Entry-level bodies as well as the mid-tier bodies (all the Rebels, but plus the bodies with 2-digit models such as the 60D and 70D) have "scene" modes.
These are basically full-automatic modes but they bias your cameras exposure settings based on an understanding of what you're trying to shoot.
For any given shot, there are lots of combinations of shuter speed, aperture (f-stop), and ISO that will add up to the "equivalent" exposure (the right amount of light is recieved at the sensor.) For example you could use a wide aperture open with a short exposure time... or narrow the aperture opening but compensate by using a longer exposure time.)
It turns out that while there are a number of ways to combine f-stop, shutter speed, and ISO to get the same "equivalent" exposure... the shots will not actually be the same.
When shooting action, for example, you probably want a faster shutter speed so you can "freeze" action otherwise you end up with a blurred subject because they moved while the shutter was open. To get a faster shutter exposure, the aperture is opened considerably so that it can gather more light in the brief moment that the shutter is open. BUT... when the aperture is wider, it narrows the "depth of field" -- or range of distances at which a subject will appear to be more-or-less acceptably focused. That narrow depth of field is bad for landscape photographers... who generally want as much to be in acceptable focus as possible.
When shooting landscape, the computer biases the exposure by using a small aperture (high f-stop value) and compensating for the fact that the lens is now limiting how much light travels through... but keeping the shutter open much longer so that it ultimately gathers the same amount of light. This results in an image with a very broad depth-of-field (lots of stuff is in acceptable focus -- even at a vast range of distances.)
The high end bodies (bodies that only have a single digit.... like the 7D, 5D, and 1D bodies) do not have these "scene" based modes because they tend to be targeted at advanced photographers (whehter professionals or advanced non-professionals.) Those shooters typically know that, for a landscape, they'd just need to set a smaller aperture (higher f-stop) and compensate by using a longer shutter speed.
BTW... since the shutter speed will be getting slower, you'll want to keep an eye on the shutter speed the camera actually plans to use. If you are attempting to hand-hold the camera for the shot, then you'd want to make sure you're able to be steady while the shutter is open -- or you can get a blurred result due to camera-movement.
A good book to help understand these concepts is Bryan Peterson's book "Understanding Exposure" -- it's specifically written to help new owners of DSLRs understand how to take control of their camera by teaching you how to shoot completely in manual mode for more creative and better looking results. The Scott Kelby Digital Photography series of books (I think there are 4 volumes now) is also very popular.
Tim Campbell
5D III, 5D IV, 60Da
