Focal Reducer/Field Flattener for SV70T 70 mm f-6 triplet apochromat
This reducer/flattener is optimized for our 70 mm triplet lens. The flattener threads into the Stellarvue 2.5” A version focuser. It will also slide into a 2” focuser for earlier model SV70ED's. 0.8X focal reduction converts the 70 mm f-6 to a 336 mm f-4.8. This is our widest field refractor!
This reducer/flattener has a standard 42 mm camera connection thread and 48mm/2" filter thread on opposite end. Standard 2" filters can be added to the reducer flattener when imaging. The backfocus of the unit is 55 mm with the included 11 mm extension tube. 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 below.
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. It is important that the distance from the back of the field flattener to the chip be maintained at 55 mm (66 mm withoput 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 below.
In this example the camera had a 35 mm backfocus, so a 20 mm extension tube was needed. It threads in between the back of the field flattener/reducer and the camera as shown.
In this case the extension tube must be a standard t-thread (M42 X.75). Our selection of 42 mm extension tubes may be viewed here.
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Optically, the SFFR-70APO does exactly what it is supposed to do and does it well. As an added bonus currently, the focal length reduction allowed imaging of a greater portion of Comet NEOWISE.
All of my “back end” optics have been 1.25” up until now, so the heft of this 2” item was a pleasant surprise. As I use a DSLR for imaging, eliminating the 1.25” adapters makes for a much more solid connection between camera and telescope. Too bad that 2” filters cost so much more, but no one ever said that astrophotography is an inexpensive hobby.
If you pay attention to getting the proper spacing from the FF/FR to the imaging chip, this product will give you round stars all the way to the corners...at least it does on my ASI1600MM-Cool. This FF/FR is a must for astro imaging!