Saturday, April 2, 2011

Exercise 1: Introduction to Focal Length

Before today, I think my understanding of my zoom lens was not uncommon. I thought that my zoom lens was pretty much equivalent to getting closer to my subject; that zooming and getting closer would produce roughly the exact same photo. However, I had read many times about how photographers shouldn't "rely on their zoom." Well, if that's the case, there must be a reason. Then I read about an exercise to learn about focal lengths, which seemed like a perfect first exercise for me.

Exercise 1: Identify a stationary object to photograph. Take multiple pictures of this object using different focal lengths, but keeping the object roughly the same size in the viewfinder.

I brought a brick into the backyard, placed it at eye-level, and proceeded to take pictures. Before I even came inside to review the results, I learned two valuable lessons.

1. I SUCK at not moving the camera. My lens is pretty hefty, but I'm really going to need to research some solutions to this problem. I have typically compensated by trying to get better lighting and upping the shutter speed. A tripod will also help with some situations, but in general, I'm really going to have to figure out how to hold the camera so that my husband can't see it moving from 100 yards away.

2. I am very dependent on my camera correcting my exposure. I typically shoot in either aperture priority or shutter priority, so I normally don't even think about keeping an eye on my exposure. Today I decided that if I'm going to start learning, I'd better switch to manual. (I left auto-focus on. Baby steps.) I found that I would take 8 or 9 pictures and then notice that I hadn't been paying attention to the exposure at all. And today was a great day to discover that, since the sun kept darting behind clouds and the lighting was changing drastically from moment to moment. Great learning experience. Really going to need to practice that.

So I zoomed in on my brick. I zoomed out and got closer. I zoomed all the way out and got even closer. I started at an F-stop of 3.5. I did it again at F/8 and again at F/22..6. I came inside to have a look.  Here's what I found. Photos below are at different focal lengths, all with F/8.

focal lengths: 70, 50, 35, 28, 24 mm

At first when I was looking at them, I was just annoyed at myself that I couldn't line up the shot the same every time. And then I noticed it! Eureka! When I used my zoom (the photo on the far left above), the background was just the stuff immediately behind the brick

When I zoomed out and actually walked up to the brick, the background behind it was in the shot. 

Who knew? OK, everybody. And there's probably a website that explains all this, but nothing beats learning it first hand. This is very useful information. You want to exclude the background of your shot, use the zoom. You want to include it, move your feet. Got it. Now I'll need to go practice that some more.


  1. When I decided to "figure it out" I also went 100% manual exposure (I use auto focus 99% of the time). Now that I think I get it I use the built in meter and aperture mode most of the time. If you read the main photo forums ( is pretty good) the majority are in aperture mode unless shooting sports/birds/etc.

    Modern SLRs are way smarter than we are and they usually get it right, or close enough that we can easily fix it at home. On our recent trip to St. Thomas one of my lenses was overexposing by about 3/4 of a stop in the extremely bright sun so I dialed it down with the exposure compensation.

    Regarding auto focus, you may be able to specify the area the camera focuses on. I usually leave mine on full frame because it has face detection and "knows" where it should focus. If I need to change it I either a) set to single point focus and move the focus point or b) set to area focus and set it to an area of the viewfinder. The camera can almost always focus better than you can so IMO let it. The exception is macro photography.

  2. Kevin, I think focus is my next project. It is the thing I look at in your photos and marvel at. You're always at F/3.5 or something comparable, but your photos are crystal clear. When I shoot at F/3.5, it's like a crap shoot. I know the purpose is to not have everything perfectly in focus, but mostly I get full blur - not exactly what I'm going for.

    I do have my camera on "almost full" auto-focus, meaning that there are eight focus points I see through the viewfinder. I could set it so that it automatically chooses the best focus point on its own, but I turned that off because I found that it always focused on the closest point to my camera - not always what I want. So I changed it so that it always focuses on the center point, I lock focus and then recompose the shot. I'm not sure this is the best method, but it's what I've been doing. So I think it's decided... next up: figure out focus! (Seems like a pretty important thing.)

  3. "So I changed it so that it always focuses on the center point, I lock focus and then recompose the shot"

    This can work but when you move the camera, you move the focal plane and at apertures of 3.5, 2.8, etc that movement can make you end up with blurry photos. It's best to move the focus point manually. It's a pain but one of the better ways to "ensure" you get what you want in focus.

  4. Kevin! That makes so much sense! OK. Off to practice my focus.