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At least a drawings showing where to measure the 91.5 mm back focus would be helpful.
Unfortunately we do not have a drawing for this product. The Backfocus of 91.5mm is measured from the T-2 thread.
The RCC has got a backfocus of 91mm, minus 20mm for the filter wheel and minus 6.5mm camera back focus leaves you with 65mm.
But a filter moves the focus point by ca. 2/3 of its thickness outwards, so for a 2mm thick filter, you should add another 1.6mm, e.g. with our Set of T-2 Fine-Adjustment rings (0,3 / 0,5 / 1 mm) - Aluminium #2457910, or one of our variable T-2 VariLocks # 2956946 or # 2956929
So, with a 2mm-filter, you are at ca. 66,6mm which need to be bridged with extension tubes.
I need to know the transmission ratios to the following bandwidth:
Calcium bandwidth : 393.368 and 396,847 nm.
H-alpha : 656,281 nm
IR : 740nm and more.
CH4 : 890nm
My big problem is that I suspect it to be fully opaque to CH4...
Thank you in advance.
Christophe de la Chapelle.
Below 400 nm and above 750 nm not just the optics calculation of the RCC1 but also the camera and other elements in the optical train might be "blind" to UV and very low at 890 nm - just as you suspect.
Transmission at H-alpha is ~98% - but we never actually measured or calculated for transmission above or below VIS.
Der RCC I – Coma-Correktor
The RCC I is designed to correct Coma in fast Newtonian imaging systems. It provides a long back-focus of 91.5 mm measured from the T-2-thread, enabling the use of Off-Axis Guiders, Adaptive Optics and Filter Wheels. Autoguiding can be done easily with the RCC, an RCC Off Axis Guider and an Autoguiding Camera.
- The RCC works from f/3.5 to f/6 - it is perfect on f/4
- reproduction scale is 1:1 - in contrast to many other coma correctors, the RCC is no Barlow lens which rely on a magnification to make the larger back-focus to the sensor possible
- The RCC is the only coma corrector which gives you enough back-focus for filter wheels or other accessories without changing the focal ratio
To attach the RCC directly to a camera (without an Off-Axis-Guider), we recommend the VariLock 46 T-2 Extension (# 2956946, T-2 part-no. #25V). It has got not only a graduated mm-scale, but also a marking at 36.5mm, to show you the perfect working distance for a DSLR with T-2-adapter. Each air/glass-surface of the triplet RCC optical system is coated with our Phantom Group Coating (R) for the best-possible transmission.
You can remove the stopper ring to place the RCC deeper inside of your focuser.
Technical Data - Overview
- reproduction scale: 1:1
- recommended focal ratios: f/3.5 - f/6 (optimised for f/4)
- Focal position (perfect distance to the sensor): 91.5 mm measured from the T-2 thread / 94.5 mm from the M48 thread
- inner connection (lens side): 2" nosepiece with M48_i filter thread for 2" eyepiece filters
- outer connection (telescope side): T2 (M 42 x 0.75_a; without the stop ring M 48_a)
- longest overall depth: 73 mm / without the stop ring 75 mm / without the stop ring and RCC Off Axis Guider 84mm
- Diameter of the housing: 50.8mm/2"
|Net weight (kg)||0.17|
|Inner Connection (lens sided)||Thread, M48|
|Outer Connection (lens sided)||Barrel, 2" (50,8mm)|
|Outer Connection (eyepiece/-camera-sided)||Thread, T-2 (M42 x 0,75), M48|
|AR-Coating||Phantom Coating® Group|
|Optimized for focal ratio||f/4|
|Working Range||f/3.5 – f/6|
|Barrel Size (in)||2"|
|Optical Design||Coma Corrector|