Farpoint Cary Focus Mask ช่วยฟอกัสให้ได้ภาพชัดสุด สำหรับกล้องที่มีขอบนอกระหว่าง 5.5" ถึง 8.5", FP423
All Farpoint Products are made in the USA at our facilities in Gold River, California.
How to select and fit a focus mask for your telescope:
In 2009, George Carey, an amateur telescope maker and astronomer from the UK, published a modification of previous focus mask designs to make a much more sensitive version of the device. This focus mask allows you quickly, easily and precisely focus your DSLR camera, webcam or CCD camera for astrophotography. The method is simple, very intuitive, and the device has universally been named after the inventor: The "Carey Mask".
Attach your camera to the telescope, center a fairly bright star in your telescope and achieve a rough focus. Then place the mask over the front aperture of your telescope by “hanging” it on the plastic screws from the front dew shield. Take a short exposure. The image of the star will show diffraction spikes.
The Bahtinov Mask requires you to judge when the central spike is midway between the two angle spikes. This is quite easy to do, but there is still a little uncertainty in determining the exact center alignment, especially when viewing in a DSLR viewfinder.
With the Carey mask the central spike idea has been abandoned. The angle between spikes has been considerably reduced. Instead of two sloping sets of slits and one central set, there are four sets of slits, with a small angle difference on each side of the mask as shown in the image below.
The diffraction pattern produced is two overlapping 'X' shapes with slightly differing angles, and at perfect focus the Xs will be symmetrical.
This animation shows focus being reached.
Farpoint manufactures this "lifesaving" astrophotography tool out of virtually indestructible ABS plastic, which comes in two major types and in a range of sizes. The mask pictured below left is a general purpose mask designed to fit refractors and Newtonian telescopes. The mask pictured below right is designed to fit Schmidt-Cassegrain telescopes. Both types of mask are available in a range of sizes to cover your imaging needs.
- Material: Plastic + metal nut
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