With many friends having kids in their family, interest in having an SLR (Single Lens Reflex) camera to snap some great pics of their kids is picking up. Some of them have asked me to explain the various terms and things associated with photography. This is the first in a series of posts that I plan to put up, based on my learnings from various gurus, magazines, online videos, books etc.
In modern DSLRs, there are tons of settings you could tinker with to make a snap look different. But for most part, I have had to think of 4 settings:
- Aperture
- Shutter Speed
- ISO
- Metering
Aperture, Shutter Speed and ISO form a triangle for a perfect image. Bryan Peterson, in his book "Understanding Exposure", mentions that there would be atleast 6 different combinations of these values, which will "correctly" - no washout, no dark image - create the image. But there is always one of those 6 combinations, which effectively makes it a "creative" exposure!
In the first post, I would be talking about Aperture and how various values affects the image. Let's first start off with understanding some technical aspects of this parameter. Most of us (actually all those who completed class 10) know different kinds of lenses - normal, convex, concave - and terms like focal length (f). In photography, the 'f' number is an indication of the size of the opening made in the lens to allow light.
E.g: If I'm clicking some shot by zooming my lens to indicate say 50mm and the f number is f/4, it means that the diameter of the opening in the lens to allow light to get through to the camera sensor, is about 12.5mm (50/4). So higher the number, the smaller is the opening. Remember, the number is in the denominator! So at 50mm, f8 means an opening of just 6.25mm.
In many a literature, you will find this mentioned a little different. Instead of f/4, it would just appear f4. or f4.0. They all mean the same and we as readers of those numbers should understand the terminology correctly. So when someone says terms like a fast lens or open wide, it means numbers like f/1.8 or f/2.8. Smaller the number, wider the opening, and more light coming through the lens onto the camera sensor.
Ahhhh, now I understand the 'f' number! In that case, shouldn't I always shoot at the maximum opening so more light comes in and I can take a quick snap?
Back to some physics basics and properties of lenses! Scared you already??? Let's make it simpler. Changing how wide the lens opens not just has controls how much light comes through the lens, it also affects something called depth-of-field. You must have clicked many images and seen many more online or in books or magazines. You will see some images where just 1 or 2 things are in sharp focus and the rest a blurred and in some images, everything from the front to the last thing at the back in an image is sharp! The amount of "field" which is in focus and sharp is simply the "depth-of-field". Hope the above was clear. If it ain't, let me know and I will explain it using Physics!
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| Img 1. Aperture & Depth-of-field |
Above is a set of 5 images which have been shot at various f-stop numbers - f4 to f32. My focus point was the middle doll.
In the left-most image, only the middle doll is sharp and everything else from the edge of the table, to the 2 black objects at the back , the sofa, the curtain, all are blurred!! As the f number is increased, the depth-of-field increases. In the right-most image, I can clearly make out the pattern of the table, its edges, the 3 dolls, the 2 remotes, the texture on the sofa and the design on the curtain at the top - everything seems to be in focus/sharp.
So going back to the statement of Bryan Peterson, only one of those f numbers is what you want depending on what you are clicking.
Small f number - Wide Opening(more light) - Shallow Depth-of-field
Big f number - Small Opening (less light) - Large Depth-of-Field
Now I know. When I'm clicking the image of my kid, my focus is only the face and do not want anything else in the background affect the shot. So I use a small f number like f4 (the smallest my lens will allow). When I'm clicking a scenery and I want the stream just in front of me and the hill in the horizon to be as sharp/focussed, then I use a bigggg f number like f22 or f32.
You nailed it!!!! Also remember, altering the aperture means, tinkering with the amount of light entering in. So changing aperture will require you to change the shutter speed and/or ISO to get right amount of light! I shot the above sequence of images, in "Aperture Priority" mode. This means, that I will set the aperture/f-stop value, and let the camera decide how long the shutter needs to open to get a proper image. As you can imagine, the higher f-numbers needed me to put the camera on a tripod to get a sharp image as the shutter time was longer!
