I'm an absolute novice at taking pictures in manual mode, so I wasn't even thinking of writing a post on it. I just started using this mode less than a week back and am still trying to understand all the nuances involved. However, when I came across this post by Aparna of My Diverse Kitchen, a fellow Goan, an ardent blogger and a fervent photographer, I decided to take one step ahead and take part in her exercise.
So here's the picture. The camera I used is a Canon EOS Rebel T3i. I don't have a 50mm f/1.8 lens (hint hint to my hubby), so I stuck to my 18-55mm kit lens and as suggested by Aparna, set the focal length to 24mm. I set the ISO to 100, changed the aperture to f/4.0 (unfortunately it doesn't go any higher in my lens) and experimented a bit with the shutter speed. Here's one where the shutter speed is 1/15s.
In this picture the focus is on the orange and lemons. The rest of the background appears a little blurred.
As I told you earlier, I'm no pro, but let me roughly explain my understanding of what aperture is. Aperture is basically the opening in your lens through which light comes in, and is measured in f-stop numbers. The smaller the f-stop number, the larger the aperture and more the light coming in. The larger the f-stop number, the smaller the aperture, with less light coming in. So for example, f/4.0 has a larger opening than f/10. I know, I know, it's counter-intuitive (because it's a fraction).
Aperture decides the depth-of-field (DOF) of the photograph. DOF is the area behind and in-front of the main subject in the picture. In other words, it's the area which is blurred - or sharp - in a photograph. DOF is shallow if the main subject is sharp and rest of the background is blurred.
In the above picture, the oranges and lemons are in focus while the rest of the background play the supporting cast. A bigger aperture (smaller f-stop number) blurs the background more and creates a shallower depth of field. A smaller aperture (bigger f-stop number) creates a greater depth of field which means the background will be sharper than that of a bigger aperture.
So why not always use a bigger aperture (more light coming in gives us a better picture, duh) you may wonder. It depends on what kind of photograph you'd like to have. For example if you want a picture which focuses only on a plate of food or on a specific person with the rest of the background out of focus, in order to highlight the main subject, then it makes sense to use a bigger aperture. However, if you want to take a picture of a beautiful scenery and want everything to be in focus, you should use a smaller aperture.
Here are two pictures for comparison. The picture on the left has a bigger aperture (f/4.0), hence a shallower depth of field. The oranges and lemons look sharp, while the coffee mugs and rest of the cast look blurred. The picture on the right has a smaller aperture(f/10), hence a wider depth of field. The mugs et al, look clearer.
One more term to remember when changing the aperture is "shutter speed"- the duration taken for the shutter to open and close. When the aperture is bigger, more light comes through the lens, hence the shutter speed should be faster, otherwise the picture will be overexposed. Likewise, when the aperture is smaller, less light comes through, so the shutter speed should be slower in order for the required light to come in.
In the above pictures for example, for the bigger aperture (f/4.0), I set the shutter speed to 1/15s (0.066 seconds) - which is faster than 0.3s which I set for f/10. You can keep varying and experimenting with the shutter speed till you get the picture you envision. Ofcourse, the light source and time of day can affect the quality of the picture. So also could ISO which determines the sensitivity of the camera's sensor to light. I don't want to go deeper into that, because it will leave me more confused than you, so let's stick to whatever I just explained. All I can say is if your picture appears too dark, increase ISO and if too bright, decrease it. If ISO is way too high then the picture will be grainy ( "noisy" in camera jargon).
If you want to take two pictures to compare, using a tripod makes sense. I did not since my shipment hasn't arrived yet, so I took these pictures holding my breath, trying my best to keep my hands in place and keeping in mind what exact position the previous picture was taken in. Believe me, it takes hell lot of a time and a good number of pictures to get the exact same position (I still haven't been successful, check out the basket at the back) so either use a tripod or a pile of books like Aparna suggests.
I still have a long way to go with food photography, and am still happily snug like a bug using macro in the auto mode, but hoping to come out of my comfort zone some day and take advantage of my DSLR even more.
