Re: [ATM] Star test with laser light sources

["Ray@J-Engineering.com" <Ray@J-Engineering.com>]

Hi All,

I found a reference, Figure 9-5,  in Suiter's book where a monochromatic 
source is used and the source is in focus.  The figure shows an airy 
disc with dozens of concentric circles around it. This is very similar 
to my observations when using an LED behind a pinhole. All this time I 
was expecting two or three rings and was wondering what was wrong.  When 
I shined the green laser pointer on a polished ball bearing I saw 
hundreds of rings (and other distracting garbage). 

I found that with my  LED's there is a sweet spot when aligning the 
source to the scope.  Once I figured out how to align things, the source 
was plenty bright.

When it comes to comparing the inside-of-focus to outside-of-focus 
images, do you think it maters if the source is monochromatic?  Even if 
there are a few dozen diffraction rings in the in-focus image?  (sorry 
for copying the whole thread but I like the history in this case)

Ray J

Jerry wrote:

>	It is not necessarily a good or a bad idea. In the case of
>artificial star testing a mirror I can think of no advantage with
>monochromatic light and none with coherent light.
>
>	Remember I did say that I had no first hand experience. I meant none
>with artificial star testing. I have used a real star. It was not
>monochromatic. I can not think of a reason monochromatic would be an
>advantage. If there is I am sure some list members will suggest that I don't
>know what I am talking about, which may be true.
>
>	I don't know if the coherence of the laser matters. I am thinking
>that monochromatic light will have more noticeable interference effects.
>White light interferes but at different locations for different wavelengths
>making it less sharply defined to the eye.
>
>	I like the Christmas ball idea for an artificial star. I think most
>people use the Sun's reflection. It probably needs to be lit by a bright
>light.
>
>	Where are all the artificial star testers I was arguing with a while
>back? I thought my "conjecture" answers would have provoked massive
>responses by now. Help me out Richard! They must be getting used to me.
>
>Jerry  
>
>
>
>Ray J wrote
>Is monochromatic light a bad idea?  For example, a bright yellow LED? 
>(Not a laser)
>
>
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