Multiple Exposure Calculations

[RmFrase]

Just wanted to know if there was an App, or Excel Spreadsheet for calculating multiple exposures. Specifically, based on different shutter speeds.

Let's say, Normal metered exposure is ISO 100, f/16 @ 125.
First exposure desired is 1/8th Sec.
Second exposure desired is 1/60th.

The application would then would then output Apature to achieve results.

Any thoughts?

[J. Gilbert Plantinga]

Go ISO 100 1/8 sec @ f64 + 1/60 sec with the lens cap on. Spreadsheet won't help much here until you get a ND filter.

[Doremus Scudder]

Exposure is close enough to additive that you can just figure it simply this way:

Assuming you want equal exposures at the shutter speeds you indicate, and using your initial starting point:

Step1:simply divide your indicated exposure into two equal parts

f/16 @ 1/125 = 2 exposures of f/16 @ 1/250 (or, if you prefer, 2 exposures of f/32 @ 1/125)

Step 2: Run the derived exposure through the aperture and shutter speed equivalents:

f/16 @ 1/250 =
f/32 @ 1/125 =
f/45 @ 1/60 =
f/64 @ 1/30 =
f/90 @ 1/15 =
f/128 @ 1/8 etc.

So, if you want one exposure at 1/8 sec, you would need f/128 for that (or use a larger aperture and an ND filter to achieve the same thing)

For the second exposure you'd need f/45 (or, again, the equivalent with an ND filter).

I find this easy enough to do on my exposure record or on my head that I don't bother with calculators/spreadsheets. You probably won't need to either.

With very long exposures and with scenes that are moving or have people/cars, etc. moving through them, I often use intermittent exposures. A 30-sec. exposure gets broken down into as many other units as needed to arrive at the 30 seconds total time (often in 5-10 installments).

Extending the same method as above, you can divide exposures into ratios, e.g., 1:3, etc.

Step1:simply divide your indicated exposure into four equal parts

f/16 @ 1/60 = 4 exposures of f/16 @ 1/250

Step 2: Run the derived exposure through the aperture and shutter speed equivalents:

f/16 @ 1/250 =
f/32 @ 1/125 =
f/45 @ 1/60 =
f/64 @ 1/30 =
f/90 @ 1/15 =
f/128 @ 1/8 etc.

You will need 4 of these to make the complete exposure, but you simply combine three into one. Lets say we want one exposure at 1/15 sec, so we use our hypothetical f/90 (or equivalent) for the first exposure.

Next combine two of the others: For example 2x f/16 @ 1/125 = f/16 @ 1/60. Now we need a quarter stop more exposure to make up the difference, which we deal with with the aperture. Final second exposure, if you want to be precise, f/12, which is one-quarter stop smaller than f/11. Since 1/3 stops are marked on most shutters, I would just use f/13, 1/3-stop smaller than f/11. The very slight overexposure would help compensate for the tiny loss of speed due to the intermittency effect.


Have fun,

Doremus

www.DoremusScudder.com

[RmFrase]

Thank you all for your assitance !