Lens focal length options
The great advantage of the SLR design is the capability to use interchangeable lenses. Some manufacturers offer dozens of lenses to choose from for all kinds of purposes. However, most of these lenses were designed for use with 35mm film cameras.
A significant issue to consider with DSLRs is the focal length magnification factor , also known as the cropping factor or field-of-view cropping factor . DSLRs are designed to work with film camera lenses, but since 35mm film is larger than most image sensors made today, most DSLRs can record only a portion of a lens’s field of view. This portion is seen by the viewer as a cropping of the image and effectively makes film SLR lenses appear longer—more telephoto&38212;than they were designed to be. This effect can be problematic when choosing lenses. (The exception is Olympus’s 4/3 system, currently manufactured only by Olympus. These cameras have no cropping factor issues, but do have an inherently smaller sensor design.)
This magnification factor is 1.5x to 1.6x on many lower priced DSLRs. What this means is that just like point-and-shoots, you sometimes must use a focal-length conversion to compare lenses. For example, a wide-angle 24mm lens originally designed for film cameras would effectively become a 38.4mm lens (24mm multiplied by 1.6) when used with a 1.6 factor DSLR. It’s worth noting that 38mm is not particularly wide-angle. In other words, to get 24mm wide-angle focal length on a DSLR requires a 15mm lens (15mm multiplied by 1.6 equals 24mm). However, these super-wide-angle film SLR lenses are expensive. Fortunately, affordably priced lenses designed specifically to address this issue are now available from major manufacturers.
Tip: A great advantages of digital capture is that scanning film introduces noise to the image data, which is amplified when enlarging the image in software. With digital capture, you can successfully enlarge digital camera captures far beyond what you can with film. Now you can make a poster of that once-in-a-lifetime shot!
Some mid-range DSLR models offer lesser magnification factors of 1.3x, and the latest top-of-the line Canon (the $8,000 Canon 1Ds Mark II ) has no magnification factor—it is a full-frame sensor. This is good news for people who already own a large selection of film SLR lenses and are in the market for the state of the art. Canon broke new ground in October 2005 with another full-frame model, the EOS 5D for $3,300 . With this in mind, the table below takes our price and megapixel table from earlier and incorporates lens-cropping data.
Digital SLR Comparison with Lens Cropping Factor
|Price Point||Megapixels||Lens Cropping Factor|
|$800||6 to 10 megapixels||1.5 x to 1.6x unless dedicated designed-for-digital lens used, or full system is Olympus 4/3 format|
|$1,500||6 to 10 megapixels||1.5 x to 1.6x unless dedicated designed-for-digital lens used, or full system is Olympus 4/3 format|
|$1,850||10 megapixels||Nikon D200, 1.5x|
|$3,300||12 megapixels||Canon EOS 5D, full 35mm frame sensor (1.0x)|
|$4,000-$5,000||8 to 12 megapixels||1.3x to 2.0x depending on model (and shooting mode for Nikon D2Xs)|
|$8,000||16 megapixels||Canon 1Ds Mk. II, full 35mm frame sensor|
DSLR dust spots
Other than bulk, complexity, weight, and attractiveness to thieves, a major problem with interchangeable (removable) DSLR lenses is dust settling on the image sensor. You can see the effects in the screenshot below.
Changing a DSLR lens can cause dust to settle on the image sensor. Dust appears in your images as shown above, circled in red. In this example, the dust spots are larger than they would normally appear because the frame above is cropped from the full frame.
Dust requires you to clean the sensor surface by using a rubber squeeze blower (do not use compressed air!) or by purchasing special brushes or swabs from companies such as VisibleDust. Some newer DSLRs have self-cleaning sensor technology built into the camera body. This may become standard on future models.
Warning: When cleaning the sensor, follow your camera’s instructions found in the owner’s manual. Significant damage may occur if you don’t follow the manufacturer’s recommendations.
As with anything, you need to clean and care for your equipment, but it can be a drag if you have only one DSLR body and like to change lenses often outdoors. You don’t have to be on safari to encounter dust or rain. Soccer fields, construction sites, hiking trails, and anywhere it rains or snows can adversely affect your camera and lenses.
Tip: Turn your DSLR off when changing lenses; the electrical charge on the sensor attracts more dust when powered on.
DSLR computer workflow
Just as with point-and-shoots, plenty of back-end software is available to manage the digital creations captured by your DSLR. But again, because DSLRs appeal to artistic photographers who want to take full control of the images they create, the software used for snapshots may not offer the control you’re looking for. DSLR workflow can be much more complicated. Workflow entails not only how you transfer the image file from your camera to a computer, but also how you adjust your image or use it with others, and how you store or archive your digital shoebox. In other words, the digital file straight from the camera may only be an intermediate step in the “development” process. The photographer may still need to make adjustments to color, contrast, cropping, etc. This reality appeals to some and frustrates others.
Many books, classes, and seminars are offered on this subject, which goes far beyond what I can offer in this excerpt (or even the full book). Start researching by checking periodicals and Web sites that speak to the style of photography you’re interested in. You will learn more from others who share your photographic interests than if you were to just sign up anywhere to get hit over the head with computer books!
Hordes of photographers tend to swear by their favorite systems and denigrate others. Along with politics and religion, SLR systems bring out the inner fanatic in otherwise normal humans. Weigh their opinions and remember that your preferences, not theirs, matter most.
[ Laurence Chen is a professional photographer and adjunct faculty member teaching photography at Seattle Pacific University. His work has appeared in the New York Times, Sunset Magazine, America 24/7, and many other places; his latest book is Take Control of Buying a Digital Camera, Third Edition (TidBITS Electronic Publishing, 2006).]