Description

Focal Reducer/Field Flattener for f-7 refractors 

This reducer/flattener is optimized for our SVR102T triplet lens and it will work with other f-7 refractors. The flattener slips into the 2" focuser. The 0.8X focal reduction converts the an f-7 refractor to f-5.6.

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 the unit is 55 mm. 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.