## Focal ratio with Focal Reducer

As the name suggests, this formula is used to calculate the focal ratio which is applicable is a focal reducer is put into use.

## $$(1-\frac{d}{f})*r$$

The values needed for this calculation are d = distance of CCD from focal reducer, measured in mm, f = focal length of FR, measured in mm, r = focal ratio of scope

ENTER THE VARIABLES TO BE USED IN THE FORMULA