Shortest focal length aspherical?

vestureofblood · Jul 7, 2011

Hi all,

I need an aspherical with a very short focal length.

I want to make something that looks similar to prop from the TV show Stargate. The Goa'uld hand device.

I would like to make it using a green LED like an XRE, but I need a lens that will focus the beam at a very short distance.

Using a laser for the project will not work either because peoples eyes will be around and there will be kids at the place I am taking it that will want to play with it.

Any ideas are appreciated.

bstrickler · Jul 7, 2011

What's the diameter of the lens you want? I would check surplusshed.com for a lens that would work for you. They have one hell of a selection of lenses of different types and sizes.

Dr.Jones · Jul 7, 2011

Expect the stronger ones having a back focal length (from the flat side) of about 2/3 of the diameter as a rule of thumb.

vestureofblood · Jul 7, 2011

bstrickler said:
What's the diameter of the lens you want? I would check surplusshed.com for a lens that would work for you. They have one hell of a selection of lenses of different types and sizes.

The diameter of the lens can be basicly anything, its not as important how it looks as how it functions.

Dr.Jones said:
Expect the stronger ones having a back focal length (from the flat side) of about 2/3 of the diameter as a rule of thumb.

Do you mean that if my lens is 30mm in diameter that the distance it takes to focus it will be about 20mm?

ma_sha1 · Jul 7, 2011

you can stack two identical lens together, it cuts the focal length to half.

arek98 · Jul 7, 2011

How tight you want it?

For example Ledil LXP real spot will give you about 6 degree beam with XP-E LED (green means that you probably will need XP-E or Rebel). It is 15mm tall + 2mm for star and little beat of heatsink/case.

Total thickness with aspheric will be probably more. Also with aspheric remember that with very short focal lengths angle of incidence gets bigger. Bigger angle means higher losses due to reflection. See some info here. I assume you not looking for highest efficiency but this is one of the reasons why it is hard to find aspheric with short focal length.

Dr.Jones · Jul 8, 2011

vestureofblood said:
Do you mean that if my lens is 30mm in diameter that the distance it takes to focus it will be about 20mm?

Yes, about that.

Shortest focal length aspherical?

vestureofblood

Flashlight Enthusiast

bstrickler

Enlightened

Dr.Jones

Newly Enlightened

vestureofblood

Flashlight Enthusiast

ma_sha1

Flashlight Enthusiast

arek98

Enlightened

Dr.Jones

Newly Enlightened

Similar threads

Latest posts