Ran

Figure 3.12. Mars 2003 - shot when only 18 degrees above the horizon. From left to right, single frame from a video; best 50 frames from a video of 250 frames; ditto sharpened; composite from 6 videos. Note the blue haze over the northern pole.

Figure 3.13. Crescent Moon Mosaic by Keith Mallelieu and David Ratledge, taken using a Philips Toucam with an 8-inch Newtonian (2x converter). The 27 sections were assembled using MAXIM. Full image (much reduced here) is 8 megapixels and has been printed more than 3 feet (90 cm) high.

Figure 3.14. Albireo - taken with Toucam Pro and 16-inch Newtonian at prime focus. Best 50 frames from a single video.

time and the working files produced can require several gigabyles of spare disk space! Registax is somewhat similar but produces interesting graphs/charts as processing progresses.

For covering the Moon, mosaics of several images can be assembled (see Figure 3.13). This enables even the smallest chip to produce a megapixel image! Not only that - with each image using only the central on-axis field the quality is the best your telescope can deliver. It is desirable to expose all the sections with identical exposure settings. This makes blending one to another much easier. For the Moon this means choosing an exposure that doesn't burn out on the brightest features and using that for all sections. To assemble the Mosaic, IRIS has a manual command (offsets have to be entered), but I prefer Maxim as it is so much easier, with images being overlaid by eye. I usually try for an overlap of about 100 pixels.

I also have tried deep-sky objects but, without modifying the electronics of the camera (see Chapter 4), this is limited to the brightest Messier objects - that 1/25th-second maximum exposure is just too short (see Figure 3.15). However, without the modification it is ideal for double stars. Traditionally, double stars have been difficult to photograph or image but using a webcam and shooting a video sequence the seeing can be (almost) frozen and excellent results obtained. The double star images shown in Figure 3.14 were obtained by shooting around 200 frame videos and selecting only the best. I found it advantageous to turn up the gain setting on the camera. IRIS was used to register and combine the images before slightly sharpening using its Richardson-Lucy routine.

Another use for webcams is guiding. For training the periodic error correction (PEC) of my drive I use IRIS and my webcam. This is so much easier than continuously looking through the eyepiece at an illuminated reticule. If the computer used for this is connected to the telescope and is able to issue commands to move

Figure 3.14. Albireo - taken with Toucam Pro and 16-inch Newtonian at prime focus. Best 50 frames from a single video.

Figure 3.15. Double stars and deep-sky objects taken with an unmodified Toucam on a variety of telescopes and telephoto lenses.

Double Cluster in Perseus

Figure 3.15. Double stars and deep-sky objects taken with an unmodified Toucam on a variety of telescopes and telephoto lenses.

Figure 3.16. Autoguiding with a Webcam using IRIS. Note how the brightest star is shown as a cross rather than as an image. This makes manual guiding for PEC training very easy.

it, then auto guiding with the webcam is also possible. IRIS includes the commands to do this for LX200 compatible telescopes, and it can autoguide in RA and DEC or RA only (see Figure 3.16).

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