Understanding Lens Aperture
One of the most difficult things to understand in photography is your lens' aperture, and the effect it has on focus. It is annoyingly complicated because the numbers seem to go backwards, and the effect they have can be very obscure unless you are shooting highly controlled, methodical pictures of little inanimate objects on a table with a tripod... Which is what we're about to do... ;-)
LARGE APETURE:
- f/1.0 (exotic, expensive)
- f/1.8 (very fast, but affordable)
- f/2.8 (fast for zoom lenses)
The best way I have heard this explained is as follows: The smaller the number, (f/1.0 for example) the smaller the number of things in focus. The higher the number, the higher the number of things in focus. (f/11.0 for example)
The reason it is confusing is because you forget it's a fraction. But that's why there is always "f/" in front of the numbers. Those numbers, f/1.0, f/1.8, f/2.8, those are denominators. And as we learned in elementary school, the BIGGER the denominator, the SMALLER the number's real value... (1/4 is smaller than 1/2, etc... So f/4 is smaller than f/2...)
(WARNING: The next paragraph is the really complicated part; skip it if your brain hurts already!)
Okay if you want to know EVERYTHING, the F in "f/1.8" stands for focal length. On this lens for example my focal length is 50mm. That was about standard for 35mm film, standard meaning it's about the same magnification as our human eyes. So if I set that f/1.8 lens to f/2, for example, 50mm/2 equals 25mm. This means 25mm is the diameter of that apeture opening. If we changed the apeture all the way to f/22, 50mm/22 equals about 2.2mm. That's one tiny opening! (See the picture below.)
Advantages to a "FAST" apeture:
1.) The bigger the opening in the lens, the more light comes in, giving you a brighter exposure. This either allows you to shoot in dimmer light, or shoot in normal light with a really fast shutter speed.
2.) The bigger the opening of the apeture, the more stuff will blur in the background and foreground. A blurry background is one of the key parts of almost every professional portrait. It's called "background separation."
SMALL APETURE:
- f/8 (standard)
- f/22 (pretty much everything is in focus)
(Remember, it's a fraction, so the bigger the number, the bigger the denominator, the SMALLER the real value...)
Advantages:
3.) Everything is in focus, sharp, great for larger groups of people, or landscape photography of course...
2.) Less light = slow shutter speed = blurring water and other moving objects, if you use a tripod.
IMPORTANT Disadvantage:
1.) Setting your lens all the way to f/22, if you're shooting digital, will cause your images to be slightly fuzzy, because of a complicated thing called diffraction. It has to do with how light photons hit the pixels on your digital sensor, and it's advised to set your apeture for f/8, f/11, or f/16 for maximum image sharpness... (FILM is affected differently by diffraction...)
:-)
EXAMPLE: ~ Wide apeture, low light, ONE subject in focus. ~ Blurry background, "shallow" depth of field. INFO: 50mm lens, f/1.8. Subjects about 1-2 feet away from the camera.
EXAMPLE: Small apeture Everything in focus, "long" depth of field. INFO: 50mm lens, f/22. Subjects about 1-2 feet away from the camera. If it were that easy, we would be done now. But two other factors affect your focus and blur. The distance between the camera and the subject, and how wide-angle or telephoto your lens is... Logically, the closer you are to your subject, the more blurry the background is. And, the more you zoom in on a subject with your lens, the more it isolates it from the background as well...
WIDE ANGLE: Wide angle lenses inherently have "longer" depth of field. It will be harder to blur the background with a wide angle lens. If you're shooting landscape, set the apeture to f/8 and enjoy. If you're shooting portraits however, the background can get distracting if you're not VERY careful... IMAGE INFO: 17mm, f/3.5 Subject just inches from the camera.
TELEPHOTO:
Telephoto lenses inherently have more "shallow" depth of field. This is the "step back and zoom in" trick- notice that eeyore is the same exact size in this image and the above image? AND, they were taken at the same apeture. Yet the 2nd photo has way more blur happening, simply because of the focal length of the lens.
What I'm trying to say is, f/3.5 on my 17mm lens looks different than f/3.5 on my 150mm lens, a LOT different!
IMAGE INFO:
150mm, f/3.5
Subject 4-5 feet from the camera.
See how using the SAME apeture but stepping back and zooming in will help you isolate the subject?
Okay so for those two shots above, I was either wide-angle and really close, or I was telephoto and kinda far away. I hope that you are curious and wondering- what happens if I get close AND telephoto? Well first of all, you're probably going to need a macro lens... Luckily, this particular 150mm lens is indeed a macro lens. Whoa, Eeyore fills the entire viewfinder, and the background is *gone*! Obviously you don't want to get THIS close when you're shooting a portrait. Most of the time you're going to be shooting from normal distances, with normal lenses...
OH, ONE LAST THING!!!
AVOID CROPPING your images, if you can. It can kill your shallow depth very quickly!
For the shot on the left, I got as close as I could and didn't crop at all. For the shot on the right I stepped back a few feet, and I took the image in photoshop and cropped it to look the same.
The camera settings were identical, and yet because of the different distance one image has MUCH more background blur!
SO in summary, the ways to achieve a nice, blurry background:
~ Open up your apeture. (f/1.8, f/2.8, or maybe f/3.5 or f/5.6 if you have a "kit" lens)
~ Zoom in, if you've got a zoom lens. Or, if you've got a fixed lens,
~ Get CLOSER to your subject...
~ Also, try to find subjects that have a distant background. This is one thing you will see professionals pay CLOSE attention to, moving side to side just a few feet in order to "frame" their subject with the best background...
RECOMMENDATION:
While professional f/2.8 zoom lenses are very expensive, standard f/1.8 fixed lenses are extremely affordable and about as "fast" as a lens can get! 50mm lenses are available for about $100, 85mm lenses are available for about $300, and assorted wide-angle lenses are available too. Buy them used in mint condition from places like KEH.com... Yes, you do have to "zoom with your feet" and switch lenses more often, but most of the time you will find that it actually helps you see and make more artistic images...
This really old Nikon 50mm f/1.4 AF lens I bought for just $199. You can get the new Nikon 50mm f/1.4 AFS for about $450, I think. Sigma also makes an (even better?) 50mm f/1.4, with SWEET background blur, for about the same price.
Email me if you'd like advice on which prime or zoom lens to purchase!
Last but not least, here's a real-world sample... I used a 150mm lens and an apeture of f/2.8. The hummingbird was about 3-5 feet away from the camera, and the background was maybe 50 feet away... This is always a recipe for a totally blurred, "creamy" background- Get as close as you can to your subject, and shoot with a background that is 10x further than the camera-to-subject distance!