2018-12-11: Good news! The mask is available again in an optimized version (optimized for enhanced producibility, same functionality).

Thank you for your patience!


  • This tool helps to find the perfect focus position during the focusing procedure
  • extremely narrow grating (spacing 0.8mm) for easily perceptible diffraction patterns
  • Material: Polyamid ("Nylon") PA12
  • Product Diameter: 98mm / 94mm
  • Product Height: 20mm
  • Color: neutral white
  • Product Weight: 20g
Focusing aid for the popular Samyang 135mm F/2.0 lens.

29,00 €

  • 0,02 kg
  • Currently not available


This so-called Bahtinov mask is a helpful tool for astrophotography. A good description of what a Bahtinov mask is and how it works can be found at its Wikipedia entry. It was invented by Pavel Bahtinov to get rid of the tiring procedure of traditional focusing where you try to find the minimum spot size. This mask can help you with focusing on stars easily when it is placed in front of your telescope.

The working principle is that the light of the stars is diffracted in a special way and creates a characteristic pattern which can be easily judged to recognize a perfect focus position of your telescope.


The product offered here is an optimized version for the 135mm f/2.0 telephoto lens by Samyang, but it can be used with any lens or refractor with a front diameter less than 94mm! (It fits perfectly to all versions of the Samyang lens, both the manual focus version and the Cine/VDSLR version. The two versions share the same sunshield where the mask can be placed.)

There are even some software tools that can assist you with the stripe alignment during focusing.

Sample application - lens and lens holder not included
Sample application - lens and lens holder not included


Liveview screenshots of a diffraction pattern. Left and right image: slightly defocused - Middle: Perfectly focused
Liveview screenshots of a diffraction pattern. Left and right image: slightly defocused - Middle: Perfectly focused
  1. Slew to a bright star to keep exposure times short
  2. Place the mask in front of the lens
  3. In your liveview of the camera you can see a diffraction pattern similar to the one shown to the left. It consists of three stripes.
  4. Start focusing. You have reached the perfect focus position when the three stripes cross each other exactly in one position.

Open Source Hardware

As a member of the OSHWA I'm totally convinced of the idea to offer products as Open Source Hardware instead of protecting them by patents. The OSHWA (Open Source Hardware Association) is one of the most well-known organizations that support the open-source-hardware ideas.

This Bahtinov mask is also based on an Open Source Hardware project hosted by me at Thingiverse:

You can find there additional informations about the creation history of this variant. It was derived from the great work by Thingiverse users brentb and Ryoko.


The source code (OpenSCAD format) can be found at GitHub:

You are invited to work on this mask, if you have any ideas. I'm always pleased to get some input, whatever to criticise is (I'm open to both positive and negative critics!). GitHub contains a pretty good issue tracker, you may enter your suggestions or issues there directly!

General Informations

Safety notes

  • Storage conditions: Store the mask protected against dust and moisture. Avoid high temperatures above +50°C.
  • Do not drop the mask and store it in a rigid box (e.g. your children's breakfast box :-) )
  • The grating is fragile, due not touch or bend it too strong! Please, handle it like any other optical device like lenses, filters, eyepieces,...
  • Keep the product away from little children. They may break the fine bars and hurt themselves!

General informations

  • The masks are produced using the latest 3D manufacturing technology, the so-called SLS (Selective Laser Sintering). This means that the surface has a porous touch which has no influence on the optical performance.
  • The white color also has no influence on the optical performance at all.
  • When permanently exposed to daylight, the material may become yellow a little bit. This does not affect the optical or mechanical performance of the mask!
  • I recommend to clean the mask only with pressure air or even by blowing the dust away by yourself!

If you have any further questions, please have a look into my FAQ collection or contact me directly!

Copyright Notice: SAMYANG is a trademark of SAMYANG OPTICS CO., LTD.

Disclaimer: I am not licensed, approved or endorsed by Samyang