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Astromania Bahtinov Mask Focusing Mask for Telescopes - FM200mm

$16

Astromania Bahtinov Mask Focusing Mask for Telescopes - FM200mm


Product Description

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.

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HOW TO USE A FOCUSING MASK

FOCUS ON A STAR FIRST, THEN MOVE THE TELESCOPE TO THE PLANET FOR IMAGING

  • A “live view” image is best if your camera or software permits it, because then you’ll be able to see the results of your focus adjustments in real time, and the focusing process will be faster. If needed, though, you can take successive still exposures and review each exposure on the screen, tweaking the telescope’s focus slightly after each exposure, then taking another one. In either case, you’ll want to “zoom in” as needed so you can get a clear view of the spike pattern and, in particular, the center spike’s position relative to the other two spikes that form the “X” (see below figure) . DSLRs often have two or more magnification settings for live view focusing, and capture programs used with a laptop often allow subframe viewing, which magnifies the image.
  • As you turn your telescope’s focus knobs to move in and out of focus, you should see that center spike move to one side and the other of the X. Make fine adjustments of the focus until the center spike lands exactly in the center of the X; that is, it bisects the X. Then you’re in focus!

Using the Focusing Mask to Focus

  • With the mask in place over the front of your telescope and your camera attached to the scope and turned on, center a bright star in the field of view. You should see the diffraction spike pattern on the camera’s LCD screen (for DSLRs) or on your laptop computer running your preferred image capture software (see below figure) . If the scope is grossly out of focus you may see the grid pattern of the mask, in which case you should adjust the scope’s focus to shrink down the grid pattern until it turns into a dot with spikes.
  • Once focus is achieved, remove the focusing mask. Then you’re all set to photograph any object at infinity focus.

Focusing for Visual Observation

  • Although a Focusing Mask could be used to focus for visual observing, it’s generally not necessary. It is intended as a tool for astrophotography.

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.

Astromania Bahtinov Mask Focusing Mask for Telescopes - FM200mm