"Returns the bellows factor, the ratio of effective aperature to actual aperture."
(1+ (magnification :focal-length focal-length :object-distance object-distance)))
-(defun extension-tube (focal-length &key original-object-distance new-object-distance original-image-distance
- original-magnification
- new-object-distance new-image-distance new-magnification
- extension-length (units :feet))
+(defun extension-tube (focal-length &key original-object-distance original-image-distance original-magnification
+ new-object-distance new-image-distance new-magnification extension-length (units :feet))
"Computes the parameters for using extension tubes.
Requires: 1. original-object-distance, original-image-distance, or original-magnification
2. new-object-distance, new-image-distance, new-magnification, or extension-length