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-   -   Flashgun "light beamer" - DIY project (https://forums.steves-digicams.com/general-discussion-11/flashgun-light-beamer-diy-project-193079/)

Ozzie_Traveller Oct 25, 2011 4:29 PM

Flashgun "light beamer" - DIY project
 
G'day all

Many years ago I wanted to do lots of night pix of possums in our aussie trees - and with a camera to subject distance of 10m ~ 25m [30ft to 75ft] is simply wasn't possible with the flash gear that I had

So I made up a telescopic sort of light concentrator, made from a cardboard tube + a fresnel lens + the external flash gun I already had. Project cost < $10

Testing the fresnel lens before buying - and it was one of those to help book readers - it seemed to focus at about 200mm [8inches]. When the tube was 200mm long, I got a perfect image of the flash-gun's flash tube onto the trees, so I had to cut 25% of the tube length to fuzzy it up a bit

images
1- here is the completed device ...
http://i54.tinypic.com/15owfwz.jpg

2- here is the cut down fresnel lens bit
http://i51.tinypic.com/x2wi2u.jpg

3- daytime shot of target / test tree > distance camera to tree about 20metres, showing my backyard & clothes drying line too !
http://i53.tinypic.com/t86a9l.jpg

4- flash in use - panasonic camera zoom at 2x [about 55mm]
http://i51.tinypic.com/s1j8yd.jpg

5- flash with extender - typical result - zoom at 12x [about 400mm]
http://i51.tinypic.com/6og0te.jpg

Hope this helps others who feel like spending a rainy night doing something different :-)

Regards, Phil

TCav Oct 25, 2011 6:39 PM

Ooooo ... Duck Tape ... I like it. :)

PeterP Oct 28, 2011 9:44 AM

Perfect, great idea!

I might have wrapped the entire tube in duct tape just to make it look more manly. :D

Grounded Oct 28, 2011 4:42 PM

My problem is in finding and identifying the correct fresnel screen for a specified distance, and also how to know the distance of the screen from the flash. At present I am not having much success.

Ozzie_Traveller Oct 28, 2011 6:55 PM

G'day grounded

The fresnel lens I bought was a $5 job from a discount store, sold as a reading aid for 'the elderly' of which I am one, having had my 65th birthday !! ... It is meant to be held "about 6" to 8" away from the page"

Holding a torch behind it and moving the torch bulb in & out, I worked out that its focal length was "about 8 inches" - so I started with this measurement

As mentioned earlier - when it was placed 8" in front of the flash, it gave a perfect sharp image of the flash tube onto the trees next door - so the cardboard tube was cut to 6" to make it go out-of-focus but still to give a concentrated burst of light onto the trees

Hope this helps
Regards, Phil

VTphotog Oct 28, 2011 7:27 PM

Since 8" is about 200mm, and the diopter # is 1/focal length (in meters), you should look for approximately a 5 diopter value for the lens, to get an equivalent of what Phil has done.
Try Wikipedia, using the term "collimator", and you should find info that will help you out.

brian


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