Rick,
? ?Maybe you could look for spatial frequencies, e.g. do a spatial Fourier transform and find a spatial frequency peak that corresponds to stars. That would be pretty processor intensive.
JPEG files are already encoded as Discrete Cosine Transform. You may be able to get spatial frequencies by examining the file. (Possibly helpful article here: <>) The JPEG will only give you spatial frequencies over 8x8 pixel blocks but that may be sufficient.
-Charlie Lasnier
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Sun Sep?6,?2015 1:43?pm (PDT) . Posted by:
A while ago I got a HyperStar for my C14, which converts it to f/2 using the primary mirror and some optics. It replaces the secondary mirror. I use it with my Nikon D600 SLR with great results.
I needed a way to focus while looking at the camera, but all the motorized focusers I could find were way out of my budget, so I decided to design my own. It uses an Arduino to control everything, running software I wrote. A stepper motor drives the focus knob, and I have a hand controller with a rotary knob and display. The Arduino is in its own box attached to the pier, so that motion of the telescope doesn¡¯t drag the hand controller around. I designed the plastic parts and had them 3D printed, the rest of the parts came from Adafruit.
If anyone is interested, I¡¯d be happy to share the design.
Now the question is, how to determine when the focus is optimal. I can drive the Nikon using gphoto on a raspberry pi (I¡¯d rather not take a laptop out to the telescope but if I have to, I will use a MacBook). With that software I can capture jpg or nef files onto the raspberry pi. Can anyone suggest software that can read a jpg and either do fwhm or some other measure of sharpness? I¡¯d really like it to report sharpness of the whole photo as a single number.
Rick
