Free photo apps that enhance your iPhone's camera
The iPhone 4S takes good photos, but there are plenty of reasons to invest in a standalone camera. A dedicated camera's main benefits lay in the hardware: You'll get an optical zoom lens and a bigger sensor, and in some cases, you'll also get manual exposure controls and a wide-aperture lens that performs well in the dark.
However, when it comes to software and in-camera features, the iPhone is catching up quickly. To be clear, the iPhone's native camera app doesn't have a high-speed burst mode, manual exposure controls, or automated panorama stitching. However, there are a number of apps that will add these capabilities to your iPhone camera, and they're all free.
Here are some of the best free apps I've used for increasing and decreasing your shutter speed, capturing panoramic scenes, shooting super-slow-motion video, and even bending time. They'll make your iPhone camera more like a standalone camera.
Take better low-light photos and long-exposure shots
The iPhone 4S does a pretty good job of snapping photos in low light without a flash, but it can't work miracles. One quick tip is to use the iPhone's built-in HDR mode, which usually brings out a few details lurking in the shadows. A post-capture trick is to use the "Lux" feature in Instagram on a photo to enhance brightness and contrast, save the photo, and then apply the Lux feature again to the saved photo.
As for actually taking photos in the dark, it takes a very steady hand, a bit of experimentation, and a free app called Slow Shutter+ Free. This app is also handy for other long-exposure shots, such as "light trails" photos of car lights at night or adding a soft effect to photos of flowing water.
Slow Shutter+ allows you to set the iPhone camera's shutter speed from 1 second to 45 seconds. Once you've captured a photo, the app lets you adjust the image's exposure levels and size. I like using the app's "Manual" mode, which works like a DSLR's bulb mode: You control the shutter time as you're taking a photo by tapping the capture button once to start capturing and tapping it again to stop.
You should really only use Slow Shutter+ when resting your phone on a flat surface, as any camera shake while the shutter's open will result in a blurry shot. This app can't work miracles, either, as your low-light shots will almost always show some visible noise or color inaccuracies. Still, it's able to take shots in settings that are too dark for the iPhone's native camera app (without the flash, at least).
Take (fake) control of your aperture
The iPhone 4S camera has a fixed F2.4 aperture, so you won't find apps that give you manual control over its aperture settings. However, you can find a few free apps that let you simulate the shallow depth of field of a wide-aperture lens or mimic the bokeh effects of different aperture blade shapes.
If you use Instagram, you probably already know the easiest way to highlight a certain part of your image by using the app's tools to blur out certain objects. The app has a blur tool you can access via the top bar of its image editor, allowing you to choose a circular or linear "focal plane" that remains in focus while the rest of the image is slightly blurred out.
It works well, but at its maximum resolution setting, Instagram saves your retouched photos as 1920-by-1920 (3.6 megapixel) images. If you want to output full-resolution images and gain a bit more control over your depth of field, try iQuikDoF. It lets you "paint" your desired focus area more freely and adjust the intensity of the blur effects in your photos, although the app takes a bit more practice to master.
And finally, if there are points of light behind the subject in your photo, you can mask them with a number of shapes using Bokehful. It's a free app meant to replicate the effects of using a high-quality lens to achieve "good bokeh." (Bokeh is the aesthetic quality of the deliberately out-of-focus parts of an image.) You touch different points of your image to add lens-flare-like bokeh effects in your choice of color and shape (circles, hexagons, star shapes, or, of course, heart shapes).
Your success may vary. I found the app to be less than accurate when it came to adding the effects in the exact places I touched the screen. There's also no way to manually control the size of each shape. Unless you really know how to fake your bokeh, the resulting photos can look like an artificial mess.
Create instant panoramas
A lot of new cameras have motion-controlled panorama modes that let you hit the shutter, pan the camera from side to side, and create a super-wide-angle image that the camera assembles automatically. There are a couple of free apps out there that work in a similar fashion, but there are some notable tradeoffs with each of them.
The best free option is probably Microsoft's PhotoSynth. It has an automated, motion-controlled mode like the one described above, but it also allows you to snap each portion of a panoramic image manually. While its image quality is sharper and generally less-distorted than the other free options I've tried, you'll need to crop the resulting image after it's taken for it to appear in an even, rectangular shape.
Another free app, Wondershare Panorama, creates evenly-shaped shots and is a bit easier to operate, but it turns out less-impressive results than PhotoSynth. You touch the shutter button and pan from side to side, and it creates a 180-degree, perfectly rectangular panorama.
However, the images I shot with this app only looked decent at very small sizes. There's a bit of noticeable blur, distortion, and ghosting in Wondershare Panorama's output.
Add a burst mode to your iPhone
Being able to capture several rapid-fire shots in a brief amount of time isn't just useful for sports and action photography. It's also a nice option to have if you're taking photos of a baby or a pet. Many apps add burst- or continuous-shooting capabilities to the iPhone camera, but most of them cost money, and none of them bring more to the table than the free, full-featured Camera Awesome.
Camera Awesome has two burst-mode settings: One that captures two full-resolution (8 megapixel) photos per second, and a "high-speed" mode that rattles off six shots per second at a reduced 640-by-480 (0.3 megapixel) resolution.
The app with the highest-speed burst capabilities will cost you $1.99. Fast Camera can capture images at a clip of about 13 photos per second at a 640-by-480 (0.3 megapixel) resolution.
Speed up, slow down, and stop time in photos and videos
A fast burst mode lets you freeze a split second of time. These free apps let you play with the flow of time altogether.
SloPro records 720p video at 60fps, which is a nice feature in and of itself for recording smoother video at the expense of full-HD resolution. However, the in-app editor also allows you to slow down portions of a clip to a simulated 1000fps. The 1000fps feature requires a time-consuming frame-by-frame rendering process, but it doesn't get any more super-slow-motion than that. It should be noted that only the paid version of SloPro lets you save videos to your camera roll or send clips via e-mail; the free version only lets you watch videos within the app or upload them directly to YouTube or Facebook. The free version also slaps a SloPro watermark on your videos.
If you feel like your trigger finger is stuck in super-slow-motion, look no further than Camera Awesome's "Prerecord Video" setting. It's a feature custom-built for capturing the key moments in sports games, fireworks displays, or other unpredictable events without having to record everything that happens. The feature saves a five-second buffer of video before you press the record button, then adds it to the beginning of your clip once you start recording.
And finally, there's Cinemagram, which lets you add a bit of motion to an otherwise still photograph. You launch the app and record a short video clip, then you select a portion of the video clip to use for your "photo." The next step involves drawing a "mask" over parts of the image with your finger; anything within those regions will remain in motion while the rest of the image stays still. Cinemagram also offers an Instagram-like sharing community, but it also outputs your work as a 360-by-480 animated .gif that you can embed or share via Twitter, Facebook, Tumblr, or e-mail.