Solar Images from a Small Telescope

Below are selected solar images I've acquired with a cannibalized inexpensive webcam (the guts of a Philips Vesta 675), cooled with two small CPU fans, and a video camera. The cameras are attached to an inexpensive 150 mm f/8.0 achromatic refractor (one of the recent Chinese imports). The CCD in the Vesta series of webcams is a 659×494 5.6 micron square-pixel Sony color CCD. The onboard electronics resamples to produce 640×480 8-bit RGB output. The video camera CCD has 768×494 pixels, 8.4×9.8 microns.

Most of the early imaging here was done both at prime focus and with a good-quality, 3-element barlow. (Some of the oldest images were obtained with eyepiece projection.) Just in front of the camera I have an 82 Angstrom FWHM filter centered on 5200 Angstroms. This completely removes the chromatic aberration from the inexpensive doublet objective lens. Most recently, I replaced the barlow with a Televue 4x Powermate stacked with a Televue 2x "Big Barlow". These are 2-inch diameter components, so I had to cobble together a 1.25-to-2 inch adapter so I could keep using the 1.25-inch Herschel wedge. Later I obtained a 2-inch Herschel wedge from APM Telescopes in Germany.

A brief description and photos of my solar imaging setup and other hardware can be found here.

Nyquist sampling for this telescope and CCD occurs around f/24 or so. Prime focus imaging is therefore undersampled and benefits from the stacking of several frames. Flat fields, suitably normalized, were divided into all frames (thus removing most of the dust speck shadows) before any kind of processing was done. Orientations indicated are approximate. The Earth images are to scale.

Recently, special attention was paid to scattered light. I coated the insides of the refractor tube and extension tubes with the coarse, non-skid material from 3M that is used on cement steps. (It has an excellent adhesive backing.) I painted everything with Krylon ultra-flat black, including the non-skid material. Until recently, I've been using a full-aperture filter made of the excellent Baader solar filter material (both visual and photographic densities). I now use a Herschel wedge, thus dispensing with the Baader filter. The images are noticeably sharper with the wedge, and much brighter, thus allowing larger magnifications. As you'll see below, I can now easily record granulation and penumbral structures, despite the shortcomings of the inexpensive, 8-bit webcam, and the not-so-inexpensive StellaCam II video camera.

Click on the thumbnails to view full-resolution images.

AR0606 on May 14, 2004

New video camera acquired and used for images from here on up. I now have an Astrovid StellaCam II, which is essentially a Watec 120N camera. The CCD has 768×494 pixels, 8.4×9.8 microns. I'm using a frame grabber from ImperX to transfer the images from the camera to a laptop hard drive. Pixels are squared off in software to 8.4×8.4 microns for the images shown here. I'm also now using a narrower, 30 Å FWHM, filter centered on 514.5 Å.

AR10380 and AR10377 on June 6, 2003

New image scale from here on up. I now have a Televue 4x Powermate in tandem with a Televue 2x "Big barlow" and a spacer. The resulting image scale (0.0665 arcsec/pixel) is well beyond what is reasonable for a 6-inch refractor, but having 15 or so pixels across a resolution element (~1 arcsec) allows aggressive removal of the webcam image resampling and compression artifacts. That I am able to get images at this scale at all is due to being fanatical about scattered light in the optical system. I'm now adding false color, which appears to enhance perceived contrast.

AR0076 on August 18, 2002 (false color)
This is a small spot in its declining phase that swung into view at the eastern limb on August 12 and gradually shrank over succeeding days, finally disappearing around August 22, about three days before reaching the western limb. Notice in this image the nearly complete lack of any penumbra, as well as the grains clogging the umbrae.

AR0079 on August 18, 2002 (false color)
Click on the thumbnail below to see a 1/2 scale image (76 kB).
For the full-resolution image (141 kB), click here instead.

AR0050 on July 29, 2002 (false color)
Click on the thumbnail below to see a 1/2 scale image (78 kB).
For the full-resolution image (143 kB), click here instead.

AR0036 on July 21, 2002

AR0030 on July 16, 2002
This magnificent complex was easily visible with the unaided (and filtered!) eye.
Click on the thumbnail below to see a 1/2 scale image (104 kB).
For the full-resolution image (206 kB), click here instead.
For a movie clip, click here (.avi, 3.3 MB, 63 seconds, 320x240 at 10 f/s; reduced from the original 680 MB recording done at 640x480 and 5 f/s).

AR0008 and AR0016 on June 29, 2002

AR9973 on June 1, 2002

AR9934 on May 4, 2002

Herschel Wedge acquired and used for images from here on up.

AR9800 showing rapid evolution over 24 hours (January 26 and 27, 2002)

A 14-second movie of AR9800 on January 27, 2002, illustrating the effects of atmospheric seeing. Note the waves passing from left to right, due to an upper-level disturbance passing over the region.

1.7 MB .avi
2.2 MB .mpg
The AVI file is better quality than the MPG. The 10 fps video is a stretched, blurred (to remove pixel defects due to Philips driver interpolation problems), sharpened, and highly compressed copy of the original AVI captured at the telescope. Observation details are the same as for the Jan. 27 still frame shown above. Orientation of the movie is South up, West to the left.

AR9787 on January 26 and 27, 2002

AR9801 on January 26, 2002

AR9787 at prime focus on January 20, 2002

AR9751-64 at prime focus on January 01, 2002

AR9742 on December 19 and 22, 2001

SE part of AR9690 on November 12, 2001. This monster spot
group was also easily visible with the (properly filtered!) naked eye.

AR9682 on November 1, 2001, at both prime focus and f/24,
as well as a prime-focus shot of the SE limb region. The AR9682
complex was visible with the (properly filtered!) naked eye.