Having the right tools.

I managed to get the Bahtinov mask I mentioned in the last post cut out tonight. There’s an astronomy site with a generator that will take your scope specs ( focal length, aperture, secondary mirror circumference, etc.) and create a picture file you can print out. [url=Https://lmgtfy.com/?q=http%3A%2F%2Fastrojargon.net%2Fmaskgen.aspx]Google can point you in the right direction[/url] if you’re interested.  In any case, I plugged in the Celestron’s pertinents and printed out the template.  I had some thick plastic sheeting I had used a section of in Hawaii to block Angus’ view of the street (to cut down on barking at the gate), so I taped the pattern to that and got to cutting.


I still think I’ll end up painting it black, but it works, so that’s all that matters.  The way it works is that you place it in front of the objective lens (the front one) on your scope, and it creates three diffraction spikes around the image of a star. These spikes align perfectly only when the star is in focus. Recall if you will the out of focus rings from the last post:


With the mask in place (and the scope closer to being in focus), you can start to make out the diffraction spikes:



Even closer to focus and you can make out the the spikes easily:



And in perfect focus everything lines up symmetrically:



Yes, you can set focus in a telescope by eye, but why worry about spending time fussing with it when you can get it dead-right in seconds every time?  I probably have less than $2 in materials, and less than an hour of time invested, and will save several minutes every time I swap out an eyepiece for a camera adapter, and vice-versa in perpetuity.  Oh, and if you’re not willing to discount your time, you can buy pre-made masks several places online for anything from $25-$100. I just thought of it as a learning exercise, and it was kinda fun too!





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