Astrophotography With A 3.5-inch Questar Telescope

Webcam Astrophotography
Digital Camera Astrophotography With Nikon 4500
Digital Camera Astrophotography With Leica D-LUX 3 (New)
Total Lunar Eclipse
Techniques and Limitations (Updated)
Hand Sketches

New - Updated 28 May 2007 to include Digital Camera Astrophotography With Leica D-LUX 3 (New)


* Note that if a "hand" symbol appears when a cursor passes over an image then clicking will expand the image. *


$ The techniques used to obtain these images are described in my Techniques and Limitations (Updated) page. $


The pictures on this page were obtained with a Philips ToUcam PRO II webcam. The technique used is "Afocal Astrophotography" in which a camera takes photographs while emplaced in a telescope's eyepiece port.

My telescope is a 1979-made Questar. It is a 3.5 inch Maksutov-Cassegrain with a focal length of 1300 mm. It has a battery-operated Powerguide II that guides the telescope along the Right Ascension coordinate compensating for the earth's rotation.

Despite windy conditions on 17 November 2005, acceptable images of the Eastern portion of our Moon were obtained as seen in the four pictures below. The fifth one represents a "photomerge" of the preceding four images using Adobe Photoshop Elements.






I also attempted Mars because its closest approach on 29 October, the perhelic opposition of 6 November and the aftermath presented favorable opportunities. Given that Mars has about half the equatorial diameter of the Earth and has a low albedo (or surface reflectance) compared, e.g., to earth, imaging it is a challenge. While the result of taking still shots with digital cameras has also been described in these pages (Digital Camera Astrophotography With Nikon 4500 and Digital Camera Astrophotography With Leica D-LUX 3 (New)), I have obtained more satisfactory results with the ToUcam especially for planets.


Shown to the left is Mars on 30 November 2005 at 9:29 pm EST. In K3CCD Tools, ToUcam was programmed to capture at a rate of 7 fps (i.e. frames per second) with a total capture time of 75 seconds (see Note i). I set the video format to 640 x 480. The ToUcam exposure value was 1/25th of a second. Gain was set to its lowest value and Brightness was minimized as much as possible.
This image is the result of stacking 369 frames out of 524 at a quality setting of 80 percent, further using Resampling (see Note ii)  at a factor of 1.2, followed by intensifying just Wavelet Layer 6 to its maximum value of 100. The resulting bitmap image was drawn into AstroArt for resizing, color balancing and unsharp masking.
i. One nice feature of K3CCD is that at any moment one can terminate image capture with a right click of the mouse button. That comes in handy should anything untoward happen to disrupt observation.
ii. "Resampling" is the name for several interpolation techniques available in Registax. The factor that goes with any of these techniques must be used with caution since the larger the factor the less impressive the result. See the discussion below in the case of Saturn. 


To better interpret the features in my image, a Mars Previewer II picture is shown on right.
Broad similarities between the two Mars pictures are pretty obvious. Thus, going clockwise in my image, note the desert-like Moab in the top right quadrant; followed by Syrtis Major ("upside down India") in the 3 to 4 o'clock position; Mare Tyrrhenum after that and the South Polar Cap at 8 o'clock. One noteworthy feature picked up in my image is Sinus Sabaeus which is a dark feature running diagonally from the center of the image towards the 11 o'clock position.

Shown below is an animation of images of Jupiter. I identified a certain feature (a tiny dark hair-thin streak) in the North Equatorial Belt by placing a blue "x" just underneath it. This feature moves by roughly twelve degrees in the twenty-minute time period spanned by the animation, given that Jupiter completes a full spin in 9.8 hours. The movement of  x  aids the eye in following the spin of Jupiter.
The images used in the animation were acquired before sunrise on Christmas Eve, viz., 24 December 2005, from 6:23 am to 6:43 am EST.


The pictures below show Jupiter as shot at 5, 7, 6 and 6 frames per second (fps) at 6:23, 6:31, 6:40 and 6:43 am on 24 December 2005. These are the images that form the input for the animation above. ToUcam was set to get frames for 90 seconds at each fps. The result was processed in Registax using a threshhold image quality of 80 percent. The ratio of the number of stacked to registered frames was 444/449, 428/629, 445/540 and 444/539 for fps of 5, 7, 6 and 6, respectively. For all images, Registax's Resampling criterion was used with a factor of 1.2. Only Wavelet Layer 6 was applied - and that was at the maximum value of 100. Lastly, color planes were adjusted using RGB shift in Registax and the color balance feature in AstroArt. As an example of the amount of detail that is seen, attention is drawn to the third image below taken at 6 fps at 6:40 am.





Taking advantage of the opposition of Saturn on the evening of 27 January 2006, I acquired the images shown below. The difference between the three pictures is that the individual frames which yielded these results were obtained at 5, 6 and 7 fps, going from top to bottom, respectively.
In stacking individual frames using Registax, I experimented with a Resampling or Interpolation scheme different from the one used (Bell's method) in the case of Mars and Jupiter above. For Saturn, I chose Mitchell's method with a factor of 1.5. The initial motivation was simple curiosity. Later, I came to understand it better after coming across comments from digital camera photographers who were familiar with the merits of various interpolation techniques.
While my resampled image is larger in size (by a factor of 1.5) compared to the original, however, it is relatively more blurred. Hence, sharpening with Wavelet Analysis becomes a necessity. This, too, was done differently from the way used for Mars and Jupiter. Thus, the value for Layer 6 was chosen to be 30. The other Layers were left at the default value of 1. The point is that Registax's Wavelet analysis is powerful enough that misapplication of it (perhaps through overzealousness) can produce unrealistic results.
AstroArt was used only to render my image lighter thereby uncovering some markings, though admittedly few, on Saturn's surface. For Saturn, I found that AstroArt's color balancing introduced details that didn't seem objective.
With a quality setting of 80%, Registax stacked 444 out of 449,  443 out of 539 and 594 out of 839 frames in the 5, 6 and 7 fps situations, respectively. In all three images there is a nice degree of clarity compared to that obtained by a digital camera, for instance. Also, visible in my best image, i.e. the second image taken at 6 fps, there is a dark band on Saturn's body near the equator. In all three images, Cassini's division between the A and B rings is seen in the wings.




Vasu Jagannathan * Washington, DC