Near field alignment question

[jors]

HI all!
Just starting to build my 1rst RGB Projector, but I have one doubt about near/far field alignment (However I've read lost of posts about, including Stanwax alignment guide!)

So, the question is:

I know all lasers must be at exact height, but what about the beam output vertical angle vs baseplate?
When turning 9mm focus barrel clockwise/counterclockwise to tune for infinite focus, I've noticed that rarely the beam is perfectly parallel to baseplate (please see attachment) . While rotating, it describes subtle round pattern far field, cause the beam is angled respect the baseplate.
I Suppose this is due the mechanical tolerances on barrel thread, press diode... even with teflon on , there is a slightly vertical angle with respect to baseplate.

I've ordered some nice cooper housings from LAsershowparts, so I suppose the 3 LD's will be perfectly fit on height near-field, but they comes with 9mm aixiz-style lens barrel too (
http://lasershowparts.com/store/inde...&productId=318
So, when projecting the 3 beam colors directly to far field (no scanner, no dichros), beams will NOT match the same height at far field, due the slightly different output angles from de 9mm barrel respect to baseplate.

Is this important for a proper near/far field alignment?? Should be the 3 beams PERFECTLY PARALELLED?

Many thanks!!

[buffo]

I know all lasers must be at exact height, but what about the beam output vertical angle vs baseplate?

The near-field alignment is measured where the beams intersect each other at the dichro face. Thus, it doesn't mater if the beams are parallel to the baseplate or not. All that matters is that they intersect (or more accurately, that they perfectly overlap) at the dichro face.

In practice, having all the beams at the same height AND having them all parallel to the baseplate makes this easy. But even if the beams are not parallel, so long as they meet at the exact same spot on the dichro, your near-field alignment will be correct.

So to answer your question, yes, it is helpful if the beams are parallel. But if they are not, you can still get your near-field alignment correct by adding shims under the laser diode mount to raise the beam so that it overlaps perfectly with the other beam at the dichro face. (Even if it's entering the dichro at an up or down angle.)

And just to review, the far field alignment is accomplished by adjusting the mount for the dichro. The near field alignment is accomplished by adjusting the beams so they overlap at the dichro face.

Adam

[jors]

Oh I see Many thanks for the explanation Buffo.
By the way, please do you know which is the "usual" or best way to enter beam on "X" galvo? this way (-) or this (l)?
Due I want to correct blue & green (Nichia 520 1w) with prism.. I input the beam like this (l) on prism, in order to correct fast axis. So without galvos, the beam will be (-) far field, but thru galvos, all my beams will be vertical (l) far field.
Generally speaking, far field output from a projector is (l) or (-) ? just an aesthetic question I suppose
Many thanks!

[buffo]

It really doesn't matter which way you orient the fast axis. It won't be apparent to your audience.

Adam

[jors]

Ok Many thanks Adam!

[buffo]

Anytime!

Adam

[WolfMax]

The near-field alignment is measured where the beams intersect each other at the dichro face. Thus, it doesn't mater if the beams are parallel to the baseplate or not. All that matters is that they intersect (or more accurately, that they perfectly overlap) at the dichro face.

In practice, having all the beams at the same height AND having them all parallel to the baseplate makes this easy. But even if the beams are not parallel, so long as they meet at the exact same spot on the dichro, your near-field alignment will be correct.
Adam

When you say dichro face, I assume you mean both dichro faces.

[buffo]

When I say "the dichro face", I'm referring to the forward face where the incident beam reflects off of it, as opposed to the rear face where the beam that travels straight through the dichro (as opposed to reflecting off it) first enters the dichro.

Making certain that the beams overlap perfectly at this forward reflective face is how you adjust the near-field alignment of the dichro. The far-field alignment can then be adjusted by tilting the face of the dichro using the adjustment screws on the mount.

But yes, you will have TWO near-field adjustments in a standard RGB projector, one for each dichro.

Adam