This is an inferior approach to UV photography. To be honest I've been reticent to post this. However someone may find a use for this.
And for the sake of disclosure I was inspired by this gentleman's work. The "softness" of the image adds an ethereal quality I like.
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Step 1: Equipment
You will need
An Ultraviolet irradiator, I used my FOD but a compact fluorescent blacklight in a reflector should work also.
A target holder, I used a pair of helping hands.
A convex lens, mine was sourced from a pair of binoculars.
A measuring stick
A fluorescent screen.
A dark room (by which I mean a room you can make dark)
A target ( preferable one which shows strong disparity in appearance under UV irradiation compared to visible light, so as to prevent DIGGer's from dying of apoplexy when you do something they're convinced can't be done.) In this case a yellow lantana.
Step 2: First Find the Focal Length of Your Lens
You'll need a light source, a measuring tape, the lens and a screen, for right now a piece of paper makes an adequate screen.
Lay the tape out on a flat surface and place the screen at the zero point. Then place the lens at 2N on the tape (with N being any reasonable number to start, say 2 inches) and the light source at 4N. Now slowly move the lens and the light source away from the screen, while keeping the distance ratio the same, until the light source is in focus on the screen. At this point the lens focal length is equal to N.
I assume this is a valid approach since 1/u+1/v=1/f The basic simple lens calculation. Sorry no image, but you can do this empirically as well.
Step 3: Next the Screen
You'll need to make a fluorescent screen to project your image onto. I tried coating a piece of Plexiglas with day glo orange paint, and also day glo green paper. The green was visually the best response, important from a focusing standpoint. Day glo green paint would probably have been the best choice as the paper was "splotchy" lowering the "resolution".
Step 4: Put It Together
Lay out the tape. The screen is located at the zero point, The lens, with a 6 inch focal length, at 24 inches from the screen and the target at 32 inches from the screen . This gives a magnification of 2x which also facilitates focusing. Place the UV irradiator off axis whilst shining on the target. The camera is placed off axis near the screen focused manually on the screen. The low light levels do not allow for auto focus so get it right before the lights go out.
Step 5: Taking the Picture
Shut off all lights and allow your eyes to adjust for several minutes. Turn on the irradiator, you should be able to see an image appear on the screen. Now gently move the target back and forth until the image is as sharp as possible on the screen, if you setup right this should be less than +- 1/2 inch adjustment. Once in focus set the camera for long time exposure (because of the focus issue it helps to lock the camera down somehow, i used double sided tape). My exposures were 4 sec with all the other settings auto, that was the best my camera could do. used the self timer with long exposure so as not to shake the camera tripping the shutter. A yellow filter was used in front of the camera to block extraneous blue light, but comparative pictures showed it to be unnecessary.
Step 6: Picture Processing
Here's how I processed my pictures. Using the gimp I used image>mode>decompose to decompose the RGB channels. With a green screen I threw out the RB channels. The green channel is then leveled using tools>color tools>levels.
Many of the images on the net of UV are false color, i have no idea how that's done, would love an instructable on how to. For comparison here's also how it really looks and how it looks with my previous method.