- We had a discussion about spot size and depth of field, etc. a little over a year ago (maybe a year and a half). It may provide some additional information...or we can build it up again. The bottom line is using gaussian beam propagation to approximate how a perfect laser beam travels, it boils down to the following expression:w(z) = w0* sqrt(1 + (z* lambda/(pi * w0^2))^2)where w0 is the size (radius) of the beam at its narrowest point (which is at the focal point of a lens if you send in a collimated beam)lambda is the wavelength, z is the position at which you want to know the spot size (z = 0 is at the narrowest point) and w(z) is the size (radius) of the spot at z (note that this is the radius perpendicular to propagation)from this you can figure out how much the beam will spread a certain distance away from a spot (for instance a 405nm, 100 um spot (diameter) will grow to 141um at a distance of pi * (50um)^2/405nm = 19mm while a 50um spot will grow to 57um in 5mmyou can also use it to figure out how close a lens (and what focal length) needs to be to create a certain size spot given a starting beam size by solving for z given w0 (desired spot size) and w(z) initial beam size: z = sqrt(w(z)^2-w0^2)*pi*w0/lambda so to get a 100um spot from a 1mm laser beam you would need to be 192mm awayto get really small spot sizes you usually have to expand your laser beam first then focus it with a small focal length lensthe reason most lasers look like they stay constant width is that they have large cross sections compared to their wavelength and that slows down the expansion so if you had a 10mm beam it would take about 90m to grow 10%Note: I'm pretty confident in the original w(z) equation -- all the examples and extrapolations assume I did my math correctly, kept track of units etc. so feel free to correct me if I didn'tjohn
FYI

· F-theta lens, 405nm, STS-0580/173, (US)$ 4733 each

Is that a lot ? Not if one is able to build large objects fast and accurate, I think.

What other expensive (new) elements a printer requires, when (re)using parts of the HP LaserJet ?

---In diy_3d_printing_and_fabrication@yahoogroups.com, <rm@...> wrote:

Ah, was looking for that ! Tnx !

---In diy_3d_printing_and_fabrication@yahoogroups.com, <grezmos@...> wrote:

The lower video is fairly good: