The Best Digital SLR For You

Printing Problems? Blame Aspect Ratio

If you never print a single one of your digital photographs, then aspect ratio will never be an issue for you.

It will also not be a problem for any digital SLR user who enjoys making 4x6 prints.

However, once you get into larger-size prints, aspect ratio becomes a bit more troublesome. What you'll find is that large portions of your original photo get cut off when you get your prints back.

A couple of things to remember: it's not your fault, and there's absolutely nothing wrong with your digital camera.

Nope, the thing to blame for this problem is aspect ratio.

Continuous Maximum Aperture

Well, here I am one day behind already. Time flies when you are having fun and I am certainly having a lot of it these days.

On to the definition!

In the previous post, I talked about maximum aperture and why it is so important for you to consider when you are buying a lens for your digital SLR camera.

Today, I'll be talking about continuous maximum aperture.

Go find a zoom lens. If you don't really want to, here's one you can look at:

Canon - Zoom lens - 28 mm - 135 mm - f/3.5-5.6 IS USM - Canon EF

Notice how the f-stop (aperture) information is displayed for this lens? f/3.5-5.6. Why are there two numbers instead of just one?

There are 2 numbers because the maximum aperture of this lens changes as the focal length of the lens changes from 28mm to 135mm. As you zoom in, the maximum aperture is getting smaller.

This is a common situation with many zoom lenses, and sometimes the change in aperture can be substantial.

Why This Is a Problem
Here's why the change in aperture can be a real problem for you: it changes the exposure of your photograph when you use manual settings.

For example, let's say that you are photographing a scene with the lens above at 28mm. You set the aperture as wide as it will go (f3.5) and find out that the shutter speed must be 1/250 to get a well-exposed photo.

Now you zoom to 135mm. The aperture changes to f5.6. If you don't also change your shutter speed, your photograph will be under-exposed.

This can also be a problem when there isn't enough light. Let's say that you have the lens at 28mm f3.5 and your shutter speed is 1/60 of a second. This is just fast enough to get a clear photo holding the camera in your hands.

You zoom - maximum aperture changes to f5.6. Your shutter speed must now be set to 1/15, which is too slow to get a clear photo. You'll have to go grab your tripod or use the flash.

Continuous Maximum Aperture
Whew! That was the long route to get this defined, but it should help you understand the definition better.

The aperture setting on a lens with continuous maximum aperture never changes, no matter how much you zoom.

A lens like this would only have one aperture number, like this:

Canon EF 70mm-200mm f/2.8L IS USM Telephoto Zoom Lens for Canon SLR Cameras

NOTE: Notice the difference in price between these two lenses. You will pay a premium for continuous maximum aperture lenses.

Once you set the aperture it's set, and the only thing that will change your exposure are changes in the environment that increase or decrease the ambient light.

Without a changing aperture to worry about, you can focus more on your photography, and less on  the settings of your digital SLR camera.

Maximum Aperture

It dawned on me today that it might prove worthwhile to use this weblog as a venue to provide you with some definitions of digital SLR camera terms.

Today's Term: Maximum Aperture

Maximum aperture has less to do with the digital SLR camera and more to do with the lens that you choose.

It's fresh on my mind since I have been working away on a guide that will help you find the best lens for your digital SLR camera. That will be available soon on the Digital SLR Guide.

Maximum aperture is important enough that it deserves to be explained here as well.

Aperture
First, a review of aperture. Aperture is a measure of how wide a lens can open and how much light it can let in.

Aperture is measured in f-stops, and is an inverse relationship: a SMALLER aperture number represents a WIDER aperture opening.

For example, f2.8 is wider and lets in more light than f5.6.

Maximum Aperture
Not all lenses can open the same width and let in the same amount of light. Maximum aperture is the widest aperture that a lens can manage.

The maximum aperture is always listed along with the name of the lens. It helps you when you're trying to compare lenses side-by-side.

Let's say that you're checking out a 100mm f3.5 lens. The f3.5 represents the maximum aperture of the lens.

A 200mm f2.8 lens has a maximum aperture of f2.8.

So What's the Big Deal?
Why does it matter how wide the lens can open?

It matters because every photo that you take will be a combination of shutter speed and aperture. The shutter has to stay open long enough to let in light, OR the aperture has to open wide enough to let in the light.

Let's say that you are taking a photo indoors. You're all ready to take the shot, but with your maximum aperture of f5.6 your shutter speed has to stay open 1/30 of a second to get a proper exposure.

1/30 of a second is not fast enough to hold the camera in your hands and get a clear shot.

If you had an f2.8 lens however, your shutter speed could be 1/180 of a second, plenty fast enough for most photographic subjects.

Benefits of a Wide Maximum Aperture

• You can take photos in low-light conditions without a tripod or flash
• You don't have to always boost the ISO when there isn't a lot of light
• You can use really fast shutter speeds to freeze action

Summary
Basically, lenses with wide maximum apertures give you more flexibility to shoot under a wide range of lighting conditions without a lot of extra gear (flashes, tripods, etc.).

Tomorrow I'll talk about how zoom lenses handle maximum aperture and why having a continuous maximum aperture can be so important.

If there are other photography terms that you'd like to have defined, please post a comment and let me know. Don't be shy, no question is too simplistic.