Why not use a lens ?

Ok here is a 6" Fresnel

and here is the inside

This first beam shot is a tight focus

this one is just a bit wider

As you can see the light is quit smooth with just a smooth reflector.

Ah, but JT, can you sneak in a pic of a ERS just for kicks

Next is the ETC source 4


Here is a shot of the lens its hard two see but there are two pieces of glass the one toward the light is smaller and by moving the front piece you can change the beam size.

Hers is a beam shot with a tight focus

and one with a soft focus

It is hard to see on this wall but the beam is very smooth.

Yayy...all fixed

Nice beam eh? Now if we could only get that in a flashlight sized package...(With cheaper bulbs)

Not sure why the beam shots are not working I tryed it three times.

Is there a limit on Pictures you can post in one thread?

There is a huge problem with fresnels for flashlight systems. Firstm off the fresnel stage light is hugely inefficient. Look at the picture you submitted. The spherical reflector only reflects light out of the back of the lamp, all light out the sides is lost into the black paint void. That is why the brightness is even from spot to flood. As the lampo gets closer to the lens, more of the side emmitted light gets out of the lens. The lamp and reflector move as one. Also a lot of light is reflected back through the lamp, heating it up and is lost to refraction. This is why many people are replacing thier stocks of fresnels with par cans(round head lights in a can) and the source four par(dissassebleable head light). These lights are great, but a 575 watt 120volt four fillament lamp or the older 1000W single fillaments get outrageously hot. The ERS or leko lights get a really tight beam not only by having good lenses but wasting a lot of light in the lens train so that only the good colminated light gets out.

Now a fresnel lens that did not have the dimpleing a theatre light has, and that was backed by a lamp in a parabolic reflector, where the lamp moved in and out would give the desired effect you are looking for in a flashlight.

For a flashlight you would really need a lens setup that colminates the beam. That requires two plano convex( one to capture light from source and reflector in a general direction and another to tighten it up) A step lens, or high curviture glass lens like the ball will give the tightest beam, with the only spill coming from very off axis light.

You are the man Sabby good thinking!

Ok everyone the BEAM SHOTS (That oughta get their attention) are up. Come and get em' before the bulb burns out

I am not saying that we need to use the same lenses or setups these lights use. I would think some company should be able to improve throw or beam quality some what with optics. I have not seen any flashlight that uses a lens for anything other than protecting the lamp.

From time to time Frys carries thin flashlights that use 4D cells or 4 AA cells and fresnel lenses. The lenses have wide diameters but the distance from front to back appears to be only something like 1 1/2 to 2 battery diameters deep.

I had a couple about ten years ago but lost them. I think they threw out a fairly diffuse flood beam.

I have two lights that that use a lens. My favorite is the Docter Aspherilux flashlight. It is a projector beam like a modern car headlight. It has a wonderful tightly focused beam and comes in a small package running on four AA batteries. Very flat and compact with a small lens at the front of the projector beam.

The other is called the HiGain 250 and uses three AA batteries. It has a much larger fresnel lens and is not very even. It does make for a flat package though.

Originally posted by Bob Snow:
I have two lights that that use a lens. My favorite is the Docter Aspherilux flashlight. It is a projector beam like a modern car headlight. It has a wonderful tightly focused beam and comes in a small package running on four AA batteries. Very flat and compact with a small lens at the front of the projector beam.

Click to expand...

<font size="2" face="Verdana, Arial">Ditto-the Docter midi 125 that I use has a wonderfully uniform, sharply defined flood beam.

The very bulbous convex lens does it. ;^)

Does anyone still sell them or can anyone post a picture?

Here are the two lights:

Google search for "Docter aspherilux" brought up about 30 hits -- one British site, one Japanese, and the rest German.

Paging North American dealers, your attention please!

There is a Docter Asperilux dealer in Arizona. somebody on CPF found it about 9 months ago, I think.

p.s.-that 125 model was available for ApX. $30. I think, as well as another waterproof model as well.

well, in regards to lenses, has anyone used HIGH quality lenses with the latest magic coatings to improve light transmission?

in the optics world of telescopes and binoculars, there's lots of goings on about the glass they use, the coatings, and in some cases, the minerals used, in light paths... one telescope i'm familiar with uses a flourite lense to help with making images as color free as possible (there's even a field flattener in there). woo.

i can't imagine that an uncoated acrylic lense is that efficient... is it?

I work for a company that does industrial and theatrical lighting, and the instruments we have all use some type of lens to achieve a smooth and focused beam. So my question is why not do this in a flash light? The only reasons I can come up with are cost and size. However looking at some of the products out there some of us are willing to pay a lot for a great light and willing to sacrifice some size.