Alpha Imagin

When you first look through an H-Alpha filter you will be struck by the deep red color of the image. It is immediately obvious that this is a redder red than you see in everyday life, and the color may be a bit off-putting at first. However, this is no problem for the CCD detector in a webcam, which is very sensitive at 656 nanometers. A monochrome webcam like the ATiK 1HS is the best choice as it is pointless using a color webcam for such narrow-band work. However, digital SLRs, and even small non-SLR digital cameras have been successfully employed and even hand-held to the eyepiece! The Scopetronix Company makes excellent digital camera-to-eyepiece adaptors. (www.scopetronix.com). Some early DSLR users have reported a moiré fringe effect when using an H-Alpha system, with the narrow wavelength somehow causing an optical interference with the camera's inbuilt filter and pixel grid but most users have reported no such problems. Some H-Alpha imagers have even used low-cost monochrome security cameras combined with a frame-grabber to collect images of prominences. However, using the same techniques as the planetary observer (already discussed at length in this book) will secure the best images, i.e., by using a monochrome webcam and processing in Registax. Of course, once you have the final stacked solar image there is nothing to stop you coloring it a more pleasant yellow/gold color in Adobe Photoshop or Paintshop Pro. In general, and especially in the cheaper, wider bandwidth filters, the solar disc is much brighter than the prominences and each may require a different degree of image processing in Registax. So, for whole disc images with a DSLR, the best solution is to use a longer exposure setting to record perfect prominences, but with an overexposed disc and a shorter exposure setting to just expose the disc features correctly. Each image can then be optimally processed and, with Photoshop or Paintshop Pro simply crop out the disc detail within the solar diameter from the shorter exposure image and paste it on top of the brighter prominence image. If using a digital camera you may well find that different color channels in the RGB image show different amounts of contrast, even though the image is supposed to be purely red! This is because digicam CCD pixel green and blue filters have some red leakage and, remarkably, the contrast in the green and blue channels can sometimes be more useful than the red!

However, for the very best high-resolution images, just use the same techniques as for the Moon and planets, i.e., a webcam, preferably monochrome, and Registax to process the AVIs. For more information on Coronado and Solarscope see the Appendix.

A digicam picture, by Maurice Gavin, using a Coronado PST, is shown in Figure 16.5. Maurice' Coronado PST itself is shown in Figure 16.6. Two superb H-Alpha images using a Pentax 75-mm refractor and a Coronado Solarmax 40 H-Alpha filter are shown in Figures 16.7 and 16.8.

Finally, whatever type of solar observing you do, do it safely. Let the camera and the webcam do the imaging and notyour eye. Eyes cannot be replaced.

Good luck on your imaging adventure, whatever object in the solar system you choose to study!

a prominence evolves over 8 hours 2005 AprlS @ 0752UT

west limb pa~270o

2005 AprlS @ 1205UT

2005 Apr 18 @ 1549UT

"Coronado PST+ Minolta DT Maurice [email protected]

Figure 16.5. An excellent montage showing the development of a solar prominence over a few hours, taken with a Coronado PST and Minolta digital camera. Image: Maurice Gavin.

Figure 16.6. The Coronado PST. A 40-mm aperture f/10 H-Alpha telescope for under $500! Image: Maurice Gavin.
Figure 16.7. An H-Alpha image of a solar prominence taken by Paolo Lazzarotti using a Pentax 75-mm refractor and a Coronado Solarmax40 H-Alpha filter. A Lumenera LU075M video camera was used. 300 out of 1,000 frames were stacked. Image: Paolo Lazzarotti.
Figure 16.8. An H-Alpha image of a sunspot taken by Paolo Lazzarotti using a Pentax 75-mm refractor and a Coronado Solarmax40 H-Alpha filter. A Lumenera LU075M video camera was used. 500 out of 2,000 frames were stacked. Image: Paolo Lazzarotti.

APPENDIX

Web Pages for

Software, Hardware, and Observers

Web page addresses (URLs) change with time, especially those belonging to amateur astronomers. If a few of these links become obsolete during the production time of this book, simply go to a search engine like Google and type in the company name/amateur's name and a few key words. The new address should be located after a bit of searching.

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