Light is what we photographers work with. Not cameras, film, lenses or digital sensors. We work with light. And understanding light is the most important aspect of understanding the craft of photography. Once you understand light you can bring that understanding to any tool designed for capturing light.
This app, LightMeter by Ambertation, is a great tool for understanding light. It uses the iPhone’s camera to record an image, analyze it and give you options for determining your best exposure. Here is the opening screen:
The first thing you do is touch one of the camera buttons at the top. That will bring up the iPhone’s camera. You can use the touch screen as a spot meter. Anywhere you touch the screen, the scene will be metered by that area. This is useful for backlit subjects. You can click around until you are happy with the exposure and then click the shutter button. The app will then show you the image and you can either click “Use” or “Retake”. There is also a zoom bar at the bottom if you want to see what you’re focusing on, but it’s not very useful in this situation, what we’re looking for is a good exposure for the whole scene.
Once you click “Use” you are taken back to the main screen. Then you use the buttons at the bottom of the roller selectors to determine what you want the app to calculate for you. For instance in the above image, I’ve clicked on the f-number button to determine the f-stop, the aperture setting of the lens. I know I’m using 400 iso film, and I’m shooting indoors. I don’t have a lot of light. You can see the EV value under the iso roller. It’s +8 EV. I’m using a 50mm lens so I’ve set my shutter speed at 1/50th as the slowest handheld speed I feel comfortable with. The app then calculates the f-number for me. As long as I have the f-number set it will tell me the f-stop when I change any of the variables.
Let’s say that now, seeing that I don’t have to use 1/50th indoors, I decide I want to use a wider aperture for a more blurry background. Then I click the shutter speed button and change the f-stop to something like f2.8. Going down 1 stop in the f-stop will change the shutter speed up 1 stop to 1/100th. This is great because you can actually see how changes to one setting affect the other.
If you click on the lock button, all the way to the right, you can now calculate all the values independent of the photo you took. This will let you play what if scenarios. In the above image, I’m calculating different values and I’m trying to keep the EV value at +15, which is a sunny day value. I know that I have a maximum iso of 800 on one of my old film cameras and a maximum shutter speed of 1/500th. Using those values, I can see that I will need an f-stop of f22 on my lens. This helps me plan my shooting, determining that I might want to use a lower speed film instead of the maximum 800.
This is a great app for just $3. A good digital light meter can cost hundreds of dollars. Like all iPhone apps it can be hard to read in bright sunlight and some of the numbers are kind of small for my old eyes to see. But if I use my glasses and look at it in shadow, I find it a very useful tool. The only thing that would make it more useful is if I didn’t have to take a picture, but could just point it something and get a live readout of the light. I highly recommend this app if you don’t already have a handheld light meter.