Want to buy a digital camera but not sure what to look for? Bought a 4-megapixel camera and wishing you had a 7? I'll explain why you are probably better off with a quality 4-megapixel camera than one with higher numbers.
Ever since digital cameras entered my life, hardly a day has passed without my snapping a photo or two. I did a lot of reading on digital cameras before making my purchase, and I made allowances on price and performance for my final decision. How did I purchase a digital camera? For me, with digicams what matters is image quality, image size, and camera speed. Secondary factors are camera size, power, storage, and zoom. I'm only interested in consumer cameras at this point, so I won't cover digital SLR cameras, but the fundaments apply to all digicams.
Image quality is affected by the lense, the image sensor, and the compression used on the image. Almost all consumer cameras use JPEG compression, and I recommend you set your camera to the highest "quality" level possible; this means less image compression. Prosumer cameras will save in TIFF or RAW formats, but that's out of my price range (more than $500).
The lense gathers the light for the sensor, so the better the lense on the camera, the better your image starts out. It is like wearing glasses; if you prescription is correct and the lense is high quality, you get to see the world for what it is, rather than blurred or distorted. Once past the lense, the image sensor takes what it sees and translates that into a JPEG file on your digicam's storage. The better the sensor, the more accurately it will translate what it sees.
Digicam that emphasis the lenses they use are probably using better lenses, so look up the lense manfactuer; it may influence your decision. That said, plenty of film cameras manufacturers have been good about using good lenses and sensors in their digicams. This explains why there are no-name, 5-megapixel cameras advertised for $119... Low-cost sensors and plastic lenses will shave a lot off the cost of a camera. Like most things in life, if it sounds too good to be true, it probably is.
What's with megapixels, anyway? A megapixel is a function of your maximum image size. Megapixels are not units of measurements in the way celcius is a measurement of temperature. You should know that your camera has a "maximum resolution" rating; mine is 2560 by 1920 pixels. To get the number of megapixels, just multiply those two numbers and divide by 1,000,000... my camera is 4.9 megapixels. When printed, about every 300 pixels translate to one printed inch, or 300 PPI (pixels per inch).
Do the math... at 300 PPI, how many pixels verically and horizontally do you need to get a 4x6 photo?
4 x 300 = 1200The minimum image size for 4x6 photo is 1800 x 1200 pixels. See?
6 x 300 = 1800
Now, you might think that you would just need a 2.2-megapixel cameral to capture 4x6 photos (1800 x 1200 / 1,000,000 = 2.16). This would be true if cameras captured pictures at a 3:2 ratio, but digicams tend to captures photos at a 4:3 ratio, which is the same ratio as most computer monitors. At 4:3 a digital camera have to capture 1800 x 1350 pixels to have enough data to print a 4x6 photo at 300 PPI.
For cameras capturing pictures at 3:2 ratios, assuming you are printing them at 300 PPI, you would need at least a 2.5-megapixel camera to print a 4x6 photo, a 3.3-megapixel camera to print 5x7 photos, and a 7.8-megapixel camera to print 8x10 photos.
Another thing that the aspect ratio of your digicam affects is the crop of you pictures. If a 4x6 is 1800x1200 pixels and a digicam captures a photo at 1800x1350 pixels, that means 1/2 inch of the picture you give your developer to print is cropped from the top or bottom of the photo. For truly picky people, it may be advisable to pre-crop your photos before having them printed.
300 PPI vs. 320 PPI
Many people print their own photos at home. Most affordable consumer photo printers print at 300 PPI. I did not want to spend the money on the paper or printer; the price per print is still higher than what I pay at Costco. I read in a recent Costco Connections magazine that Costco uses Noritsu 3111 printers for processing film; the Noritsu produces photos at 320 PPI.
Redoing the math, at 320 PPI, I would need 2.8-megapixels for 4x6 prints, 3.8-megapixels for 5x7 prints and 8.8-megapixels for a 8x10. My camera will give me a maximum of 6x8 prints, so I should stick with 5x7 prints.
I would suggest purchasing a high-quality 4-megapixel camera with good lenses and performance over a 7-megapixel camera. After 4-megapixels, the next meaningful leap is almost 9-megapixels! Everything else inbetween isn't really adding anything for you, except giving you more lee-way to take a shot and crop off large areas. If you want the room to trim your photos, 5-megapixels should be plenty.
The bottom line is: for a consumer camera, go for brand name digicams with quality lenses that feel fast to you. Do not purchase anything less than 3-megapixels but don't bother buying anything more than 5-megapixels.
For an alternative viewpoint and some good tips on purchasing in general, check out this PC Magazine article on Digital Cameras.
For another explanation of megapixels and lenses, see this PC Magazine article.