Digital Cameras

Last Modified: January 3, 2006.

Introduction

If you can afford a decent digital body today, you should probably forget about film. The only exception I can think of is if you're primarily interested in black and white photography. If that's the case, be sure to read my notes on digital black and white photography.

The image of the Snowy Egret on the right was taken with a Nikon D2x. Click on it to obtain a larger version, and even that larger image is still scaled down by a factor of three.

For reference, I own and have experience with three digital cameras: one point-and-shoot and two Nikon SLR bodies.

The Sony DSC-S85 is a high-end digital point-and-shoot (or was high-end when I bought it). It originally cost about $800 and can take photos with 4 million pixels. That camera is now out of production, although the price dropped to about $500 before Sony replaced it with new models. From what I can tell, equivalent cameras today cost about $300.

My other cameras are a Nikon D100 body and a D2x body that can use almost all my old Nikon lenses. The D100 has a resolution of 6 million pixels and cost about $1700. Don't be fooled into thinking I made a mistake and only got 2 million pixels for more than doubling the price; the Nikon pixels are "better" as I shall describe later in this document. The D2x cost around $5000, and has a 12 million pixel resolution. I have only had the D2x for about a month, but I used the D100 heavily for about two years. The funny thing is that in the month that I've had the D2x, I have already taken more photos with it than I did in the entire two years with the D100.

I still have more experience with film cameras, but by now I and starting to feel very comfortable with the digital cameras. If you'd like to see some of my digital work before reading on to make sure I can walk the walk as well as talk the talk, I've got some example web pages. The best shots by far are taken with the D2x:

Birds at the Palo Alto Baylands

Here are a few others:

Costa Rica 2002 volunteer work
Costa Rica 2002 as a tourist and
Burning Man, 2002

were taken with the Sony.

The Nikon SLR has now made a few trips and you can see my first digital SLR attempts on these pages from:

Costa Rica 2003
Palo Alto Baylands and
Burning Man, 2003.

What is a digital camera?

As a first approximation, a digital camera is basically identical to a standard film camera except that in place of the film, the incoming light shines on a CCD (charge-coupled device) that senses the incoming colors electronically. Then, instead of recording on film, the data from the CCD is written to some sort of electronic memory. This may be something like a memory card, a small disk drive, or even an optical CD. In the field, instead of changing rolls of film, you'll change to a new memory card or a new CD when you fill one with photos.

But unlike standard film, after you have copied the data from your memory card to a computer or something you can erase that card and reuse it. In fact, you can review each photo as soon as you take it, and erase it immediately, in the field, if you do not like the results.

Depending on the cost of your camera, it may be equipped with most of the same options that a standard 35mm camera has: zoom lens, macro setting, flash, exposure control, auto and manual focus, exposure locks, et cetera.

In addition, some are equipped with various electronic filters that can be applied to the photo to produce things like black and white, vignetting, solarization, sepia prints, et cetera. In my opinion, these features are worthless--why not do your digital retouching at home on your computer where you can see what you're doing and no doubt have far more powerful image processing programs?

Often the camera (this is true of digital point-and-shoots, especially) has the ability to record short MPEG movie clips, including sound if you want. I didn't think this would be too important, but have actually found a few nice uses for this feature.

Here is the best example I know of. I was in Costa Rica and one of the people in our group was a professional photographer who has helped produce films for the BBC, et cetera. We saw a nice line of leafcutter ants and I wanted to get a photo, but the photographer was filming, and I got in his way. He's a really nice guy, but he started joking about what he would have said if he were a real photographer. At that point I silently changed my camera to record an MPEG video while he demonstrated what a real photographer would say. Ignore the video in this mpeg clip; I had the camera sideways and all I really cared about was the audio.

What are the pros and cons of digital cameras?

• By far the best thing about digital cameras is the instant gratification you get when you use them. Take the photo and look at it right away on your viewer. Most viewers allow you to zoom in and pan around your image, so you can get a good idea if it is in focus, if the exposure is correct, et cetera. If you don't like what you got, you can delete it on the spot. Depending on your subject, you may even be able to try to take the photo again after you adjust what was wrong in the initial photo.
• You don't need filters (except perhaps polarizers and split-level filters or other special-effects filters) on a digital camera. The way most filters work on a standard camera is to block or partially block certain frequencies of incoming light, so by adding a filter, you simply reduce the light reaching the film. But you can do most of that later in image processing programs on your computer, and can even make some parts of the image brighter. You cannot, however, turn on a digital polarizer since polarization information is lost when the film records the image.

  The other type of filter that might be useful is one of those split level filters. These are half clear and half some other color, normally gray. Then if you've got a very bright sky and a dark foreground you can put the split right on the boundary and it'll be easier to get a good initial exposure range by darkening the sky relative to the foreground. Digital cameras have the same problem that normal cameras do in the sense that they can only record light in some range. Anything brighter than one end of the range will record as white and anything darker than the other end of the range will record as black. By using a split level filter, you can reduce the range of light that the camera sees, allowing you to record details both in the sky and in the forground. Without the filter, depending on how you expose, you'll get a detailed foreground and a burned out sky or a detailed sky and a blackened foreground. Use the dark part of the filter on the sky and the clear part on the foreground.

  On the other hand, if you've got an unchanging scene, you can put your digital camera on a tripod and take the same shot with different exposures and combine those photos later with software like Adobe's Photoshop to yield a much larger range of light levels than you could with any single photo. If it's already digital, there's very little problem with registration.

  But the uniformly-colored filters can easily be replaced with a computer program, since all they do is remove light from the photo. Similarly, many of the special effects filters (like the ones to add highlights or rainbows) can probably be done even more efficiently in an image processing program like GIMP, Adobe Photoshop or many others. In fact, Photoshop has built-in filters that imitate all the standard color filters: the 81A, 81B, et cetera.

• There is no painful scanning process to turn your slides or prints or negatives into a form suitable for electronic dissemination. On the other hand, if you want to have a standard slide show with physical slides, you'll need some way to convert your digital images onto standard film.
• Even if your camera has a limited zoom capability, you can effectively increase it by shooting at a higher resolution and cropping the resulting image. You can, of course, do this on a standard film camera as well with exactly the same drawbacks.

• The memory sticks or cards (if your camera uses them) are expensive. Of course you can reuse the sticks, but if you are on a long vacation, or if you like to take the highest quality photos, it may be expensive to carry enough sticks for your whole trip. However, these memory cards are getting cheaper and cheaper. Today (May, 2005), you can get a gigabyte card for about $79 and a two gig card for $220 or so. But today the images are bigger, so you need bigger cards: the Sony shot images that took about 2 megabytes each at the highest resolution. The D100's high-resolution shots are about 9 megabytes; the D2x shoots 20 megabyte files.

  My Sony camera, for example, can record resolutions up to 2272 by 1704 pixels. For a 64 megabyte memory stick, this is about 30 photos, sort of like a roll of film. But instead of $5 for a roll of film, I needed to spend around $100 for each stick. Today, the prices are, of course, lower and will continue to get lower. On the newer Nikon, the story is even worse. The highest quality image burns up 9.6 megabytes in "raw mode" per photo. I use a 1 gigabyte microdrive and it'll hold 103 photos at this highest quality and resolution.

  There are a couple of ways around this. First, take lower-resolution photos. Almost nobody has a computer screen (at least today) that can display 2272x1704 images (or 3008x2000 in the case of the D100). But I like the highest resolution since I often crop drastically. A nice compromise for me is to shoot at 1600 by 1200 and I can get about 64 shots on a memory stick at that resolution. Of course at the lowest resolution I could have gotten 900 shots per stick.

  Also remember that you get to erase the bad shots right away, so you probably need only the storage capability for half of what you'd take on regular print or slide film. Or if you're a bad photographer like me, you can erase a much higher proportion of the shots as soon as you take them.

  Finally, if you carry a laptop on your vacation, you can just download the photos from your camera at the end of each day and get away with one or two memory cards, even at the highest resolution. I recently spent three weeks in Italy with two 64MB Sony memory sticks, took all my photos at the highest possible resolution, and never came close to running out of memory, even in the most scenic places. At the end of each day I just downloaded all my photos to the laptop and erased the memory sticks.

• The resolution of digital cameras is not as good as that in standard cameras, at least not today. Every year, however, things get better, and I'd guess that in 2 or 3 years (by 2005 or so) they will be equal, and after that, the digital cameras will be better. A good estimate is that standard 35mm cameras have an effective resolution of about 3000x2000 or perhaps as much as double that. This is what you'll get with a "6 or 7 megapixel camera" or if it's double, then a "14 megapixel camera". Mine are about 4 and 6 megapixels. Also, the prices will continue to fall, so on the digital end, things will just get better and better. In a few years, this comment will move from the list of cons to the list of pros. See the section on digital SLRs for more information about this, however.

  But resolution isn't everything. The CCD that collects the light in the smaller digital point-and-shoot cameras like my Sony is very small compared with the size of normal 35mm film. The CCD in the big SLRs is now approaching and in some cases equaling the size of a 35mm slide. Even if the resolution of a 35mm digital SLR is the same as in a point-and-shoot, the results will be much better. The reason is that the area of the CCD devoted to each pixel will be much larger, so random variations in the number of photons collected for each pixel will be statistically smaller. If you look closely at digital photos from a point-and-shoot, you'll see that if you look at something that is pretty uniform, like the sky, that if you stand back, the average color is pretty good, but if you look at the individual pixels, they vary a lot. Thus big enlargements will suffer unless you do some good filtering.

  To see the quality possible with a 35mm camera with a decent-sized CCD, take a look here. The photo of the Barn swallow is particularly good, I think. This was taken with a Nikon D100.

  Also, when a digital camera is advertised as having "4 million pixels", that's really more like 1 million pixels as we normally think of them, since four of their pixels are used to gather what amounts to one pixel on your computer screen. Usually, they collect on four adjacent spots on the CCD two green samples, a red sample and a blue sample. (You need extra green for technical reasons.) Each pixel on your computer screen has a red, green and blue component.

  Digital cameras can increase the effective resolution with software, so the situation is a little better than what I described in the previous paragraph. And Sigma has something called the "Foveon" technology that also does better, but it's still expensive and it's not clear they'll be able to make a business of it.

• You can't take photos as fast with a digital camera. That's because after each photo the data on the CCD (which can be a lot; 4 million pixels worth of data on my camera at maximum resolution) has to be copied from the CCD to the more permanent memory of the camera. This may take between a half second and a full second for high resolution photos. By contrast, you can get standard 35mm SLRs with motor drives that can take 10 photos per second (and with effectively higher resolution, at that).
• If you're planning to take a lot of photos on your trip, you'll probably need to take along a recharging cable and/or extra batteries.

Digital SLRs

• The camera is designed very well to make it an easy transition to it from a standard film SLR. Almost all the controls have similar functions.
• At first I was disturbed by the fact that you still have to use the viewfinder to take photos. In other words, with a digital SLR you cannot view the photo-to-be in the digital display on the back of the camera as you can on the less expensive point-and-shoot digital cameras.

  This has a huge advantage, however. Using the relatively tiny digital display on the back of the camera, it is impossible (for me, at least) to tell if a photo is in sharp focus. With the standard SLR-like setup, you get to preview the photo on ground glass for an extremely accurate preview. It would be nice if both options were available; I'm not sure what the technical reason is that they are not. Can any of you readers help me?

  From a reader:

  "The reason why the display does not go on at the same time you are taking the picture is because the LCD screen on the back and the CMOS chip are so closely put together that they create a magnetic field and can distort images. The field, for some reason isn't strong enough in a CCD , which is what most point and shoot digital cameras use, however this is not the case with the higher end CMOS chip."

  The comment above makes some sense, since the 35 mm SLRs have to use the same lenses they did with film, so the CCD has to sit exactly where the film did, relative to the lens. If you're designing a point-and-shoot, you can use a lens that focuses closer to the front of the camera to keep it away from the CCD. The 35 mm digial SLR manufacturers could make the back of the camera fatter, but maybe it would be so fat that it's not worth the trouble.

• Your old flash does not work in TTL mode on this camera. To use TTL metering, you need a new digital TTL. The old TTL system works by measuring the amount of light that's reflected off the film and the flash is quenched when enough light has arrived. For some reason, this is difficult or impossible with a CCD, so the way digital TTL (Nikon calls it D-TTL) works is that a series of microscopic pre-flashes are sent out and the amount of returning light is measured. The proportion returning allows the flash to determine proper exposure.

  You can, of course, use the old flashes in manual or semi-automatic modes, but with the introduction of TTL, all my brain cells that remembered how to do this died.

• There is a problem with most digital SLRs except for a couple at the time this was written (Canon and Kodak have cameras that solve the problem, but they are very expensive).

  The digital CCD is smaller than a standard piece of 35mm film, so you are effectively cropping out the center of each shot. You paid gobs of money for lenses that could produce a good image over the entire 35mm film area, and you're now using only 2/3 of it or so. This makes it very difficult to take wide-angle photos. If you compare full-frame shots taken with the same lens on a film and my digital 35mm cameras, digital camera effectively multiplies the focal length by about 1.5. So if you slap on a 300mm lens, it's like using a 450mm lens on a film camera.

  This seems cool if you use telephoto lenses a lot, but if you want the equivalent of a 20mm wide-angle shot on a digital camera, you'd need to purchase a 14mm lens, which is not a cheap prospect at all.

• The situation with pixel count and resolution is more complicated than I originally thought. When you but a digital camera with, say 6 million pixels, it probably does not mean what you think.

  When I think of a pixel, I think of one spot on a computer screen that can display any color; a combination of red, green and blue. But on a camera, the advertized pixel count is simply the number of receptors. Each receptor can only (except on the Sigma Foveon cameras) receive one color -- red, green or blue. So at first glance, it looks like you should divide the advertised number by 3. But it's worse -- you really need to divide by 4, since the green receptors don't work as well and almost every digital camera uses two green receptors for each red and blue.

  What the digital cameras then do is to take the data from all these red, green, green and blue receptors and expand it to be a much larger number of pixels with clever extrapolation algorithms.

  On a digital SLR, however, it isn't quite that bad, however. A typical pixel on a computer screen has 8 bits of accuracy in each of the channels. In other words, it can distinguish 256 levels of red, green and blue for a total of 236x256x256 colors -- around 16 million. But the receptors on the Nikon, at least, can distinguish 12 bits of color for 4096 different shades of red, green and blue. This extra information makes the extrapolation more efficient, but it is hard to know the exact relationship between the advertised number of pixels in a digital camera and the number of "good" screen pixels you'll get on your computer.

• Most digital SLRs (and I think some of the digital point-and-shoot cameras as well) have a "raw mode" where what is recorded on the memory device is not translated in any way, but simply represents exactly the information recorded by the receptors on the CCD. If you take and store your photos in this mode, then in a sense you can do "anything" with the results later. If you save in, say, jpeg format, you've tossed out some information, and you'll never be able to get it back.

  The penalty for storing images in raw mode is simply the size. On my D100, each raw-mode image requires 9.6 megabytes of storage which can add up fairly quickly. If you get a 1 gigabyte IBM microdrive, it holds 103 raw-mode images on the Nikon D100. By contrast, it would hold more than 300 of the highest-quality jpeg images, or thousands of the low-quality images.

  Here are some additional notes on RAW mode that you may find helpful.

  If you decide to take raw mode photos on vacation, you'll need to take a laptop along to transfer your images every evening. This has the added advantage that you can toss out the ones that are bad, but not so bad that they don't look OK on the monitor on the back of the camera body. Obviously, for a day trip, 100 photos is usually plenty, especially since you can blow away the obvious errors just after they're taken.

• One of the drawbacks of my camera relative to the more expensive bodies is that it can be connected to the computer from the camera only by means of a USB connection which is relatively slow -- about 15 or 20 seconds per raw-mode image. With 100 shots, this can be a chunk of time. The more expensive bodies connect via firewire (IEEE 1394) which is significantly faster. You can, of course, get a firewire reader for the compact flash (or whatever storage device your camera happens to use).
• More expensive digital bodies also have larger buffers so that you can take more photos before you run into the bottleneck related to writing your data to the memory card (or microdrive). On my camera, I can take about 4 shots in raw mode before the buffer fills up. To wait for the buffer to completely empty, it takes around 15 seconds. Of course after about a quarter of that time, there's room for one more photo, et cetera.

  There is also a limit to how fast the data can be read out of the CCD to the buffer. On my camera it's about 1/3 second per shot. The bottom line is that I can take at most 3 shots per second, for up to four shots. Then I have to wait about 4 seconds for each additional shot. This doesn't seem too bad, but for flying birds or fast-moving sporting events, it's a pain in the butt, where a Nikon F5 can take 8 shots per second for a whole roll of 36.

Nikon School

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