[ATM] A challenging 28" project

[Richard]

Hi Mike,

Friday, August 3, 2007, 6:27:35 PM, you wrote:

ML> NA goes up (not down, Richard) as focal ratio decreases

Yes, I know!. I actually thought about it before I posted about it
too. NA is one of those things I just don't have an intuitive feel
for. I always resort to the logic that low power = wide field = low
NA, therefore low NA = wide field, but it's wrong of course :)

ML> I found objectionable fringe artifacts with the microscope objectives 
ML> I had which were broadband AR coated -

Try a small matching lens between the laser and the microscope
objective, one of the small laser aspheric collimating lenses works
nicely. If you bring the laser to a focus at the back conjugate of the
objective, the objective then received something approaching a
spherical wavefront rather than a glaring parallel beam. You get
better light distribution over the beam and less of the effect you
refer to. I also got much better nulls when using a matching lens.

ML> I'm only dealing with laser light I found that Edmunds has a 
ML> reasonably priced, mounted (in a microscope objective-type housing 
ML> with the same threads) laser singlet

They look really useful, not seen them before.

ML> Actually I will have to simplify my test setup in order to test these 
ML> small, fast mirrors.  Much easier than testing a 28" F/1.1 hyperbola!

Ah good, I can go back to f/2 then ;)

-- 

Best regards,
  Richard in the UK