Light beamer

[Grounded]

Being a clever know all smartyI decided to make a light beamer, bought a 2" square freznal screen and painstakingly made from cardboard, a frame to suit my camera, all coming along fine, now after 3 hours toil the thing makes no difference It suddenly occured to me that the silly camera is, "being a through the lens type", adjusting the output. I have 4 settings, Auto, auto red eye, forced flash and slow sinc! the question now is which one would be most likely to put more light on distant subjects, especially birds? I should mention the Freznal screen is 2 and a half inches from the flash any pointers? Or am I wasting my time.

[TCav]

Has the fresnel lens actually "beamed" the flash?

Which flash are you using? Most modern flashes zoom to illuminate the angle of view of the lens, up to some maximum focal length. Your beamer would concentrate the flash onto the central portion of the frame for focal lengths within the zoom range of the flash. Is that happening?

[VTphotog]

I would suggest trying some test shots using the side of a house or a wall for a target. Probably the forced flash setting will provide the best comparison. Take shots at the same settings with and without the lens in front of the flash. This should give you a good idea of how much the beamer is concentrating your flash. You should probably also try adjusting the distance between the flash and the fresnel lens if possible. Fresnel lenses are not all the same, any more than regular lenses are, so the focal length may not be correct for a flash concentrator.

brian

[Grounded]

After dozens of test shots I have found in auto flash, the light has increased by a very small margin, more so close up where I don"t need it. Shining a torch through the freznen dosn't do much either, so it's back to the drawing board, with probably a magnifying glass in place of freznel.

[TCav]

Originally Posted by Grounded

After dozens of test shots I have found in auto flash, the light has increased by a very small margin, more so close up where I don"t need it. Shining a torch through the freznen dosn't do much either, ...

Is it possible that the fresnel lens is too strong, and that it's focusing the flash?

[Bob Nichol]

Here is an example of a commercial product called The Better Beamer http://www.luminous-landscape.com/re...r_beamer.shtml
They are about $40 but the link shows you the proportions but no clue as to what the diopter of the Fresnel lens however.

[Grounded]

Had a look at that Bob, I have a freznel screen the size of an a4 which is far to big, but it does concentrate the light, with a torch anyway, which is more than the 2" one does so perhaps TCAV has the problem sussed. I think I will try a different aproach, gimme a couple of weeks to come up with something, silver paper works wonders.

[TCav]

Try using it a different distances, pointed at something big like the side of a barn. Shoot from 2, 5, 10, 20, & 40 feet away, keeping the focal length constant, and at the (35mm equivalent) maximum zoom of your flash, and see what the flash pattern looks like.

If your beamer is working the way you want, the flash pattern should be the same in every shot.

[VTphotog]

You may be using a diffuser rather than a concentrator. If you hold the lens in front of a newspaper, does it make the print look larger?
I have a piece that fits on my old Vivitar 285 flash, which slides in to give a wider angle to the flash, and it looks much like a fresnel lens, but with a negative diopter.
If the large lens seems to work, try cutting it down to fit, if feasible.

brian

[Ozzie_Traveller]

G'day Grounded

Don't wanna take away from your thread for a DIY I did years ago - I will post it into a new thread ... hope it is of interest

Regards, Phil