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Digital Focuser
I have a problem as Astronomik filters and Hutech filters have a slightly different focus position with the same optical train. To get a set of narrowband and wideband images is difficult as you need a bright star to focus visually.
Here is a solution stick a digital vernier caliper on the focuser. I have established there is 1.4mm difference between the two types of filters and if you stack two Hutech filters 2.8mm difference.
Below are two pictures of the caliper and method of mounting (hose clip and superglue!). An animated gif with focus changing by 0.2mm between each frame. And a pic of Terra.
Bert
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