Friday, April 1, 2011

Testing the Optec Lepus 0.62x Focal Reducer

Testing the Optec Lepus 0.62x Focal Reducer with the 11" Celestron EdgeHD telescope and the SBIG ST-8300M (monochrome) CCD camera. The telescope's stock rear adapter (with SCT threads) was replaced with an Astro-Physics 2" Visual Back (AP part # ADASCTLC) in order to install the focal reducer as close as possible to the OTA, as recommended by Optec.

I'm pleased to report that, overall, I found the reducer to produce very satisfying images, resulting in a reduction factor of 0.69x. See http://www.pbase.com/wjshaheen/optec_lepus_062x_focal_reducer_testing for full scale test images as well as an f/10 baseline image.

Update 24-Apr-2011: I resumed testing after resolving several issues having to do with the baseline - i.e., SCT collimation, guide-camera flexure and focuser flexure (yes, the Feather Touch focuser resulted in a slight drift, which was not mirror shift).

Visit http://www.pbase.com/wjshaheen/optec_lepus_062x_focal_reducer_testing and see the 4 images of M57 (Ring Nebula) taken this date - on the bottom row.

Some coma is noticeable in the lower left corner only and may be due to a tilted plane, which itself may be the result of, again, the leading edge of the reducer stopping at the edge of the internal field flattener. This is being researched with the vendor.

On another note, I have a professional source whose contact at Celestron indicates they will be releasing a reducer this summer. It will have a respectable back-focus (90 to 110 mm) but may not have the coverage originally desired. It will however cover an APS size chip and certainly the 8300.

Update 11-May-2011:
Update on the question of the reducer possibly not seating squarely (the leading edge of the reducer stopping at the edge of the internal field flattener), I just received word from Optec that they "have developed a different mounting configuration for the Edge HD scopes. For the C11 HD and C9.25 HD scopes a spacer is required to keep the lens housing from touching the Edge HD retaining ring." . (At the time I ordered mine from OPT, they had the former version in stock.)

Optec is sending me the new lens and housing gratis and I will be testing it in about a week.
(Thanks, Jeff!)

As an aside, I've replaced the ST-8300M with a QSI-583wsg - solves a host of flexure issues up and down the imaging train as well as with any mirror flop or guidescope flexure. The Starlight Xpress Lodestar connects easily to the QSI's guideport, given the standard C-mount adapter) and so far I've had no problem locating a guidestar.

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