![]() ![]() Focusing is accomplished by turning a blue ring around the lens, but unlike many such focusers (including that on the Fire-i camera), this ring is comfortably stiff and textured, so that the action of turning the focuser is positive and accurate. The design of the iBot is conventional in many regards, a spherical camera on a mount, though with a FireWire cable hanging from the back instead of a USB one. In this Corner… the iBot Pro from Orange Micro The solution is to avoid the USB bottleneck by using FireWire, a much faster interface (400 MB per second) that allows both high resolution and rapid frame rates. Basically, with USB you can either have high resolution or a fast frame rate, you can’t have both. This is especially obvious if you are using the webcam on a microscope or telescope where the target object covers only a small part of the CCD, and you want every scrap of image fidelity you can get. Aggravating the problem is the compression, which is lossy, so that while each frame appears reasonably detailed, small features can become blurry. What normally happens is the frame rate drops to keep the image quality of each frame within the parameters desired, so instead of a flowing, real-time movie you only get more of a slide show effect, with only five or ten frames per second. Up to a point, this works, but if you try to record high resolution movies (say, 640 by 480 pixels) in full colour and with a decent frame rate (around 30 frames per second), the compromises the camera has to make become very evident. What USB webcams do is to compress the data before sending it down the USB cable that way they keep the actual amount of data being sent manageable while trying to keep the image quality reasonably high. This creates a bottleneck between the image data the webcam is collecting at one end and the computer receiving the data at the other. The USB interface is convenient and reliable, but it is relatively slow, with a maximum data transfer rate of about 1 MB per second. The main reason for this has been the widespread use of the Universal Serial Bus (or USB) version 1.1 interface by both Apple and the various PC manufacturers for their computers, making it cost-effective for webcams that support both operating systems to be produced and distributed. Until recently, the majority of Mac-compatible webcams have been USB devices. Although inferior to cooled, long-exposure CCD cameras, webcams do have the benefit of costing far less and being simple enough to get good results with almost at once. But my favourite use of webcams is for simple astrophotography. ![]() I’ve used webcams to film kittens for a cat breeder, to produce movies for kids to share with their parents, and to photograph astronomical equipment for my web site. They can be used to take stills of adequate quality for webpages and the like, and as movie cameras they are great for recording family events for burning to CD and sharing with others. Webcams are among my favourite computer accessories because they are inexpensive and versatile.
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