Wasn't keen to haul out the Celestron Optical Tube Assembly to do measurements. But then I remembered the Bahtinov mask project. So tracked down the PDF. I recalled the grating was at the exposed glass edges so I could use that as a reference... Hold the phone! I grabbed the actual focusing mask I made. I had modified it to fit inside the OTA! That would help me easily and quickly get all the measures, including the secondary mirror!
Measured the diameters.
- OTA inner diameter (ID): 22.7 cm
- opening: 20.5 cm (that seems good, an 8-inch mirror is 203 mm)
- central obstruction (CO): 70 mm
OK. Fired up Visio and located the apodisation mask I had made for the little Meade ETX.
Considered scaling up the ETX but didn't feel completely comfortable. So I started from scratch.
Like with the focusing mask, it ran off the page, too big for a single "letter" size sheet. So I cut the mask at a logical place. Printed on the laser in greyscale and cut out the pieces. Couldn't find the white glue so I used wood. It went fine.
Ready to try.
But now I'll probably have to wait 10 months... Hrrm.
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