Starwave Bahtinov Masks

Product code: SWBM-
£8.75 (ex. VAT)
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Product information

Altair Bahtinov Mask

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 TM Bahtinov masks are adjustable to fit a wide range of optical tubes, unlike masks which are only able to fit one telescope. They have an adjustment lattitude of about 50mm in aperture making them very versatile.
Starwave TM Bahtinov masks 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 masks which are made from thick, heavy, brittle and hard acrylic plastics.
Starwave TM bahtinov masks grip the telescope tube gently but firmly with three metal posts covered in non-scratching silicon sleeves. This prevents slippage, whilst allowing the mask to remaining perfectly central. This is unlike other masks with two posts, which rely solely on gravity to hold them in position. Because of this 3-post mounting, 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 is measure the outer diameter of your telescope tube or deshield, 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 TM Bahtinov Mask Size Chart:
Product Code:Specification:
SWBM-65-100mmStarwave Bahtinov Mask to fit 65-100mm OD tubes
SWBM-85-120mmStarwave Bahtinov Mask to fit 85-120mm OD tubes
SWBM-105-150mmStarwave Bahtinov Mask to fit 105-150mm OD tubes
SWBM-125-180mmStarwave Bahtinov Mask to fit 125-180mm OD tubes
SWBM-150-200mmStarwave Bahtinov Mask to fit 150-200mm OD tubes
SWBM-175-220mmStarwave Bahtinov Mask to fit 175-220mm OD tubes
SWBM-195-240mmStarwave Bahtinov Mask to fit 195-240mm OD tubes
SWBM-215-260mmStarwave Bahtinov Mask to fit 215-260mm OD tubes
SWBM-250-290mmStarwave Bahtinov Mask to fit 250-290mm OD tubes
SWBM-290-340mmStarwave Bahtinov Mask to fit 290-340mm OD tubes
Altair Refactor Model:Bahtinov product code:
Lightwave 66ED-R RefractorSWBM-65-100mm
Lightwave 72ED-R RefractorSWBM-85-120mm
Lightwave 80ED-R RefractorSWBM-85-120mm
Starwave 70ED RefractorSWBM-85-120mm
Starwave 80ED RefractorSWBM-105-150mm
Starwave 102ED F7 RefractorSWBM-105-150mm
Starwave 110ED F7 RefractorSWBM-125-180mm
Starwave 102 F11 Achromat RefractorSWBM-105-150mm
Starwave 152 F5.9 Achromat RefractorSWBM-150-200mm
Wave Series 80EDT F6 Triplet RefractorSWBM-85-120mm
Wave Series 102EDT F7 Triplet RefractorSWBM-105-150mm
Wave Series 115EDT F7 Triplet Refractor SWBM-125-180mm

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. The image below shows how star images appear during focusing. (Click to enlarge). The difference in focuser position is only a few tenths of a millimetre, however the diffraction lines shift considerably. This sensitivity means less time hunting for best focus. There's no more need to guess when you are focused during times of poor to moderate seeing. Simply put the mask, and the status of your focus will become immediately obvious.
Starwave TM Bahtinov Mask Focusing Pattern:The focussed star-image as it appears in a camera / eyepiece:
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 regardless. 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.
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?
Q: Do Starwave Bahtinov Masks work with both reflectors and refractors? Yes they do. Even though reflectors have a central obstruction caused by a primary mirror, there is no difference whatsoever in the performance or these masks on a reflector or a refractor. Basically, the reflector secondary mirror just covers the central portion of the mask but the outer clear aperture still carries the pattern.

Technical specifications

Brand Pegasus
Product Code SWBM-
Weight 0.5kg