1. Multiple Exposure Calculations

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?

2. Re: Multiple Exposure Calculations

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.

3. 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

4. Re: Multiple Exposure Calculations

Thank you all for your assitance !

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