Time lapses have been among  the most visually stimulating elements of cinema since their introduction in the late 1800′s. They are no as popular as ever and as easy as ever to create, that is if you have all the right tools (iPhone doesn't count!). One of the most commonly asked questions is “How many seconds between each shot?”, or “At what interval do I take photos?”. Usually you will get an answer from a friend or on a forum between 1 and 6 seconds. But how and why did they choose that interval other than past experience and/or guesswork? Below I will show you how to calculate that interval as well as all other aspects of your time lapse so you can be knowledgeable and prepared before even getting on location. There are a small number of other Time Lapse Calculators out there and it is becoming a stock mode on many new cameras, but those just spit out the answer for you with the information you provide them. I provide below an actual equation which I have formulated so that you may solve for any variable based on each of your shots’ particular needs. Furthermore, this equation will not only enable you to proficiently time your shots so that you may perfectly elapse 8 hours into 30 seconds, but will give you the complete ability to transform any amount of hours into any amount of seconds by finding each shots specific interval (rounded to the nearest second).

[pmath size=52]X= {H(3600)} /{ FR(dtrt)}[/pmath]

As long as you’ve got a calculator this is very easy to tackle. Here’s what it means.. In most cases your solving for X but you can go about it any way you like.

X= Interval inSeconds between photographs. 

H= Total Hourstaken for time lapse in real time.

FR= Frame Rate in which pictures will be displayed in your editing timeline ( 24, 25, 30, 60 etc.).

dtrt= Desired Total Running Time in seconds.

So you want to film the sunset and you’ve only got two hours. You’re using it for a title sequence and you want to last 50 seconds in a 24p timeline. Just plug it in and it reads 2X3,600/ 24X50.

  [pmath size=52]X= {H(3600)} /{ FR(dtrt)}[/pmath]      add variables      [pmath size=52]X= {2(3600)} /{ 24(50)}[/pmath]      solve      [pmath size=52]X=6[/pmath]

With X equaling 6, that is the interval at which you should take your shots to get the desired results. Meaning set your intervalometer to 6 seconds.

So in this example you would now know before you even went to shoot, that if you set your intervalometer to 6 seconds and took a picture of the sunset for 2 hours, opened them as a 24p video, your clip would be exactly 50 seconds long. Like magic!

If

x < 1

or

x ≤ stutter speed

, interval will not be possible. If this is the case try lowering Aperture or increasing ISO until functional shutter speed is achieved.