DOF/Aperture/focallength chart?

[SWPhotoImaging]

Is there such a thing as a tool that would show what the DOF might be using a particular focal-length lens at a specific aperature and distance?

I realize this would be more of an array than a matrix, given the variables, but it seems possible using a calculation against a set of input variables.

Just curious. I always think about things like "wow, that f1.8 lens would sure allow me to shoot in low light", but in reality, unless I am using it at maximum focal distance, or purposely going for a blurred foreground and background, the shallow DOF of f1.8 would probably render most photos unusable.

I was thinking that, if someone could build the calculations, you could input the f-stop you think might be necessary for a given lighting situation, and see a grid of what ranges could be expected to be in-focus at what distances.

Maybe I should have another margarita and stop thinking too much about it.

[bfaust]

here are a couple of sites to look at.

http://dfleming.ameranet.com/dofjs.html

http://www.marcjutras.com/ehyperfocal.html

or calculate your own

Camera to near distance = (H x S) / H + (S-F)

Camera to far distance = (H x S) / H - (S-F)

where H= Hyperfocal distance
S = Distance from the camera to object
F = Focal length of Lens
(all values must be converted to common measurement)
since the F is so little you can convert the formula to

DN= (HxS) / (H+S) and DF= (H x S) / (H-S)

Hyperfocal distance = F squared / fc or Fd / c

where
F= focal length
f= relative aperture
d=aperture diameter
c= circle of confusion diameter expressed as a fraction of focal length. The usual C of C for 35mm photography is considered 0.025 mm.

another formula which helps is
f number = F x 1000 / distance of object
ex: focal length 35 mm distance to object 6096 (20 ft) the f number = 5.6
all numbers must in same units

[SWPhotoImaging]

Yeah, I remember when my teachers tried to tell me you could do math with letters in it! HAH! Everyone knows that math is for numbers and letters are for writing . . .

But seriously, thanks for both the links and the formulae.