UVA Long Throw Source

[7ehfrr]

I'm looking for a UV light source for night photography, something with a long throw (rather than flood).

 

I currently own the following 2 lights. The are the best I've found but still not even close to what I'd like. The Convoy C8 is the stronger/smaller/lighter of the two:

 

Convoy C8+

1x LG LEUVA33U70RL00 LED with ZWB2 filter

 

uvBeast V3

3x unknown/proprietary LEDs with unknown filter (assuming ZWB2)

 

For projecting UV farther than the Convoy C8, Ive come up with the following two possibilities below. Both solutions are $4,000-$5,000 USD and its out of pocket so I'm hesitant.

 

Wildfire VioStorm 120 (spotlight version)

Ive seen the Wildfire 400W Blacklight Cannon before. Metal halide system, nice light but very heavy. The VioStorm is supposed to be a comparable LED setup but I haven't seen it in action.

 

375nm UV Laser diode

Custom job - laser diode could be put in a robust "laser pointer" host running off 2x 18350 cells with a screw-on beam expander

 

Any thoughts/ experience/ advice? I like to shoot things at 200mm. If nothing else, I need at least a little bit of light on something to focus, and the 0.5 watt 405nm laser does not cut it, not even close. Due to focal shift in in UV/IR with my lens, going filterless for focus isn't a great workaround.

Edit: clarified the 405nm source was a laser

[Stefano]

If you want to throw far, you need a small light source and a big collimating lens/parabolic reflector. If you use an LED, if you use a lens, having a second small convex lens on the LED chip will help to collect all the light, this way you will have more efficiency but the spot will be bigger (the LED will appear bigger and so will be its projected image). If you use a parabolic reflector instead, having a lensless LED or, why not, a concave lens on your LED (directing light to the sides and not the front) will be better. More light will end up on the reflector walls and directed forward.

 

There's always a limit on how tight you can collimate a light sorce. Ignoring diffraction (diffraction will significantly affect your beam if you want something like a 5 mm spot 100 meters away, ending up with Airy's disks, not you case I think), and so considering light as rays, the only limit is that you can not collimate anything in a way that exceeds or can make you exceed the surface intensity of the original source. If you have, say, a source emitting 1 W/cm² of light, you can't use lenses, mirrors or anything that doesn't do work (a solar panel does work) to end up with more than 1 W/cm². So, if you increase the tightness of the beam, keeping the divergence low, you have to decrease the intensity (if you are at the maximum concentration possible). For example, partially covering the LED will make it appear smaller but also weaker. It is very complicated to collimate something well and efficiently.

 

I don't have an answer. You need a very small and intense source. If you use reflectors, use smooth ones, not orange-peel ones. If you are looking for matrixes of LED chips, try to find the most compact one, with less space wasted between the chips. The smaller the light source the smaller the projection. I probably went beyond what you needed to know, just use this information if you want to follow the DIY route.

[dabateman]

Some thoughts:

What is your distance to subject?

Can your lights be close to subject and your camera further for the 200mm look?

Does it have to be portable or will an extension cord work?

 

Cheapest idea in my head is to get some fluorescent black tube lights and use a battery powered unit to run them if an extension cord will not work.

You can get a battery power under the sink unit and then flip out the bulb for a black light one.

 

F8T5 blb bulbs are easily available.

 

The code is F for fluorescent, don't buy G for germicidal.

8 is for 8Watts.

T5 is the pin type on end.

Blb is black light coated, so will look black/purple. If only Bl, then will not have woods glass and will leak visible. Also BL lights might have higher 313nm mercury line.

[7ehfrr]

Thank you both for responses.

 

Stefano: Do not really care about the Airy Disk effect, does not matter for just finding focus. For an actual shot, Id take a long exposure and move the source just like how you would for a light painting effect. I do this with my UV flashlights to avoid a central hot spot.

 

dabateman: For distance, 500' (150m) to 3300' (1000m); more often on the closer end. For the light being close, Id have to have a second person on a cell phone with the light, or figure out some other remote setup I feel comfortable leaving alone outside for up to a few hours. Ideally it would run off 13850 lithium cells. I can plug it in and throw a large Li battery with an AC outlet in my backpack, but that's an absolute last resort - kind of where I was going with the Wildfire system. The idea with the fluorescent tubes could definitely be useful for other applications, but with this one there is not enough output from fluorescent tubes. I assume I'd need LED, high intensity discharge lamp, laser diode, etc.

 

With infrared Ive successfully managed this on something 2.3 miles away (12,144 feet or 3,701 meters) not including vertical gain using an 808nm laser pointer. Im very aware UV scatters more, but 500' (150m) should be doable.

[7ehfrr]

Example image using an 808nm infrared source at 2.3 miles/3,700 meters, this is much farther than I would attempt in UV

 

Infrared Light: f/5.6 for 30 sec; 400mm; ISO 1600; Infrared >720nm pass filter

Image Reference: 7ehfrr.2020.0624.0028.IR

[dabateman]

Those distances might be do able. I remember Jonathan post here:

https://www.ultravioletphotography.com/content/index.php/topic/3654-uv-ir-vis-and-uvvis-tasmania-visit-2020/page__view__findpost__p__32444

 

Why not try sunlight first to see what your ideal is then factor in what you might need for UV.

 

Shinning a uv light more than 500 feet will be tricky. Making a focusing system for an led would be cheapest. But a laser might still be needed.

 

I should add that using this type of light will look suspicious and you would most likely need permission. Also a UV light at this distance and magnitude might burn up stuff in the way, like flying bats or insects.

 

So may still be best to get permission, hange a bunch of 4 tube per unit remote fluorescent lights and set up the shot. Close spot lights might also work.

[ulf]

I think even 150m will be tricky for several reasons.

Camera sensors are much less sensitive to 365nm light than >720nm, needing a much longer exposure time or higher ISO setting.

 

It will be difficult to get a beam, tight enough to illuminate an area small enough to still have an usable intensity at that distance.

With a spread half angle of just 1° the illuminated spot will be 21m². That is a rather big area to illuminate bright enough.

 

This is likely the most difficult part, needing some custom designed optics.

A super tele lens at roughly 1000mm has such narrow FOV, but are very seldom UV-capable.

 

There is also the risk of hurting someone in the path of the beam, especially close to the light source.l

I think power levels of at lest the same as the Wildfire system will be needed.

[Andy Perrin]

A different unrelated thought: if your subject is the same kind of tower you showed above in the infrared example, it is very unlikely to reflect much UV at night. In the daytime, the sky will be bright in UV and provide good contrast for a tower or something, but at night even with good illumination, your subject might just gobble up all the light and you won't have a contrasting sky to see it against.

 

For example, this is a bridge in daytime. Imagine if the sky were dark:

 

 

There is also the risk of hurting someone in the path of the beam, especially close to the light source.l

I think power levels of at lest the same as the Wildfire system will be needed.

 

Honestly at this point we are discussing that scene in the movie Real Genius:

http://commentaramafilms.blogspot.com/2015/03/film-friday-real-genius-1985.html

[Andy Perrin]

Also, it occurs to me that if you succeed in getting good UV illumination of your target, anything that fluoresces on the target should also glow nicely. If you were imagining this as a covert photo, you may wish to take the UVIVF into account!

[dabateman]

Yes a solid chemical UV laser is exactly what we need with the right cooling matrix. Not a silly ionized gaseous one.

"Like lasing a stick of dynamite".

 

I love that movie. So many great lines.

[SteveE]

My amateur radio club had our repeaters in a facility similar to the one pictured, located on the top of a strategically placed butte. We got kicked out of there when a couple of three letter agencies installed communications systems in the same building. Perhaps shining high intensity UV beams at installations of the black SUV set might be contraindicated.