Exposure Calculator App
My exposure calculator app is now available in the Google Play store. Free. No ads.
There are countless apps available to help you research a photography project but once I'm actually on a shoot, I generally use my phone for just one thing: calculating exposure times. My goal for this app was to focus exclusively on that one task, making it as simple and intuitive as possible.
The long exposure technique is one of my favourite aspects of photography. At night, exposures of 30 seconds or more can give dramatic results under all manner of artificial lighting conditions, while during the day, natural density (ND) filters allow for the creative effects possible with long exposures, such as blurring bodies of water for a serene looking image.
For those new to this type of photography, I'll describe my procedures for a shoot like this and in doing so, explain how to use the app.
The scenario is a daytime shoot of a landmark beside a river and your goal for the final image is to show the river with a smooth, almost mirrorlike, surface as foreground interest to complement the building. A fashionable (some might say clichéd) approach at the moment.
This effect requires an exposure time somewhere within the 30 secs to 2 mins range. So as well as a tripod, you'll definitely need an ND filter, like my 10 stop Lee Big Stopper here. '10 stop' denotes the strength of the filter in terms of how much light it blocks. For every 1 stop increase, half the amount of light enters the lens so 10 stops will allow exposures of 2 minutes or even longer during the day.
Take care of the basics before attaching the filter. Frame up your composition and get it in focus. Once this is done, make sure you're in manual focus mode so the AF doesn't re-focus when you press the shutter release. Choose your aperture - f/8 or f/11 is a good starting point for this subject. Now you need to set the shutter speed for a correct exposure. Time for the app.
A few test shots may be required before you've happy with the exposure but you don't want to be waiting several minutes for each test. Instead, select a high ISO setting, say 3200, and adjust the shutter speed until you've nailed the exposure. On a bight day you'll be somewhere around the 1/1600...1/800 range I'd expect, because of the high ISO. Much kinder to your battery. Of course, you don't have the desired effect yet - this is just an exposure test.
Open the app and use the buttons in the Test shot settings row to record the shutter speed, aperture and IS0 values that gave you a correctly exposed test shot.
Next we'll adjust the camera settings for your final image. First up, reduce the ISO to 100. This will eliminate any unnecessary noise and improve the quality of your photo. If you started at 3200 that's already a 5 stop drop in your exposure so you'll need to increase the shutter speed by 5 stops to compensate for that.
Back in the app, record the new ISO in the Adjusted settings row. You haven't attached a filter yet so the nd filter button should be on 0 stops. The Exposure time display box shows the shutter speed you should set to maintain the exposure of your test shot.
Nothing revolutionary so far. All you've done is use the same number of command dial clicks to increase the shutter speed as you did to decrease the ISO and doubtless you're still well within the range of your camera's regular shutter speed settings - 1/25 or thereabouts. This will begin to blur the movement of the river but won't give you the beautiful mirrorlike effect. Now's the time to attach an ND filter, taking care not to mess up your focus or composition, then use the app's nd filter button to enter its strength.
Now we're into the realm of long exposure photography. The longest shutter speed on most cameras is 30 seconds before you have to engage Bulb or Time mode and time the exposure manually. If your required exposure time is longer than that, countdown controls appear at the bottom of the screen. Set the camera's shutter speed to Time and when you're ready, simultaneously press the shutter release and start the countdown in the app. A notification will let you know when it's finished and you should stop the exposure.
Check your image. The exposure should be spot on assuming the level of natural light hasn't changed too much since you took the test shot. Maybe the water isn't as smooth as you'd like in which case you have a few options.
Use the compensation buttons on either side of the Exposure time display to alter the time in -10 or +10 second increments. A small change won't make a great deal of difference to the photo's exposure but could be just enough to perfect the result. If not, try lowering the aperture or using a stronger (or additional) ND filter if you have one. Either way, make sure to update the app's settings to see what your new exposure time should be.
The same principles apply on a nighttime shoot although you won't need filters. When it's dark, longer exposure times and wider apertures are needed just to see any shadow detail. You'll need to be careful not to blow out the highlights too much so experiment with more test shots, using the highest native ISO setting on your camera for the fastest possible shutter speed, before dropping it to 100 for the final image.
When your scene is lit by an array of artificial light sources; street lamps, neon advertising, traffic headlights, illuminated buildings and so on, the results of long exposure photography are less predictable but can also be spectacular.
So give the app a try next time you're planning to take some long exposures. I hope you find it useful and straightforward. It only does one job so I hope it does it well. Ideally, you should be able use the app without even thinking about it, leaving you to focus on taking your shot rather than fiddling with your phone. If I've achieved that, please give me a nice review in the Play store. If not, let me know how it can be improved.
