This Astro-Tech 35mm long x 2” diameter extension tube can be used to make up for the loss of light path when a 2” star diagonal is removed from many refractor telescope focusers and replaced by a camera and camera adapter for imaging. In some cases, it is also useful to replace the light path lost when a full-sized 2” diagonal is replaced in the scope by a shorter light path 1.25” diagonal.
This Astro-Tech extension tube can also be used with Astro-Tech Ritchey-Chrétien reflectors. With these Astro-Tech scopes, the scope’s focuser is used by itself or (more typically) in combination with one or both of the thread-on extension rings supplied with the scope to place the camera at the telescope’s focal plane.
In some cases, however, there may not be quite enough focuser extension for webcam use when using both thread-on extension rings with an Astro-Tech R-C, or the two extensions might be too long to bring a DSLR to focus while one extension might not be long enough. This 2” compression ring extension tube can be slipped into the 2” accessory holder of the Astro-Tech R-C’s focuser to add the extra focuser length needed. Optional Astro-Tech 50mm and 80mm extension tubes are also available. A little experimentation will be called for to determine what combination of focuser and extension tube(s) will be needed for your particular combination(s) of visual and/or photographic components.
One end of this Astro-Tech 2” diameter x 35mm long extension tube fits into 2” focuser drawtubes. This end is threaded to accept 48mm filters. A shallow safety groove is machined into the barrel of the extension tube. This groove engages the thumbscrew or compression ring of your focuser to prevent the extension tube and your camera from falling should the focuser thumbscrew loosen accidentally during use. The barrel extends 35mm into the focuser drawtube to provide a secure tilt-free installation when the focuser thumbscrew is firmly tightened.
The opposite end of the extension tube has a 2” diameter accessory holder with a non-marring brass compression ring. A single thumbscrew tightens the compression ring on your 2” accessories to hold them firmly in place. This accessory holder adds 35mm of extension to the light path when the extension tube is seated firmly into your focuser. The overall length of the extension tube is 70mm, 35mm extending into your focuser with 35mm of external light path extension. The extension tube is machined of aluminum, anodized black. The interior has anti-reflection threading.
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