Your DSLR mode dial lets you decide how much the look of your photos is decided by a computer, and how much YOU want to control.
Truly, the mode dial on your digital SLR camera is not the most confusing aspect of digital SLR technology, but since it is the main entry point to all of the camera's primary settings, it's pretty important to understand.
Virtually every DSLR mode dial is divided in half: one half lets you choose between different automatic modes, while the other lets you select a variety of manual modes.
In the paragraphs that follow, I'll describe what each of the setting on your mode dial will allow you to do. While all mode dials are laid out pretty much the same, I'll also talk about some of the differences between the different camera manufacturers.
Let's begin with the automatic modes, since many people are already familiar with these. There are really only two main categories for automatic modes:
Some cameras will have additional automatic modes with fancy names like "Intelligent" auto and "auto +" but in the end, they are really just auto mode.
Here's the thing to remember about the auto modes: when the camera is set to automatic (yes, this includes scene modes), the engineers that designed the camera are making decisions about your images, not you.
Yes, you get to choose the subject matter and decide what the composition looks like but everything else – color, tone, brightness, shadow, highlight – is being handled by the computer chips inside the camera.
This explains why the exact same photo captured by two different camera brands won't look identical. At some point, the camera designers made a choice about what a "good" image looks like and that's what is encoded within the camera's "brain".
When you select a manual mode on your DSLR mode dial, you are now taking responsibility for how your photos look. The "quality" of the image is no longer decided by the company that made your camera – now you are in the driver's seat.
This can be both intimidating and overwhelming to anyone who's never moved beyond automatic mode before.
Let me help ease some of your concerns:
Think of it like this: the worst thing that will happen if you switch to manual mode is that some of your pictures may not turn out well.
The manual side of a DSLR mode dial lets you take baby steps toward full manual control so that you don't have to become a master photographer as soon as you turn the dial.
My favorite mode for beginners just getting comfortable with a DSLR is Program Mode. Seriously, you can set your camera in Program Mode and be hard-pressed to see any immediate difference between it and full AUTO.
However, in full AUTO, you have zero control over how your images turn out. In Program mode, you can tweak settings like exposure compensation and make your images appear brighter or darker – without learning ANY other manual controls.
No, all mode dials are not created the exactly the same, but they certainly do share a lot of common symbols. For example, Program Mode is P and Manual Mode is M on every DSLR I've ever used.
Beyond this, DSLR mode dials are unique, sometimes including special features that are only available on specific cameras.
The mode dial from the Canon 600D T3i includes a lot of what you'd expect from an intermediate camera: there are a variety of different scene modes that you can select to match your subject, plus a dedicated "no-flash" mode. The specialized A-DEP mode is for "automatic depth of field" and lets you specify two focus points in your image - ideally everything between these two points will be kept in focus (provided there's enough available light).
Here's the mode dial from a Nikon D5100. At first glance it appears to have less scene modes than the Canon, but then you notice the dedicated SCENE option, which provides you with access to a slew of additional modes via the menu. You can also select EFFECTS to add an artistic look (using a variety of filters) to any photo that you take. Shutter Priority mode is indicated with an "S" rather than "Tv".
The mode dial on the Olympus E-510 looks pretty simple compared to the ones on Canon and Nikon. Like the Nikon, additional Scene modes are available when you select the SCENE option. There isn't a dedicated "no flash" option on this mode dial, but you can disable the flash from popping up automatically by selecting P mode.
Pentax cameras include a special ISO sensitivity setting available on the mode dial, like the one on the Pentax K20D. It's indicated by the Sv on the mode dial. In addition the K20D also has a "bulb" option where the shutter can be open for extremely long periods of time for night photography. A USER mode lets you select preferred settings quickly and easily.
Sony has gone in a unique direction with their cameras, which is why the options on their mode dials are quite different. The one shown here is from a Sony SLT-A57, and it includes some special modes that only exist on the SLT line of cameras like "Sweep Panorama" and "3D Image" (which can be viewed on a Sony 3D Television with 3D glasses).