use.

 

 

[JCDowdy]

Assuming that you know that the lens is not limiting UV transmittance, as you say. Then any of the several means to estimate the limits of a lens should be a good place to start.

see:  

A narrowband double monochromator is preferred but should be coupled with some means to at lease normalize intensity.

[colinbm]

@JCDowdy Thank you, I don't have access to this kind of equipment in my little corner of the world 

[Stefano]

My university has (at least) one, I used it in an experiment. Maybe you can have access to one.

[colinbm]

@Stefano I have never been in a university nor do I have one near by ?
I have a bunch of UVA, B & C LEDs, plus 222nm Excimer tubes & a collection of filters over the same range.
I have two spectrometers to test these LEDs & filters, one 200nm to 430nm & one 250 nm to 850nm.
I have a full spectrum Sigma fp with CFA intact. I have a UV Nikkor 105mm lens.
The limiting factor for UVC reach is the cameras unknown reach.
I have presented what I think is a photo at 260nm at 2 seconds exposure.
I have presented what I think is a photo at 310nm at 2 seconds exposure.
I don't think these 2 second exposures are excessive for the perhaps 5 watt flashlights ?
I hope to have a full spectrum mono converted Sigma fp with quartz cover glass in place to compare with in two weeks.
I am just trying to be useful on this UVP forum & push the UVC boundaries, to the best of my abilities.

[JMC]

Col,

The testing of reach is huge a challenge as the sensitivity drops so much at short wavelengths, especially without access to a spectrometer that can accurately measure at those short wavelengths.

Simple monochromators can be a problem as JC mentioned.

The simplest way is to try and block the area that you think it is working at while letting through everything else.

I've done this with a Schott WG305 filter when I first started looking at UVC - https://jmcscientificconsulting.com/uvc-photography-at-254nm-into-the-darkness/ . If I image with and without the WG305 filter in place, I get very different images, hence I can be confident that I am at least seeing below 300nm with that setup.

Can you source a 2mm or 3mm thick Schott WG305 filter where you are, in a size which can be fitted on the front of you UV Nikkor? If so that might be the simplest way to at least see if you are imaging below 300nm.

Good luck with it, and if you have any questions drop me a PM.

[ulf]

22 minutes ago, JMC said:

Col,

 

 

 

The simplest way is to try and block the area that you think it is working at while letting through everything else.

I've done this with a Schott WG305 filter when I first started looking at UVC - https://jmcscientificconsulting.com/uvc-photography-at-254nm-into-the-darkness/ . If I image with and without the WG305 filter in place, I get very different images, hence I can be confident that I am at least seeing below 300nm with that setup.

Can you source a 2mm or 3mm thick Schott WG305 filter where you are, in a size which can be fitted on the front of you UV Nikkor? If so that might be the simplest way to at least see if you are imaging below 300nm.

https://www.edmundoptics.eu/p/n-wg-305-50mm-dia-longpass-filter/20605/

[colinbm]

Thanks for your inputs @JMC, @ulf 
I have ordered one, Schott WG305 50 x 3mm, I should have it next week.

[ulf]

Often a 50mm filter glass round fit in a 52mm filter ring, even if 3mm might be too thick for the retaining ring.

That might be worth the trouble for easier handling.

I have bought macro filter lenses in deeper rings for such purposes. Sometimes you can find such used for little money at eBay.

[colinbm]

Thanks Ulf
Yes I have done that before or glued them in.

I have used stack caps & cut a neat opening in both sides.

Actually I am looking for a few Nikon UR-2 filter holders for the Nikon Gel Filter Holder AF-1, that fits the UV Nikkor 105mm.

[JMC]

No problem Col. Note the datasheet provided by Edmund is for a 2mm filter, not a 3mm one. The right transmission data can be got from one of the online calculators - https://www.pgo-online.com/intl/schott-filter-calculator.html

 

There is a self contained Excel file for calculating these profiles somewhere. If you can't track it down let me know and I'll see if I can dig it out.

 

3mm thick will give you plenty of blocking below 280nm.

 

I've also used normal UV filter filter rings before for 50mm diameter glass filters.

 

One thing to note. It will probably fluoresce under UV, so I would put this in front of any UV transmission filter when running your test (closer to the subject). If you put it behind the UV transmitting filter, the UV coming through can cause the WG filter to fluoresce and you can pick this up as a ghostly glow in the image. These WG and especially the GG filters do fluoresce under UV unfortunately, to varying degrees, and it is an example of where order of the filters in the optical setup can influence what you see. Any questions, let me know.

 

Good luck with it.

[colinbm]

Thanks @JMC
It was interesting to read your research on 254nm UVC colour photography.....
https://jmcscientificconsulting.com/uvc-photography-at-254nm-colour-images/
Importantly you don't mention the filtered output of the lamp ?

[JMC]

36 minutes ago, colinbm said:

Thanks @JMC
It was interesting to read your research on 254nm UVC colour photography.....
https://jmcscientificconsulting.com/uvc-photography-at-254nm-colour-images/
Importantly you don't mention the filtered output of the lamp ?

The spectra is in the previous post on the subject - https://jmcscientificconsulting.com/uvc-photography-at-254nm-into-the-darkness/ - but only up to 800nm as that is the limit of where my spectrometer is calibrated to for irradiance.

[colinbm]

Thanks @JMC
That looks like a UV Products lamp, does it have the Hoya 325c filter ?

[JMC]

38 minutes ago, colinbm said:

Thanks @JMC
That looks like a UV Products lamp, does it have the Hoya 325c filter ?

It is a UVProducts lamp. I'm not sure what the name of the filter is, but is what came with the lamp.

[colinbm]

@JMC I am sure it is the Hoya 325c filter. It doesn't pass all the 254nm, just the right hand half.
They have now an expensive dichroic filter that has a half width of 240 to 375nm so pass a bit more light.
 

[colinbm]

@JMC, Jonathan suggested I get a Schott WG305 filter to test with my setup with Sigma fp converted to full spectrum & with a UV Nikkor 105mm lens, using 2 x 255nm LED lights.
I have used a beaker of water with some aluminium foil in it, with a sheet of PTFE behind.
The 255nm LEDs have a ZWB1 filter. The UV Nikkor has a Asahi ZUS0325 filter, & for the second photo has an added WG305 filter.
My Spectroscope shows no IR is present.
My observation is that the blue fluorescence on the PTFE has been eliminated with the WG305 filter.

 

[lukaszgryglicki]

@colinbm can you quickly summarize how you totally block above 320nm? I'm searching for an option to block > 320nm with OD6 without luck.... I want to be able to illuminate the scene with low pressure mecrury lamps (I can have a dozen of them) but avoid ANY leaks other that the main line at 253.7nm...