[ATM] A challenging 28" project

[Mike Lockwood]

Richard,

On-list,

Richard wrote:
> 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 :)

I know you knew better.  :)

> 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.

Already done - using another microscope objective.  Still had 
artifacts even though that one was putting out a nice uniform center 
spot.  Helps tremendously on light distribution.

> They look really useful, not seen them before.

Yes, quite useful, already mounted, and affordable.  You can also buy 
the unmounted lens for $22.

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

Sure!

Richard, I should mention that I have two of my 20" F/3 blanks 
polished out to fairly good spheres, ready for figuring.

One last thing - I want to add a huge thank you to Stan Truitt for his 
friendship and advice in helping me out with many of these testing 
issues.  His advice was invaluable in making this test equipment work. 
  Stan normally lurks on the list and chimes in occasionally with sage 
advice.  Heed his words - he knows of what he speaks/types!

	Mike Lockwood