Digital Camera Astrophotography With Nikon 4500

The pictures on this page were obtained with a Nikon 4500 Digital Camera. The technique used is "Afocal Astrophotography" in which a camera takes photographs while coupled to a telescope's eyepiece.

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.

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It is instructive to compare the images of Jupiter, Mars and our Moon on this page with those obtained by a Philips ToUcam PRO II webcam as shown on my Webcam Astrophotography page. The webcam, in conjunction with image processing software such as Registax, achieves a wonderful and superior level of detail.

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460x. Two hundred 1600 by 1200 pixel fine quality images each recorded at half a second exposure were stacked via Registax, processed in Maxim DL to realign color planes and unsharp masked and reduced in size with AstroArt. Cassini's division at a third of the way from the outermost portion of the ring as well as some shading on Saturn itself is apparent. 19 September 2004.

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Jupiter at 288x. One hundred 1600 x 1200 pixel sized images taken at 1/4 s shutter speed were aligned and stacked with Registax. Then processed for color balance, contrast and sharpness with AstroArt. 

For comparison here is the result at 264x. Twenty-six 1280 x 960 pixel sized mages taken at 1/8 s shutter speed were aligned and stacked with Registax. Then processed for color correction, brightness/contrast and sharpness with Adobe Photoshop Elements.

 

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In both images, Jupiter's North Pole is at the 2 o'clock position. The Equatorial Belts are immediately obvious. As are the shaded Polar Regions. The Great Red Spot is not seen. Although, in the first image, there is something over in the 10 o'clock position in the South Equatorial Belt. That's where one would have expected to see the Spot.

 

The oblateness of the Jovian disk (especially in the first image) became truly apparent to me on seeing this image. Indeed the ratio of the polar to equatorial diameter is 15:16 according to Norton's 2000.0 StarAtlas. This degree of oblateness is the net result of a tug-of-war between centrifugal and gravitational forces; the former arising from Jupiter's relatively high speed rotation of 9.8 hours (nearly two-and-a-half times faster than the earth's) and the latter from its mass which is 317.8 times the terrestrial one.

 

Recorded before sunrise, between 5:34 and 6:14 am, on 15 November 2004.

 

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Topmost is Mars on 28 October 2005 at about 8:15 to 8:30 pm EST one day before closest approach of 29 October. 54 images were recorded continuously at 1/15th sec and mag 230x. They were processed in Registax under the following conditions: lower quality setting of 95% which eliminated 31 images; wavelet processed in layer 2 at a value of 30.3 (default value of 1 in all other layers); used the RGB option to adjust color planes; tweaked HSL and, finally, rotated image to facilitate comparison with the corresponding image in "Mars Previewer II" (shown directly below my work). South is therefore up (and East is left). Incidentally, a gibbous Mars is not uncommon en route to full opposition (this time around on 6 November).  

 

Note: Mars Previewer II is a freeware program developed by Argentinian amateur

Leandro Rios. It can be downloaded from

http://skyandtelescope.com/resources/software/article_328_2.asp.

 

Looking from left to right, along an axis from  7 o'clock to 1 o'clock, my image shows Syrtis Major on the extreme left of my image as a slight dark shadow extending downward. That is followed on the right by Mare Tyrrhenum which passes over to Mare Cimmerium. Polar caps are visible.

 

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Eastern side at 230x. "Registaxed" 23 images each at 30th of a sec.  36 hours after full moon. 18 October 2005.

"Last Easy Old Moon" at 76x on 30 October 2005, 48 hours before new. Horizontally flipped Questar's mirror image. Stacked 33 out of 46 images. Optimized using Wavelets in Registax 3.

 

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Zeroing in on the northeast section of the Pleiades cluster at 70x. This is a single high quality image obtained after an exposure of nearly half a minute. The noise reduction feature in Nikon 4500 was turned on. 

 

While the clock drive in my telescope tracks well along the azimuth, lacking a device to compensate for errors in elevation, I have to make continuous manual adjustments during the time the image is being actually acquired. This trial and error approach requires me to strike a balance between using longer exposure times to bring out more detail while incurring greater tracking error. Many images have to be discarded before a decent one can be found.

 

I processed the original image in AstroArt so I could use color balance to bring out legitimate details. While color balance introduces an artifical graininess suggesting a glow that, given my exposure time, I do not expect Pleiades to have, it is pleasing that a comparison of the above image with a textbook diagram of Pleiades as shown below validates my approach. What is seen in my image is indeed present in Pleiades.

 

For stellar or deep sky astrophotography a longer exposure time will win out over stacking many shots at a shorter exposure time. 12 February 2005.

 

To aid the viewer relate my images to the components of Pleiades, shown below is a textbook diagram of Pleiades with numbered stars. It is taken from p. 60 of Crossen and Tirion's "Binocular Astronomy" (Willmann-Bell, 1992). The diagram can be expanded by doubleclicking on it.