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Sunday, July 1, 2007

Lenses For Panoramics

Perspective Control In Panoramics • Tripod Shopping • Megapixel Printing • Is What You See, What You Get?

Megapixel Printing

Using an 8-megapixel camera, what are the largest prints I can reasonably make?
B. Johnson
Via the Internet

There are a lot of variables here, starting with the kind of camera you’re using. All megapixels aren’t created equal. A point-and-shoot or advanced compact digital camera typically has a 5.32x7.18mm sensor. That’s a lot of tiny pixels packed together on a very small surface, and the potential for noise and image degradation is noticeably greater when prints are enlarged from these cameras.

At the other end of the 8-megapixel scale, the midrange digital SLRs have a sensor of approximately 23x15mm—nearly 10 times the surface area of the smaller sensor. The pixels are larger, allowing better light-gathering capability and better color, minimizing noise. The files captured with these cameras are capable of producing much larger prints.

But it’s not only pixels that matter. The maximum print size is a subjective decision for each photographer, but I’d set a maximum of 13x19 inches from an excellent capture (sharp, good color, proper exposure and controlled contrast) taken with the smaller-sensor cameras. A capture from an 8 MP D-SLR with the same excellent file qualities is capable of a print in the 16x20- or 17x22-inch size. Of course, these results require that the prints are being made on a photo-quality inkjet printer, with proper media profiles. You can extend the size if you print on a watercolor or canvas media because less detail is required on these surfaces.

Is What You See, What You Get?

I’ve heard that the information I see on the LCD on the back of the camera isn’t very accurate when compared to the actual image file captured. Is this true, and if it is, how do I get better information?
B. Williams
Via the Internet

What you’ve heard is right. That little LCD isn’t capable of giving you an image that matches the file. That said, the newer 2.5-inch LCDs can give you most of the information you need to determine whether your capture is well composed, sharp and properly exposed. It’s this last feature that requires some extra attention when you’re working in the field.

The image on the LCD can give you reasonably accurate exposure information at a glance if you first keep the brightness of the LCD to its middle setting (usually this is the default). Some photographers set the brightness up when working outside so that they can see the image better. But this gives a false sense of the brightness of your image capture.

You can circumvent this problem by throwing a dark cloth over your head and pretending you’re shooting large-format. No, just kidding. You can get the HoodLoupe by Hoodman (www.hoodmanusa.com), a handy little gadget you hang from a strap around your neck. It fits over your LCD and slightly magnifies it, letting you get a clear view even in bright sunlight.

The LCD can also tell you whether you’ve overexposed the highlights; you’ll see a flashing highlight-warning that indicates blown-out areas that have no detail. The "blinkies" reflect the camera’s JPEG setting, so if you’re shooting JPEGs, you can believe what you see. But if you’re shooting in RAW, you’ll need to make some adjustments in your camera software to get a correct "blinky" reading. Setting the JPEG contrast parameter to its lowest setting will give you an accurate reading in RAW.

Finally, learn to love—and believe—your histogram. A histogram that’s piled up against the left, or black, axis is telling you there are no details in the shadows of your image. A high pixel count against the right, or white, axis, says you’re overexposed and have no detail in your highlights. Unless you’re shooting coal or a pure white sheet of paper, you want to keep your histogram off those two edges. Check it, and adjust your exposure as necessary to move the captured data away from either end.

The LCD may not give us as perfect a rendition of our images as we can see on our computers, but it gives us enough information so that there’s no excuse for bringing home images that lack the critical elements of sharpness, composition and exposure. One of the great benefits of shooting digital is the ability it gives us to make our corrections in the field and to get the best possible image file before we begin to optimize it in the computer.

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