Many users find the primary mirror focusing mechanism of Schmidt-Cassegrain telescopes (SCT) cumbersome to use. There is some amount of image shift and precise focus cannot be found easily. This is inconvenient for visual use and a serious problem for astrophotography. GSO's (Guan Sheng Optical) latest Crayford focuser model is a gorgeous, all-black, rotatable focuser for Schmidt-Cassegrain telescopes that elegantly solves these problems.
CNC machined from aluminum and anodized black, this focuser will screw on to the rear cell of any* SCT telescopes sold by Meade and Celestron having a standard SCT thread. The standard SCT rear cell thread is 2" diameter male thread with a thread pitch of 24TPI (threads per inch).
This dual-speed Crayford focuser is a joy to use and you will wonder how you ever lived without it once you install it! By design, SCT Crayford focusers eliminate the annoying backlash and image-shift that plagues many SCTs. You will experience very smooth and precisely controlled focuser motion.
The inner drawtube glides on 4 precision bearings and a roller shaft. The inner barrel is baffled and painted a flat black to minimize reflections for maximum contrast. This barrel is also black anodized and features a laser-etched mm (millimeter) scale. It provides 1" of focus travel which is more than adequate for SCTs. You first use your SCTs focusing knob to achieve coarse focus and then switch to the Crayford focuser for finer focus and control. Depending on your range of eyepieces and accessories, you may never need to touch your SCT's main focuser again!
The 2" focuser barrel features a brass compression ring and can accept standard 2" refractor-type diagonals and other 2" accessories (Note that the use of this focuser converts your telescope's rear SCT thread to a 2" visual back. As a result you will not be able to use an SCT-type diagonal with this focuser; you will need a refractor-type diagonal instead). Also included is a 1.25"-2" adapter with brass compression rings and threads to accept standard 2" filters. This deluxe model features a 360-degree rotatable ring that allows you to orient the focuser (and hence your diagonal/eyepiece) to the most comfortable viewing position.
GSO's rated load capacity for their Crayford focusers is a little less than 6 lbs (2.7 kgs). The focuser also has two large thumbscrews. The thumbscrew on the telescope side can be used to lock the focuser, allowing the use of heavy accessories or cameras without fear or slippage or losing focus. The other thumbscrew on the eyepiece end can be used to adjust the tension of the focuser to achieve a focusing "feel" that you like. At the easiest (lightest) setting, the focuser moves extremely smoothly. At tighter settings, you can still use heavier accessories without sacrificing much of the smooth focuser action.
Please note that some larger Meade and Celestron SCTs (11" and larger) have a larger 3.25" rear thread, so please make sure that you have an adapter that reduces that larger thread to the smaller 2" SCT thread. If you have a standard 1.25" SCT visual back, all you need to do is unscrew the visual back and screw on the SCT Crayford focuser in its place. The focuser is shipped in a foam-fitted box.
• Minimum focuser height (with 1.25" adapter) = 4.29" (109mm)
• Maximum focuser height (with 1.25" adapter) = 5.28" (134mm)
• Minimum focuser height (without 1.25" adapter) = 3.90" (99mm)
• Maximum focuser height (without 1.25" adapter) = 4.88" (124mm)
• Tube travel = 0.99" (25mm)
• Focuser weight (with 1.25" adapter) = 1lb-10.5oz (751gm)
• Focus knob diameter = 1.57" (40mm)
• Microfocus knob diameter = 1.02" (26mm)
• Maximum outer barrel diameter = 3.3" (84mm)
-Thread: Standard SCT female thread (2" x 24TPI)
• Millimeter markings on focuser drawtube: Yes
• Rotatable: Yes
• Dust plug: One 1.25" dust plug included
Please note: Most GSO Crayford focusers have or will soon develop two bearing marks/lines on the upper side of the drawtube. This is caused by wear on the barrel anodizing where is makes contact with the roller bearings. In some focusers, you have to look hard to find these marks. In others, it is very prominent, even for brand new items received from GSO. This does not indicate a defective or used product and is essentially just cosmetic.
* Please also note: Some Celestron telescopes made in the late 1970s and early 1980s did not have a standard thread pitch. This focuser will not fit those, and there is no way for us to know what threads you might have on your telescope.
• User Manual: Optimizing the Performance of your GSO Crayford Focuser
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