Tagged: G2 lens
- June 30, 2017 at 6:44 am #37130
I have finally collected all the goodies from around the world and have assembled the same. I have:
1) 12V TTL 200mW To 2W 445nm 450nm Laser Diode LD Power Supply Driver Board (984552) which is described on the PCB as “GOOD LASER A-11”
2) NDB7875 9mm 445nm Blue Diode in Copper Module W/Leads & 405-G-2 Lens sourced from DTR Laser shop.
I splashed out and went with the “better” lens which might have been a mistake.
Using this setup the laser only starts coming into focus when the lens is less than 10mm (1/2″) from the target certainly not 55mm as described in the write up.
Is this the expected focus point for the G2 lens, if so I will buy the 3 element one listed in the write up?
In my hands the second Chinese (via Bangood) laser driver behaved as described with the LED going off when the current potentiometer was turned ant1clockwise. My first module (at the price I bought 2!) didn’t turn off but only dimmed. It subsequently stopped working.
DennisJune 30, 2017 at 10:11 am #37143
10mm, is the lens in backwards maybe? How are you focusing it, you should be able to screw and unscrew the lens housing in and out and mine focuses well pretty far out, only a few threads in. If that makes sense.June 30, 2017 at 11:54 am #37184
The lens element is nearest to the diode ( which according to DTR is where it should be ) and the threaded lens carrier is almost falling out so sounds the same as yours. I have asked DTR what the difference in focus distance is between the 2 lens types and I’m waiting for a reply.
Might end up going back to the optics I learnt at school 35 years ago and haven’t used since, should be fun!
DennisJuly 2, 2017 at 7:12 am #37299
Having decided that the Schrodinger approach wasn’t working I decided to look inside the box (i.e the diode module) and do some research courtesy of Google and Wikipaedia.
The DTR laser shop site gives the datasheet for the NDB7875 which shows the beam angle is 14 degrees parallel and 44 degrees perpendicular so pretty average. The laser66.com/html/405-G-2.html site gives a datasheet for the 405-G-2 lens (which is trademarked). It is a planar convex lens with an effective focal length of 4.0mm and a back focal length of 2.4mm and is mounted with the convex face pointing to the diode. The total depth of the lens is 3mm and the planar component is 1.67mm
If we think about laser pointers then to achieve that beam spread the diode output (if we treat it as a point source) should be at the focal point of the lens, i.e. 4.0mm from the diode. This means that unlike the 3 element glass lens which everybody says needs to be almost unscrewed the G-2 lens has to be screwed almost completely in (remembering that the focal length distance is from the plane of the lens not the surface. Then it is possible to fine adjust the focus
DTR laser shop recommend that for engraving with the G-2 lens there should be 30mm from the aperture of the lens to the work but at the moment I am finding that 55mm works.
Ryan: It might help future forum members with the same issue if the title of this thread could be modified to include 405-G-2, not sure I can do that but I have tagged this with G2 lens
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