We Got White!! :)

[James Lehman]

Ummmmm. If a prism can split this white beam into it's red, green and blue lines, with a decent angle between them, then why can't you do it the other way and point the red, green and blue beams into the prism at the same angles and get white out the other side? Is it a difficulty of alignment thing?

I guess the angle isn't all that great. The prism would probably have to be 12 feet way from the lasers.

James.

[buffo]

I guess the angle isn't all that great. The prism would probably have to be 12 feet way from the lasers.

You just answered your own question, James! The other limiting factor is the optical losses within the prizm. But apart from that, there's nothing preventing you from using one... It's just that dichros are more efficient and easier to align.

Audry;

With a budget of $5000 US, you should be able to hit the power level you were aiming for with ease. And by using 635 nm for red, your color balance will actually be very close to ideal. (Remember that 635 appears much brighter than 660 nm.) Be sure you get analog color modulation and you'll be golden.

As for running your scanners at 50K - don't forget that a lot of the existing artwork is designed to be scanned at 30K. One of the advanced techniques that ILDA animators use is a concept called "pulling points". Essentially, they arrange points in an image that are much farther apart than they should be. So the scanner has no hope of actually reaching the target point before it gets sent off to the next point in the pattern. This results in a smooth curve with the scanner moving at it's maximum speed. (Ballistic motion, just like when you're scanning the center circle in the ILDA test pattern.)

The problem is that if you bump up your scanner speed to 50K, the scanners are moving fast enough that they can reach these "pulled points" in the image. So the nice smooth curve becomes a jagged, angled line. (Yuk.) If you have the famous "mermaid" ilda animation, you can see this technique in use. (Her eyes have pulled points, and I think parts of her tail do as well.)

This is why most people run their scanners at 30K, even if they are rated for higher speeds. (The other advantage of faster scanners is that they'll give you a wider scan angle when you run them at 30K.)

So don't worry too much about the modulation speed of the lasers. So long as they're good enough for 30K, you should be fine. (Of course, trying to compare modulation speed between different laser manufacturers is a challenge in itself because there isn't any standard for the spec.)

Adam

[James Lehman]

...optical losses within the prizm. ... dichros are more efficient ...

Really !!! ???

Like how efficient? I noticed, from looking at these pictures, that there seems to be almost no "leakage". They must have made great strides in dichro coatings since the one I have was made. It leaks like crazy! I just have the one that combines the Argon and the HeNe.

James.

[buffo]

Like how efficient? I noticed, from looking at these pictures, that there seems to be almost no "leakage".

Depends on how much money you're willing to spend! Consumer-level dichros in the $45-$50 range boast reflection efficiencies of 98 to 99 %, with transmission efficiencies of 95 to 98 %.

However, if you don't mind spending a couple hundred bucks on a dichro, you *can* get 99.5% or better on reflectance, and 99% or better on transmittance.

The one's from Edmund's are OK, but they're not great. I loose about 3 % of my green through *each* dichro, and I loose about 3% of my red through the second dicrho. However, the reflectance numbers are very good. I probably loose around 1% of my blue to reflectance from the second dichro, and maybe another 1.5% of the red off the first one. (My projector has the green laser at the back, then I mix in red at the first dichro, then I mix in blue at the second dichro before I hit the shutter and then the scanners.)

In the grand scheme of things, however, these numbers aren't so bad.

For what it's worth, I've heard from a few members here that the dichros that Bridge sells (the Laser-Wave ones) have better efficiency numbers than the one's from Edmunds, but I haven't checked them myself...

They must have made great strides in dichro coatings since the one I have was made. It leaks like crazy! I just have the one that combines the Argon and the HeNe.

Could be that the one you have is also sensitive to polarization angle. There are a number of older coatings that only reach peak efficiency when both the angle of incidence *and* the polarization angle are aligned correctly. Or it could be that the coatings were optimized for different wavelengths. Or it could just be a cheap dichro. I've seen broad-band trichros that exhibit 5-7 percent losses on each face! Then again, they're 15 years old too. So yeah, it's fair to say that dichro technology has improved!

Adam

[James Lehman]

Those numbers are amazing. I had no idea that they could be that good.

James.