DoF calculator with a regular calculator

Ale Reynoso · April 16, 2009

Perhaps most of you know the trick and it´s not nothing new, but I learned it in a focus puller course and I´ve been using a regular calculator as depth of field calculator in an easy, fast way.

I only know how to handle it in meters, as focal and Cc are in metrical measures. Don´t know how to handle Cc in inches and DoF in feet:

“x” multiplied by

“x=” square (means x multiplied by x for the calculator)

“%” divide by

“% =” inverse (means 1/X for the calculator)

“-“ less

“+” plus

“M+” add to memory

“MR” memory recall

(F): focal length

(f): f stop

(Cc): circle of confusion (25 for 35mm and 17 for 16mm. Not 0,025 or 0,017)

(Dist): distance of focusing

(F) x = % = x (Cc) x (f) = 1/H. M+

This way you have added to memory the inverse of hyperfocal. Make % = to know the hyperfocal in meters. If you don´t change the f stop just keep this memorized and add the different focusing distances to find the DoF. :

(Dist) % = - MR = % = farthest limit (in meters)

(Dist) % = + MR = % = closest limit (in meters)

You can use it with focal lengths not available in tables or fraction of a stop.

(f) x 1,12 = (f) one third

(f) one third x 1,12 = (f) two thirds

(f) x 1,19 = (f) split (f plus half a stop)

Easy. Nice to know if you run out batteries in your palm, cel phone or just lost your tables.

Best regards

Alejandro

John Sprung · April 16, 2009

This method works when the distance is significantly larger than the focal length. If you need to work with miniatures, tabletop stuff, macro work, etc., you need the complete formulas. I have it all in an Excel spreadsheet, unfortunately, this site doesn't let us upload spreadsheet files.

-- J.S.

Ale Reynoso · April 16, 2009

May be it´s a simplification. But the point is that is a simplification that works well in the fields, without any other tool than a regular calculator.

It works well and can replace a DoF Table. The tables of a regular set of lens wouldn´t help in macro jobs either.

Good luck!

Alejandro

David Auner aac · April 16, 2009

This method works when the distance is significantly larger than the focal length. If you need to work with miniatures, tabletop stuff, macro work, etc., you need the complete formulas. I have it all in an Excel spreadsheet, unfortunately, this site doesn't let us upload spreadsheet files.

Hi John,

drop me a note and I'll host it on my site for you. You could then post just the link!

Cheers, Dave

David Rakoczy · April 16, 2009

“x” multiplied by
“x=” square (means x multiplied by x for the calculator)

“%” divide by

“% =” inverse (means 1/X for the calculator)

“-“ less

“+” plus

“M+” add to memory

“MR” memory recall

(F): focal length

(f): f stop

(Cc): circle of confusion (25 for 35mm and 17 for 16mm. Not 0,025 or 0,017)

(Dist): distance of focusing

(F) x = % = x (Cc) x (f) = 1/H. M+

This way you have added to memory the inverse of hyperfocal. Make % = to know the hyperfocal in meters. If you don´t change the f stop just keep this memorized and add the different focusing distances to find the DoF. :

(Dist) % = - MR = % = farthest limit (in meters)

(Dist) % = + MR = % = closest limit (in meters)

You can use it with focal lengths not available in tables or fraction of a stop.

(f) x 1,12 = (f) one third

(f) one third x 1,12 = (f) two thirds

(f) x 1,19 = (f) split (f plus half a stop)

Reason enough to be sure my iPhone is always charged. pCam (iPhone app.) ROCKS!

LOVE it! :wub:

Ale Reynoso · April 16, 2009

You should have quoted this:

F x = % = x Cc x f = M+

Dist % = - MR = % =

Dist % = + MR = % =

Just a few buttons. It´s always good to know basic technology can help you in case anything else fail.

Just wanted to help somebody (newbie?) that could find this usefull.

No problem.

Best regards

Alejandro

David Rakoczy · April 16, 2009

Yes it is!.. and I was very impressed with your mathematics.. please don't take me wrong. :)

It is just that I have so much to think about on Set, as it is, that I am very grateful for things like the pCam App and the Steele Chart.

As far as DOF goes.. if all else fails, I'll use my eye as I will be lost in your mathematical, numerical complication... I mean computation!

Ale Reynoso · April 20, 2009

The maths are from a former AC now DoP that gives courses in the national film union, who employed some time and patience to simplify the DoF formula and make it suitable for a regular calculator: his mantra is, "make it simple and it will always work".

I´ve done some focus pulling in 16 and 35, I don´t use the i phone or palm, and I just used this method to find my limits. My 2nd AC had a DoF program in his cell phone, so we were always re-cheking results and comparing how quickly each one got them. I would add some more marks if the DoF was shallow...and started to sweat...

How do you handle handheld and steadicam shots? Are you using the panatape or the Arri equivalent?

Thank you

Best regards

David Rakoczy · April 20, 2009

My ACs use a cloth tape measure and chalk or tape marks on the ground.

Ale Reynoso · April 20, 2009

Thank you! ;)

Best regards.

Chris Keth · April 21, 2009

Thank you! ;)
Best regards.

There are a lot of tricks to make it happen. The really tricky thing is that a lot of people use handheld work (and to a much lesser extent steadicam) as a platform for "lets try it and see what happens" type shooting. For you, that leads to having to visually estimate focus distance a lot of the time since without rehearsals you can't have marks. In these situations, I do what I call "knowing the room." I''ll measure various dimensions of the room such as from the couch to the TV, from the kitchen sink to the fridge, etc. Knowing a variety of those, I find I can estimate a lot of unknown situations. Will there be buzzes? Probably, but I can't be perfect without knowing what's coming up. Reaction time can't be overcome, unfortunately.

Ale Reynoso · April 21, 2009

"In these situations, I do what I call "knowing the room." I''ll measure various dimensions of the room such as from the couch to the TV, from the kitchen sink to the fridge, etc. Knowing a variety of those, I find I can estimate a lot of unknown situations"

That´s a very good trick. I used to measure different places inside a place from the camera where I couldn´t lay marks on the floor and needed references, but making some kind of "grid" with the furniture or whatever sounds very effective. ;)

Thank you!

Best regards

Alejandro

Tom Jensen · April 21, 2009

At the risk of sounding nuts here, I'm going out on a limb and I'm going to say GET A REL DEPTH OF FIELD CHART! I had 3. One was a hard plastic one with the metal nut in the middle, the second was the thin plastic wheel that had a little booklet type case and last was an ASC manual. Don't reinvent the wheel here. Go with simple. If I saw an AC punching in numbers on a calculator, I think I would lose it. :blink:

Chris Keth · April 22, 2009

At the risk of sounding nuts here, I'm going out on a limb and I'm going to say GET A REL DEPTH OF FIELD CHART! I had 3. One was a hard plastic one with the metal nut in the middle, the second was the thin plastic wheel that had a little booklet type case and last was an ASC manual. Don't reinvent the wheel here. Go with simple. If I saw an AC punching in numbers on a calculator, I think I would lose it. :blink:

I have to agree here. I know the math and can do it but I don't think I've ever had the time to figure out the depth of field the slow way. Imagine figuring out what stop is needed for a split like that. I've done it once for a class and that was enough.

Ram Shani · April 22, 2009

i am lost :(

can you give example with numbers:)

Chris Keth · April 22, 2009

i am lost :(

can you give example with numbers:)

OK, so you are on a process trailer shooting a raking 2 shot in a car. The lens is a 32mm. You need to hold focus from 3'0" to 6'6". What stop do you have to shoot at for it to be possible? Where do you set focus on the barrel in order to do it?

I can figure that out on a DoF calculator in a few seconds. How fast can you do it with equations? I could do it but it would take a whole lot longer than a few seconds.

John Sprung · April 24, 2009

If you're by yourself doing inserts or something, it might not be too bad to do the math as you shoot. But if you have people waiting around, it's just too expensive.

The trouble with printed tables is that tradeoff between the tables being huge and covering the range of conditions you need. For average shooting, they're OK.

But suppose you need something special. Say you get to use an f/0.7 lens like Kubrick did. Or you know you'll be using particular in-between stops, or a narrow range of distances, or a focal length that's not in the published tables. For those situations, maybe the best idea is to use a spreadsheet program to do the math beforehand, and print out the special tables you need for exactly what you're doing.

The greatest advantage of doing your own tables with a spreadsheet is that you get to choose your own circle of confusion. Sharpness doesn't fall off a cliff at the DOF limits, it rolls off gradually. The DP should have the opportunity to decide how soft is too soft. The mathematical implementation of that decision is the number you use for circle of confusion. You can shoot some diagonal newspaper tests and pick the CoC that you think is right for your particular lenses and format.

I've done one as an Excel .XLS file. Dave Auner is going to put it on his website. It has two sheets, one for metric, the other foot and inch.

-- J.S.

Ale Reynoso · April 25, 2009

So in a way or another everything that was said is true. As in everything else, there is not a “right way” to do things. Some ways are better than others, and some people prefers one way than another. What matters is the result in a fast, practical way (and that is different in different situations) . As many ways to do a certain thing we know, the best to find the best tool at a certain situation.So I don´t think if you see your 1st AC cliking in a calculator you “lost him” or something like that. (at a certain moment) is more or less like digging into the numbers of a chart or using the iPhone. Different methods works on different people giving the same result in more or less the same time. An iPhone or a calculator to someone used to it can be as fast as a chart. Or just add specs that a chart doesn´t consider as they said.

Good luck

Alejandro

Bob Hayes · April 27, 2009

Dave Eubanks has a great app for you the i phone called pcam. It isn't cheap but it has some great tools.

Hal Smith · April 27, 2009

Programmable calculators like the HP scientific and engineering series (HP48, etc.) could be programmed to handle the actual DOF formula and have variable inputs for parameters like COC. I built a program once for my HP48G that could have been used to land the Apollo moon mission LEM's on autopilot. But then I was teaching Physics in those days and had a reason to show off!