Spatial Filtering Video

[polishedball]

And some quick pics. Can't wait to try it with matched lens and mounted.

[planters]

Edit couldn't wait just grabbed 2 odd lens out of my box.

Anticipation...it can make you strong but it IS hard. Oh, and just to mess with ya, this works very well with the 445nm diodes as well.

[masterpj]

Really cool video.
Thanks for making it. Liked and subscribed.

Is there an alternative method that would require less space? It's really cool but the space requirements makes it inconvenient for most smaller sized projectors.

[Displaser]

Hello Eric,

These videos are really nice - thanks for taking the time to share this with us.

Is there an alternative method that would require less space? It's really cool but the space requirements makes it inconvenient for most smaller sized projectors.

My thoughts as well ^ If this could be condensed into a smaller footprint, it would be nice to use this in a smaller projector.

Greg

[polishedball]

Ill be trying it today with a total footprint of 70mm for the filter. Will see how it tunes up.


John

Hello Eric,

These videos are really nice - thanks for taking the time to share this with us.



My thoughts as well ^ If this could be condensed into a smaller footprint, it would be nice to use this in a smaller projector.

Greg

[planters]

In my satellite projectors I have less room and I used a 50mm and 75 mm lens pair because the necessary adjustment is a 50% increase in beam size to fit the scanner aperture. The shorter FL lenses work every bit as well, but the care required to position the blades goes up. It is still, even at that scale, something I can do by hand. However, I wasn't sure, so I built a screw adjustable filter that works VERY WELL, but it is clearly over kill.

https://www.youtube.com/watch?v=QO4_RDo_Y9k

I also think that a single filter for all colors might work just before the scanner. I would use achromatic lenses however, so the far field doesn't loose the combined focus.

[Stiffler]

Eric,

Why do you feel it necessary to fill up your scanners, wouldn't the beams appear brighter if you left them small?? I'm sure the answer is "divergence", but I still can't wrap my brain around how just expanding a beam makes it diverge less....

[mixedgas]

Yep, Divergence.

Steve

[planters]

The best way to get a solid "feel" for the trade off between near field beam size and divergence is to get a few optics and try manipulating the beam. In the mean time, the reason you can trust my statement, even if at this point it is unclear why this is so, is to consider this; if the initial beam size was not inversely related to divergence then we would all be using very small mirrors on the scanners to benefit from the much higher scanning speeds that would be achievable and obviously we are not.

The way I like to think about this is to remember that we never really collimate these lasers. We are always focusing them even if this focal point is 20M away. So, imagine these lenses as an imaging system. The diameter of the beam as it exits the final lens/the distance to the screen = the F-ratio. The smaller the diameter of this beam for a given distance the higher the F-ratio and the greater the magnification of the lens. This is the same effect operating in telescopes, microscopes and telephoto lenses. The magnification of all the properties of the beam such as the dimensions of the final spot (divergence) are proportional to the F-ratio.

There is no free lunch. You are right that the beams will be brighter, near the projector, if they are small, but these relatively low quality multi-mode laser beams diverge pretty quickly and the brightness quickly drops off. You trade the near against the far field. At the extremes, 1 mm beam on the scanner = flashlight on the screen and a 25mm beam on a monster (slow) scanner will cut nice trenches into your walls!

[Stiffler]

Thank you for explaining:-)