I’m really impressed with the video capabilities of the iPhone. I have an iPhone 4S and I’ve shot some great videos on it. The audio can leave a bit to be desired, but it’s not that hard to overcome that with an external microphone (like the one in the earbuds that came with the camera.)
If you’ve got an iphone and you are starting a web series, or even if you are shooting on a different camera, I encourage you to give your iphone a shot. [UPDATE: I recently wrote a comparison between different camera types for online video.]
A few tips on using your iPhone for video:
Hold it horizontally. This was hard for me to adjust to – if you’re a Vine user, you need to hold it vertically, but for all other video, it must be horizontal. Periscope now allows vertical or horizontal video.
Get close to your subject. The earbud microphone is great – if you use that, you’ll be only a few feet from your subject. Especially with web video – you need to get close!
Pay attention to lighting. You don’t want your main subject too dark or too light – the background matters much less. You can usually move your subject to a good location for good sound and light. Think about moving into the shade so your subject isn’t squinting in the bright sun. And press and hold on your subject to lock the exposure.
If you want to get a bit more serious, I highly recommend buying the training from iPhone Video Hero. This $99 training is packed with useful tips and is broken into 5-7 minute lessons on things like sound, lighting, focusing, depth-of-field, etc. It’s a fast paced training if you’re a beginner, but it’s easy to comprehend.