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Astromania Bahtinov Mask Focusing Mask for Telescopes
The Bahtinov mask has become the preferred method of focusing a telescope, either visually or when imaging with a CCD camera, DSLR or webcam.They are an inexpensive tool which will allow you to achieve pin-sharp levels of focus, saving you time and improving your work. Simply place the mask over the front of your ‘scope, align the scope towards a star. The mask displays a unique diffraction profile; one part of the diffraction pattern moves in response to changes in focus and displays error as a displacement from a clearly defined point.
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.These high quality Bahtinov masks are adjustable to fit a wide range of optical tubes, unlike masks which are only able to fit one telescope.The masks grip the telescope tube gently but firmly with three metal posts which have non-scratching silicon sleeves to protect you valued telescope surface. This prevents slippage, whilst allowing the mask to remaining perfectly central. Because of this 3-post mounting, the mask remains centered, whilst fitting a wider range of telescopes.There is a myth about different Bahtinov grating pattern is required for different focal length telescopes. 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.
Please be assured that these focusing masks will work excellently for both reflectors and refractors with whatever focal length. All you need to do is to measure your telescope tube size and choose the right size of the mask.
Attach the three rubber-sleeved grip posts to the mask as shown in Figure. Loosen the three thumbscrews a turn or two and slide the grip pegs outward as far as they will go. Then place the mask over the front of your telescope. Slide each of the three grip pegs inward until they contact the telescope’s front cell or dew shield, then tighten the thumbscrews.
To make sure the mask is centered on the front of the scope, adjust the pegs so that each is at roughly the same position in its slot. To ensure a tight grip, loosen one thumbscrew slightly, then push the grip peg inward while pulling the mask gently toward the loosened grip peg. This will make sure that the other two grip pegs are contacting the telescope when you retighten the third thumbscrew. Now the mask should be well secured in position over the front of the telescope. You’re ready to focus!
Place the mask over the front of the telescope, then slide the grip posts inward until they contact the telescope’s front cell or dew shield before tightening the thumbscrews.
FOCUS ON A STAR FIRST, THEN MOVE THE TELESCOPE TO THE PLANET FOR IMAGING
Using the Focusing Mask to Focus
Focusing for Visual Observation
As the telescope’s focus is adjusted, the middle spike of the diffraction pattern moves left and right of center of the “X” formed by the other two diffraction spikes. Adjust focus until the middle spike is exactly centered in the X; that’s when precise focus has been achieved.