From: "Jerry B. Hillman" 
To: 
Reply-To: "Jerry B. Hillman" 


Hi all,
I did get to do preliminary star testing of my 16.5" tonight.  Seeing
wasn't that good even though skies were clear.  The image 'boiled'

Ronchi test - With 5 or 6 lines showing they appeared straight but I did
notice that as the lines moved across the FOV that as each line came into
view the ends hooked towards the edge of the mirror and then straightened
out then hooked towards the opposite edge just before dropping off the
mirror. (I was star testing on Arcturus. I couldn't see Polaris well
enough.) Does this mean the edge is turned?  The middle lines didn't show a
hook that I could see.

Star test at 495x.  The image boiled to much to get a good reading but I
did see this much.  Inside of focus, a sharply outlined triangle. Outside
of focus a more rounded triangle rotated 90 degrees.  Inside of focus the
image was fuzzy and if I didn't have my eye centered well part of the image
disappeared. Outside of focus the image was better defined but boiling like
crazy.  I turned the mirror about 1/4 of a turn and the inside of focus
image changed from the triangle to a nearly perfect circle. Still fuzzy
though. Outside of focus it was also a circle, better defined but boiling.
The in focus star wasn't quite a point at 495x.  At 190x it was.

My conclusion: My mirror cell is stressing the mirror. I posted the design
to my web page and the link in an earlier post today. I guess I will make
another try at learning plop to design a proper flotation mirror cell.

The fact that part of the image dissapears if my eye isn't centered may
mean my secondary is to small, or I am not properly collimated, although in
a further outside of focus image the secondary shadow seems to be properly
centered.  Any thoughts?

Thanks for all your comments and help. Clear skies, Jerry

--- BBBS/NT v4.01 Flag-4