Astro-Physics CCDT67 CCD Telecompressor…
This AP telecompressor will provide full coverage of the ST10E chip with scopes ranging from f/9 to f/18 focal ratio. The 2-element cemented design transmits close to 99% of the incoming light over the range of 420 to 700 nm. The focal length of the telecompressor optics is 12". For refractors, the field is compressed by 0.67x (when using a Color Filter Wheel). If you have a moving mirror system, the native focal ratio will increase.
The design allows full corner-to-corner illumination of the ST-10 and ST-8300 chips with most catadioptric telescopes. This design does not add coma to the wavefront, and thus can be used with all flat-field and coma-free telescopes such as Maksutov-Cassegrains, Schmidt-Cassegrains, Ritchey-Chretiens and refractors. The inherent resolution of the telescope is not compromised when using this compressor.
Please review the exploded diagram to see how this item will fit into your imaging system.
If you want a higher compression ratio, but do not use the color filter wheel, you can add one or more of the 2” Barrel Extension w/ 48 mm Threads (A3703) between the CCDT67 and the nosepiece of your camera. This has the advantage of inserting the CCDT67 forward in the light cone so that in-travel (backspacing) requirements are reduced. An alternative is to use T-2 extension rings from Baader Planetarium, and thread the 15mm T-2 Extension Ring and 7.5 mm Extension Ring between the CCD camera and the nosepiece. This will approximate the spacing of a color filter wheel. You can also experiment with a single extension or other combinations. Please note that as you increase compression, you decrease the size of the image circle at the focus point.
At 0.67x, the CCDT67 will cover the chip of the ST-10 and ST-8300. It can never cover the chip of an STL series camera or the newer large size digital SLR chips, because its clear aperture is no larger than their CCD chips.
- The clear aperture of the AP CCD Telecompressor is 1.75". It is designed to screw into the 2” Tapered Nosepiece (AP16T) or any other 2" nosepiece with 48 mm threads that is designed for CCD cameras. It will not thread all the way into the nosepiece provided with SBIG cameras since the threads of that nosepiece are not deep enough.
0.67x Compression ratio for SBIG ST7/8/10 + Color Filter Wheel, when used with refractors. Fully illuminated circle: 29 mm
0.75x Compression ratio for SBIG ST7/8/10 (without Color Filter Wheel or T-2 extensions), when used with refractors. Fully illuminated circle: 34 mm
Approximately 5 inches of back focus is needed to achieve focus on the CCD chip. It will not work with the AO7.
The focal length of the CDD Telecompressor is 12" (305 mm).
- Astro-Physics CCD Telecompressor