Stellarvue Reducer/Flattener for SV70T
This is a Reducer/Flattener that has been optimized for Stellarvue's 70mm Triplet Lens. It threads smoothly into a Stellarvue 2.5" A version focuser, and will also slide into the 2" focuser for earlier model SV70ED's. 0.8X focal reduction converts the 70 mm f-6 to a 336 mm f-4.8- Stellarvue's widest field refractor to date!
This reducer/flattener has a standard 48 mm filter thread, and standard 2" filters can be added to the reducer flattener when imaging. The adapter takes camera's with a 42mm thread on that end of the link. The backfocus of the unit is 55 mm with the included 11 mm extension tube- but remove this tube and the backfocus increases to 66 mm. Since a DSLR with t-ring has a 55 mm backfocus, thread the SFFR-70APO and extension tube into the cameras t-ring, then screw it to the focuser as shown in the images above.
If you are using a CCD camera, an additional set of extension tubes may be needed depending on the backfocus of the camera. You need to know how much distance there is between the cameras T-thread and the ccd chip, as it is important that the distance from the back of the field flattener to the chip be maintained at 55 mm (66 mm without the supplied extension). So if the CCD camera has a backfocus of only 35 mm, the supplied 11 mm extension and an additional 20 mm extension will be needed. See the example above.
Questions & AnswersAsk a Question
How does one measure the back focus distance? From the back glass of the flattener to the sensor of the DSLR? or from the back end of the flattener to the sensor of the DSLR? How much play is there with this 55mm figure? Not all DSLR are similar.
I can answer this as I use the exact same reducer with my SV70T for imaging. The 55mm back focus is measured from the base of the T-thread at the rear of the reducer with the SV70 spacer ring attached. The tolerance depends on your sensor size, but it i