Farpoint Carey Focus Mask for Celestron C11 SCT with Fastar or Hyperstar # FP433H
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Product Details
Carey Focus Mask for all newer Celestron 11" SCTs. Virtually all newer Celestron SCTs have the larger secondary holder for Fastar or they are "Fastar Ready." The FP433H also works without HyperStar. Select FP433H for newer Celestrons.
Farpoint Crey focus mask for astrophotography - Manufacturer part number FP433H.
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".
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 is a general purpose mask designed to fit SCT telescopes.
Carey Focus Mask - Description and Use
(Description courtesy of Farpoint Astronomical and George Carey)
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.
Inside and outside focus the Xs will be displaced. Because the angle of each X is slightly different, it will be easy to spot when out of focus, and also which way focus should be altered.
Manufacturer part number: FP433H
Additional Information
Product Video: How to select and fit a focus mask for your telescope
Other Information
- Country of Manufacture: United States