Digiscoping Primer--page 4

6) Link the camera to the scope...

One way or the other, you need to hold the camera securely so that the camera lens is as close as possible(!) to the eyepiece lens (preferably without a metal-glass contact that could scratch the lens). There are two strategies here. First is to attach the camera to the eyepiece or scope support. This isn't easy, as the scope manufacturers never anticipated hanging a camera back there; you will need some sort of mechanical adapter. Links to several suitable devices are in the "Linking camera to scope" discussion. An advantage of this method is that the transmission of hand shake--your heartbeat and involuntary muscle tremors--is minimized, so you can shoot at lower speed. However, one serious disadvantage is that the mechanical adapter complicates the act of looking through the scope. Another is that adding the weight of the camera to the scope can radically change the balance atop the tripod (and, of course, is more weight the support must carry vibration-free).

The other approach is to hand-hold the camera to the scope eyepiece. Since the scope eyepiece is usually of larger diameter than the Coolpix lens, it's useful to have a mechanical means of locating the two lenses along their centerlines. This way, you can look through the scope as usual, and quickly align the camera for a photo when you see the opportunity. The support doesn't need to be strong enough to support the camera--it simply helps to steady the camera lens in the center of the scope eyepiece. People have used 35 mm film canister caps, cut sheet rubber, and pill bottles as hand-held adapters. For the Leica 32x eyepiece, a useful device is a 28-37 mm step-up ring, a non-optical annular disk that threads into the Coolpix lens; its outer diameter fits just inside the slightly-extended eyecup of the eyepiece. Hold the camera firmly against the eyepiece--if your support is solid, the scope shouldn't shake or change its pointing--focus, and gently squeeze the shutter.

7) Memory is cheap!

When you press the shutter button, the CCD unloads its content (the image) into a memory buffer. From this buffer, the camera transfers the image to your memory card. Each pixel records an intensity level from 0 to 255 for each of the red, green, and blue channels. Since there are three channels per pixel, the total image size is 3 times 3.3 Mpix, or close to 10 megabytes. It takes 8 bits to represent a number up to 255 as a byte, so the camera is said to operate in 24-bit mode.

The camera could store the entire 10 Mb file on your memory card--with the Coolpix, such a file is stored in TIFF format. However, such large files are slow to manipulate and would rapidly fill your memory card. The camera therefore gives you the option of compressing image files as they move into the buffer. The degree of compression is set with the "Quality" command on a Coolpix, and compressed files are stored in JPEG format. The Coolpix 990 stores non-compressed files with the "hi" command, and 1/10, 1/20, and 1/40 compression factors at "fine", "normal", and "basic"; the resulting files are about 1 Mb, 500 kb, and 250 kb respectively. Note that regardless of compression level, every image retains the same number of pixels--compression changes the amount of memory each pixel requires, not the number of pixels.

File compression has two great advantages. Since the image files are smaller, you can store more on a single memory card. For bird photography, an equally important benefit is that you can take more photos in rapid succession if the files are smaller. This is because the camera's buffer is of fixed size, about 4 Mb; once the buffer fills, the camera must send the buffer contents to memory. In "single" mode the buffer flushes to memory after each shot. This process takes several agonizing seconds during which the camera is unresponsive. However, if the image files are small, several can fit into the buffer before it flushes. This allows you to shoot at two frames per second, in "continuous" mode, from four to eight frames (at "fine" or "normal" quality, respectively) before the camera must pause to write to the memory card.

Why is it useful to shoot several photos in rapid sequence ("continuous" mode)? Because birds are dynamic, you may capture several interesting poses as the bird moves, looks around, tends to nestlings, etc. From a technical perspective, shooting several frames in sequence also reduces camera motion for two reasons: first, you've already depressed the shutter button, so the motion induced from that action has faded; and second, if working in autofocus mode, the camera will not refocus during the sequence (it focuses prior to recording the first frame).

The disadvantage of JPEG compression is that it is "lossy". The JPEG algorithm works by discarding image information judged to be unimportant; the more extreme the level of compression, the higher the threshold of "importance" is set. On a computer screen, images saved in "fine" or "normal" mode are generally indistinguishable from those saved, uncompressed, at "hi". If you intend to print photos, however, save at least in "fine" mode; remember that printers use much higher resolution than the best computer display. Use "basic" mode only if camera memory is critically short.

Click "Stop" to stop animation

Birds blink frequently!

The best shots are candid shots

Shoot as many frames as you can. If one in ten is exposed nicely, focused crisply, and has a compelling image...you're doing well!

Continue to Image Processing Primer

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