{"id":44416,"date":"2023-04-21T07:32:27","date_gmt":"2023-04-21T07:32:27","guid":{"rendered":"https:\/\/www.skyatnightmagazine.com\/?p=118163"},"modified":"2023-04-21T07:32:26","modified_gmt":"2023-04-21T07:32:26","slug":"how-to-make-a-bahtinov-mask","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/how-to-make-a-bahtinov-mask\/","title":{"rendered":"How to make a Bahtinov mask"},"content":{"rendered":"

Our DIY Bahtinov mask guide contains a link where you can download a printable, adaptable PDF template. <\/p>

By Mark Parrish\n \t\t<\/p>

Published: Friday, 21 April 2023 at 12:00 am<\/p>

\n\n

A Bahtinov Mask<\/a> is a mask that makes use of diffraction, an optical effect that happens when light passes through small openings.<\/span><\/p>\n

A<\/span>chieving focus is arguably the most important aspect of successful astrophotography<\/a>.<\/span><\/p>\n

This project is a focusing aid\u00a0 based on the design developed by astronomer Paul Bahtinov to help you achieve pin-sharp stars and therefore pin-sharp images.<\/span><\/p>\n

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Diffraction effects can be observed with a Newtonian telescope that has a \u2018spider\u2019 support for the secondary mirror, or a camera lens with an iris that has straight edges \u2013 in both cases, bright stars appear to have lines (called spikes) radiating from them.<\/span><\/p>\n

Our Bahtinov mask has three sets of diffracting slits through which the starlight passes.<\/p>\n

On one side, two sets of angled slits produce a cross pattern, while the straight slits on the other side create a line that passes through the cross.<\/p>\n

When the image is properly focused, this line passes exactly through the centre of the cross, but when unfocused it is offset to one side.<\/p>\n

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Exagerrated spikes created by a Bahtinov mask are one way to achieve sharp focus. Credit: Will Gater<\/span><\/figcaption><\/div>\n

Building a robust Bahtinov<\/strong><\/h2>\n

Most DIY versions of Bahtinov masks are made from card, but our design is slightly more robust and should last longer.<\/p>\n

However, it\u2019s still easy to make, using just a few basic materials, a craft knife and glue.<\/p>\n

The Bahtinov mask panel is cut from a sheet of thin craft foam and the sleeve is built up from strips of cork.\u00a0These were bought from our local hobby and craft store.<\/p>\n

A very sharp knife is essential for a neat mask, so pop a new blade in, use a cutting mat to protect the tip, and make the mask panel before cutting the cork strips.<\/p>\n

There is no need to work out the design of the slits because there\u2019s an online tool that does it all for you.<\/p>\n

Go to satakagi.github.io\/tribahtinovWebApps\/Bahtinov.html<\/a>\u00a0and type in your telescope\u2019s focal length and aperture.<\/p>\n

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With the Bahtinov mask in place, light from a bright source (for testing we used a green LED) produces three crossing spikes which are aligned when perfectly focused.<\/span><\/figcaption><\/div>\n

If your telescope has a central obstruction, add the diameter of this too.<\/p>\n

The tool generates a CSV file that can be printed from various applications, including MS Word and Google Chrome.<\/p>\n

Once your mask is completed, you can use it by taking a series of images of a convenient bright star (or use live view) and adjusting the fine focus.<\/p>\n

When you have the line and cross aligned, lock your focus, remove the mask, and reposition the scope to take an image of your desired deep-sky object.<\/p>\n

What you\u2019ll need<\/strong><\/h2>\n
  • Scalpel or craft knife, cutting mat, safety rule, pencil<\/span><\/li>\n
  • Thin, black craft foam (size to suit tube diameter), thin cork sheet<\/span><\/li>\n
  • Black spray paint, PVA glue, masking tape, low-tack glue or spray mount<\/span><\/li>\n
  • Rubber bands, clothes pegs<\/span><\/li>\n<\/ul>

    Build a Bahtinov mask, step-by-step<\/strong><\/h2> <\/body><\/html>\n
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