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Portable FAP Red

Hemlock_Mike

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Chris -
That's the problem I have with "your" lens Ass'y too. I built a similar housing using
an SMA RF connector BUT I got a PCX lens for it and have the same problem :-(
I can replace the lens in the housing I made or make another. I am looking
at Surplus Shed for a small PCV lens but they appear sold out.
I worry a bit about a concave surface facing the fiber. A bit scared from the past!
For testing lenses, I use glue which breaks easily with an Exacto blade.
HM
 

Alaskan

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Yea, the beam spreads too fast with that SMA coupled FAP lens to burn stuff at much distance, but close in, it remains fairly tight and will put things to flame quickly. As you found, putting another lens in front close in won't allow focusing it to a spot far away due to being collimated already. Maybe just take the raw divergent output from the fiber and then collimate with a larger diameter PCX lens which has a long FL (but not too long, or the spot will over shoot its diameter), vary the distance to focus to a spot?

I had to remove the IR filter lens from a cheap CCD camera to see what was going on with the beam to do this stuff, but I never tried the output of a length of fiber. Since the failure last time was due to heating from a reflection, maybe the fiber will be more resilient to back reflections. If it fails, the FAP itself should be fine, only toasting the end of the fiber.
 
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Hemlock_Mike

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That's why I'm using the fiber!!! It is my protection.
The one I burned may be that I blew the lens housing
out with that canned stuff. Difluoroethane - It may
have stayed in there and burned. I don't know but I'm
not trying that again.
HM
 

Alaskan

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I'd try that, with the fiber in front. I remember you bought it to prevent a repeat of the back reflection problem last time, but putting that small lens in front of it won't allow a tight beam several feet away to burn stuff, the divergence is just too high (edit: and as you found, close in it's too tight to do anything with it using another lens in front).
 
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paul1598419

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I have severe doubts about trying to collimate the output of the fiber array. It was never meant to do that and may not be possible. Just because you can focus it doesn't mean it will make a collimated beam.
 

Alaskan

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It's not collimated in the sense we normally refer to a single source, instead it makes a bunch of parallel collimated beams, far enough out you can see splits between each beam, if viewing with a IR sensitive CCD camera. Mike just wants to burn stuff at a distance, I think, if so, he doesn't need a collimated output, just a small point focused output.

E:



You can see how wide that spot is on the tree about 100 feet away, terrible divergence. I calculated it to be about 16 mRad for the entire fiber bundle output.
 
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paul1598419

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I guess it will depend on how far away he wants it to focus. If it is very far, it might not be doable.
 

Alaskan

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I'm betting he can (e: within 10-30 feet which I think is all he wants) if he removes that SMA coupled lens from the fiber jumper to shoot the raw output directly into a PCX lens, if he can find the right diameter and FL lens to match how wide the beam diverges.
 
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Hemlock_Mike

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Burning stuff is simply a simple indicator of focal point in this system. I'm not looking to "POP" a balloon at 30'.
My input lens holder has been re-machined to position the fiber closer to the diverging lens. This diverging lens is now a meniscus lens with a -32 mm FL and has a good pattern at about 1" from the output side. It gets WIDE at 3". (hard to measure).



My plan is to put a short FL PCX in there followed by a longer FL PCX to see if I can control it. I need to find an open space here to try it. I want to keep the optics "bench" to about 12".

I have been able to "burn" at 24" but that is nothing. I want a controllable spot at greater distance and this FAP is a challenge!
HM
 

Hemlock_Mike

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Alaskan -- Chris,
The bestus flash tube I have found for an SSY is a replacement for a Nikon SB900.
The price is right but the specs are as follows:
OD 3.61 mm
Length 47.6 mm
Arc Len 32 mm

This is a bit small but should light up most of the rod. The Dia is also small but should
take 15 to 25 J depending on the cap bank and voltage. Because the tube is a little short,
I've put a dab of silicone on each end of the tube to keep it centered.

I am also working on the 808 FAP trying to get a 3 lens expander to work.
Keep your head down over there!

HM
 
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Alaskan

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Thanks, I will look into getting a couple of those, I’m at the airport in Frankfurt this morning headed to Atlanta next.
 

paul1598419

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Good luck on your training, Chris. Hope you get to the states without any problems. Wish it were happen here instead of 3000 miles away.
 
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paul1598419

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Yeah, that pesky T right next to the Y, got me again. I usually catch those, but this one got away.
 




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