Saturn Astrophotography

The photos below were taken using my 4" Takahashi refractor, and either a 5x TeleVue Powermate or a 2.5x TeleVue barlow, an IR blocking filter, and a Philips ToUcam Pro in 640x480 pixel mode. The maximum duration of ToUcam videos is 5 minutes. At 2 frames/second, the rate of download that gives minimal duplication (redundant) images with the USB1.1 connection, I obtain nearly 600 frames in a 5 minute video. Each video is processed using RegiStax, which collocates the individual frames and provides for the application of various image processing algorithms, and the result is a single image. I apply six linear wavelet filter layers of magnitude 1, 3, 10, 10, 10, and 10. I also experiment with the Gamma setting. In Paint Shop Pro I may apply an unsharp mask, and I center the processed image and add the labels. Using the 4" Takahashi with the 5x Powermate the effective focal length is f/40. With this set-up the system is working near its limit for Saturn. The longest exposure, 1/25 second, is needed with the amplifier gain set to 100%. Tests at 1/25 second with the gain at 75% and 50% gave images that took on an abnormal yellow tone. 1/33 second exposures at 100% gain also had a yellow cast, but it was not as bad as the reduced gain tests at 1/25 second, and the images are quite acceptable. With the 2.5x barlow the effective focal ratio is f/20, and I can lower the gain to 50%, which results in less amplifier noise. With the smaller image scale the subtle hues that characterize the belts and zones on Saturn are more distinctive compared to the images obtained at f/40 with the 5x Powermate.
The first section gives the best images using the 5x Powermate and the 2.5x barlow. The second section shows the progression of quality as the videos are processed, and the various filters are applied.

Click on the pictures to see full size versions.
Here I compare the benefit (or lack thereof) of combining raw images from separate video images in RegiStax, and then applying the various filters etc.. When raw images are combined from separate videos they are given equal weighting despite the fact that each of the images may have been distilled from a different number of raw frames.

Saturn (13kb) 22 January 2004 4" Takahashi, 5x Powermate, IR block 1/25 second, 100% gain 1693 frames from 4 separate videos Gamma=0.7, Unsharp mask of radius 3 This image is a balance between a smooth disk and a sharp Cassini Division.			Saturn (11kb) 22 January 2004 4" Takahashi, 2.5x Barlow, IR block 1/25 second, 50% gain 597 frames from 1 video Gamma=0.5 With the smaller image scale compared to using the 5x Powermate, the color saturation is improved.
Saturn (16kb) 22 January 2004 4" Takahashi, 5x Powermate, IR block 1/25 second, 100% gain 1196 frames from 2 separate videos Gamma=0.7, Unsharp mask of radius 3 This image has the sharpest Cassini Division, but the disk is a bit noisy.			Saturn (11kb) 22 January 2004 4" Takahashi, 2.5x Barlow, IR block 2 Videos: 1/25 second, 50% gain 2 Videos: 1/25 second, 75% gain 1833 frames from 4 separate videos Gamma=0.5 Stacking additional videos does not lead to any discernible improvement.
Saturn (14kb) 22 January 2004 4" Takahashi, 5x Powermate, IR block 2 Videos: 1/25 second, 100% gain 2 Videos: 1/33 second, 100% gain 2271 frames from 4 separate videos Gamma=0.7, Unsharp mask of radius 3 The 1/33 second exposure videos contri- bute to the slight yellow cast and the graininess of the disk.			Saturn (11kb) 22 January 2004 4" Takahashi, 2.5x Barlow, IR block 1/25 second, 50% gain 597 frames from 1 video Gamma=0.5, Unsharp mask of radius 3 Application of an unsharp mask results in excessive contrast.

The process of generating the images above is demonstrated here.

Saturn (53kb) 22 January 2004 4" Takahashi, 5x Powermate, IR block 1/25 second, 100% gain This is a high quality single raw frame from one of the ToUcam videos. The Cassini division is well defined, and there is little evidence of pronounced atmospheric distortion that afflicts many other frames. With the 100% gain set- ting, notice the pixelation in the image.			Saturn (30kb) 22 January 2004 4" Takahashi, 2.5x Barlow, IR block 1/25 second, 50% gain This is a high quality single raw frame from one of the ToUcam videos. Compared to the single raw frame obtained using the 5x Powermate (to the left), Saturn exhibits less noise. Over the remainder of the frame less pixelation is evident owing to the reduced gain setting. This probably accounts for the lack of further improvement by stacking images from additional videos.
Saturn (12kb) 22 January 2004 4" Takahashi, 5x Powermate, IR block 1/25 second, 100% gain This is the raw image from combining all 598 frames from the ToUcam video that contained the above raw frame. This raw image was combined with raw images in an additional RegiStax session to yield the images at the top of the page.			Saturn (11kb) 22 January 2004 4" Takahashi, 2.5x Barlow, IR block 1/25 second, 50% gain This is the raw image from combining all 280 frames from the ToUcam video that contained the above raw frame.
Saturn (23kb) 22 January 2004 4" Takahashi, 5x Powermate, IR block 1/25 second, 100% gain 598 frames from 1 video This is the result of applying the six linear wavelet filters of magnitude 1, 3, 10, 10, 10, and 10. Notice the improved contrast compared to the image above.			Saturn (12kb) 22 January 2004 4" Takahashi, 2.5x Barlow, IR block 1/25 second, 50% gain 280 frames from 1 video This is the result of applying the six linear wavelet filters of magnitude 1, 3, 10, 10, 10, and 10. Notice the improved contrast compared to the image above.
Saturn (13kb) 22 January 2004 4" Takahashi, 5x Powermate, IR block 1/25 second, 100% gain 598 frames from 1 video Gamma=0.7 Further definition is obtained by reducing the Gamma setting to 0.7. The belts and zones and the Cassini Division have better definition.			Saturn (11kb) 22 January 2004 4" Takahashi, 2.5x Barlow, IR block 1/25 second, 50% gain 280 frames from 1 video Gamma=0.5 Further definition is obtained by reducing the Gamma setting to 0.5. The belts and zones and the Cassini Division have better definition.
Saturn (13kb) 22 January 2004 4" Takahashi, 5x Powermate, IR block 1/25 second, 100% gain 598 frames from 1 video Gamma=0.7, Unsharp mask of radius 3 Finally, I apply an unsharp mask of radius 3. Application of the unsharp mask is balance between further improvements in contrast and degradation due to grain.			Saturn (11kb) 22 January 2004 4" Takahashi, 2.5x Barlow, IR block 1/25 second, 50% gain 280 frames from 1 video Gamma=0.5, Unsharp mask of radius 3 Application of the unsharp mask at this image scale results in excessive contrast.

All photos are copyright K. R. Sperber

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