Question: I have purchased my first DSLR (a Canon 500D) and have been playing around quite a lot within the aperture priority mode, with auto shutter speed and ISO.

Anyways as I would like to become a better photographer I would like to start taking *all* my photos in Full Manual mode.

Are there any general rules that I should use to help me select a shutter speed and ISO combination? Currently I am using trial and error and while I get there in the end, it often takes a while. I understand that I will learn this with experience, but anything to get me started will help.

Further to this, do most 'Professional' photographers set these manually? The auto settings work so well for an average shot, and it seems too time consuming to adjust these for every angle and light variation.

Answer: 
Shooting manual mode doesn't make you a better photographer, understanding what all the settings effectively do will. Your camera has three basic settings:

* **Aperture**: Use this to control depth of field (DoF). This is usually the most important setting to most photographers, as it influences both subject matter and composition. You're not going to be taking pictures of things if they're too big to fit into focus.
* **Shutter speed**: Use this to control in-frame movement and blur. While very important, there's really not much of a difference in a typical print between a normal, semi-still image shot at 1/250 and 1/8000. As a general rule, if you're trying to keep motion frozen you want this above 1/125.
* **ISO**: This determines the "image quality" of an image. Keep this as low as possible.

The most common strategy is to first set the aperture, make sure that you have enough DoF to cover your entire subject (or whatever you're trying to achieve). Have your ISO set to the lowest possible value (without going into 'extended ISO' modes) and check your shutter speed. Is it at least 1/60 or 1/125? No? Bump the ISO up a stop.

Your 500D has a exposure level reading that you can see the bottom of [its viewfinder](http://www.bobatkins.com/photography/digital/500d/t1i_viewfinder.jpg). Use that to determine where your exposure needs to be. For example, if you're dialed in at f/5.6 and 1/500 @ 100 ISO, but the meter reads -2, you know you're going to underexpose with those settings. You can change your shutter speed to 1/125 or increase your ISO to 400 to get to the 'correct' exposure. If it reads +1, increase your shutter speed or lower your ISO to compensate.

All that said... experiment. Play around with it. You're shooting digital, who cares if some of your shots are blurry?

You can also try using the Sunny 16 rule, it might help you 'get' exposure. The Sunny 16 rule says: on a bright, sunny day, you can set your aperture to f/16 and your shutter to the same speed as your ISO value (so 1/100 for ISO 100, 1/400 for ISO 400). On a sunny, but slightly less so day, try f/11 or f/5.6 on cloudy day. 

Manual mode's number 1 use is for consistency. When you take a series of photos in non-changing light conditions, you want your known color values to stay as close to each other as possible. With constant metering, especially in-camera metering, you can't hope for that kind of consistency. Point your camera at a white wall, look at the readings, then put a piece of black paper on that wall and see how wildly the meter reading changes.

There are also situations where in-camera metering doesn't do you any good, mainly in the studio. I don't know of any camera that meters for strobe/flash light effectively. 4
First, stay away from the "icons" on your 500D. These are the automated settings, and offer no freedom to choose your aperture and shutter speed.

Once you do that, here are four simple rules I follow:

Rule #1: stay above 1/60.
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If you are using a tripod, you can go below this speed, but when hand holding the camera, always stay above this speed. If you do not, you will tend to get blurring from camera movement. Yes IS can help....but just remember the rule, its easy.

Rule #2: Keep your shutter speed 'above' your lens focal length.
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This also helps ensure reduction of blur from camera shake. If you are shooting at 200mm, be sure your shutter speed is above 1/200th a second. If you are shooting 75mm, stay above 1/75th. If you are shooting 35mm, stay above...careful...1/60th.

Rule #3. Remember to choose bigger aperture numbers when you are shooting things farther away.
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When shooting landscapes or other scenes, or when you want your background in focus, choose a "bigger number" for aperture. This actually selects a smaller aperture, but the result is that you get more distant objects in focus, even if you are focusing on a subject fairly close by. Basically, the camera is 'squinting its eyes" , just like you do, trying to bring distant objects in focus. This suggests that you can use aperture to manage the 'look' of your image, which indeed is what you do: pick an appropriate shutter speed (rules 1 and 2) and then adjust aperture until you get the look you want, within rules 1 and 2.

Rule #4: if you can not take your shot within any of the above 3 rules, adjust your ISO up, until you get a rule to apply.
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So if you shoot at ISO 100 or 200 (and you should basically all the time), move up to ISO 400, then 800, etc until you can follow the rules.

Finally,

Rule #0: Check your ISO DAILY!
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Always check your ISO before you use your camera, as you will be very upset when you shoot a critical event at ISO 3200 and have awful grainy shots when you didn't need ISO 3200.