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Large apurture anyone ?

DrSid

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Did anyone tried 445 nm diode with large aperture lens ? I was doing some experiments with 62mm aperture diameter, 500mm focal length photographic lens .. and it looks promising !
I only tested my low-powered direct drive, which does under 100mW with my current battery, so I can't really much about burning capabilities .. but I can get dot under 1x1 mm on 10m distance.
I could not test it at longer rangers at the moment, and I don't expect it to be much better at long distances, as the problem with 445nm is different divergence in each axis, which this setup does not solve at all. But it seems to extend the distance where dot is getting smaller with range a lot. It would help with medium range burning.
I'm working on how to mount my 1.5W to the thing.
 

BShanahan14rulz

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yes, but we are constrained by the NA and diameter of the lenses we use. If we didn't mind a big 62mm lens on the end of our pens, then more people would try this.

There are a lot of "cheap" aspherics on e-bay, esp. for the HID headlamp retrofitting community, you will see things like TSX-r and TL-r and ZKW-r for replica lenses for these projectors.
 

Seoul_lasers

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Did anyone tried 445 nm diode with large aperture lens ? I was doing some experiments with 62mm aperture diameter, 500mm focal length photographic lens .. and it looks promising !
I only tested my low-powered direct drive, which does under 100mW with my current battery, so I can't really much about burning capabilities .. but I can get dot under 1x1 mm on 10m distance.
I could not test it at longer rangers at the moment, and I don't expect it to be much better at long distances, as the problem with 445nm is different divergence in each axis, which this setup does not solve at all. But it seems to extend the distance where dot is getting smaller with range a lot. It would help with medium range burning.
I'm working on how to mount my 1.5W to the thing.
yes, Indeed I have tried this out. It works. One thing you have to remember is that some of the lenses like to absorb 400-445nm and as such you'll get reduced output. Quartz based lenses are the best hands down. They are totally transparent to UV to visible light. I have been able to easily burn at 50ft using such lenses. To properly burn you have to first expand your beam then focus it down to sub mm.

I tried using a square quartz lens from an old overhead projector. I had no idea 1W could set a fire from 50ft away! Well, it sure can!
 

DrSid

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Interesting idea with those projectors !

That lens of mine is Schmidt–Cassegrain with Barlow element. It might even work without the Barlow. In which case it would be only 2 glass/air surfaces and very thin piece of glass !
 

Seoul_lasers

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As long as the glass is quartz, go for it. BTW, the Scmidt-Cassegrain style optics are the same ones used on the portable IR laser defence systems. :)

Long range pencil killer?
 
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Yup I got an 8in s.c.t. first time I shined my spartan down the eyepeice it looked like a blue death star beam..hmm never thougt of using the barlow...do you think it would burn at like 100meters or more if
The telescope is focused at that distance?
 

Seoul_lasers

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hmm, doubtful. Remember that you are only using 1W or less of blue. Give it a shot at 25ft and see what happens. Your best effect will be with a quartz 15-30x optic spotting scope. I have had pretty excellent results with that already. I have been able to get focussing down to some pretty small points.
 

DrSid

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There are several things to achieve
1) to achieve small dot at a distance
2) to achieve large aperture, to use as much area of the output aperture as possible (ie. why use large lens if only small part of it is used).
3) to use as few lens as possible, so the losses are minimum.

I only was successful in achieving all 3 with photographic lens.
With binoculars and similar lens system, you have fixed eyepiece, and prisms inside. Eyepiece allows good focus with beam of the naked diode, but all the glass inside is not good.
With astronomic telescopes, you can usually remove the eyepiece, and for example mine is Newton - no lens at all, just mirrors. But there I have to place the diode into the focal point of the telescope .. and to put all light onto the primary mirror. My telescope has focal distance 910mm, and diameter of main mirror 114mm. That is about 12 degrees angle. But the beam from the diode has about 60 degrees (never measured it actually). So without some other lens, I can't use such telescope. On the other hand, it is perfect for DPSS green lasers without any optics. My next project is to mount my 400mW o-like to this .. it will shine to the Moon and back (well .. not).
All photographic lens on the other side have inner aperture and distance from it roughly same, making it perfect for 60 degrees beams. Sure, most of photographic lens are complex system with lots of lens. But the Schmitt-Cassegrian of mine is not the case. It has only two mirrors, and two glass elements, one of which is the Barlow.
 




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