With webcam and laptop ready to go, it's time to take the whole set up into the field. When imaging at home (there's no need to go to a dark site for planetary picture taking), use an extension cord from the house or a garden outlet to provide AC for the computer. Yes, laptops have built-in batteries, but most will poop out in an hour or less. Nothing is more annoying than having the computer battery die just as the good images are starting to roll in.
Power ready and scope aligned and tracking, it's time to hook camera to scope. How? For high resolution images, insert the camera's nosepiece into a Barlow lens and insert this Barlow/camera combo into the scope's visual back. Start with a 2x Barlow, and, once framing and focusing become easy (with practice), move up to a 3x for even higher resolution—assuming atmospheric seeing will allow that. The more magnification supplied by a Barlow, the more the image will fuzz-out under poor seeing.
The initial challenge for the novice webcam imager is twofold: framing and focusing. Even with an accurate go-to scope, it can be incredibly difficult to get Jupiter (or anything else other than the Moon) in the field of the camera. In the beginning, in fact, this will seem like an almost insurmountable difficulty. Webcam chips are small, and at a focal length of 4000mm (2x Barlow + 2000mm C8) even bright objects are hard to find. The fact that the planet will probably be way out of focus at first doesn't help, either. One trick that can be used to get a planet pinned down is to set the webcam control program for "autoexposure." The image will be very overexposed, but it will be easier to find if it's a big, bright blob.
The best way to find planets with a webcam? With a flip mirror. A flip mirror, like Meade's $150 model #644 seen in Plate 71, is a special sort of star diagonal. It threads onto the scope's rear port and normally sends light up a focus tube to an eyepiece, like any other diagonal. There's a knob, however, that allows the mirror to be flipped down, sending images straight out the back of the assembly to a Barlow lens and camera. Center Jupiter in the field of the eyepiece, flip the mirror down, and the planet should appear on the laptop display. Flip mirrors' eyepiece tubes can be adjusted via a helical focuser, so that what's in focus in the eyepiece is also in focus on the camera (some minor focus tweaking will probably still be required). The tilt of the flip mirror can be adjusted if necessary so whatever is centered in the eyepiece is precisely centered on the webcam chip. Flip mirrors make the difference between a hair-pulling experience and a pleasant one.
Focus is the other bugaboo for webcam imagers. Close is not good enough. At high magnifications precise focus makes the difference—more difference than anything else—between good images and poor ones. It's not unusual to spend a half hour focusing initially and to continue to tweak focus throughout an evening. What should good focus look like? The planet should be reasonably sharp edged (Jupiter's limb is never razor sharp), and some surface details should be discernable, if not nearly as detailed as they will be in a finished image. K3CCD Tools includes a focus indicator that displays changing numbers. The better the focus (brighter the image), the higher the numbers. Details invisible no matter how focus is adjusted? Probably seeing is not good enough for planetary imaging. Sometimes seeing improves as the night wears on, but it's usually best after sunset, and if it's poor then it's usually time to pack everything up and wait for a better night. Such is the nature of amateur astronomy.
Plate 71. (Meade 644 Flip Mirror) A
flip mirror like Meade's model #644 makes it easy to center planets on tiny webcam chips. Credit: Author.
How about exposure? Webcams have several settings that will need adjustment. The first is frame rate, which can typically be set so the camera delivers images to the computer at 5, 10, 15, and more frames per second. This should normally be set to 5fps. Higher frame rates are achieved by compressing images before they are sent to the laptop—which doesn't do anything good for resolution.
Exposure time and brightness need to be set as well. The goal should be the shortest exposure possible; one in which the "live" on screen image looks a little dimmer than what would look good for a finished image. It's probably best to keep brightness no more than about ? of maximum. There are also controls for hue and saturation and gamma. Leave these at their halfway settings at first and play around with them later. The final control is sharpness. Leave this low, but not at zero. Too much sharpness will introduce noise, but too little will cause weird artifacts in finished images. Jupiter will take on an "onion skin" appearance around its limb. Leave sharpness at about 1/5 of its travel or a little less.
Once everything is set, start taking pictures. Try to obtain at least 10 to 15 "good" .avi sequences of 60 to 90 seconds. Next? The real work begins—image processing beginning with Registax. Registax takes an .avi video and stacks the hundreds or thousands of frames into a still image. Not only that, it will automatically throw out any frames that don't meet a baseline for quality that's established by the user picking a "best" frame before beginning the stacking process. Stacking many frames in this fashion results in a final picture that's much less noisy than any of the individual frames in the .avi video sequence.
Registax doesn't stop there, though. It's also got an array of image processing tools. Some of these are similar to what's found in Photoshop or similar programs, but one is unique, the "wavelet" filters. This consists of a set of sliders that adjust the sharpness of the image's various "layers." Each one of Registax's multiple sliders works on a different size of detail. What the wavelets do is apply unsharp masking to the various detail sizes in the image. To truly understand the way this works would mean mastering some fancy math, but using the wavelets doesn't require that. Once stacking is finished, play around with the wavelet sliders to see what looks best. The results, even in the beginning, will be astounding.
What makes Registax able to produce images so much better than what was possible before? By using Registax, amateurs are, for all intents and purposes, equipping themselves with adaptive optics. Professional scopes use various complex and expensive systems to counteract seeing effects. The process often requires firing a laser beam into the sky to create an artificial star for use as a reference. Amateurs, however, are doing the same thing with our cheap webcams and laptops. By taking many, many frames and including only those taken during the best seeing in the final composite image we are accomplishing the same things the pros are doing with lasers and tilt mirrors.
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