Quote Originally Posted by Randy Moe View Post
Another question is how do we make and use a DIY Optical Bench.
Randy, this is straight... My bench is my Norma "optical bench" with also a lens board in the back standard, I've two special lens boards, one has an F mount bayonet on it to attach a dslr (without the dslr lens,projwecting on the sensor), the other one has an x20 eyepiece. This isn't a pro bench becuase it's not precise enough to account for the field curvature, but with shifts/rise it allows to reach the circle boundaries, if checking focus again for each time we move the position then we have good information, good enough to check the best shimming.

The shim is calculated by counting the tours we unscreew until the optimal position, and then we multilpy by the thread pitch. It requires some work because we need to balance the effect in the center vs corner.

A dslr may have 250 pix per mm, so some 125 "pixel pairs" per mm, this may be good enough for this optimization work, or even we may use other (cheaper) cameras with a very small sensor having a higher pixel density, like an old smartphone with its lens removed, this is a nice solution because we see the screen in the other side, and we operate the camera from that screen, or with a regular mouse attached to the usb with an OTG adapter. I had used the mouse to remove vibrations.

I made tests with a Sony Z2 that has the lens broken, sensor is 1/2.3 diagonal having 5248 pix in 6.17mm, so 850pix/mm, so a trash Z2 with the lens broken, glued on a sinar lensboard and with a PC mouse OTG connected... this is actually a high precision instrument for DIY optics!