From: "James Lerch" 
To: "Jeff Anderson-Lee" ,
        
Cc: "ATM List" 
Reply-To: "James Lerch" 


----- Original Message -----
From: "Jeff Anderson-Lee" 
>
> "James Lerch"  wrote:
> > Here's the setup:
> >
> > Charlie's 12.5" F/4.49 mirror
> > 80 LPI ronchi grating (need to make/buy something better)
> > USB 640*480 CCD (no Lens)
> > Laser Diode from laser pointer
> >
> > A Static stand was made to support the CCD and Laser diode like this:
>
> So the CCD and light source are a fixed distance while the grating moves.
> Interesting.

Hi Jeff,

Yes, the experiment was interesting, but perhaps wrong... (see below)

>  Did the grating cover the light source and imager or just the
> imager?

Just the imager,  the light source is so small it fit between the lines of
the ronchi grating.

>  Roughly how far in front of the CCD was the grating at the null
> position?

My 0 position image has the Ronchi grating 30mm in front of the CCD.  BTW,
the light source is 44mm in front of the CCD.

I made an effort to make comparisons between my images and diffract, and
the results are interesting.  Let me refer to the results first, then I
mention my concerns.  (all file names reference the "X-R,mm"  I
entered in diffract to create the image.

http://lerch.no-ip.com/atm/2ndTry/A_Ronchi/-4.62mm.gif    (238KB)
http://lerch.no-ip.com/atm/2ndTry/A_Ronchi/1.27mm.gif     (216KB)
http://lerch.no-ip.com/atm/2ndTry/A_Ronchi/8.89mm.gif     (179KB)
http://lerch.no-ip.com/atm/2ndTry/A_Ronchi/12.7mm.gif     (216KB)
http://lerch.no-ip.com/atm/2ndTry/A_Ronchi/15mm.gif        (210KB)
http://lerch.no-ip.com/atm/2ndTry/A_Ronchi/18.25mm.gif   (203KB)
http://lerch.no-ip.com/atm/2ndTry/A_Ronchi/19.5mm.gif     (202KB)

Or as one big zip file:
http://lerch.no-ip.com/atm/2ndTry/A_Ronchi/Ronchi_Comp.zip (1.4MB)


Below is a table of my first concern, which shows the "X-R,mm"
value I had to use in Jim Burrow's Diffract, to make a comparison to my
images.

Diffract            Measured
-4.62mm         -10.16mm
  1.27mm         -1.27mm
  8.89mm           6.35mm
12.7mm            12.7mm
15mm               16.51mm
18.25mm          16.51mm
19.5mm             21.6mm


My second concern is the farther outside RoC I go, the more deviation between my
images and those produced by Diffract.  For instance the 19.5mm animation
shows roughly the same number of Ronchi lines, but Diffract shows a
stronger curvature
for these lines than I imaged.

Asides from those two concerns, there are some strong similarities between
Diffract and my images, especially near RoC.

For those interested in repeating this experiment, here's the data used to
configure Diffract:

D = 317mm
R = 2829mm
b = -1
N=512
Width,mm = 320
Source Diam, mm = 0.01
Test = Ronchi
Lines/mm = 3.15 (80lpi ronchi?)
Source = Fixed
Color = Red

I tried the "Read mirror file" option in Diffract to import the
Sixtests's surface profile from my Robo-Data, but I get a "Spline fit
failed" message, so I
did all my simulation reference a perfect parabolic mirror...

As Jeff said,  "Interesting"  :)

Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)

"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"

--- BBBS/NT v4.01 Flag-5