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.
- Celestron EdgeHD C9.25 large thread.
- Lepus camera-specific mount. See this table for supported cameras.
#19410 Lepus-HD C9.25 Edition diagram showing the optimal back-focus distance to image sensor.