Open wide:
How do I know that this picture (taken at a recent magazine shoot) was taken at f/2.8?
Given the lens (a 16-35mm f/2.8 lens), I look at the shape of the out-of-focus lights in the background. If the aperture was stopped down, they would be hexagonal or octagonal. Round out-of-focus spots means the lens was wide open: f/2.8, therefore.
Again, why “fast” lenses?
A tip for newcomers to SLR photography.
I often hear: “Why do I need so-called “fast” lenses – like the 50mm f/1.8 lens Michael keeps talking about? Surely my 18-55 lens also covers 50mm?”
Well yes it does. But:
- Less sharply. A “prime” (i.e. non-zoom) lens is sharper.
- A prime lens is also smaller and lighter.
- And especially: the prime lens has a lower minimum “F-number” – i.e. a larger aperture. The lower the “F”-number, the better. Your kit lens is f/3.5-5.6 (meaning zoomed out it can go as low as 3.5; zoomed in it can go only as low as 5.6. The 50mm f/1.8 can go as low as 1.8).
Why is this important?
So in today’s class I took two shots of a student in available room light. One at f/5.6, and that is what you would get with your standard “kit”-lens. It looks like this:
Two things happen:
- Because of the small aperture (high “F-number”), the camera has to keep the lens open for a long time. This means that unless I use a tripod and tell the subject not to move, in indoors light I will get camera shake (the shot needed 1/10th of a second). And sure , do.
- The lower the “F” number, the shallower the depth of field, i.e. the blurrier the background. The higher the F-number, the sharper the background.F/5.6 gives a background that is somewhat blury.
Now look what happens when I use an aperture of f/1.8 (for which you need a lens that can do that, like the 50mm f/1.8 lens):
Much better – a pretty dramatic difference on both counts!
So the best way to immediately get great portrait shots is to:
- Get yourself a 50mm lens. On most cameras this is simple; do note that on a Nikon D40/D60/D3000/D5000 you need to manually focus this lens (that is why I recommend Canon cameras at the entry level).
- Learn Aperture Priority mode (A/Av) and use a low “F-number”.
- Turn the camera sideways and get close!
Have fun.
(Wow, three numbered lists in one blog post!)
Eye
Portraits? Then use a 50mm f/1.8 lens (affordable, fast, sharp) and shoot in Aperture (A/Av) mode with it wide open (preferably by window light).
Look at this recent available-light shot of a student:
This gets you the dual advantages of low-light ability (no flash needed!) and blurry backgrounds. As long as you make sure the closest eye is the sharpest.
So, set your camera to the widest aperture (the smallest F-number), use high enough ISO (indoors this might be 400-800 ISO), and use one focus spot, and aim that spot at the closest eye. Click!
f/1.8 lens, stopped down, shot with f/1.4 lens, open
I have many times recommended 50mm f/1.8 lenses, and I’ll try to inspire you once more to go out and get one right now. Most manufacturers have a cheap lens like this:
As you will have heard me say many times, this lens is cheap, small, light, fast and sharp.
Ideal for portraits or for low-light subjects or images where you want to dramatically blur the background. If this lens is not in your kit yet, I recommend you add it immediately.
As you will have seen in the previous post, I shot Prof Dawkins yesterday with just sich a lens (my 50mm f/1.4).
leave a comment