DEPTH.BA				By Glenn Neufeld
	
	
		DEPTH.BA is an interactive depth-of-field 
	calculator. It is intended for photographers who must 
	know the actual depth-of-filed of their photographic 
	setups.

		Depth-of-field is a term used in photography to 
	describe that part of a photograph in the foreground and 
	background about the subject which remains as sharply in 
	focus as the subject itself. As one reduces the amount 
	of light entering the camera (stops the lens down), more 
	objects in front of and behind the main subject come 
	into focus (increased depth of field).

		DEPTH is operated via the function keys on the 
	Model 100.  Each key either sets a value for the 
	calculation or performs that calculation.

	F1: {cc/?}	 This key sets the so-called "Circle Of 
	Confusion".  This describes the smallest size point that 
	we can resolve as being fully in focus with the lens.  
	In essence, this is the absolute resolution of our lens. 
	As the lens gets better (or the film area increases), 
	the smallest point our lens can make out grows smaller.  
	Normally accepted values are shown.  If you press enter 
	withoput giving a number, the setting does not change.  
	THIS IS TRUE FOR ALL THE INPUT FUNCTION KEYS.

	F2 {f/?}	This key sets the focal length of your 
	lens.  As the focal length increases, the depth of field 
	get shallower.  This is because longer lenses 
	(telephotos) cause forshortening, and give less 
	depth-of-field.

	F3 {f/?}	This key sets the f-stop value.  As the 
	f-stop increases (meaning the lens opening decreases), 
	the depth-of-field becomes deeper.  As it decreases, the 
	depth-of-field becomes shallower.

	F4 {D/?}	This key sets the focus for the lens you 
	are using.  If the lens was focused at 10 feet (10' on 
	the lens-ring), you would tell the program 10.  Thus it 
	can tell you the actual distances to which your photo 
	will remain in focus.

	F5 {>DF<}	This key performs the depth-of-field 
	calculation and displays its results for the current 
	settings.  This should be self-explanatory.

	F6 {>f/<}	This key makes a rather feeble attempt 
	to estimate the f-stop nescesary for a desired depth of 
	field.  You enter the desired near and far focus points, 
	and it approximates the f-stop for the current settings. 
	Since this is (klugily) done by succesive approximation, 
	it is both slow and not very accurate.  It was 
	(obviously) added as an afterthought. Anyone with a 
	better algorithm is invited to contact me directly.

	F7 {Help}	All programs require a key like this.  
	It is for quick reference to the key definitions.

	F8 {Menu}	Resets the function keys to the basic 
	defaults and returns you to the Main Menu.

	Please send me any comments/ideas.  Have fun.
	
						-Glenn Neufeld
						 [75076,753]