I made this little guide for beginners on how to use your (d)slr camera and how different settings effect the picture. Hopefully this will help someone.Basic settings:
Iso or asa(used with films at times) is the sensors(or films) sensitivity to light. Higher the iso, higher the sensitivity of the sensor is to light. When you use higher sensitivity, naturally the sensor doesent so much light so create the image, but higher sensitivity creates more noise. You should use low as possible iso to maintain the quality of the picture, but sometimes(usually) you cant use lowest iso of the camera to use other settings(shutterspeed and aperature) as you want. Iso is usually the first thing you should compromise on, but if you want to maintain quality you cant compromise with this too much, unless really needed to.
Better sensors can use higher iso without getting too much digital noise(same on films), so you need to learn how your camera behaves on this matter.
There are ways of getting rid of the noise in post processing, but it will make the image softer and lower the quality.
This is the hole in the lens that limits the light from getting to sensor. Lower the f-number more light will get to sensor(with same shutterspeed), but focused area on the pic will be smaller with lower f-number allso, thats why you need to limit the light with this usually. Zoom lenses mostly have higher minimum f-number, than prime lenses(no zoom). Cheap zoom lenses have changing minimum f-number depending on how far you zoom, so if you want to shoot wide open all the time and then zoom, it will limit the light from getting to sensor, so you will need to change other setting to match changing f-number. Usually high minimum f-number makes zooms a poor choise for low light situations or if you want really small area in focus on the pic.
This is usually the second thing where you should compromise, if you dont want background to be too blurred.
When using lens wide open(lowest f-number), image quality isnt as good as using bit higher one. Image is softer, there is more chromatic aberration and stuff like that, unless you use bit higher f-number than the minimum. How much image quality will get better with using higher f-number depends on lenses.
Shutter speed(exposure time):
This is the time that camera will let light on the sensor. Longer the time is more the camera shake/motion blur will show, so you dont want to compromise with this too much. Thumb rule to eliminate camera shake is to use ateast same shutterspeed as you lens has focal lenght, meaning with 50mm lens you should use 1/50 sec shutterspeed. Longer the focal lenght(more zoom) is more easier hand shake will show, this is why thumb rule says you should think about the focal lenght. But 1/50 sec wont stop motion blur of moving objects very well, and stopping the motion of moving objects might even take like 1/5000 shutterspeed or shorter, usually something between 1/100 to 1/400 sec is ok tho. By using tripod you can eliminate the camera shake completely, so it will allow you to make exposures of even several hours. Naturally tripod wont stop the world around the camera, so moving people for example will get blurred when using long exposure time, but you can use this as advantage to get cool effect for the pic.
How long shutterspeed you can use depends how steady you can keep your hands, if you got shaky hands you might even need to double the thumb rule. If you want to take extreme sharp pic of still model you should use something like 1/125 to 1/250 sec shutterspeed. You might pull the pic out even with 1/80 sec, but you will get motion blur on the model more times out of ten frames, so better to play it safe and use shorter shutterspeed, so you wont miss a good pose.
This usually is the last thing you should compromise on when choosing the right settings, but sometimes you will need to compromise on all 3 of these settings to get the right exposure. If you need to compromise with this too much you will need a tripod, then you can allso use lower iso and higher f-number allso, since the camerashake is eliminated completely enyways.Focal lenght:
Cheap dslrs have cropped sensor(x1.5 crop on nikons and x1.6 crop on canons(exept x1.3 on 1d series) and meny other brands), so you will get more out of the millimeters than you would with film or full frame sensor. This can be good thing when you want to shoot with long focal lenght at far away objects or macroing. Focal lenght has effect on how big area is focused with same f-number. Wider lens(shorter focal lenght) gives wider focused area. Difference on this matter with 10mm lens and 250mm lens is really huge, since you will notice difference even on 10mm and 20mm. Focal lenght wont change depending on sensor size, but it seems that way because smaller sensor doesent show as much on frame on the corners. Focal lenght allso has effect on the perspective of the picture, wider the lens is you need to go closer to subject and when you look something closely naturally the perspective changes quite alot to what you get from far away and "zooming in" using longer focal lenght. When using shorter focal lenght(wide angle), it pic will show wider area of the background too, even if you frame the corners on the pic same way as with longer focal lenght. Change of perspective should be the main reason for choosing the focal lenght, but sometimes you have to use longer focal lenght to get pic of the object you want to. You cant usually get close enough of bird for example to shoot with 10mm lens without scaring it away.
Here is example(from wikipedia) of change of perspective to focal lenght:
http://upload.wikimedia.org/wikipedia/commons/e/e5/Focal_length.jpgChoosing the right settings:
There is no right settings. Settings you want depends on what you want from the picture. Choosing the right settings for right situation is where you need to do the most learning about the technical side.
Effects of the light with different settings:
Light is measured by by stops. Settings for iso, exposure time and f-number are usually changed by 1/3rd of stops.
Double iso number is one stop more light.
Double exposure time is allso one stop.
Full stops for f-numbers goes like this:
f/1.4 - f/2 - f/2.8 - f/4 - f/5.6 - f/8 etc
If you change one setting iso for example one stop down(for example from 1600 to 800), you get same exposure if you turn if you turn exposure time one stop up(from 1/200 sec to 1/100 sec). Naturally you can change these setting like this by 1/3rd of stop for example.Reading the light meter:
Usually light meter shows from -2 stops to +2stops of under/over exposure. Most cameras show the stops by 1/3rd of stops. They are displayed like this usually -2 . . -1 . . 0 .. +1 .. +2 And 0 is the right exposure, +1 is 1 stop overexposure for example and dots are 1/3rd of stops between full stops.
If you use right metering mode you should get the exposure "right", but not allways the "right" exposure is what you actually want from the picture. Learning to use right exposure mode and exposuring the pic the way you want takes some practise and/or some testing for the situation.Dept of field(area in focus):
This depends on 3 factors: f-number, focal lenght and how far the focus is. Sensor size allso effects this, but for very different reasons. When you got larger sensor you will need to get closer to what ever you are shooting with if you want to frame it the same way than when using smaller sensor. Getting more close will effect on how close you will need to focus and closer you focus more blur you get. Or then you will need to use longer lens and that has the same effect as focusing closer in this matter. If you use same focal lenght and and shoot at same distance, the image area will be larger, focused area will remain same, but there will be more blur on the corners naturally since larger sensor will show larger area on the frame.
When you want small area focused with alot of background blur, you should focus as close as possible, use lowest f-number possible and use longer focal lenght. For headshots with totally blurred background something like like 50mm lens with f/1.8 should be enough unless you look for extreme small area in focus. 50mm with f/1.8 will usually even have too small area. Then you look for focused area to be all over the frame, you will need to use higher f-numbers, how high depends on you lenses focal lenght and how close you focus. If you shoot macro you cant get the whole frame in focus even if you use highest possible f-number and wide as possible lens(you cant use wide angle lens for macro since you cant get close enough with one).
Overdoing the background blur or having too much on the frame in focus will end up with bad resaults, but for example landscape shots cant have too much in focus.
Foreground blur just like background blur can show up on things that fall out of focused area. However foreground blur doesent show up as easilly as background blur, because to get foreground blur, you need to focus far away and that will increase the area in focus.Exposure modes:
Some cameras have different exposure modes or theyr called in different names, but these are the main ones:
This is what you should use when situation doesent require really fast change of settings(light changes fast). Especially when learning to use your camera you should use it on full manual mode, so you learn what effects different settings have. If you go with full auto or half auto mods you wont learn to use your camera fully. This mode is allso where you got most creativity, since you can adjust the settings just the way you want to.
This is something you should never use or atleast use it on very special cases. It chooses all settings for you(not all cameras have auto iso tho), so you cant control how big focused area is or choose right shutterspeed on moving objects.
Aperature priority(AV or A):
This is the only auto mode i personally use. It lets me choose iso and f-number. Choosing the f-number myself i can control the focused area and choosing iso i can control what the shutterspeed will about be. On some cameras you can choose min to max shutterspeed, so if you suddenly get less light to camera because of light change the pic will be less exposured, but i wont get motion blur. You can change exposure when/if processing the picture from raw http://forums.d2jsp.org/index.php?showtopic=25681018&f=265
Changing exposure in raw is same as changing the sensitivity. Since raw has more data of pic than jpg or whats showing on the screen, you can bring up stuff by changing the exposure to certain limits(depending to original iso and sensor) and it will look allmoast same as only changing iso on camera.
Shutter priority(TV or S):
This is where you choose the shutterspeed and f-number will change automaticly. Its good when you shoot fast moving objects(in changing light) and when stopping the movement is more important than area in focus.
This is like full auto, but you change iso yourself. Basically you can change on how much the camera concentrates on shutterspeed over f-number or other way around. This is better than full auto, but still shouldnt use this other than extreme situations.Metering modes:
Choosing the right metering mode is important, so that you know what the camera reads the metering from to light meter and you get the right exposure for the situation. Some cameras have more or less different metering modes and for different brands they might have different name.
This reads the metering from the smallest area(1-5% of frame depending on camera model). Its good when you want to read exposure from small areas, for example when shooting at birds(that dont cover much of the frame) with strong backlight. It reads the exposure from focus point used.
Multi spot metering:
This function usually doesent exist in cheaper dslrs. This is where you can choose several spots where you read the exposure and camera will calculate right exposure between them.
This reads the metering from whole frame calculating right exposure based on all light that comes to sensor. This is good when you dont have big changes on the the lights. If half frame is heavilly lit and other half is much darker, it will calculate exposure between them, this causes darker areas to be too dark.
Center-weighted average metering:
Here camera will adjust the metering more on the center of the frame, so if you got heavy light coming from corners it doesent make the center too dark. With this mode camera will concentrate about 60-80% to the center frame.
This is basicly same as spot metering, but reads the metering from 10-15% of the frame. Usually reads it from the focus point like spot metering.
Multi-zone metering(Evaluative metering, matrix):
This is where camera reads light from several zones automaticly, but reads more from the focus point. This is the best choise generally. personally i use this or spot metering all the time and spot metering only on special situations.Focusing modes:
With this mode camera will try to autofocus continously if subject(or your camera) moves while your focusing, trying to keep the right focus all the time.
This is good when shooting at moving objects, like running dog or stuff like that.
This is where camera will focus automaticly and lock on it after finding the right focus. If you dont have focus point at the spot where you want to focus, you can focus first with this and then frame again, but be carefull of keeping the same distance.
This focus mode is best for most situations, because ai-servo might try to find the right focus too hard all the time and you cant take pic if camera tries to focus.
No autofocus naturally, you focus from the lens. When using manual focus, you should still keep in mind that camera reads light metering from selected focus point, even tho it wont focus the lens to that point automaticly.If you got something to ask, ask here or pm me. But before asking make sure you read this all and try to understand it.
Sorry about typos or bad english, but hopefully you get what im saying