1W 520nm Nichia Laser Diode TEST

[planters]

Spatial filtering cures a whole bunch of artifacts and with the smaller laser sources possible with all-diode set ups, there may be more room to incorporate the filter components. Kecked is looking at simultaneous filtering of multiple colors and this might make the technique even more attractive.

A funny thing I notice when aligning the lasers for a projector, is that after carefully perfecting the overlap at exactly the projection range in the far field, the beam crossing the room is white and without any halo, but then I'll scan a test pattern and there seems to be a huge blue border around all the lines. As I walk toward the screen the border shrinks and then disappears. I think the short wavelength does not focus through my eye glasses as well as the green and red and this may also be effecting video and stills of laser projections creating or enhancing artifacts that are invisible when viewed differently.

[norty303]

Spectacles play all sorts of havoc with lasers.
Don't forget that if you are not viewing the pattern through the very centre of your lens, you'll get shift with wavelength, so parts of the pattern in your peripheral vision will be shifted by refraction where the centre isn't. Blue is aweful for it I find. Put a test pattern on the wall and turn your head around to see everything swim! (Mine maybe worse, I'm -5 at least and I have astygmatism in both eyes)
When I'm aligning far field, I go right up to the wall without my specs on, and check it is perfectly aligned. I thien return to my seat, move my head so that the pattern is perfectly aligned, then put a small dot with marker on the lens that aligns with the centre of the pattern.
I can then very quickly return my head to the point I know is least affected by the shift - very handy if aligning multiple projectors!

[planters]

Good technique! I also find a pair of binoculars helps a lot and allows me to stay at the projector.

[m0f]

I don't wear glasses and I actually get the same effect with the scanned blue appearing much wider from a distance than it really is. Upon walking closer to the projection it disappears. I figured maybe the eye just doesn't focus so well on the short wavelengths, or perhaps is to do with differences in scattering. Either way it's definitely a visible artifact even without glasses.

[norty303]

Hmm, I wonder if its associated with the halo and weird vision effects you get when viewing UV sources?

[LightningStalker]

Nah, it's not something a spatial filter can correct and definitely not my eyes. The pattern turns along with the lens, so it's in the lens itself. I'm not saying anything bad about the G2. It's a good lens, just pointing out something I noticed.

[polishedball]

Nah, it's not something a spatial filter can correct and definitely not my eyes. The pattern turns along with the lens, so it's in the lens itself. I'm not saying anything bad about the G2. It's a good lens, just pointing out something I noticed.

Isn't that pattern reflections off the barrel when the lens isn't close enough to the diode? Are your barrels shinny, brass, or completely black? On the inside.

[LightningStalker]

It could be. It is the standard shiny brass barrel that comes with the G2 lens. I can't think of a way to isolate the problem without taking the lens out of the barrel.

[planters]

If adjusted properly a spatial filter can remove lens artifacts, scatter due to dust and internal reflections. A spatial filter is a frequency filter and higher frequency aberrations such as surface ripple in the lens will not focus to as sharp a point, at the aperture, as the lowest order, full diameter beam, due to the effects of diffraction. When I demonstrated a quick spatial filter set up, I intentionally did not use precision pinholes and translation stages to show how easy the technique can be. And even here scatter due to hairs on the steering mirror were eliminated.

[Meatball]

Therein lies the disadvantage of having to focus the beam again after spatial filtering. If the lens is what causes the high order noise, then won't the correction lens on the back end of the filter re-introduce the same type of noise?