Farpoint Bahtinov focus mask for astrophotography - For P Series Cokin filter holders. Manufacturer part number FP475.
Please Note: The Bahtinov focus technique, when used with camera lenses, works best with longer focal lengths. It gets less useful and harder to focus with shorter focal lengths. The practical useful limit for this is around 100mm lens focal length or longer.
About the Bahtinov Mask:
Farpoint Bahtinov Masks are by far, the easiest, fastest and most consistent manual focusing aid available to the amateur astrophotographer. In 2008, Pavel Bahtinov, a Russian amateur telescope maker and astronomer, published an ingenious new way to easily 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 Bahtinov Mask.
Prior to the innovative design of the Bahtinov Mask, astrophotographers could spend ten minutes or more just obtaining a reasonable focus. Problems with seeing, exposure length, and camera noise all increased the difficulty of and time spent finding perfect focus. With the Farpoint Bahtinov Mask, the process of finding the perfect focus whether it be through a DSLR, CCD or a WebCam takes a matter of seconds because the process is unaffected by seeing, noise and allows short exposure lengths!
Using the Bahtinov Focus Mask for DSLR Camera Lenses:
Focusing with your Bahtinov mask is simple. Start by sliding the Bahtinov mask into the appropriate sized Cokin Filter Holder ("P" size only for this item). [Cokin Filter Holder and Cokin Adapter Ring not included; must be purchased separately]. Center a fairly bright start in your camera and achieve a rough focus, then loosely screw the filter holding the mask onto your camera lens.
Take a short exposure. The image of the star will show diffraction spikes. The “center” set will most likely be shifted to one side or the other. This is showing the defocus.
Adjust the focus of your camera and re-expose the star, once again showing the diffraction spike pattern. Iterate the process until you get the central diffraction spike centered against the star and the other spikes. When you achieve a symmetrical pattern, you have achieved the best possible focus. Remove the mask, center your target object and take your images!
Farpoint manufactures this "lifesaving" astrophotography tool out of virtually indestructible ABS plastic and in a range of sizes. The Farpoint Bahtinov Mask will ensure that you spend more time imaging and less time focusing for years to come! Whether you focus manually or electronically, the Farpoint Bahtinov Mask is an essential tool for any astrophotographer.