If iPhones and the like weren't such incredibly useful devices, we'd all probably be tired of reading about them by now. The fact is though, they are indispensable for many of us and for those with low vision or no vision, and the facility these devices offer makes them incredibly useful.
I have been using my iPhone as a telescope for years now. I use it all the time to read street signs, house numbers, store tags that are too high, wall mounted menus behind a counter, etc. I'll tell you and show you the tricks I've learned so that you can do it too.
Just to establish a baseline, I'm using an iPhone 4s running iOS 8.1.2 (latest operating system as of this writing) and the standard camera app included with the phone. Most of this will certainly translate to other smart phones though too.
To get started, press either the power or home button on your phone to wake it up then flick upwards on the little camera icon in the lower right hand corner of your lock screen. This will launch you into your camera app.
Image Caption: Fig. 1. iPhone lock screen with camera icon in bottom right corner.
Below is a screen shot of my iPhone camera displaying a vision testing card. The card is about eight and half inches across and I am standing about eight feet away from it. This is perhaps similar to trying to read a product tag in a big box store on a high shelf.
Image Caption: Fig. 2. iPhone screen showing image of vision testing card with no magnification.
Now, here is a screen shot after I've pinch zoomed in on the same subject, standing at the same distance. To do this, simply place two fingers in the center of the screen and move them apart until the viewfinder image zooms as big as it will go. Roughly, this is about five times magnification. At this stage, if you're able to see the content you need, wonderful! You're done.
Image Caption: Fig. 3. iPhone screen showing same test card pinch zoomed in.
If there's still not enough magnification for me, I take a picture while zoomed in. Once I take the picture, I tap on the Photo and Video Viewer button (Fig. 3) in the lower left hand corner of the screen. This takes me directly to the picture I just captured. Once looking at my picture, I pinch zoom again (Fig. 4). In most cases, when you pinch zoom an image that you shot that was itself pinch zoomed in the view finder, you will be able zoom past the point of text and details being legible. Before this occurs, you might have achieved up to 12x or 15x useful magnification over the original view finder image.
Image caption: Fig 4. iPhone picture of Fig 3 pinch zoomed for extra magnification.
You can now slide the view around with one finger to view the rest of the text in the image at this level of magnification.
This text certainly lacks clarity and contrast. By zooming in on an already zoomed image, we are pushing past the resolution limits of the camera. An optical telescopic monocular will offer a much clearer image with more contrast. If you're a student or someone who needs to do a lot of distance reading of white boards or overhead projections in class, you'll likely be better off using a monocular or a dedicated electronic distance magnifier. However, my method may just work in a pinch if you need to spot check something in the distance.
Some other points to be aware of:
If the image is a bit dark, you can increase the brightness with an upwards one finger flick on the screen (also, don't forget that your screen brightness setting will affect this too).
I always hold the phone in the same orientation as what I am trying to see so, if it is standard text that I am trying to see, I hold my phone in a horizontal orientation. If it is something with a vertical orientation, like a bus schedule, I hold the phone in the vertical position.
In low light, it can be difficult to get a steady shot. You can try to lean against something solid to steady your shot or turn on your flash if your subject is close enough to benefit from this.