Q&A: Comparing Pixels to Film
I'm looking to make the move from film to digital. How many megapixels would a digital camera need to have in order for its resolution to be equivalent to a 35mm SLR? 6.3? 8? 11? More? My current thinking is to begin by purchasing a high-resolution scanner and getting a digital camera later. What kind of quality do I need so I can't tell the difference between a digitized 35mm slide and a real 35mm slide when projected on a screen?
--Andrew Apicos, San Diego
You've asked the million-dollar question, Andrew. Everyone always wants to know how many pixels it takes to match film.
Unfortunately, the answer isn't easy to pin down. I have to agree with all of the numbers you put out. It simply depends. If you shoot ISO 400 film with your 35mm camera, then 6 megapixels is probably enough to reach parity. If you shoot on ISO 25 slide film, you're going to need more like 12 megapixels in your digital camera to get a similar result.
And don't forget that the quality of your photographs--both digital and film--is strongly influenced by the available lighting, the shutter speed, and other factors.
The simplest answer is that 6 to 8 megapixels is a good starting point for matching the quality of film. Higher resolutions allow you to make progressively bigger prints or perform more aggressive cropping and still get a high-quality print.
Comparing digital and film slides has similar complexities. If the size of the projected slides is small enough, the digital resolution is almost irrelevant. The longer the throw of the projector, though, the more resolution becomes an issue: Obviously, the larger the image, the more obvious digital artifacts and jagged pixels will become.
But all that's theoretical: It's simply not possible to project a full-resolution 12-megapixel picture anyway. That's because even high-end HDTV projectors--models that cost $10,000 to $20,000--deliver a native resolution of 1280 by 720 pixels. That sounds low, but the results can be stunning.