A beginner's guide to Bahtinov masks

• Using a Bahtinov mask for astrophotography
• Bahtinov masks and imaging deep-sky objects
• 5 of the best Bahtinov masks
• Vbestlife Bahtinov Mask
• Rother Valley Optics Advanced Bahtinov Mask
• StarSharp Bahtinov Focus Masks
• Starwave Bahtinov Masks
• Astromania Bahtinov masks

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A Bahtinov mask is a specially cut visor made from cardboard or plastic that you place on the front of a telescope to help you focus accurately.

The special shape of the cut-outs in the mask produce a set of diffraction spikes in the same manner as the secondary mirror spider vanes on a Newtonian reflector.

However, the Bahtinov mask’s diffraction spikes form a very specific shape comprising a cross with a line passing through it.

Observing a diffracted bright star with this mask in place and adjusting the focus until the line perfectly bisects the cross ensures that accurate focus is achieved.”

Using a Bahtinov mask for astrophotography

Credit: Tony Rowell / Getty Images

Focus is the single most critical component of any successful image but it can be remarkably difficult to achieve.

Despite the use of digital cameras and their live view features in astrophotography, determining when a test star is at perfect focus is rather subjective.

However, the use of a Bahtinov Mask makes achieving accurate focus really simple.

Just as a Newtonian Reflector’s spider vane produces diffraction spikes on bright stars, the ‘vanes’ on a Bahtinov Mask produce a complex diffraction resulting in a cross and a horizontal line.

Adjusting focus until the line bisects the cross confirms perfect focus.

Bahtinov masks and imaging deep-sky objects

Accurate focus on deep-sky objects is key to successful imaging, but it’s surprisingly difficult as many objects are too dim to focus on.

However, focusing on a bright star is much easier and if the stars are in focus, deep-sky objects will be too.

A Bahtinov Mask makes it easy to get stars in focus.

As we've noted above, when placed on the front of a telescope aimed at a bright star, you'll see a distinct diffraction pattern comprising an ‘X’ and a horizontal line.

Capturing a series of exposures of the diffraction pattern and checking them allows you to adjust focus between images until the line perfectly bisects the ‘X’, which indicates the best focus position.

Below we've picked out some Bahtinov masks that are available to buy online.

5 of the best Bahtinov masks

Vbestlife Bahtinov Mask