NEW! StarWave Bahtinov Masks
Whether you’re doing planetary visual observing, planetary imaging or deep sky imaging, the Bahtinov Mask is a great accessory to get the best focus for your telescope quickly and easily. Credit goes to Russian amateur astronomer Pavel Bahtinov for making his idea available to the astronomy community.
Starwave Bahtinov masks are adjustable to fit a wide range of optical tubes, and are made from precision laser cut ABS plastic, which is stiff enough to remain in position, yet has enough “give” to make them tough without being brittle in the cold, unlike acrylic versions. The telescope tube is gripped gently but firmly by 3x metal posts with non-scratching silicon sleeves on the rear side of the Bahtinov mask to prevent slippage, whilst remaining perfectly central - unlike other masks with two posts which rely solely on gravity to hold them in position. Because of the 3-post mounting method, the Starwave Bahtinov mask remains centred, whilst fitting a wider range of telescopes, saving you money if you decide to change optical tubes. So, all you need to do it measure the outer diameter of your telescope tube and choose a model corresponding to that OD dimension.
The following range of sizes are available to fit just about any amateur telescope on the market, as well as DSLR camera lenses:
Starwave Bahtinov Mask to fit 65-100mm OD tubes
Starwave Bahtinov Mask to fit 85-120mm OD tubes
Starwave Bahtinov Mask to fit 105-150mm OD tubes
Starwave Bahtinov Mask to fit 125-180mm OD tubes
Starwave Bahtinov Mask to fit 150-200mm OD tubes
Starwave Bahtinov Mask to fit 175-220mm OD tubes
Starwave Bahtinov Mask to fit 195-240mm OD tubes
Starwave Bahtinov Mask to fit 215-260mm OD tubes
Starwave Bahtinov Mask to fit 250-290mm OD tubes
Starwave Bahtinov Mask to fit 290-340mm OD tubes
Q: How does a Bahtinov focusing mask actually work? When in place, the Starwave Bahtinov mask works by forming a diffraction pattern of “spikes” of light around a star or point light source, which is easily visible in your eyepiece or DSLR/CCD camera in live view mode. (See the thumbnail image above, or click on this Bahtinov Mask diffraction pattern example). When the pattern becomes perfectly symmetrical, the telescope is perfectly in focus. Focusing is quick, easy and it saves you time “hunting” back and forth to find the optimum focus, whilst trying to judge the size of a tiny point source of light. A Bahtinov mask useful for a quick focusing re-check if the temperature changes during your imaging session.
Q: Is it true that a different Bahtinov grating pattern is required for different focal length telescopes? Although there has been endless discussion about this on internet forums, there is no real practical reason for the use of special patterns for different telescope types and focal lengths. In fact, the frequency and angle of Bahtinov mask patterns aren’t really that important. The diffraction effect is so sensitive to changes in focus, that the results are excellent. We see no need to constrain the use of a mask to a particular telescope, and seeing they are adjustable in diameter, it’s better to make a Bahtinov mask which can used with a wide range of telescope models. This allows us to produce them on a large laser cutting machine, which means customers pay less per unit, whilst keeping quality high. Physics is a great leveller!
Q: Does it matter if the aperture of my telescope is slightly larger than the aperture of the Bahtinov mask? No, it doesn’t really matter. Provided about half the radius of the pattern on our masks is included in “clear aperture”, and the mask is reasonably central, you will still see the same old diffraction pattern every time. Isn’t physics great?