4. SFFR102-2 Reducer for 102mm f/7 Refractors

Product Description

This reducer/flattener is optimized for a 102 mm f-7 objective and it will work with other refractors of similar focal length. The flattener slips into the 2" focuser. The 0.8X focal reduction converts the an f-7 refractor to f-5.6. Please note that the performance of this unit is directly related to the accuracy of the objective lens in your telescope. 

This reducer/flattener has a standard 42 mm filter thread. Standard 2" filters can be added to the reducer/flattener when imaging. The backfocus of this reducer/flattener with the extension on the back is 55 +/- 0.5mm. Since a DSLR with t-ring has a 55 mm backfocus, plug the reducer/flattener into the focuser and then thread on the camera/t-ring to the flattener 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. So 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. So if the ccd camera has a backfocus of only 35 mm, a 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.