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Old 02-01-2014, 07:20 PM
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Logieberra (Logan)
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Join Date: Mar 2010
Location: Canberra
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Something else that I came across---

Astronomics sells a dedicated Focuser collimating ring for 10" and 12" Astro-Tech Ritchey-Chrétiens.

Details here:

My question is, I wonder if this will be needed for the 12", 16" and 20" truss line? Or has the 'fix' been incorporated? If not, I dare say that this is an essential upgrade - regardless of the focuser you intend on using.

Here's their blurb:

This Astro-Tech FCR1012 focuser collimation ring is an economical and very useful addition to the imaging train of Astro-Tech 10" and 12" Ritchey-Chrétien astrographs to improve your image sharpness when imaging with DSLRs and CCDs that use large format 35mm-class CCD sensors.

The focuser on 10” and 12” Astro-Tech Ritchey-Chrétien astrographs threads directly onto the rear cell of the central baffle tube/primary mirror assembly. Machining tolerances in the various components can sometimes lead to a very minor tilt in the alignment of the focuser and camera in relation to the scope’s optical path. This is rarely visible in images taken with an APS-C size imaging sensor (up to an approximately 23mm diagonal).

However, with large format 35mm-class DSLR and CCD sensors, image sharpness in the corners of your images will be improved if your camera is precisely aligned with the scope’s optical path.

This focuser collimation ring allows you to do just such a precise alignment, by letting you separately align your focuser/camera combination to the scope’s optical path completely independently of the baffle tube/primary mirror alignment.

The focuser collimation ring consists of two spring-loaded rings with push/pull collimating screws that let you tilt the rings slightly in relation to each other and then lock them firmly in place. The collimation ring fits between your scope’s rear cell and your focuser/camera combination. Once installed, you can then adjust the tilt of the collimation ring to zero out any tilt in your focuser during final scope collimation.

The telescope side of the collimation ring has M117 x 1 female threads that connect to the rear cell of your scope (or to any 117mm extension rings you have attached to the rear cell to provide the proper scope to camera spacing). The camera side of the collimation ring has M117 x 1 male threads for attaching your focuser. The collimation ring takes up only 15mm of back focus.
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