A novel IR-UV light source as a multispectral focusing aid

[Taylor]

I've been looking for focusing aids for IR and UV multispectral imaging, and while browsing on a whim at our local salvage store, Urban Ore, in Berkeley, I happened across an item that might be useful.  It's a vintage face tanning device with both a UV lamp and IR resistance-heating sources.  I'm guessing it dates to the '50s or '60s.  It's a German made device by "Dr. Kern & Sprenger, KG" and it runs on 220V AC.  I picked it up for $10.  I haven't checked, but I wouldn't be surprised if you could find one of these on eBay.

 

The IR heaters would radiate mostly in the thermal-range (3,000 to 30,000 nm, or 3-30 microns), outside the range of the CMOS sensors on most cameras, but they certainly also radiate in the near IR (700 to 1,300 nm).  However, I'm thinking of disconnecting them or rewiring the switches because they draw a lot of watts and produce mostly heat.  They can't be switched off while the UV lamp is on, unfortunately (the switches offer only IR "Wärme," or IR+UV "Sonne + Wärme").  I also have an IR LED flashlight from maxmax.com.

 

I'm trying to find out more about the UV lamp in this device, particularly about the spectrum it emits and whether there are modern lamps that I can replace it with to get specific UV wavebands.  It appears to be a high-pressure mercury lamp, but could also be a low-pressure lamp.  A label on the back of the device identifies it ("Typ UV Brenner") as a "UV800".  I've attempted, but haven't yet found a way to remove the lamp to replace it.  It emits quite a bit of visible light, and while testing it I've been wearing sunglasses with a good UV-blocking rating to protect my eyes, and I avoid looking at the lamp directly.

 

I'd also like to find out if I can attach dichroic or other filters in front of the UV lamp to specifically select certain wavelengths or wavebands of UV light.  For safety reasons, I'd like to filter out any UVB and UVC.  If anyone has experience with filtering for specific UV bands on the light source, I'd be interested to hear of your experiences.  Other UV light sources for use as focusing aids would be welcome.  I know others in this forum have made good suggestions for UV sources for actual imaging.  For UV imaging, here's another example of a tunable UV light source: 

"High Power UV LED Radiation System: 365nm 385nm 395nm 400nm 405nm"
http://photographyoftheinvisibleworld.blogspot.de/2012/09/high-power-uv-led-radiation-system.html

Dr. Schmitt's blog is my favorite resource for UV photography, and his inventory of macro lenses is another fantastic resource:

The Macro Lens Collection Database
http://www.macrolenses.de/

Thanks to Dr. Schmitt for permission to link to his sites here.

 

Anyway, apart from the novelty appeal and low cost, the tanning device is relatively small and light, and it has a nice hinge that allows the light to be directed at various angles.  It's an interesting addition to my inventory for multispectral RTI.

[kds315]

Hi Taylor,

 

yes, you have my permission to link to my sites here!

 

Such old lamps can be quite dangerous esp. as they emit toms og UV-B and UV-C so good eye protection is mandatory (better also protect skin too!)

 

Best wishes!

[GeorgeBevan]

I'd reiterate Klaus' word of caution. UV-B and UV-C sources are very dangerous. 

 

Generally for filtering UV sources like quartz and xenon bulbs for reflected UV or fluorescence you'd want Schott UG-11: http://www.schott.com/advanced_optics/english/download/schott_uv_bandpass_ug11_2008_eng.pdf

or (what we use) the Schott UG-1 (much cheaper): 

http://www.schott.com/advanced_optics/english/download/schott_uv_bandpass_ug1_2008_eng.pdf

 

It won't get you the specific wavelengths you want but it's quite effective. Schott has some high-pass filters in their KV series but I haven't used them:

http://www.schott.com/advanced_optics/english/download/schott_interference_filter_catalogue_july_2008_en.pdf

 

As for focusing in UV, if you get the Coastal Optics 60mm you won't regret it. Just focus in visible light, drop in your UV filter and you get nice sharp images. You'll never look back. 

[Taylor]

Thanks for your words of caution and information about filters, Klaus and George.  The safety concerns you mention are not overstated.  The item isn't quite an antique, but one would never know from the woman bathing in the beam on the box that such a device would not be a safe way to get a tan!

 

For an upcoming project, we are considering renting the Coastal Optics UV-Vis-IR 60mm lens, which largely eliminates the need for refocusing in IR and UV.  It is indeed a fine and expensive piece of optics.  Dr. Schmitt's database of lenses provides some less expensive alternatives for UV, many of which are great lenses, but I think few, if any, have the ability to remain in focus across such a wide range of wavelengths.

[marlin]

Interesting thread! I'm following this. Good stuff. (bad tan!)

[kds315]

Btw. I would rather filter the light the camera enters, i.e. selecting the wavelengths the sensors "sees", instead of filtering the light source (also cheaper, as the needed filters are usually smaller). This is, if reflected UV recording needs to be achieved. I have done so down to about 300n with wide-bqand and very narrowband UV transmitting filters. make sure they are completely blocked for VIS and IR, otherwise leakage will be recorded and not UV!! See the following link and itw continuations on my BLOG)

http://photographyoftheinvisibleworld.blogspot.de/2012/08/leakage-in-reflected-uv-ultraviolet.html

 

If "UV induced visible fluorescence" (UVIF for short) is intended, then teh UV lightsource will be filtered suitably (expensive, since usually large filters are needed) and the camera needs a very good UV/IR Cut filter, I use the Baader UV/IR Cut filter for that (420-700nm) as it has great out of band blockage.

[andish]

Hi !
I have this device.

It's light is rather valuable to give the skin a sideways kick to reduce symptoms of neurodermitis, than to tan.

 

(I used e.g. 30 secs in dark winter days to the face in 0,5 to 0,7m distance. Combine therapy e.g. with birch bork-, mallow-, calendula-lotio, probiotics etc., and meditation 30'/d to get good results..)

 

But please use some UV dosimeter as they are available for small money for sun bathers.

 

It is indeed a high pressure Hg lamp.

see https://en.wikipedia.org/wiki/Mercury-vapor_lamp

 

The IR heating resistor elements replace the otherwise needed current limiting coil.

Do not leave it out without replacing it with other current limiting circuity!

 

Such a setup with coil can be found in old street lamps, where high pressure hg lamps are used as well.

You can cut away the outer (flurescence) bulb glass, and inside you will see just the same hg lamp as in these old fry-my-face UV tanners.

 

Don't break the inner high pressure hg steam cell by overcurrent or hard drops, as the amount of Mercury is not as small as in modern energy saving bulbs.

 

 

When you want to keep away unnecessary levels of UV from old artifacts, it may be worth the effort to filter out unneeded wavelengths at the source side. But I'm no expert what you can place on some old canvas without harm. If you can reduce the exopsion time to some seconds, it may well not count.

 

Upon ignition, the spectrum is quite different, as I remember from old sprectral experiments, its coherence is higher, it is more narrow-banded and shows different lines. As the Hg pressure rises, the number of bumps per second grows, so interrupted radiation processes get more likely, and the spectrum gets wider.

Likewise intensity grows.

 

Still I don't know how many interrupted cold starts with cut-off after some seconds the bulb will survive, just let it burn to full brightness a couple of minutes from time to time. Re-Start after full burn is only possible after condensing of Hg at the electrodes, could be you have to wait some minutes, up to 10.

 

As for sun protection glasses, I don't know the effectiveness. Not looking at it is certainly adiviseable. 150W at 65lm/W is the output of a street light Hg lamp after conversion of UV to VIS. The original yield of UV, on some small 1cm^2 area, is much higher.

The eye protection goggles the tanner came with are just 2 ovals of thick black bakelite plastic, bound together on a elastic string across the nose and another around the hind head. 100% (UV) blocking warranted.

 

Don't forget exchange the room air, open the window and let out out all the O3 ozone after burning a while. You will smell the difference...

 

Hope it helps a bit.

 

Andi