William Optics Bahtinov Mask 172-235 mm

William Optics Bahtinov Mask 172-235 mm

The Bahtinov mask is named after its inventor Pavel Bahtinov. This focusing tool enables precise adjustment of your astro pictures to the focus plane of your telescope or camera lens.

These new focus masks made from optical acrylic glass provide 92% transparency.

The imprinted pattern provides a diffraction structure which is around three times brighter than classic metal masks. The acrylic glass masks therefore produce a clearer diffraction pattern and enable focusing with the help of fainter stars.


This is how focusing of your camera on your telescope or lens works:

Attach the mask to your telescope and slew the telescope to a bright star.

Turn on your camera and watch your selected star on the live view screen.

If the image isn´t yet in focus, the central line of the Bahtinov pattern is shifted. Adjust your focuser until this very line sits exactly inbetween the other two lines.

Now you have achieved optimal focus. Remove the mask from your optics and you can start the exposure of your object.

Practical advice from Teleskop-Service

Using a Bahtinov Mask for focusing works especially well for deep sky photography. Correctors and Barlow lenses are not a problem.

Ideally you want to use a star with medium brightness for focusing. It should neither be too dark nor too bright. The lines of the Bahtinov diffraction pattern have to be clearly visible.

The chosen star shouldn´t be positioned in the center of your live view, because most telescopes or lenses, although corrected, do not produce a plane field of view. We recommend to position the star in the outer third of your image. That way, you will achieve a better overall sharpness across your field of view.

- Bahtinov mask
- Mounting material

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