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PCX Lens FL Question

RedCowboy

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Alaskan

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I just watched a video on these over on youtube, and I see now, when I tapped on the outer lens it was clearly plastic, I didn't open the thing to find the center lens was glass, but I still have them in Alaska, four of them. No way to get them here, buried in all my junk, my wife would never find them. I might order some on ebay and have them mailed here. I won't be able to get one of these huge lenses built into the end of the pointer lifetime has made for me, it's just too huge, but fun to play with.
 

steve001

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Yes, a given, they relate to one another. Truth is, I want to yell out "tell me something I don't know" :p. OK, here's one, why did that optics guru over at PL say an aspherical lens is the best lens to collimate the output of a laser? Why best? I suppose due to less spherical aberration, I don't know what else it would be.
Did he specify the particular application? You don't mention that.
Lasers are monochromatic and aren't subject to spherical aberration.
You want to get the best than consider glass type too.
See Edmund Optics for glass types and how different types perform vs wavelength.

For right now with your goal in mind I'd stick with pcx lenses of long focal lengths.
 

Alaskan

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Nice find! I see several different projection TV lens sets on ebay, the Delta 250's are less expensive than the 260 model, do you happen to know the difference between the two model numbers? I am guessing the diameter is larger with the 260.

The guru was talking about the best lenses to collimate a laser diode, regardless of wavelength. I thought spherical aberration was due to the curvature of the glass, not due to the wavelengths going through it having slightly different focus. I know that achromatic lenses are made to correct for that using layers of glass with different refraction indexes.

Edit: googling spherical aberration, I believe my earlier impression was correct, the problem is the way the light comes to a point of focus regardless of being monochromatic, or multiple wavelengths. I can believe the problem is compounded when passing different wavelengths through the lens, but also a problem for monochromatic sources too.

 
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RedCowboy

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These work best with a pre lens such as a G2 then you can use the larger lens at a longer FL to reach out, the G2 lets you tune the width to fit the lens power, otherwise you get the dreaded wings. I still like to correct the uneven divergence with a C pair 1st after a G2 of course, then use a concave/convex BE a really big one would be nice.

p.s. I do most by trial and error, I'm not an expert on lenses, but I can start a paper bag on fire across my backyard :D
 
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Alaskan

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I've done that, defocused my G2 to adjust the size of the spot for use with a larger collimation lens, a sort of poor mans expander without needing a concave lens, so instead of three lenses, just two.
 

RedCowboy

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I have tested a few and using a G2 primary with a 6X Cyl pair sets up a good beam that you can use with a beam expander ( 44 diode ), even with the sanwu 3X BE ( 25mm ) ignites paper bags at 50 feet, building a 2 lens BE maybe a 3 inch could hold 9X power without clipping, so how to do the math to find the right concave, convex for a 3 inch output 9X BE, the input only needs to accept 7- 8mm beams.

Using the raw diodes output has limits, the lens size needed to match cyl correction grows fast, I know we did this before and the length of the device and width of lens grows fast without correcting the uneven divergence 1st.
 
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steve001

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I've done that, defocused my G2 to adjust the size of the spot for use with a larger collimation lens, a sort of poor mans expander without needing a concave lens, so instead of three lenses, just two.
Most fixed power expanders only use two lenses.
The G2 lens has a positive focal length. Using it with an additional positive lens creates a Keplerian expander.
 

Alaskan

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Yes, agreed. It's a way to reduce the loss compared to using a two lens beam expander, I like it, have done this for several of my laser pointers.
 




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