Understanding Camera Lenses: Part 2

Having trouble understanding camera lenses? If you want to understand lens quality, as well as what your lens' maximum aperture is all about, watch the video!

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Did you catch Part 1 of this series about understanding your camera lenses?

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Video Transcript

What makes one lens different from the next? I've been getting lots of questions about lenses lately, so I'm doing a little mini-series about them. Hi, I'm Julie from Ultimate Photo Tips. In my last video, I explained the focal length and field of view. Today, I want to talk about two more aspects of lenses: glass quality and maximum aperture.

Understanding Camera Lenses: Glass Quality

First of all, let's talk about one of the biggest differentiating factors between lenses: the quality of the glass. The best lenses are sharp. But sharpness is not the only quality you want to look for. To one degree or another, all lenses suffer from certain optical aberrations, like blur (lack of sharpness), distortion, vignetting, loss of contrast, and chromatic aberration. Those are the effects that you want to minimize. So, a high quality lens is one in which these negative effects are not as pronounced.

Understanding Camera Lenses: Maximum Aperture

Now let's talk about some more numbers. When you hear someone describe a lens as a 24-105mm f/4, you now know - from my last video - that 24-105mm refers to the focal length. Let's look at the other number, f/4. What does that mean? That number refers to the maximum aperture of the lens. What's the widest it can open? Lenses that can open wider are usually more desirable (and heavier, larger, and more expensive!) So an f/2.8 lens is better than an f/5.6 lens. Why is a good to have a larger maximum aperture?

There are two reasons. First, a wider aperture means that under the same lighting conditions, you could use a faster shutter speed to get the same exposure. That's why lenses with a wide maximum aperture are sometimes called "fast" lenses. This can be very useful if you are hand-holding your lens, and want to keep your image sharp.

The second reason that a wider maximum aperture is desirable is to get a bigger drop-off in sharpness. Being able to shoot with a very wide aperture will let you blur your background. Soft backgrounds can be desirable for portrait photography, close-up photography, and more.

Something else to know is that on many zoom lenses, the maximum widest aperture varies with the focal length. So, you may see the lens listed as a 28-135mm, f/3.5-5.6 lens. That means that when the lens is at 35mm, the maximum aperture is f/3.5, but when you zoom in to 135mm, the maximum widest aperture changes to f/5.6. Remember, the range is referring to the maximum aperture, not the overall range for the lens. That maximum aperture is often written on the end of the lens near the glass. It may appear as 1:3.5, rather than f/3.5.

One final thing to note is that you may actually want to avoid using your lens at its minimum and maximum apertures, and come in a stop or two. At the extremes, you may experience more of the lens aberrations I mentioned earlier.

That's it for today! Check out more tips over at ultimate-photo-tips.com, and make sure to sign up for my newsletter while you're there. That's where I share ideas and inspiration that I don't share anywhere else. Happy shooting, and I'll see you next time!

EXERCISE - Understanding Camera Lenses:

As I've just discussed, a zoom lens may have a different maximum aperture when set to it shortest and longest focal lengths. Play with your own zoom lens to check this out. Set it to the widest angle focal length first, and then (in aperture priority or manual mode) change the aperture to its widest setting. Now, zoom your lens to its longest focal length, and check what happens to your aperture setting. Did it change?

Reminder: Here's Understanding Camera Lenses: Part 1.

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