Make Your Own Bahtinov Focusing Mask

A Bahtinov Mask will help focus your telescope or camera lens on distant stars,

This is a quick and easy solution to make your own Bahtinov mask for a telescope. This design should be adaptable for different sized telescopes as well as for camera lenses.

I have used telescopes for several years and I’ve taken my share of photographs over the years as well. Recently I decided to join those 2 activities. I have Newtonian reflector I needed the T-ring and adapter for my Canon EOS DSLR.

I shopped around, did my research on getting started in Astrophotography and made my purchases. Now I was all set. And as expected, it was a simple task to mate the camera to the telescope and shoot my first pictures. And, they were all slightly out of focus. Besides being new to astrophotography and trying to hurdle that obstacle, I also wear glasses. This seemed to mean my focus was off due to my eyesight and I had to make compensations . During my research on astrophotography I had read about Bahtinov Masks and how easy a paper mask is to make.

Tools Needed to make this version of the mask:

- Utility knife
- Metal straight edge
- Table saw with metal cutting wheel
- Sand paper
- Metal File
- Vinyl cutter

Materials Needed

- Metal coffee can with plastic lid _(large diameter to fit telescope tube)
- Paint/ primer to suit
- Foam tape

I set out to make one of simple paper as a test.

Print a mask using the generator at Astrojargon (http://astrojargon.net/MaskGen.aspx) and cut it out using you knife and metal straight edge.

I tested the paper mask by focusing on a bright star and found the design worked.

Now I was ready to make a more durable mask that would stand the test of time and the wear and tear of repeatedly being packed off to viewing sessions.

The next step was to find a design that would meet the criteria I had imposed upon myself. The mask had to be durable, easy to attach and remove from the telescope, and be low cost. Why make a mask that would cost the same or more as a commercially available one?

I considered making the mask from a plastic binder, but ultimately decided on using a plastic lid from a coffee can. The next issue would be to print the mask and cut it out then use as a pattern to transfer to the lid. While thinking of ways to get the pattern affixed to the lids so it would not move during the process, I thought of using my vinyl cutting to cut a mask from vinyl and then applying that to the plastic lid.

The mask generated from astrojargon is saved as an .svg file. My vinyl cutter doesn't have the capability to use this format so I converted the mask in Adobe Illustrator to a bitmap image.

At this point I cut the final mask and prepared if for placement on the lid.

After the vinyl pattern was affixed to the lid, utility knife and straight edge to carefully cut the openings in the lid. Take your time and be precise, the more accurate your cuts the better performance of the focusing mask.

After the mask is cut, carefully and gentle sand and rough edges with very fine sandpaper.

To cut the coffee can to the proper length, measure your telescope tune from the from edge to the finder scope. Subtract at least 1/8" from this and mark your coffee can. If your coffee can is corrugated, make your mark at the bottom of the valley before your mark.

Set the rip fence on your table saw to the proper position to make the cut at the needed length and begin to cut the can. slowly turn the can while cutting without much pressure on the can to make a smooth cut. Make multiple passes until you are through the can.

After the cutting is complete, you will need to file and sand the edge to make it smooth enough to not be a cutting hazard. Remember, you will be using this in the dark and sharp edges and darkness don't mix well.

After the edge is smooth, prime and paint if you choose.

After you paint is dry, put foam tape inside the can to make a snug but not tight fit over the telescope tube. Attach the mask and your mask is ready to use.

My new durable mask was made from items I had around the house and my cost was nothing, far below my goal of low cost. Using the mask has made my focusing much sharper and rewarded me with better images.