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light "artefacts" or bad focus with G8 lens?

Mannitu78

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Dec 19, 2019
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Hello,
excuse that bad foto please, i used a long shuttertime and the pic did get a bit too much light. Its about that blue area, that i encirceld red. Some amount of light seems not to be focused, but its leaving sideways and appearing around the spot. The spot itself is pretty small like you would expect from a G8 lens. But these "light fugitives" look at least as bad as with the 20cent-plasticlenses that come for free when you buy a copper modul. Maybe even worse. Is this normal with a G8 lens? Or did i buy sheit maybe?
 

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RedCowboy

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There are many lenses for sale online that advertise the title " G8 " that are not the real G8 or even a single element wide band AR coated 8mm FL lenses comparable to the real G8, but if you have a real G8 and are getting spherical abbreviations/artifacts ( which are a fact of life for us laser folk ), then try using a shroud or spacial filter ( a rolled up length of dark paper such as black card stock or construction paper is a good test ), or just use a different lens.

How about a G3 or a G2 ? Most laser enthusiast have a variety of lenses on hand but if you don't then maybe just use a 3 element or what came with your laser and save your G8 for when you get one of many other laser diodes that work will with it.
Note the acrylic lens will melt/burn if used with anything but low power lasers such as 80mw single mode reds.

Also make sure you have your lens installed in the correct direction and that your lens is clean, I use Zeiss lens wipes myself.

P.S. Both this one and this one are good G8 spec lenses that work well with most laser diodes.
 
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Mannitu78

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its a Nichia 5,5 watt recapped diode, 450nm. So that doesnt automatically prove that the lens is garbage? The lens stays cool....the other ones i have feel almost like the glow, that hot after just a few seconds.
 

RedCowboy

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Have you used any other lenses of just your " G8 " ?
What was your result ?

Some laser diodes are going to throw the wide spherical aberrations, I like to use a shroud, you can use THIS as a shroud.

I like to use an empty M9x0.5 lens barrel in the adapter to help block the aberrations or you can use a piece of rolled up black card stock paper inside the adapter which works well in my experiences.
 

Mannitu78

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Dec 19, 2019
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like i said, all the other lenses i got are better in this regard. its basically all cheap lenses that came with moduls or prebuild china lasers. Now i got that 18 eu G8 lens and it shows more of this stuff than any other lens.
 

ZRaffleticket

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Yes it could be a fake G8, but can I say that this is normal behavior for the G8 and that diode... And many other "exorbitantly powerful for the wavelength" class of diodes. Think the 5W+ blues, 1W+ greens, 700mW+ reds.

Basically this is the problem: This pattern often shows up when the diode's raw output before a lens goes past the working area of the lens. Think of the square shape the diode makes going past the edges of your lens, this is why you should see two of those splashes mirrored across from each other. The G8 is a long focal length lens, meaning it sits farther away from the diode -- consequently giving it more distance the raw output can expand past the bounds of the lens. You'll see those start to go away if you keep screwing your lens in farther and farther, and closer to the diode. Your other lenses either have shorter focal lengths and sit close enough to the diode for this to not be a problem (G2) or just filter out the beam clipping better than the G8 does.

If those splashes bother you too much, I would advise the shroud as Red did, or just use another lens since you have them.
 




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