Product Overview
Special Considerations for C9.25 EdgeHD OTA
The Celestron C9.25 EdgeHD OTA is unique among Celestron's EdgeHD models with a slightly slower primary mirror compared to the other SCT telescopes produced. Like the other EdgeHD models, a full aperture corrector plate and 3-element corrector lens group in the baffle tube make the C9.25HD is a fully aplanatic SCT design. The C9.25HD features an optimized back-focus of 146mm and native focal ratio of about f/9.9. The field is flat with an image circle approximately 42mm in diameter.
Attaching the Lepus-HD C9.25 Edition telecompressor to the back of the OTA will yield an approximate f/6.4 light cone at the recommended on-axis back-focus distance of 96mm. The effective field of view is reduced to 28mm with some light loss beyond about 24mm which is correctable with good flat-fielding techniques. Because the C9.25HD corrector lens group is mounted very close to the end of the baffle tube at the exit port (see diagram), the Lepus-HD C9.25 Edition includes a 5mm thick aluminum spacer to ensure the corrector lenses and telecompressor lens do not make physical contact
User Tested and Optimized for Best Results:
Ronny Kaplanian of Australia spent several weeks perfecting the back-focus distance between his Celestron EdgeHD C9.25 and Lepus telecompressor. We found that the optimal distance on-axis is about 4mm shorter for the C9.25HD compared to the original design back-focus of 100mm. The diagram at bottom shows the recommended back-focus distance of 96mm or 101mm as measured from the flange. Ronny's results below speak for themselves.
Celestron C9.25HD / Lepus-HD Results:
The NGC2818 image at left was provided by Ronny Kaplanian and taken with his Celestron C9.25 EdgeHD, Lepus-HD C9.25 Edition telecompressor, and his Starlight Xpress SXVR-M25C camera in a monochrome mode with separate RBG filtered images. The image sensor on the SXVR-M25C measures 23.5mm x 15mm for a diagonal measurement of nearly 28mm. The image was combined and further processed by Terry Hancock with only slight cropping to remove the stacking artifacts. Click here for a full size image in pdf format.
The NGC2818 image at left was provided by Ronny Kaplanian and taken with his Celestron C9.25 EdgeHD, Lepus-HD C9.25 Edition telecompressor, and his Starlight Xpress SXVR-M25C camera in a monochrome mode with separate RBG filtered images. The image sensor on the SXVR-M25C measures 23.5mm x 15mm for a diagonal measurement of nearly 28mm. The image was combined and further processed by Terry Hancock with only slight cropping to remove the stacking artifacts. Click here for a full size image in pdf format.
