A Foucault tester is needed to do the zone testing and ensuring we have figured the mirror to correct parabola accuracy. This test was developed by French physicist Leon Foucault and is widely used by amateur astronomers to test the accuracy of their mirrors due to its simplicity.
In below videos I have described about my new and old tester. My new tester is based on the plan given in Sam Brown’s book and few ideas from Stellafane Tester. You can also google search more designs made by other makers.
My New Tester
My Old Tester
My old tester was based on the design given in Sam Brown’s book “Homebuilt Reflector Telescope”. In the below video, I have explained about my old tester. Sorry for the bad audio 😀 Language is a mix of English and Hindi. This tester was initially a slit/pinhole tester (or fixed source) which I converted into slit-less one (a.k.a Moving source) due to its obvious benefit over a fixed source tester.
Pics when this tester was fixed source
slit and KE 
frosted glass and hole for a small bulb. 
front view of the KE and light source 
Light from source and returned image next to KE 
full tester 
dial indicator. 50 parts one turn of 1/4 -20 screw. So precision is 0.001 inch (=(1/20)/50 inch) 
full tester 
base board with carriage pipe 
V cut wooden block to move over carriage pipe 
slit made using razor blades 
Final setup before testing
Pics while converting the tester to moving source
making structure for moving source and KE 
Due to lockdown, used thick cardboard. 
removed fixed ligth source 
100 lip grating and KE on same slide 
slide from front 
3 LED from led strip 
checking the connection 
checking the setup 
Final setup with one LED 
half moon configuration for foucault testing. Returned image form few mm above the LED 
behind the viewing window
Astro Khan Telescope Making 