The LongTime Exposure Calculator is a lightweight app for the iPhone that automatically works out what shutter speed you should use when adding a neutral density filter over the lens.
When you're using standard ND filters such as NDx2 and NDx4 you may have never needed a calculator as you have a good grasp of shutter speed and aperture values. If you add a filter you can quickly compensate. But then along came the Lee Filters Big Stopper with it's 10 stop increase...and that's when things started to become complicated. It's easy to go two or three increments, but ten can be quite challenging. And that's where this wonderful little calculator comes in.
LongTime Exposure Calculator: Features
There's nothing much to this app. It has one splash (info) screen and the calculator page with a simple user interface featuring two scales for filter, from 1x to 20x value, and exposure value, from 1/8000sec to 30 seconds, set using a touch slider.
LongTime Exposure Calculator: Performance
You simply touch the screen and slide the left hand side filter type into the centre view position. Then on the right you slide the current shutter speed into view. Instantly you're given the calculated new shutter speed to set on your camera.
One thing that soon became apparent is that the shutter speed values are in full stop steps. This means if you're using a modern camera with half or even one third increments, the shutter speed you may have displayed in your viewfinder may not correlate to the display on the calculator so some jiggery pokery is needed.
LongTime Exposure Calculator: Verdict
The calculator is an excellent tool, but it's a shame that half stop steps are not included in the scale on the right as users of most modern cameras may be shooting at speeds of 1/90sec or 1/13sec and not necessarily the old fashioned single stop values such as 1/125sec or 1/30sec. That said it's easy enough to adjust the aperture to end up with a common shutter speed. It's certainly saved me time counting out 10 stops when I'm using the Lee Filters Big Stopper
LongTime Exposure Calculator pros
Makes light work of long exposures
Easy to use
LongTime Exposure Calculator cons
Only full stop shutter speeds
VALUE FOR MONEY
The LongTime Exposure Calculator is available from the iTunes Store for free. For more information please visit the HPR-Solutions website