Digital Photography from 20,000 Feet
by Wesley Fink on September 25, 2006 12:05 AM EST- Posted in
- Digital Camera
Taking a Picture: Putting it All Together
Now that the basics of how a digital SLR works have been covered, we are ready to put it all together. For those who have had enough of new ideas to remember and balance it should be pointed out that you don't really have to understand or adjust any of this to take images with a digital point-and-shoot or a digital SLR. All the digital SLR cameras on the market are autofocus and auto-exposure, and some even have the very consumer-oriented programs that make decisions for you in tough situations like backlight or sports. However, without understanding a bit about what your automatic camera is doing you will never figure out why that kit zoom takes blurry shots of your family on Christmas morning or your son's birthday party or your daughter's dance recital. With understanding you can make choices to fix these problems.
Why the Kit Lens is a Dog
For some reason, the world has moved to zoom lenses. There is no doubt they are definitely convenient for cropping in the camera, but most people would rather have a sharp picture they can cut in Photoshop instead of a blurred one that is already cropped. You see, people seem to have forgotten the compromises of most zoom lenses. To better understand this let's look at equivalent exposures.
If you followed our discussion of the basics, all of the exposures above represent the same amount of total light. As shutter speed increases (less light) then aperture decreases (more light). The chart below also shows equivalent exposures - we have just shifted the values to a common indoor scene at a moderately "fast" ISO of 400.
As you can clearly see our old normal f1.7 can shoot this between 1/125 and 1/250 - which is plenty fast enough to get a sharp picture with equivalent 75mm f1.7 normal on a digital SLR. A 28mm f2.8 would behave like a 42mm f2.8 normal lens and also be fast enough to shoot at 1/60s. Our kit 18-55mm is equivalent to a 28 to85mm,. At the short end at 1/45 s it is probably fast enough to capture a sharp image, but it gives out quickly and will definitely yield blurred images at anything above about 45mm. At the telephoto end of 85mm (55mm) the shutter speed for the fastest f5.6 is 1/15s - which will definitely be a blurry picture. If you were shooting at ISO200 nothing would be sharp with your kit zoom under these conditions, as everything would shift a notch to the left. At the default ISO 100 the best you could do would be between 1/8 and 1/15s and blurry.
The point is, your kit zoom is for shooting outside and indoors with flash at limited range. It is the wrong tool for available light photography. If you have followed this it is our advise that you buy a normal lens as your first interchangeable lens for your digital SLR. Canon and Nikon still make reasonable 50mm f/1.8 lenses, which also happen to be the sharpest lens in either lens lineup. The bonus on a digital is it becomes a 75mm f1.8 fast short telephoto, which is great for portraits and available light photography. Bonus two is that the close focus is the same but the image is magnified by a 1.5 to 1.6x factor, making the lens a terrific macro lens. Minolta has a great 50mm f1.7, as does Pentax, but used prices have been rising recently. The other option is a 28mm or 35mm lens. There are plenty available at f1.8 to f2.8 on the used market and you get a fast true normal lens of 42mm to 53mm focal length. Since the APS C or DX format only uses the center of the image, the third bonus is that even mediocre lenses with edge falloff in the corners on 35mm are normally very sharp in the area used in digital SLR photography.
There is also a new market developing for fast fixed focal length lenses for the APS C/DX. Several companies have announced new 30mm to 50mm f1.4 to f2.0 lenses for the smaller APS C/DX format. Sony picked up the Minolta 50mm f1.4 for their new lens line, though we wish they had also picked up the excellent and reasonable 50mm f1.7 instead of just the $350 f1.4.
There is also the option of fast zoom lenses, but zoom lenses are rarely if ever as sharp as fixed focus and the prices for fast zooms are high. There are several independent and brand name zooms in the 28-75mm f2.8 format. They range in price from $450 to $5000 or so. Fast, quality zoom lenses cost big money, because they are hard to design and expensive to make. A fixed focus lens gives you that pro quality at a much lower price - particularly if that fast fixed lens is a normal 35mm lens.
Image Stabilization
Image stabilization was first introduced by Nikon and Canon in specialized lenses designed for action photography. These lenses were first designed for pros at pro prices, but they quickly found their way to consumer zoom lenses with wider zoom ranges than kit zooms. The advantage of the image stabilization is that the stabilized zoom lens can produce sharp images at a couple of f-stops slower than the normal rule. That means a 125mm focal length can be handheld with sharp results down to about 1/30s, while a 28mm wide angle can go down to 1/8s or less. The problem with these "image-stabilized" lenses is that they are relatively expensive, starting at $300 or so and going up to thousands of dollars.
More recently, Minolta introduced image stabilization into the SLR camera body. That means any lens mounted on the camera can have the advantage of image stabilization. The Minolta Maxxum 7D was the first interchangeable lens SLR to offer this feature, which was also continued on the mainstream-priced 5D. Sony has continued this feature in their new 10.2 megapixel $899 A100 and improved the effectiveness, they say, to 3 to 3.5 stops. Sony has also licensed the steady shot technology to Pentax, which uses it in their K100D and the announced K10D. It will also appear in future Samsung SLR cameras, since they use the Pentax mount and are basically relabeled Pentax cameras.
Image stabilization, with custom lenses or built into the camera body, allows normal zoom lenses to act like they are faster - some 2 to 3.5 stops faster - and this makes them usable in the difficult situations we described above for zoom lenses. It is a good feature, but keep in mind that the body-integral steady shot also works with any lens, including the fast normal lens. This extends the useful speed of the normal lens even further, just as it does the zoom lens.
One significant advantage of image stabilization with a normal lens is the ability to shoot greater depth of field in available light. Shots that were doable before with shallow depth-of-field, can now be shot with a greater range or depth of sharpness. This is particularly useful for things like we do at AnandTech - shooting motherboards in available light to avoid hot spots, while still keeping the entire board in sharp focus.
Now that the basics of how a digital SLR works have been covered, we are ready to put it all together. For those who have had enough of new ideas to remember and balance it should be pointed out that you don't really have to understand or adjust any of this to take images with a digital point-and-shoot or a digital SLR. All the digital SLR cameras on the market are autofocus and auto-exposure, and some even have the very consumer-oriented programs that make decisions for you in tough situations like backlight or sports. However, without understanding a bit about what your automatic camera is doing you will never figure out why that kit zoom takes blurry shots of your family on Christmas morning or your son's birthday party or your daughter's dance recital. With understanding you can make choices to fix these problems.
Why the Kit Lens is a Dog
For some reason, the world has moved to zoom lenses. There is no doubt they are definitely convenient for cropping in the camera, but most people would rather have a sharp picture they can cut in Photoshop instead of a blurred one that is already cropped. You see, people seem to have forgotten the compromises of most zoom lenses. To better understand this let's look at equivalent exposures.
| Shutter Speed to f/stop Comparison | |||||||||||
| Shutter Speed | 1/4 second | 1/8 | 1/15 | 1/30 | 1/60 | 1/125 | 1/250 | 1/500 | 1/1000 | 1/2000 | 1/4000 |
| f/stop | f/45 | f/32 | f/22 | f/16 | f/11 | f/8 | f/5.6 | f/4 | f/2.8 | f/2 | f/1.4 |
If you followed our discussion of the basics, all of the exposures above represent the same amount of total light. As shutter speed increases (less light) then aperture decreases (more light). The chart below also shows equivalent exposures - we have just shifted the values to a common indoor scene at a moderately "fast" ISO of 400.
| Shutter Speed to f/stop Comparison | ||||||||||||
| Shutter Speed | 1/2 second | 1/4 | 1/8 | 1/15 | 1/30 | 1/60 | 1/125 | 1/250 | 1/500 | 1/1000 | 1/2000 | 1/4000 |
| f/stop | f/16 | f/11 | f/8 | f/5.6 | f/4 | f/2.8 | f/2 | f/1.4 | - | - | - | - |
As you can clearly see our old normal f1.7 can shoot this between 1/125 and 1/250 - which is plenty fast enough to get a sharp picture with equivalent 75mm f1.7 normal on a digital SLR. A 28mm f2.8 would behave like a 42mm f2.8 normal lens and also be fast enough to shoot at 1/60s. Our kit 18-55mm is equivalent to a 28 to85mm,. At the short end at 1/45 s it is probably fast enough to capture a sharp image, but it gives out quickly and will definitely yield blurred images at anything above about 45mm. At the telephoto end of 85mm (55mm) the shutter speed for the fastest f5.6 is 1/15s - which will definitely be a blurry picture. If you were shooting at ISO200 nothing would be sharp with your kit zoom under these conditions, as everything would shift a notch to the left. At the default ISO 100 the best you could do would be between 1/8 and 1/15s and blurry.
The point is, your kit zoom is for shooting outside and indoors with flash at limited range. It is the wrong tool for available light photography. If you have followed this it is our advise that you buy a normal lens as your first interchangeable lens for your digital SLR. Canon and Nikon still make reasonable 50mm f/1.8 lenses, which also happen to be the sharpest lens in either lens lineup. The bonus on a digital is it becomes a 75mm f1.8 fast short telephoto, which is great for portraits and available light photography. Bonus two is that the close focus is the same but the image is magnified by a 1.5 to 1.6x factor, making the lens a terrific macro lens. Minolta has a great 50mm f1.7, as does Pentax, but used prices have been rising recently. The other option is a 28mm or 35mm lens. There are plenty available at f1.8 to f2.8 on the used market and you get a fast true normal lens of 42mm to 53mm focal length. Since the APS C or DX format only uses the center of the image, the third bonus is that even mediocre lenses with edge falloff in the corners on 35mm are normally very sharp in the area used in digital SLR photography.
There is also a new market developing for fast fixed focal length lenses for the APS C/DX. Several companies have announced new 30mm to 50mm f1.4 to f2.0 lenses for the smaller APS C/DX format. Sony picked up the Minolta 50mm f1.4 for their new lens line, though we wish they had also picked up the excellent and reasonable 50mm f1.7 instead of just the $350 f1.4.
There is also the option of fast zoom lenses, but zoom lenses are rarely if ever as sharp as fixed focus and the prices for fast zooms are high. There are several independent and brand name zooms in the 28-75mm f2.8 format. They range in price from $450 to $5000 or so. Fast, quality zoom lenses cost big money, because they are hard to design and expensive to make. A fixed focus lens gives you that pro quality at a much lower price - particularly if that fast fixed lens is a normal 35mm lens.
Image Stabilization
Image stabilization was first introduced by Nikon and Canon in specialized lenses designed for action photography. These lenses were first designed for pros at pro prices, but they quickly found their way to consumer zoom lenses with wider zoom ranges than kit zooms. The advantage of the image stabilization is that the stabilized zoom lens can produce sharp images at a couple of f-stops slower than the normal rule. That means a 125mm focal length can be handheld with sharp results down to about 1/30s, while a 28mm wide angle can go down to 1/8s or less. The problem with these "image-stabilized" lenses is that they are relatively expensive, starting at $300 or so and going up to thousands of dollars.
More recently, Minolta introduced image stabilization into the SLR camera body. That means any lens mounted on the camera can have the advantage of image stabilization. The Minolta Maxxum 7D was the first interchangeable lens SLR to offer this feature, which was also continued on the mainstream-priced 5D. Sony has continued this feature in their new 10.2 megapixel $899 A100 and improved the effectiveness, they say, to 3 to 3.5 stops. Sony has also licensed the steady shot technology to Pentax, which uses it in their K100D and the announced K10D. It will also appear in future Samsung SLR cameras, since they use the Pentax mount and are basically relabeled Pentax cameras.
Image stabilization, with custom lenses or built into the camera body, allows normal zoom lenses to act like they are faster - some 2 to 3.5 stops faster - and this makes them usable in the difficult situations we described above for zoom lenses. It is a good feature, but keep in mind that the body-integral steady shot also works with any lens, including the fast normal lens. This extends the useful speed of the normal lens even further, just as it does the zoom lens.
One significant advantage of image stabilization with a normal lens is the ability to shoot greater depth of field in available light. Shots that were doable before with shallow depth-of-field, can now be shot with a greater range or depth of sharpness. This is particularly useful for things like we do at AnandTech - shooting motherboards in available light to avoid hot spots, while still keeping the entire board in sharp focus.
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Zaitsev - Monday, September 25, 2006 - link
That was a very interesting article. I've always wanted to learn more about cameras and photography, in the hopes of making it a hobby once the time and money is available. So thanks for explaining the background info for noobs like me :) I'll be looking forward to the rest of the series.