Bahtinov Focus Mask for Celestron 11" SCT Telescope

The focusing mask takes all the guesswork out of doing precise focusing for astrophotography. Often, if the seeing is not perfect, it's hard to focus on an ever-shifting image. With the focusing mask you can go to a bright star, center the diffraction spikes, and then go to a planet. Or, sometimes I have even used this method directly on the planet. Using it on jupiter's moons is perfect. If you increase your exposure and gain you even eliminate the jiggly jumping of the spikes because over a long exposure you get the AVERAGE position. The price is a little high for such a simple item, but at least it will last forever.

Works great on my Celestron CGE1100! Focusing my camera was a cinch. The star has to be quite bright in order to see the diffraction spikes, though (not really the fault of the product, just something to take note of). I do wish it had a small tab or something to hold onto to lift it off the corrector plate though so I don't actually touch the corrector plate.

I mainly purchased this mask to obtain a perfect focus with my Canon 20D camera on the telescope. I had to look through the camera's viewfinder to achieve it. There was not enough light and clarity to be able to see any kind of a star-burst on Arcturus to make any adjustments in the focus. I'm sure it works fine looking through an eyepiece, however, if I focus through an eyepiece, then remove it and put my camera in its place, the camera will need to be refocused.

The minor problem is that the 11" mask doesn't have anything to aid the removal. It relies on your fingers not going through and touching the glass. My major problem is that the mask for the 11" doesn't exactly fit my Celestron 11"! The hole in the middle is too big by 1/2 inch. This let's light through the middle that defeats the purpose of the precise slots. It is too difficult to get info about the fit to be sure you will get the proper mask.

A quick low tech way to get a perfect focus. Uses an interference pattern to achieve this optimum focus. Use it by placing the mask over your telescope's objective while looking at a bright star and move the center line within an X pattern to the middle with your focus knob and viola you have a perfect focus.

Saves about a half hour of tinkering with the camera focus every time. If you change out the lenses for higher / lower magnification just set it back on the glass and in seconds you can have the camera focus spot on. Makes our limited viewing time so much more enjoyable.

It isn’t difficult. You place it on the front of the scope and follow the easy instructions. It works. What more can be said. For astrophotography sharp focus is a must. This focus mask allows you to achieve perfect focus.

Good quality, solid built and thick enough to last. It is strong enough for me to cut it with a slim hack-saw and not damage it. Needed to cut it in half so I can use it with HyperStar!