- Aug 5, 2009
EDIT: This thread is now an on-going tutorial for a DIY beam expander.
The problem, with the commercial ones, is that the lens are different diameters, so are made on request with custom curvatures ..... in an inverting (or galileian, if you prefer) expander, the two lenses must have the same identical FL, also if different in diameter, and this is the wrong part, trying to build an unit at hobbyst level (cannot ask for custom lenses and hope they are cheap )
The better choice, for hobbysts, is start with two identical lenses also in diameters, also if this sacrificate a bit the mechanical aspect ..... as example, i found these ones:
SIMPSON OPTICAL PCX FIELD LENS 23MM DIA X 40MM FL CTD - Surplus Shed
4$ for AR coated glass lenses, don't look too high, as price ..... and with 23mm of diameter, can also be achieved a decent 18 / 20mm of expansion, with tube long enough (but i suppose the more searched use for these things is to shrink the beam, not to expand it, or not ? )
Otherwise, need something similar to these ones, with 15 mm FL or similar, for keep it more short (but this increase a bit the distortion)
Then all can be built with a principal tube (holder for all), a front tube threaded (expander moving lens), a rear cap with a threaded border and a threaded hole (threaded border go in the main tube and keep the first lens fixed, threaded hole is for screw in the aixiz glass lens holder .....
like in the schematic draw attached (is a draw made on-the-fly, if you need measures, i need to know diameters and FL of the lenses)
Edit: @ Krutz : the regular collimating lenses have a short FL, and introduces too much distortion ..... can work the same, anyway, for make some experiments ..... i think that, if you use a pair of them, considering their FL and shape, you can achieve some results in fact of better collimatoin with an unit not much more long than 5 or 6 cm (all the assembly)
No identical focal lengths lenses won't do a thing.the two lenses must have the same identical FL