Thursday, May 31, 2007
Is There A Medium-Format Digital In Your Future?
When it comes to ultimate digital image quality, nothing beats medium-format cameras and digital backs. The word 'medium' might be tepid—the image quality is anything but.
Not Your Mama's Point-And-Shoot
Beyond simple economies of scale, there are physical differences between small- and medium-format sensor design. The use of microlenses, for example, proliferates in D-SLR technology, but not in medium format. Because image sensors aren't completely covered by light-sensitive pixels and photosites react to light differently than film, microlenses are often used to focus light away from dead space and direct it at a more perpendicular angle directly into the pixels. This improvement in quantum efficiency translates into better sensitivity, or higher ISO capability, for the sensor.
So why wouldn't all medium-format sensors utilize microlenses? Because they're in professional cameras built for professional photographers.
“This is their business,” says DeLuca. “This is their livelihood, this is a photographic tool. The way medium format operates, you can take your back and put it onto multiple things. The person who's putting out a pretty significant capital purchase to get this tool for their business needs to be able to use it in multiple different applications. If you have an integrated camera and the back never comes off, and you're always putting lenses on and you have a system where the camera can identify what the lens is because it's all electrically connected, that's a pretty well-contained system. It's very similar to what happens in a D-SLR system. You can set up microlenses and optimize it, and it works great. If you're working in a back configuration, where you're taking the back and putting it on multiple cameras or taking the back and using it in a shift/tilt situation, you have no way to know the orientation of the back to the lens. So when you put microlenses on the device, they can actually interfere with the performance because they're trying to focus the wrong way. So today, the large sensors that we make—like the 39-million-pixel device—don't have microlenses for exactly that reason. While shift/tilt is a very small part of the market, it's a very important one.”
Because one-size-fits-all doesn't work for professionals, some medium-format sensors are packaged with microlenses—mainly for photographers who consider increased sensitivity integral to their workflow.
“In a studio, the difference between ISO 100 and ISO 160 is probably not that big of a deal because you can compensate around that pretty fast,” says DeLuca. “Now, in other applications, like if you're working a wedding and you're handholding, and you're able to pick up a stop, that's huge. In that configuration, getting as much sensitivity as possible becomes much more important. That's why our 31-million-pixel device does have microlenses on it.”
Another major difference between medium-format and D-SLR sensors is also about size—file size. Larger files not only mean more work for photographers in post-production and management, but they're also a concern for engineers who must put these high-powered sensors into functional cameras and backs.
“Great,” says DeLuca. “The size of the sensor is physically large, you've got 39 million pixels. Now you've got 39 million pixels! You've got to deal with a whole bunch of data, you've got to come up with an architecture to read it off of the sensor and then process it in the camera. That's a lot more things to think about than if you only have 5 million pixels.”
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