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Bahtinov Mask Generator
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A Bahtinov mask is a focusing aid for astronomy in general, and astrophotography in particular. It consists of a disk made of opaque material fitted over the telescope objective with slots cut out in a specific pattern devised by amateur astrophotographer Pavel Bahtinov. For more information, look at this thread on CloudyNights  or here at
incredibly well-made commercial offering from spike-a.comlaser-cut from acrylic using file from


Designing a mask using drawing, design, or CAD software can be challenging, as the specifics of the mask change for each telescope based on aperture, focal length, and how you plan to attach the mask to the scope. This generator makes generating masks significantly easier - simply enter some parameter values specific to your telescope on the next page, press the Generate! button, and out pops an SVG file with your design.

You can save that SVG file and load it into an SVG editor (e.g., Inkscape, OpenOffice, GIMP) for printing (or further tweaking). Note: While using the browser to preview the SVG is useful in understanding the effect of changing parameters, I no longer recommend printing these directly from the browser. Testing larger aperture designs yielded printed masks that were increasingly "off" - also sometimes known as "wrong." Besides, there's no way to print masks that are larger than the physical page directly from the browser.

Note that the values entered are actually stored in the SVG as XML comments - you can open SVG files with any text editor to view them - or, if you're viewing them in Firefox, right-click on the image and select "View Page Source."


No warranty, express or implied, yada, yada, yada....


All credit for the mask goes to Pavel Bahtinov for creating the design, and to Dennis Sakva for championing it on Cloudy Nights.  Thanks, guys!

If you have questions, comments, issues, suggestions, or if you'd like to be notified when the generator is updated, shoot an e-mail to david at astrojargon dot net.

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Copyright 2009