Discussions in Google Groups indicated I should keep fairly modest expectations when conducting unguided 35mm Astrophotography (AP) and much of that advice was held to be correct but only to a degree—hence these observations.
Having had my first encounter with star trails a few months previously I had all but given-up attempts at unguided AP with the exception of the moon which, thanks to good glass and clear skies, had proven a rewarding subject.
However, I decided to give the smaller stuff one more try albeit with a little more planning and research this time around. First, I had to find what maximum exposure I could expect to achieve with my lenses before star trails took over. Another stop at Google Groups revealed the best approximation I have found to date, namely to simply divide the lens focal length into 600. Using this calculation a 300mm lens would permit a maximum unguided exposure of just 2 seconds without noticeable star trails (e.g. 600/300=2).1
However, a 17mm lens would permit an exposure of up to around 30 seconds. At this point it looked as if I was going to have to restrict myself to wide field constellation photography with my 17-35mm and lunar photography with my 300mm as anything else would likely exceed my limited set of exposure scenarios.
However, I decided to press on and conduct my own trials. I wanted to see if I could retrieve any detail of Saturn and its rings using my Nikkor 300mm f/4 AF IF-ED. The first exposure settings I tried was ISO 1600, 2sec @ f/4. However, this just rendered Saturn as a circular white hot flare. Some fourteen exposures later, I managed to reduce the exposure to a point where Saturn was rendered as a small dull orange/yellow disc. Needless to say that even a 5x interpolation failed to reveal Saturn as anything but a warm coloured fuzzy oval—a classic example of the need for telescopes.
Undaunted, I revisited my Wife’s Astronomy software the next day and noted that during the previous night the Crab Nebula had been immediately adjacent to Saturn. I began to wonder if my initial overexposed shots of Saturn from the previous evening may have captured some semblance of the Crab Nebula. To check this I cropped a 252 pixel area adjacent to Saturn that contained what appeared to be a green ‘splodge’ of colour and ran a 5x interpolation. I feel that in context with the toolset the results speak for themselves and indicate quite good detail and colour rendition for such a limited exposure and focal length.2
Pleased with the results (read easily amused) I decided to see if I could pluck something else from the dark reaches of the solar system. I had previously been concerned that any attempts to reveal the bright red clouds of the Great Nebula of Orion were being thwarted by the brightness of the Trapezium which would glow brighter and larger with successively longer exposures.3 However, shorter exposures tailored to correct this were insufficient to expose anything remotely like a fog of red cloud in the Orion Nebula. I decided to revisit these shorter exposures to see what I could reveal about the Trapezium itself. Again, I made a small crop and ran a 5x interpolation using bicubic resampling in Photoshop® but in addition to this I pushed the curves in the red channel revealing a spidery red halo around each member of the trapezium.4
In conclusion, I am beginning to see some good results from the Fuji S2 Pro’s 12 megapixel mode in combination with fast and sharp glass such as the Nikkor 300mm f/4 AF IF-ED and the Zoom-Nikkor 17-35mm f/2.8D. I am also keen to add the 2 stops faster Nikkor 85mm f/1.4 D to my astrophotography toolset if I can ever afford it. I am very appreciative of the fact that living on Magnetic Island, Queensland some 12 Kilometres from the Australian coastline means relatively unpolluted skies and I’m certain that this has played a major factor in the results I have achieved to date. Consequently, I am going to continue my attempts to capture some of the dimmer objects normally considered out of reach of us telescope impaired astrophotographers.
Footnotes:
1. This may be true when examining captures at around 50% resolution. However, a 12MP Fuji frame at 100% resolution indicates noticeable albeit slight object movement even at this modest exposure using a 300mm lens.
2. Clicking the Crab Nebula thumbnail will load a 50% crop jpeg with no sharpening, colour adjustment or any other Photoshop® jiggery pokeryâ€â€just a straight interpolation.
3. Again using my Nikkor 300mm f/4 AF IF-ED
4. Now, by rights I should have pushed the curves in the master channel in order to accurately render the colours but doing so rendered purple halosâ€â€I wanted red!