This T-adapter has a filter holder and allows you to connect a DSLR with T-ring to your Celestron 8-inch EdgeHD telescope and install 2-inch filters into the optical path.
It can work in two different length configurations, one suitable for the nominal f/10 backfocus of 133.35 mm, and a shorter configuration for the nominal 105 mm backfocus of the Celestron f/7 focal reducer.
CCD cameras can also be accommodating using T-thread spacers to make up the difference in backfocus between a DSLR and CCD. Contact Starizona for help choosing the right spacers for your setup.
Starizona C8 EdgeHD T-Adapter w/Filter Holder Installation
Celestron's EdgeHD Schmidt-Cassegrain telescopes require a specific backfocus in order to give the best optical quality over a large field of view.
A T-adapter is used to attach a DSLR or CCD camera to the telescope. This T-adapter offers the ability to mount a filter, such as a light pollution reduction filter. It can work for both f/10 imaging, and imaging at f/7 with Celestron's EdgeHD 0.7x Reducer.
Backfocus Th:e nominal backfocus of the C8 EdgeHD at f/10 is 133.35 mm. This is measured from the end of the male threads on the rear cell of the telescope to the imaging sensor in the camera.
With the f/7 focal reducer in place, the nominal backfocus is 105 mm. The backfocus, or flange focal distance, of DSLR camera vary, but when a T-ring is used to adapt the bayonet to a female T-thread mount, the backfocus is standardized at 55 mm. So at f/10, a T-adapter must be 133.35 – 55 = 78.35 mm long. At f/7 it must be 105 – 55 = 50 mm long.
In the case of a CCD camera, the backfocus of the camera will generally be much shorter. In this case, and extra spacer is required between the T-adapter and camera, the length of which is equal to 55 mm minus the CCD backfocus. Normally this is simply a spacer with female T-threads on one end and male T-threads on the other, but could be different if the CCD camera has a different thread mount. Contact OPT if you need assistance choosing the correct spacer.
Using the Starizona C8 EdgeHD T-Adapter w/Filter Holder: There are two configurations for the T-adapter; one for f/10 use and one for f/7.
For use at f/10, the T-adapter should be in the longer configuration with the spacer installed, as shown below. The T-ring should be threaded directly onto the filter holder. For use at f/7, remove the spacer and thread the filter holder back on to the shorter configuration as shown below. The T-ring should be threaded directly onto the filter holder.
If using a CCD camera instead of a DSLR + T-ring, thread the required spacer onto the top of the filter holder, then thread the camera onto the spacer. The base ring can be loosened while the camera and T-adapter are installed on the telescope to allow rotation of the camera angle.
Installing a Filter: The filter holder is split and the thinner top portion can be unthreaded. A standard 2-inch (48 mm) filter can then be threaded into the female threads on the inside of the top portion. Thread the top portion back onto the bottom part and the filter is now installed in the light path.
Certain CCD cameras may be able to use 1.25-inch filters, and a step ring to convert the 2-inch filter thread to 1.25-inch is available made by Starizona. However, a 2-inch filter is recommended for DSLRs to avoid significant vignetting.