Lepus HD – C9.25 EdgeHD Edition (19410) Optec

Description

Special Edition Lepus telecompressor for the Celestron EdgeHD C9.25 Telescope

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.  

Specifications

Telescope-Side Compatibility:

• Celestron EdgeHD C9.25 large thread.

Camera-Side Compatibility:

• Lepus camera-specific mount.  See Below for supported cameras.

Back-Focus Diagram:

#19410 Lepus-HD C9.25 Edition diagram showing the optimal back-focus distance to image sensor.

Lepus Mounting Plates

Camera-Specific Mounts for the Lepus Telecompressor

The Lepus telecompressor has a design back-focus distance of 100mm on-axis. Each of the camera mounting plates below are designed to maintain that back-focus for the best overall image quality and a reduction of 0.62X. Varying the back-focus distance will alter the magnification (reduction) but may introduce undesirable optical aberrations as well. We recommend using the Lepus telecompressor only with the recommended camera-specific mount.

Each camera mount consists of a 2.1″ ID tube of various lengths and a mechanical interface such as a T-thread, C-mount, or STL thread. This ID tube fits over the camera side of the Lepus telecompressor, which features the OPTEC-2100 male circular dovetail mount. The camera mount is held securely to the Lepus dovetail using three oval point setscrews located 120 degrees apart. 

It is important that the overall back-focus distance be set as closely as possible to the design distance of 100mm on-axis. Measured from the flange at the bottom of the OPTEC-2100 dovetail, the distance works out to 105mm as shown in the PDF at left. 

Most of the mechanical camera interfaces require an additional 1/10th inch or 2.5mm of back-focus. The camera backfocus distance, BF, should be known to within about 1mm for best performance and should include the thickness of any filter wheel, off-axis guider or other adapter between the Lepus and camera sensor. Use the table below to find the appropriate mounting plate for many commercially available cameras and configurations. If your camera is not listed below and you know the optical back-focus, BF, and mechanical interface (i.e. T-thread) you can determine the stock number as with the following calculation:

TUBE LENGTH = 105mm – FLANGE THICKNESS – CAMERA BACK-FOCUS

Mechanical Interface	Flange Thickness	Stock No. Prefix
T-thread	2.5mm	#19392
Pentax thread	2.5mm	#19395
SCT thread	2.5mm	#19396
STL 2.156″ thread	2.5mm	#19398
C-mount	2.5mm	#19399
Canon and Nikon DSLR requires T-thread and brand specific bayonet mount.	varies with bayonet	#19392

Next use the TUBE LENGTH value calculation above for the suffix.  For example, nearly all C-mount cameras share a 17.5mm BACK-FOCUS value. The C-mount stock number prefix is #19399 and the TUBE LENGTH would be equal to 105mm – 2.5mm – 17.5mm = 85mm.  The Optec stock number for a C-mount camera would therefore be  #19399-85 as shown in the table below.

NOTE:  The minimum tube length is limited by the height of the OPTEC-2100 dovetail plus the press-flange of the mechanical mount (usually about 0.2″ or 5mm).  The standard Lepus telecomprssor minimum tube length is 15mm while the Edge HD specific Lepus telecompressor is 17mm.

Reference Table of Camera-Specific Mounts

Camera Type	Tube Length (mm)	Thread	Stock No.
Any C-mount camera with standard lens mount	85	C	19399-85
Any CS-Mount Camera	90	C	19399-90
Apogee D02 Housing – U47, U77, U4000, U8300 std. body	76	SCT	19396-76
*Apogee D02 Housing – U9, U10 std. camera	75	SCT	19396-75
*Apogee D06 Housing – U6, U9, U10, U4000 camera	89	SCT	19396-89
Atik Instruments 4000/*11000	88	T	19392-88
Atik Fira M1 motorized filter wheel	83	SCT	19396-83
*Canon DSLR Camera – Canon bayonet mount	47	T plus bayonet	19392-47C
Fishcamp Starfish	91	T	19392-91
Meade Deep Sky Imager	94	T	19392-94
Meade Deep Sky Imager with RGB filter bar	77	T	19392-77
*Nikon DSLR Camera – Nikon bayonet mount	46	T plus bayonet	19392-47N
Orion StarShoot Pro	82	T	17482-82
QSI 504 full body camera with filters	67	T	19392-67
QSI 504 full body camera without filters	67	T	19392-67
QSI 504 medium body camera without filters	79	T	19392-79
QSI 504 slim body camera with filters	88	T	19392-88
QSI 516, 532 full body camera with filters	67	T	19392-67
QSI 516, 532 full body camera without filters	67	T	19392-67
QSI 516, 532 medium body camera without filters	80	T	19392-80
QSI 516, 532 slim body camera without filters	88	T	19392-88
QSI 516WSG camera with Off-Axis guider and no filters	52	T	19392-52
QSI 516WSG camera with Off-Axis guider and filters and standard T-thread.  Note:  T-thread mount must be turned down for clearance of the OAG.	53	T	19392-53Q
QSI 583WSG camera with Off-Axis guider STL 2.156x24tpi thread	49	STL	19398-49
QSI 520 full body camera with filters	67	T	19392-67
QSI 520 full body camera without filters	67	T	19392-67
QSI 520 medium body camera without filters	80	T	19392-80
QSI 520 slim body camera without filters	88	T	19392-88
SBIG ST-7/8/9/10/2000 with CFW-10 filter wheel mounted directly on camera without  face plate and with D-block	62	T	19392-62
SBIG ST-7/8/9/10/2000 with CFW-8/8A/9 with new 0.25 inch thick  front plate on camera and no D-block	59	T	19392-59
SBIG ST-7/8/9/10/2000 new 0.25 inch thick front plate and D-block with T-Thread	77	T	19392-77
SBIG ST-2000XCM with AO-8	24	T	19392-24
SBIG ST-8300	85	T	19392-85
SBIG ST-8300 with CFW5/8-8300	64	T	19392-64
*SBIG STL with 3mm thick filters	65	STL	19398-65
*SBIG STL without filters	64	STL	19398-64
*Starlight Xpress SXVF-H9 camera plus filter wheel	62	T	19392-62
Starlight Xpress SXV-H9 T-thread camera	84	T	19392-84
Starlight Xpress SXV-M25C camera	84	T	19392-84
QHY-8 camera (T-mount depth to IR Filter=0.160″	81	T (short)	19392-81
QHY-8L camera	82	T	19392-82
QHY-8Pro camera (without “tile adjust ring”, add 3mm to BF for ring)	84	T	19392-84
QHY-8 camera with Orion SteadyStar	41	T	19392-40
QHY-9 camera	102	T	19392-102
QHY-9 camera with 2″ color filter wheel	46	T	19392-46
QHY-10 camera	82	T	19392-82
Older Camera Mounts
SBIG ST-7/8/9/10/2000 with CFW-8/8A/9 filter wheel with old 0.20 inch thick front plate and no D-block	60	T	19392-60
SBIG ST-7/8/9/10/2000 with old 0.20-inch thick front plate on camera and D block with T-thread	78	T	19392-78

* denotes vignetting may occur with Lepus telecompressor.