Defocus Test Before Re-Figuring

b4-00.jpg (585012 bytes) The cardboard center disk is used while performing an eyepiece test for turned down edge.
The black outer ring was used to block the outer 1/4 inch of the mirror where the turned edge was most apparent. Our borrowed more powerful laser is in the background.
b4-11.jpg (22484 bytes) This is the image taken fatherliest inside of focus. This far inside of focus the silhouette of the spider legs can be seen. Compare this picture to the picture fatherliest outside of focus at the bottom of the page. Note that the silhouette of the spider is offset in the opposite direction. This could have been fixed by adjusting the tailgate bolts.
b4-10.jpg (20386 bytes) Inside of focus there is a stringy light on the outside of the de-focused image indicating that some part of the mirror is focusing light too distant from the mirror. Outside of focus the stringy pattern appears inside the de-focused image. So far as I know this aberration cannot be seen in the Ronchi or knife edge tests.
b4-09.jpg (17372 bytes)  
b4-08.jpg (14469 bytes)  
b4-07.jpg (15393 bytes) Just inside of focus. 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.
b4-06.jpg (13505 bytes) Best focus.
b4-05.jpg (13505 bytes) Just outside of focus.
b4-04.jpg (18078 bytes)
b4-03.jpg (17702 bytes) Outside of focus there is a stringy light in the center indicating that some part of the mirror is focusing light too distant from the mirror. Inside of focus the stringy pattern appears outside the de-focused image. So far as I know this aberration cannot be seen in the Ronchi or knife edge tests.
b4-02.jpg (19674 bytes)  
b4-01.jpg (23508 bytes) This is the image taken fatherliest outside of focus. This far out of focus the silhouette of the spider legs can be seen. Compare this picture to the picture fatherliest inside of focus at the top of the page. Note that the silhouette of the spider is offset in the opposite direction. This could have been fixed by adjusting the tailgate bolts.

Return to calling page