Sort coffee break - time to jump in here again.
Mark, think of a coffee mug (now why does that spring to mind?) into which you have inserted a funnel and are going to pour in 1 litre of hot water. Yes I know, large mug. You pour in this 1 litre and note the time which for arguments sake takes 1 minute. Now you want to halve this time (30 secs) so what do you do - of course, double the size of the funnels hole. End result, the same 1 litre of water but in half the time.
The same applies to light entering the lens. Set f/5.6 on your lens and note (in the viewfinder or display) what shutter speed is being shown which in this example we'll say 1/125 sec. Now, if you decide this is too slow a speed (moving leaves in the wind say) and want a faster speed you need to enlarge the aperture (hole). Open the aperture by one stop and you'll notice that your shutter speed increases, also by one stop. The same amount of light overall enters the lens only you've set about capturing it in a different way.
The question of whether you set Av or Tv on the camera depends both on the subject, but more importantly, the effect you are trying to achieve. Shallow depth of field = large aperture whilst a larger depth of field = a smaller aperture. Remember though, depth of field (DOF) also depends on focal length. Setting f/2.8 with a focal length of 100mm will giver you a very shallow DOF whilst the same aperture setting at 300mm will give you even less DOF.
Grasping these basic principles will allow you to move onto Manual more quickly. Here you can set both Aperture and Shutter speed to your liking although even here the camera will indicate to you how far wrong it thinks you are. Fore instance, setting f/5.6 in manual and then setting f/125 the viewfinder information will indicate either that you are spot on or that you are under or over exposing. Here you have to make the judgement call based on experience.
Also, take note of the histogram but bear in mind that when shooting RAW the histogram is a representation of what the embedded jpeg image looks like so use it only for guidance and don't treat it as gospel. Yes, the lcd image is a jpeg image as RAW data has first to be processed in order to be viewed. What I mean by using the histogram for guidance is that in the case of your tree image (other thread I think) most of the image contains shadows with nothing that one could really call highlights. Therefore the histogram will show most of the detail to the left which you would expect.
One other thing not related to this really. Have you considered setting your camera up so that you can focus using your thumb and meter with your index finger? Going into Custom Functions, scrolling to C Fn IV and setting this to 3 allows you to use the AF-ON button to focus using your thumb whilst a half depressing of the shutter button now only controls the metering and not the focusing as before. This takes a bit of getting used to but once mastered you'll never go back I promise you. It's great for subject such as our Robin friend who keeps bobbing from one branch to the next. Now you can quickly adjust focus using the AF-ON button using your thumb whilst firing the shutter as normal with the index finger. It's not only convenient but overall a lot faster. Using only the shutter button means you keep having to release it followed by a half press to set the focus (and metering) before finally pressing the shutter. In the meantime the little darling has flown off.
That it, coffee break over - back to the grindstone.
27-10-09, 12:29 AM
