How to make simple Bahtinov mask
Focusing mask which was invented by Pavel Bahtinov is considered to be the easiest, fastest and a very accurate tool for presize focusing. During focusing procedure the mask is placed on telescope's aperture. The telescope then should be pointed to a bright star. Bahtinov mask produces 3 types of diffraction spikes, which form an "X" shape, and another spike inside the "X" which moves left or right, according to focus position. When a precize focus is achieved - the pattern becomes symmetrical. This method is very sensitive, and the displacement of diffraction spikes is apparent even with slight movements of focus.
Instead of bothering with wood and complicated cutting tools - I've made myself a Bahtinov mask using materials commonly avaliable in any office supply store.
Required tools and materials:
- Binder made from non-transparent, hard and thin plastic
- Stanley knife and scissors
- Contact glue
- Ruler and a marker pen
- Printer (A3 if possible)
First step was to generate a mask using this bahtinov mask generator, and then print it. I just printed it using Firefox, on A4 printer. Since the mask didn't fit on one page - I printed two halves on two pages and connected them. A3 printer would certainly make things easier.
Then I cut one half of the plastic binder, and attached printed mask to it . I used a masking tape, making sure it's smooth and held firmly in place. In bahtinov mask it's important to keep the parallel lines straight.
Then the annoying task - cutting the plastic. I did it by placing a ruler over each slot, and sliced with a knife, without too much pressure, several times over each cut.
after the slots were cut out and the paper removed - the mask looked like this:
Next step was to measure the telescope outter diameter, and draw a circle on plastic of the same diameter. Then I cut the plastic with scisors around, while leaving 12 small sections around the circle (I left 2.5cm), for attaching the mask to telescope's tube. These sections should be bent 90° inside after cutting:
Then I cut few strips of plastic, whic width fits the 12 sections on the mask (2.5cm in my case). I glued the strips to bent sections using a strong contact glue:
The final result:
