Defocus Test

Eyepiece Defocus Test, Figuring 018

	At this stage you must wait until the telescope has come to the same temperature as the outside air. Otherwise you can't see a thing through the turbulence. The seeing is not good enough to see the diffraction rings.



	If there is any astigmatism you will see it by focusing just inside and outside of focus. If your eyes are astigmatic as mine this test will always fail if done without glasses. Also you should have your head vertical because when your head is tilted the astigmatic correction in your glasses won't work correctly.
	The digital camera tries to compensate for my defocus. This increases the range where focus is good.
	I can see no astigmatism but the stringy pattern seen when correcting the 12 inch mirror is just discernable.

Eyepiece Defocus Test, Figuring 023

	At this stage you must wait until the telescope has come to the same temperature as the outside air. Otherwise you can't see a thing through the turbulence.
	Since the bright ring outside of focus indicates a turned down edge does the bright ring inside of focus indicate a turned up edge? Maybe- have to ask Mr. Dobson.


	No astigmatism and no stringy pattern and a nice sharp focus.

Eyepiece Defocus Test, Figuring 025

	At this stage you must wait until the telescope has come to the same temperature as the outside air. Otherwise you can't see a thing through the turbulence.






	No astigmatism and a nice sharp focus. ( Considering all the turbulence. )

Eyepiece focus Test, Figuring 025

Artificial Star Focus Test

Upper frame, using an uncoated 8 inch F 7.8 mirror through a 9 mm eyepiece captured by a Sony S30 digital camera.

Lower frame, same picture set after adjusting contrast and sharpening in Microsoft PhotoDraw.

Simulated images in good 'Seeing'.

Upper frame, an image suitable for correction by one element of an adaptive optic mirror.

Lower frame, image element after correction by an adaptive optic mirror.
( Or an image from space. )

Diffraction ring is not simulated.