Is There A Reverse DOF Calculator

[Red]

I've been playing around with the DOF Calc for some upcoming shoots with cars. I need to work out which lens I'll be using to buy a polariser filter ahead of time, and so I look a tad more professional!
The problem I've found is that it's a case of plugging in figures until you get a DOF that suits you. Not only is this time consuming, but dull. Surely anyone working out a DOF has a depth they are trying to achieve, so the calculation needs to be the other way around.
Does anyone know of one that does? And dare I go as far as to ask for one for a PocketPC/PDA?

[slin100]

If I understood you correctly, then pCAM (http://www.davideubank.com/) can do this. It allows you to enter the focal length, near and far distance and it will tell you the aperture necessary to bring those distances into focus. It, of course, has the usual mode where you enter the focal length, aperture and distance and it calculates the DOF.

[MrChevy]

Not for a PocketPC it can't. It only runs on a PalmOS. PocketPC's run WindowsCE. :)

These are some links for PocketPC's and Desktop PC's too:

http://home.comcast.net/~jonsachs/

http://www.olympus-pro.com/index.eu.en.html?content=/eu/en/downloads/depthoffieldcalculator.html

http://www.to-tech.com/mobileviews/websites/PocketPCApps.asp

http://www.devbuzz.com/content/init_listings.asp?action=sort&orderby=AddDate&direction=desc

http://ailab3.engr.uconn.edu/~noriravi/homepage/Tools

http://www.xs4all.nl/~wiskerke/html/toollink.html

[Red]

Lots of those end up being links to the Jonathon Sachs program, which isn't reverse. :evil:

Thanks anyway

[philm_on_4]

Had a go at it lunchtime, I'll get to tidy it up one day maybe :o)
I basically rearranged the std equations to get a quadratic with Aperture as the variable against the TOTAL depth of field

I ran it on a freeware basic for windows util - seems to work
http://www.justbasic.com/

You should be able to run it on nearly anything PDA or whatever - or paste the formulas into a spreadsheet etc...

all measurements are in mm!


' Change the following number to suit required DOF in mm
DOF = 500
' Change the CoC to suit
CoC = 0.019
' Focus distance to target
D = 4000
' Focal length of lens
L = 50
' partial calcs - because I'm lazy with the algebra
q = L^2/CoC
p = D-L
' solve the quadratic
' stage 1 - calc coeff of Ap^2
a = 0-p^2
' stage 2 - calc coeff of Ap
b = 0-( 2*D*p*q/DOF)
' stage 3 - call constants
c = q^2
' finally...
Ap = (0-b - (b^2-4*a*c)^0.5)/(2*a)
print "For a total DOF of "; DOF
print "Your required Aperture is ";Ap
print
print "Don't forget you'll have apportion the near and far focus points!"



Any use? It's not a great leap to make it 'nice' and give the f-stops either side of your required DOF etc....

cheers
Phil

[Red]

That does look handy. I'll see if I can splurge that into a speadsheet for PDA. Thanks

[philm_on_4]

Let me know if you find any probs. I wrote the 'original' in excel, but figured it's easier to publish in a programming language.

I've got an old Handspring palm thingy which I'll probably end up porting all my utility bits to at some point.

all the best,
Phil