Bahtinov Mask

A Bahtinov mask is a device used to accurately focus an astronomical telescope. The mask is placed over the aperture of the scope. It produces spikes on the star image. When the spikes are symmetrical the scope is in perfect focus. The mask is then removed and images can be taken.
The crucial point is that the position of the central spike tells you which way you should adjust the focus.
The bright star in this example is Capella.
See my website for how it works http://www.btinternet.com/~gfcarey/bahtinov.htm
Also see the 'Carey Mask' at http://www.btinternet.com/~gfcarey/careymask.htm

Category:

Science & Technology

Tags:

• bahtinov
• mask
• astrophotography
• star
• image
• focus
• capella
• telescope
• carey

[JeffreyJaguar]

How easy is it to see the diffraction spikes through a camera viewfinder? I use a Canon Digital Rebel and I wonder how easy it is to actually see the spikes. I'm thinking about getting one of these but I'm skeptical that it will work with a small scope such as a WO 66ED and Canon Digital Rebel. Wouldn't the image be too dim to accurately line up the diffraction spike? Thanks for the post.

[geocarey]

It is very easy to see the spikes in the viewfinder. I also use a Canon Rebel. Get the image well centred and then use the zoom function to blow up the image. Even quite faint stars can be used although it is obviously best to focus on a bright on.

[DJsNorthWest]

i seen this with my naked eyes last night very bright and more spikes than in the pic ....why is this??

[rshellrshell]

Take a look at the Stiletto focuser. It doesn't depend on your ability to line up anything accurately. It basically takes the accuity of your vision out of the focusing equation altogether.

[JeffreyJaguar]

Thanks, I got one but haven't had a chance to try it out yet.