(t
(error "Must set two, and only two, of the parameters: image-distance, object-distance, and focal-length."))))
-(defun close-up (&key focal-length object-distance image-distance magnification (units :feet) &aux bellows-factor)
+(defun close-up (&key focal-length object-distance image-distance magnification (units :feet))
"Computes the parameters for focusing closer than infinity.
Requires two, and only two, of the input parameters.
Returns: focal-length object-distance image-distance magnification bellows-factor."
"Returns the bellows factor, the ratio of effective aperature to actual aperture."
(1+ (magnification :focal-length focal-length :object-distance object-distance)))
+(defun n-args-not-nil (n &rest args)
+ "Returns T when count N of input args are not nil."
+ (= n (count-if-not #'null args)))
+
+(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
+Returns: original-object-distance, original-image-distance, original-magnification, original-bellows-factor
+ new-object-distance, new-image-distance, new-magnification, extension-length."
+
+ (when (or (not focal-length) (not units)
+ (not (n-args-not-nil 1 original-object-distance
+ original-image-distance
+ original-magnification))
+ (not (n-args-not-nil 1 new-object-distance
+ new-image-distance
+ new-magnification
+ extension-length)))
+ (error "Invalid arguments.
+Must set 1 of the following original-object-distance, original-image-distance,
+or original-magnification parameters as well as one of the following parameters
+new-object-distance, new-image-distance, new-magnification, or extension-length."))
+
+ (flet ((ret (ood oid om obf nod nid nm nbf e)
+ (list :focal-length focal-length :original-object-distance ood
+ :original-image-distance oid :original-magnification om
+ :original-bellows-factor obf :new-object-distance nod
+ :new-image-distance nid :new-magnification nm
+ :new-bellows-factor nbf :extension-length e)))
+
+ (multiple-value-bind (focal-length-original o-od o-id o-m o-bf)
+ (close-up :focal-length focal-length :object-distance original-object-distance
+ :image-distance original-image-distance :magnification original-magnification :units units)
+ (declare (ignore focal-length-original))
+
+ (cond
+ (extension-length
+ (multiple-value-bind (focal-length-new n-od n-id n-m n-bf)
+ (close-up :focal-length focal-length :image-distance (+ o-id extension-length) :units units)
+ (declare (ignore focal-length-new))
+ (ret o-od o-id o-m o-bf n-od n-id n-m n-bf extension-length)))
+ ((not extension-length)
+ (multiple-value-bind (focal-length-new n-od n-id n-m n-bf)
+ (close-up :focal-length focal-length :object-distance new-object-distance
+ :image-distance new-image-distance :magnification new-magnification :units units)
+ (declare (ignore focal-length-new))
+ (ret o-od o-id o-m o-bf n-od n-id n-m n-bf (- n-id o-id))))))))