adjustable "focus"(spot/flood) mechanism

Iam building a dive light and trying to find a simple but effective way for adjusting the light from flood to spot.
Lets say aprox. from 4 degrees to 90.Was thinking to put a lens 4-90 degrees on a ring with magnets and control this lense with another magnetic ring on the outside.Any recommendations or any other ideas on how to build it ?

I think there should be some pictures on the forum (if they weren't lost in the crash a few years ago) of a light from MBSUB.
It has a focussing mechanism that is fairly simple but difficult to explain without the pictures. I searched but couldn't find the thread. Perhaps you have more luck.

greenforce also has some focusable lights. they screw on the front lid. The top side of the light housing first has o-rings and then a thread that allows you to twist the lid without leaking. in the lid, there's also an o-ring that prevents you from twisting the lid off the thread (stops the lid when the o-ring hits the thread).
The reflectors are then fixed in the lid but this should be done easily with an fresnel lens as well.

I assume you want to use a lens to focus the light. Did you want to use a glass lens or a fresnel lens? The fresnel lenses will probably be easier since it's just 2mm thick and plastic (less weight to move in case you want to use magnet).
I think someone ones already suggested this approach with magnets, but I never saw the end result (perhaps it didn't work well enough?)

I can help you with some fresnel lenses if you want (see signature).

Johan

jspeybro said:

I assume you want to use a lens to focus the light. Did you want to use a glass lens or a fresnel lens? The fresnel lenses will probably be easier since it's just 2mm thick and plastic (less weight to move in case you want to use magnet).
Johan

Click to expand...

What are the advantages of a fresnel lens vs the glass lens beside the weight?

jspeybro said:

I can help you with some fresnel lenses if you want (see signature).
Johan

Click to expand...

If i will use fresnel lens i will need at least a 100mm in diameter.
The led is quite large

mikews said:

Iam building a dive light and trying to find a simple but effective way for adjusting the light from flood to spot.
Lets say aprox. from 4 degrees to 90.Was thinking to put a lens 4-90 degrees on a ring with magnets and control this lense with another magnetic ring on the outside.Any recommendations or any other ideas on how to build it ?

Click to expand...

The SIMPLEST way would be a simple push rod and track with a rubber boot for the tail...so it can move in/out mechanically to change the focus, etc.

Plan B would be for a second lens OUTSIDE the light (In front of it) that mechanically moves in/out, or even just flips in front of it, etc.

TEEJ said:

The SIMPLEST way would be a simple push rod and track with a rubber boot for the tail...so it can move in/out mechanically to change the focus, etc.

Plan B would be for a second lens OUTSIDE the light (In front of it) that mechanically moves in/out, or even just flips in front of it, etc.

Click to expand...

These 2 ways sound really easy.On the plan B which is the easiest to build,
iam afraid that the water between the lens and the light will cause some distortion or not?

maybe you will find some help in this (old) thread :

http://www.candlepowerforums.com/vb/showthread.php?257702-DIY-Cree-R5-focusable-U-W-light

The MOST simpliest way is a Fresnel or Aspheric lens in Combination with a normal threaded light like the "turn to switch on"-Backup Lights as a head.
Radial Sealing with two or three O-Rings are bulletproof and well reputated in every common Tecci BackUp-Lamp.

By turning you alter the distance between the emitter and the Lens and thus focus/defocus the light very accurate.

I have never built one of these due to lack of time. But it is possible, relatively cheap doable and bulletproof.

mikews said:

These 2 ways sound really easy.On the plan B which is the easiest to build,
iam afraid that the water between the lens and the light will cause some distortion or not?

Click to expand...

LOL

The water INFRONT of the flashlight will not cause LESS than that.



As long as its for underwater use, not land, that should be OK.

The water between the LED and lens will change the focal length. This will mean the light will have different properties in and out of the water.

What LED are you using?
I think you may need to readjust your expectations of a 4 to 90 degree beam.

Packhorse said:

What LED are you using?

Click to expand...

This one here

I think you may need to readjust your expectations of a 4 to 90 degree beam.

Click to expand...

Why do you say this ? Is there something i can do or change?

mikews said:

What are the advantages of a fresnel lens vs the glass lens beside the weight?


If i will use fresnel lens i will need at least a 100mm in diameter.
The led is quite large

Click to expand...

How do you get to this number?
A fresnel lens is not really different compared to a glass lens so a fresnel lens doesn't need to be bigger than a glass lens.

I agree with packhorse regarding your 4° beam angle.
With lenses, you should calculate the magfication to get an idea of the size of the image. from that you can deduce an angle if you want, but it doesn't work in the same way as a reflector.
using such a big LED, it will be difficult to get a nice and tight spot. It may be 4° but still be a meter wide. capturing all the light will probably be impossible so light bouncing off the side walls will create spill.

If you have 1 lens inside the housing creating a good focus, adding a second lens outside the housing to create a flood could work but may not be very easy to develop since you'll need to test it underwater (as others mentionned, focal lenght of the lens changes if the medium that is in contact with the lens has a different refractive index (air: 1, water: ~1.5).

mikews said:

This one here Why do you say this ? Is there something i can do or change?

Click to expand...

You can change the LED, you could change the lens, or you could change your expectations.

The smaller the LED the tighter the beam. You are looking at a COB LED and its huge! Its really only useful as a flood beam or video light. To get it to produce a spot beam would require a huge optic. Im not sure a 1 meter wide torch is going to be all that practical.
Regardless of what LED/optic combo you use you will get such a wide range of 4 -90 degrees with out some very complicated optics. A bare LED produces about 120 degrees. But set that back 10mm inside a 50mm light head and the beam is reduced substantially.

jspeybro said:

...... It may be 4° but still be a meter wide......

Click to expand...

Im not sure I follow or agree with that.

How do you get to this number?

Click to expand...

The lens that comes with the lens is around 100mm.

Regardless of what LED/optic combo you use you will get such a wide range of 4 -90 degrees with out some very complicated optics. A bare LED produces about 120 degrees. But set that back 10mm inside a 50mm light head and the beam is reduced substantially.

Click to expand...

Ok, i see what you mean.I had no knowledge on the subject.You helped to understand a little.I will be doing a lot of testing with lenses to try and have at least an acceptable result.

For widely focusable lights, you probably want to avoid reflectors and fancy lenses like TIR because (I think) they lose a lot of light once you get off optimum focus. So you are looking at lenses, either spherical or aspheric. Aspheric are probably better but I'm no expert. 4 degrees is possible with a small emitter and (relatively) large lens. I don't think it's possible with an XM-L and 28mm aspheric. IIRC, I was getting around 6 degrees half angle with that combination.

But assuming you will accept a more reasonable tightest focus (probably more like 8-12 degrees full angle), it is quite possible to go from there to 90 degrees (full angle) with aspheric lenses. You will certainly see changes in optical efficiency over the focus range, but in my playing around with Ahorton and jspeybro 28mm lenses with XM-L's, min - 90 is not a bad target range.

Thanks DIW.
These guys here i think they have the same kind of led and they can change lens on field for 40,60,90 or 120 degrees beam. Price is 3k plus.:duh2:

Experiment with Led and optics today and by narrowing the beam more than 100 degrees light efficient drops dramatically.Maybe with a good reflector i can do with 90 degrees but not further than that.
So expectations changed :naughty:

Again, a reflector is probably not best for variable focus. A 27mm aspheric with XM-L can do 12-90 without huge change in efficiency.