02-09-2014 12:47 PM
I am learning my T4i I just bought.
It looks as if you set the dial to "P" it is the same as "Auto" if you leave all the settings as they are (default)?
I realize P gives you options whereas Auto doesn't.
02-09-2014 04:08 PM
Yes - "P" (Program mode) does give many options that full automatic (green box on the mode dial) mode does not offer.
Auto is, for the most part, fully automatic and will not allow the user to over-ride camera decisions. It's "safe" in that if you are very new, most of the buttons that would change settings are locked out.
Program mode does allow you to control all settings... you can decide if you do or don't want flash, you may set set your ISO, etc. Although when you meter a shot, it's going to select initial settings much like it does in full Auto mode. It will pick both the aperture and shutter speed (it will pick the ISO as well if you dialed the ISO to the "Automatic" setting for ISO choice). But the difference is that with Program mode you can change those settings before you take the exposure. You can do this because of a feature called "Program Shift".
Getting a correct exposure means getting the right amount of light to the sensor. You can reduce the size of the aperture opening to cut the amount of light that flows through... but increase the shutter exposure time so that ultimately the same amount of light ends up reaching the sensor.
It turns out that the settings aren't arbitrary. Light and lenses behave differently when you use large vs. small aperture sizes. Small aperture sizes increased the range of distances at which subjects will appear to be in acceptable focus. So for a landscape shot, you might want everything to be focused so you'd pick a small aperture. With that small aperture however, comes the need to keep the shutter open longer. If you were shooting action photography, you'd want a short exposure time so that you can "freeze" the action and avoid having motion blur. If you were taking a portrait, you might want your subject focused but deliberately de-focus the background. For any given amount of light, there are typically quite a number of combinations of aperture setting and shutter speed setting (and even ISO sensitivity setting if you add that to the mix) that would all result in a "correct" exposure. But the ability to change settings provides some very creative differences -- the amount of light collected may be the same, but the image will not be the same.
For this reason, these settings are referred to as the "creative zone" on your camera. You can alter the exposure settings, still collect the "equivalent" amount of light for a correct exposure, and yet the creative result can be completely different.
If you aren't familiar with the basics of exposure, this is a great video to watch:
"Program Shift" is the most automated way to do this. The camera will START by finding a "correct" exposure, but once you've metered, you can adjust the main dial on the front of the camera (just behind the shutter button) and the camera will "shift" the exposure, trading stops of exposure in aperture for stops of exposure in shutter speed. The camera will prevent you from taking an exposure that isn't possible (e.g. if the maximum apeture size possible with your lens for your focal length is f/5.6, it will NOT let you dial down to f/4 (even though a different lens or even a different focal length might allow that).
You can think of the "Program" mode as a much more powerful version of the "Automatic" mode because Program allows for Program Shift and full Auto does not.
As you get more experience, you'll realize that sometimes you know that you just want to shoot a portrait at, say, f/4 to control the depth of field and keep it shallow (depth of field is the range of distances at which the image will appear to be acceptably in focus)... or you want to shoot a landscape at f/11 or f/16 (for a very broad depth of field where everything is in focus). You will realize that for sports, you probably need to shoot with a minimum shutter of 1/500th (sometimes you can get away with 1/250th -- but most of the time 1/500th (and faster is preferred) is required). So rather than using "Program" mode to let the camera meter, and then rolling the wheel to "Program Shift" until your aperture or shutter speed of choice turns up (because you'd have to do this for every shot -- it's not retained. Each time you re-meter for the next shot you have to re-shift) -- it's easier to just pick the "Av" (Aperture value priority) or "Tv" (Time value priroity) modes... because now you can just set the aperture or shutter speed you want and let the camera pick the complimentary setting.
02-10-2014 01:41 PM
The video explaining the relationship between aperture, shutter, and ISO isn't mine... that's Matthew Gore's. That's a link to his publicly posted YouTube video page. If you click the "YouTube" link in the lower right corner of the video it will take you to his YouTube page -- and ultimately you can use the "about" link on his YouTube page to find his web page at lightandmatter.org.
There are, of course, numerous books and videos that try to explain how to shoot on "manual" by explaining the relationship between aperture, shutter, and ISO. I try to remind people that it's not just those three... often you CAN change the light being contributed to the shot by moving your subject to a location with better lighting or by augmenting the shots with your own lighting (I come across a lot of questions which lead me to suspect that it may not actually occur to some shooters that many shots can be fixed just by moving to a different location.) I happen to think this one is one of the best I've seen.
I don't see much explaining the difference between auto & semi-auto modes. Many people are unaware that the key feature of Program is the fact that you don't have to take the exposure it initially offers when you meter a shot... you get to use Program Shift to pick different "equivalent exposures". Also you get to use exposure compensation in P, Tv, or Av modes.
02-10-2014 02:57 PM - edited 02-11-2014 12:39 PM
@Tim Campbell. All understood. Just that trying to explain that 1/500 @2.8 & 1/250 @f4 Allows the same amount of light on the film plane/sensor but the focus will change... And watching their eyes glass over like I'm speaking Klingon... Sometimes I go to the cup of water... 1/500 @f2.8 will pass the same amount of water into the cup as 1/250@f4... And watching their eyes glass over. That's when I tell them to shoot in green-box mode ;-}>