FIRST ATTEMPTS @ DIGITAL ASTROPHOTOGRAPHY
When it comes to astrophotography I'm a photographer first and an astronomer second. I began using film cameras when I was 11 years old, an Eastman Kodak No.0 model A 127 Box Brownie given to me by my great Aunt Sarah, who'd presumably had it since she was a young woman. It was made in Canada in 1916. It took roll film, black & white, and shot 8 exposures per roll, 15/8 " x 21/2" negatives. I made all the mistakes any tyro makes. Forgetting to wind on the film after an exposure, so you get a double exposure. Shooting into the Sun so everybody is in silhouette and you got lens flare. Thumb over the lens. Buildings leaning backwards. Sloping horizons. Gradually I learned to avoid all of these pitfalls.
My next roll film camera was an Ilford Sporti 4, which shot 12, 4cm x 4cm exposures on 127. It was advertised in Meccano magazine and cost £2/9s/8d for the camera and 17s/5d for the ever ready leather case. It was aimed at young photographers but was far too expensive for me to afford in 1963 on 2s/6d (half-a-crown) a week pocket money. It must have been a birthday present, probably from my paternal grandmother.
Progressing from roll film cameras to an Ilford Sportsman viewfinder camera followed by a Halina Super 35X and subsequently a Arette 1A rangefinder camera all of which took 135 format 35mm film cassettes made life a lot easier. The viewfinders were far clearer, so framing your shot was less awkward. The shutter was also linked to the film advance knob, so you couldn't accidentally double expose; auto-lock film advance. And you could focus the lens at a selected distance, and the lens had an iris, so you could control the depth of field. The 35mm film cassettes were also much easier to load into the camera, and you had a far wider choice of film types. To set the lens focus accurately I used a flash shoe Watameter accessory split-image rangefinder.
I began shooting colour slides in 1966, and bought a Boots slide projector and a screen. I amazed my family with cinema style slide shows of the snaps I took on our holidays. The film I preferred was Agfa-Gevaert 25ASA (CT15). When these transparency slide films became available in the late 1950's their ratings were very slow. Ilfachrome was only 10ASA, Kodachrome was only 12ASA. Agfachrome was also only 12ASA. High Speed Ektachrome, introduced in 1959 was an astonishingly fast 80ASA and you could force process it @ 160ASA. After 1960 colour film speed ratings doubled following the revision of ASA speed rating standards. Colour transparency film was also very expensive. Ilfachrome process paid colour slide 35mm cassettes cost 22s/9d for 24 exposures and 34s/1d for 36 exposures, returned in cardboard mounts.
Ilfacolour print film was less costly. Ilford introduced 127 roll colour film in the spring of 1961; 10s/7d per roll, but processing and printing was expensive, processing 6s/6d and 31/2-inch square prints 2s/3d each. A roll of Ilfacolour 127 when exposed, processed and printed, would produce 12 small square prints for the sum of £2/4s/1d. In 1961 or 1962, £2/4s/1d was a lot of money, especially to a schoolboy on 2s per week pocket money. That is why most of my photographs prior to 1966 were shot in black and white, either on Ilford Selochrome Panchromatic 80ASA or Kodak Verichrome Pan 80ASA. Colour photography was restricted to our annual summer holidays.
None of the viewfinder cameras I owned throughout the 1960's had a built in light meter. What I really wanted was a hand held light meter but I could not afford one. Ilford, Agfa and Kodak used to supply exposure guides, printed on small pocket sized cards, available free at photographic dealerships. Johnson's of Hendon also sold a relatively inexpensive exposure calculator for 4s/6d.
Once I started work as a Technical Apprentice at English Electric's Strand Road plant in Preston in September 1966 I could afford a modest light meter. At first I used a simple "Sixtry", but in 1968 managed to save up for that coveted light meter, the Weston Master V, the British, "Queen of exposure meters", so accurate that it was the universal benchmark by which other exposure meters, hand-held and built-in, were measured. The Selenium cell Weston had no spot-metering capability or serious low-light sensitivity, and light measurement was done in two stages; the meter needle indicated an EV value which was set manually on a dial from which the exposure settings (in 1/3 stop increments) were then read. But it came easy with practice, and its 180 degree invercone for incident light readings provided the most reliable metering method for reversal films available. Shortly after that, for my 21st birthday, my Uncle bought me an Exa1a SLR. I had the beginnings of a 35mm SLR outfit.
Now the thing about an SLR camera is that you can see the image made by the lens. You pretty well see all the frame the lens will image on the film. The lens is also removable. You can fit lenses of different focal lengths. You can fit shorter focal length lenses that give a wide angle view and you can fit long focal length lenses, telephoto lenses, that give a magnified view. More importantly, you can buy a special adapter that enables you to fit your SLR to your telescope, so you can take photographs of the Moon, and maybe even the stars.
My Exa1a was a good beginner's SLR, but it had its limitations. I came across a very handy book in a second hand book shop in Blackpool, written by a German amateur astronomer by the name of GŸnter D. Roth. It was entitled "Handbook for Planet Observers". I still have it. It is an amazingly detailed book written in a clear and easy to understand style.
The only other book dealing with astrophotography at the time was Rackam's, "Astrophotography at the Telescope" published by Faber & Faber. I still have a second hand copy. It is not an easy book to follow, and Rackham's method of determining Moon exposure times was convoluted, to describe his method politely. Roth's book was simple and concise. The author recommended a specific SLR made by Ihagee, the same company that made my Exa1a. Roth recommended the Exakta Varex IIa. I mentioned this to a fellow amateur astronomer at Warton where I worked as a draughtsman. He told me he'd seen one in Holden's camera shop on Fishergate in Preston. He kindly went into the shop and bought the camera for £25 and passed it onto me. It was originally made in 1958, and needed servicing, which Holden's did, for another £25. It needed cleaning because the mechanism was full of sand, and it also needed a new shutter blind.
The freshly serviced and calibrated Exakta Varex IIa, which I still have, and is still in full working order to this day, was a remarkable piece of German engineering. It not only had interchangeable lenses (& a huge choice of compatible lenses - far more than you have with a modern day DSLR), it had interchangeable viewfinders & focussing screens. I bought a Magnear viewfinder - a sort of microscope that enabled critical focusing. I also bought a matt focussing screen with a 10mm clear centre and a ruled cross hair. I learned the "aerial" or "parallax" focussing technique, by which you shift your eye ever so slightly side ways, to & fro. The image shifts as you do so, and you know the image is precisely focussed when the image and the cross hairs move together, as one. When the camera was attached to the 6-inch Cooke refractor at the Assheton Observatory, Rossall, the Moon filled the field of view. Wow, what an image. But an ordinary SLR with a fixed pentaprism viewfinder, and a fine ground screen, could not be focussed accurately. The image looked dim and the ground glass screen at f/13.5, the focal ratio of the refractor, looked like a snow storm. My Exakta Varex IIa, with its Magnear viewfinder, and clear centre spot screen, gave a view just like looking through a medium power eyepiece. The image was bright and clear, and using the "aerial" focussing technique, a cinch to focus. I was away, and I began to experiment with different black and white and colour slide films, and various exposure times. Roth's book explained how you can calculate the exposure time knowing the Moon's phase, the telescope's focal ratio, and the film speed. It didn't give an exact exposure time, but it was near enough, and I used to bracket exposures ±2 f/stops (or EV).
There was one more trick my Exakta Varex IIa had up its sleeve, that no other SLR on the market had. You could do cassette to cassette loading. Instead of loading the supplied 35mm film cassette into the camera, and placing the film leader into a fixed wind on spool, the wind on spool was removable, and you fit the leader into what was called a "Shirley-Wellard" self loading cassette. What this meant was that in the darkroom, you could load your own cassettes with black and white film, and then use cassette to cassette loading in camera. The Varex IIa had a built in film knife, so you could shoot say 20 exposures, and then cut the film, open the camera back, and take out the "Shirley-Wellard" ready for processing.
Practice makes perfect. After a couple of years and thousands of exposures and dozens of self loaded rolls of a very special black & white film called Adox KB14 (because it was rated at 14DIN or 20ASA - exceedingly fine grain film made by EFKE in Zagreb), I could reel off a cassette with every frame properly focused and correctly exposed. I'd mastered the art.
The other part of black & white photography is printing. I built my own makeshift darkroom, and fitted it with a Czechoslovakian made Opemus enlarger. I learned how to dodge and burn Lunar prints, to burn in the bright limb and hold back the dim terminator. I also learned how to make unsharp masks using Lyth film. All great fun, and very messy and smelly. The fixer used to smell of cat's piss. Walk into any photographer's darkroom and that is the smell that lingers in your memory; forever! You could get hooked on the smell of fixer, ah the aroma of Ammonium Thiosulphate. Once fixed the prints needed washing, in the bathroom - for hours. All trace of fixer had to be rinsed away, otherwise when you glazed the print on a glazing plate in the print dryer, it would end up covered in yellow stains, and it would be back to the darkroom again.
In 1976 I saved up a lot of money for a professional SLR, a Canon EF. I still use this camera from time to time. I've had it serviced each decade, to keep it in top working order. Its a great camera. Instead of having a cloth shutter curtain, which moves sideways, it has a titanium shutter that moves vertically. The shutter is split into 5 segments, a bit like a five bar gate. The reason I bought it was because of the silicon blue cell light metering. It was the first aperture priority automatic SLR. You selected the shutter speed, and the camera automatically set the lens aperture. This was revolutionary technology.
By the early 1980's I'd moved away from black & white printing, and onto colour slides. Colour slide films had improved significantly. Film speeds for Ektachrome rose to ASA200, ASA400 & ASA800, that could be pushed 1 or 2 stops without changing the colour balance. I was also using a Quantum 6 Mak-Cass, which although slow @ f/15, was ideal for Lunar photography. I remember shooting an excellent series of slides of the Total Lunar Eclipse on January 9th 1982. The garden was covered in frozen snow 6 inches deep, and the air temperature was 12¼F. My slides were gorgeous, the deep ruby reds and vivid oranges of the totally eclipse Moon, faithfully reproduced on Kodachrome 25 and Agfa CT21.
I used a newly acquired Pentax LX system SLR, which had a very sensitive built in light meter, a very special sort of light meter, which determined the exposure by measuring how much light actually fell on the film during the exposure, technology introduced by Olympus in their 1975 OM2 SLR. Some of the exposure times, mid Totality, because this was an unusually dark eclipse, were as long as 3 minutes. My Quantum 6 tracked the Moon with unerring accuracy throughout each and every exposure. There was not a dud slide on each of the 36 exposure cassettes. I used to mount my own slides, and there was a good reason for doing so. If you sent the film away for processing and mounting, because there was so much black sky around the Moon images, the automatic film cutter couldn't necessarily find the frame boundary, usually a 1mm to 2mm black strip between frames. So you could end up with your Moon pictures all neatly sliced down the middle. You sent your precious film away to be processed and NOT mounted. You cut and mounted your own slides.
The Pentax LX was a system SLR, meaning it had interchangeable backs, and viewfinders, and an auto-winder. I acquired a full outfit over a few years in the early 1980's, and sold it last summer for more than I'd paid for it, which is an achievement because the sudden uptake of DSLR's has rendered most film SLR's practically worthless.
And there the technology of SLR's reached a plateau. Cameras were introduced with auto everything, even auto-focus, but an experienced SLR user didn't really need them. I stuck with my Exakta Varex IIa manual SLR, & Canon EF & Pentax LX. There was no need to "upgrade" because you don't need auto-focus on an SLR film camera, the whole point of any SLR is that what you see in the viewfinder is what you get on the film. You also don't need an auto-exposure system. Any photographer worth his or her salt, selects the shutter speed and relative aperture to suit the subject. You want to control the depth of field, and choose a shutter speed that will enable a shake free image at that aperture setting.
I remember my first reaction to being shown an auto-everything SLR. I felt cut off from my picture taking. I didn't want the camera to decide the shutter speed and aperture. And I soon discovered, much to my horror, that trying to rest control of the camera back to me was not at all easy. If I wanted to decide the shutter speed, aperture, and point of interest on which to focus, the wretched camera fought me every inch of the way. The only reliable way to rest control to me was to switch the camera to manual mode. And what was the advantage in doing that? As far as I was concerned, having learned how to take photographs through the school of hard knocks, these auto-everything cameras were a confounded nuisance. They didn't help me take better photographs, they got in the way of my picture taking creativity.
And that is where SLR technology languished throughout the 1980's and 1990's. All the while, during the 70's & 80's lurked an alternative technology, the charged couple device, invented by George Smith & Willard Boyle in 1969. Alas Smith & Boyle were not interested in new imaging technology. What they wanted, for Bell Laboratories, was a faster computer memory, that could store data in a more rapidly accessible way than the magnetic analogue tape drives or matrix bubble memory. Charge leakage and charge overspill (blooming) made it a poor storage device, but they soon realised it could be developed into a linear or even an area imaging sensor. What started out as a bubble charge 8-bit shift register morphed into a photo-electric effect charge accumulator.
During the 70's I was vaguely aware that professional astronomers were building increasingly sensitive ccd cameras. What they really wanted were bigger reflecting telescopes, but they were hamstrung to some extent by the current mirror making technology. All the while thin and segmented mirror technologies were being developed, and improved upon, the light grasp deficit was being made up by ccd cameras which had far greater quantum efficiencies that Kodak 103a series panchromatic plates. More of the captured photons produced a picture element in a ccd photosite than the silver halide crystals in a film emulsion, by a factor of 10 to 20 times. Also the ccd camera could continue collecting photons in a linear way, whereas a film lost sensitivity during long exposures, an effect well known to deep sky photographers, and referred to as "reciprocity failure". Exposures longer than a few seconds did not build up in a linear fashion. An exposure of 5 seconds would record "x" number of star images. But a 10 second exposure would not produce "2x" number of star images, in fact it would only produce something like "1.2x" the number. Exposures using cold plates (chilled with frozen carbon dioxide or dry ice) could drag on for hours. Other ways of sensitizing astronomical emulsions were tried, including baking the plates in dry nitrogen, and hyper-sensitizing plates and film stock in pure hydrogen, or a less explosive mixture of hydrogen and nitrogen known as "forming gas".
Ccd cameras needed none of these labour intensive treatments. What a ccd camera did need was cooling. And cooled they were, not just dry ice, but liquid nitrogen, liquid hydrogen and even liquid helium. Ccd cameras were ludicrously expensive. They cost more than a house. And you could hardly "try this technology at home". Your average amateur astronomer was not in a position, either financially or technically, to emulate the professionals.
But as the production technology moved on, the cost of ccd chips began to drop, until by the late 80's, ccd cameras aimed at amateur astrophotographers began to appear, made by firms such as SBIG and StarLight Xpress SXL8-P. The trouble with these ccd cameras was that you needed a personal computer to use them. These were not cameras in the conventional sense. All they were was a box with a ccd sensor and some of the necessary electronics to make it function. They either had a peripheral box of tricks, or you needed a personal computer and software to see the image, focus the camera, and make an exposure. The resulting image could also be far from encouraging. It needed an awful lot of post exposure image processing to make it look something like a film image. You had to experiment endlessly with exposure times, focusing, post exposure manipulation, and you also had to take what were referred to as "dark frames" in order to subtract image noise, and "light frames" in order to remove the effects of dust on the sensor and telescope optics, and optical vignetting. It was all very involved, and to a conventional photographer, quite frankly unappealing. Those wonderful ccd images, amazing though they were, involved way too much hard work. Hours and hours spent staring into a computer monitor held no appeal for me. My idea of a camera is a box you look into and can see what you're photographing. The idea of photography is to capture a "moment in time"; a still frame that can be either printed or projected, for others to see, so you can share "the moment". What photography ought not to be about is using a device that produces an image you cannot see without a personal computer, and an awful lot of post exposure image processing and image manipulation.
Ccd cameras intended for astrophotography were also monochrome. They were sensitive to all the visual and parts of the UV & IR spectrum, but they produced black and white images. If you wanted a colour image you were obliged to take three separate exposures in red, green and blue, plus a luminance exposure, or alternatively a set of cyan, magenta and yellow, complementary exposures, and then post exposure, assembly the images by stacking each of the filtered frames. This exceedingly laborious process reminded me of the initial attempts at colour photography by James Clerk Maxwell in the early 1860's. This was not a step forwards, it was a giant leap backwards. Amazingly, dedicated deep sky ccd imagers still prefer this outdated and outmoded method, claiming it produces better image fidelity. But at what cost in terms of time and effort? Is it really worth all that time sat at a personal computer?
The answer of course lay in a ccd equivalent of an SLR. A proper camera, that used a ccd instead of film. The trouble was ccd sensors were not all that big. And the big ccd sensors used by professional astronomers cost the earth. DSLR technology began its nascent development in the late 1980's but most photographers I knew were oblivious to the Nikon SVC exhibited at Photokina in 1986. It was a prototype analogue still SLR. What you and I would recognize as the first DSLR was released by Kodak in 1991, the Kodak DCS-100. It consisted of a modified Nikon F3 SLR body, modified drive unit, and an external storage unit connected via a parallel port cable. It had a 1.3 megapixel (Mp) ccd sensor, and it cost a whopping $30,000. It was rapidly followed by the Kodak DCS-200 with an integrated storage unit.
The way a ccd (or nowadays cmos) sensor can be used to produce a colour image is by using a photosite colour mask. The mask was designed by Bryce E. Bayer working for Eastman Kodak way back in 1976. The images from the different colour channels are combined using an algorithm and the colour image is processed in camera. It is a complex channel mixing system, but a good analogy is the first successful colour film system called Autochrome patented in 1903 by the LumiŽre brothers. Autochrome used an overlaying additive colour screen plate, a random mosaic of microscopic dyed potato starch grains with lampblack filling in the space between the coloured grains, lying over a panchromatic silver halide emulsion.
Ccd astrophotography purists who insist on using tri-colour imaging, argue that the Bayer mask reduces the sensor's resolving power. This is utter nonsense. The resolving power of a ccd or cmos sensor is related to the photosite spacing, not the wavelengths to which those photosites are sensitive. A monochrome ccd produces less noisy images than the same sensor with a Bayer mask, but noise and resolution are not the same thing. In any case, as cmos sensor packing densities increase, and noise is reduced, these arguments are rendered specious. The fact is some folk just like to make hard work for themselves.
Over the next decade, DSLRs were released by various companies, including Canon, Nikon, Kodak, Pentax, Olympus, Panasonic, Samsung, Minolta (later Konica Minolta, whose camera assets were later acquired by Sony), Fujifilm, and Sigma, with higher resolutions and lower prices.
In 1999, Nikon announced the Nikon D1, the first DSLR to truly compete with, and begin to replace, film cameras in the professional photojournalism and sports photography fields. This camera was able to use current auto-focus Nikkor lenses available at that time for the Nikon film series cameras, and was also able to utilize the older Nikon and similar, independent mount lenses designed for those cameras. A combination of price, speed, and image quality was the beginning of the end of 35 mm film for these markets.
In January 2000, Fujifilm announced the FinePix S1 Pro, the first DSLR marketed to non-professionals and in November 2001, Canon released its 4.1 megapixel EOS-1D, the brand's first professional digital body.
In 2003, Canon introduced the 6.3 megapixel EOS 300D SLR camera (known in the United States as the Digital Rebel and in Japan as the Kiss Digital) with a retail price of $999, directed at the consumer market. Its popularity encouraged other manufacturers to produce affordable digital SLR cameras, lowering entry costs and allowing more amateur photographers to purchase DSLRs.
Since 2003, the number of megapixels in imaging sensors have increased steadily, with most companies focusing on build quality, high ISO performance, speed of focus, higher frame rates, the elimination of digital 'noise' produced by the imaging sensor, and price reductions to lure new customers.
As of 2008, DSLR sales are dominated by Canon's and Nikon's offerings. For 2007, Canon edged out Nikon with 41% of worldwide sales to the latter's 40%, followed by Sony and Olympus each with approximately 6% market share. In the Japanese domestic market, Nikon captured 43.3% to Canon's 39.9%, with Pentax a distant third at 6.3%.
The duopoly of Canon and Nikon is sometimes referred to as "Canikon" or "Nikanon" in online forums in sceptical challenge to the presumptive acceptance of these manufacturer's cameras as always "the best". Canon and Nikon have used their professional market presence especially persuasively in the sale of entry level offerings to the uninitiated general public who presume that everything from Canon or Nikon is superlative. Online contributors often challenge the "Canikon/Nikanon" supposed superiority when they believe there are superior innovations from the smaller DSLR manufacturers.
The DSLR market is dominated by Japanese companies, including all of the top five manufacturers (Canon, Nikon, Olympus, Pentax, and Sony), as well as Fujifilm, Mamiya, Panasonic, and Sigma. Kodak pulled out of the DSLR market altogether in 2005.
Present-day DSLRs (full-frame or smaller image sensor format) are currently produced by Canon, Fujifilm, Leica, Nikon, Olympus, Panasonic, Pentax, Samsung, Sigma, and Sony. Hasselblad and Mamiya also produce expensive, high-end medium-format DSLRs.
Canon's current EOS digital line includes the 1000D, 500D, 50D, 5D Mark II, and the 1Ds Mark III. Canon's latest cameras, the 500D, 7D, and 1D Mark IV were introduced in 2009. As of January 2010, all current Canon DSLRs use CMOS sensors.
Nikon also has a broad line of DSLRs currently including the D3000, D5000, D90, D300S, D700, D3S and the D3X. The D3, announced in August 2007, was the company's first full-frame digital SLR.
Fujifilm currently sells the Fujifilm FinePix S5 Pro DSLR, compatible with the Nikon F-mount lens system. It is based on the Nikon D200 camera body, but utilizes Fuji's sensor technology (Fujifilm SuperCCD SR Pro) and menu system. Fuji previously offered the Fujifilm FinePix IS Pro, which has the unique ability to capture light in the infrared and ultraviolet spectrum.
Olympus makes DSLR cameras and lenses as part of the Four Thirds System. Current Olympus models include the E-620, E-30 and E-3. Unique features include a smaller size, an effective sensor dust reduction system, and in-body image stabilization, along with a crop factor of 2 (compared to 1.6 in most DSLR's) and an aspect ratio of 4:3 (instead of 3:2). Four Thirds lenses are especially highly regarded.
Pentax (in collaboration with Samsung) currently offers the Pentax Km, Pentax K200D, and K20D, while Samsung offers the Samsung GX-20, a clone of the K20D, and the GX-10, a clone of the now-discontinued Pentax K10D. Innovative features include in-body image stabilization, dust reduction system, use of standard AA batteries in the K200D and Km, weather-proof sealing (first introduced on the K10D, and otherwise found only in more expensive semi-pro models like the Nikon D200), and adoption of Adobe's DNG standard raw image format. Also, they offer extensive backwards compatibility, accepting all Pentax K mount lenses made since 1975 (though the automatic light metering functionality of some early lenses does not work).
Sony, which acquired Konica Minolta's DSLR line in 2006, produces DSLRs under the Sony ? brand. Up to June 2009, they offered the ? 200, ? 300, ? 350, ? 700,? 850 and ? 900. The three lower-end models have been updated to ? 230, ? 330, ? 380, offering colour differentiations in DLSRs for the first time. The ? series offers in-body sensor-shift image stabilization and retains the Minolta AF lens mount.
Sigma produces DSLRs using the Foveon X3 sensor, rather than the conventional Bayer sensor. This is claimed to give higher colour resolution although headline pixel counts are lower than conventional Bayer-sensor cameras. Their current model is the Sigma SD14. Sigma is the only DSLR manufacturer which sells lenses for other brands' lens mounts.
What I was awaiting was the introduction of a full format, that is 135 format, DSLR without the pro-photographer price tag. I decided I would get an Fx DSLR last spring, and was going to buy the latest Canon 5D MkII service release B in April 2009 when I read a review of the Sony alpha 900 in "Amateur Photographer", (my favourite camera magazine, and a magazine I would recommend to any keen photographer. I've been a regular subscriber since 1964). The Canon 5D MkII had all the features I was looking for, but it also had a live view LCD view screen and the ability to shoot HD video. I am a stills photographer, I do not make movies and I have no inclination to acquire movie making skills. I admire Terry Devon's skills as a movie maker. He uses movie cameras though, not a DSLR. Stills photography is to movie making, as a word is to writing a novel. A still is a frozen moment in time, a movie if it is worthy of the name, is a story. And why does a DSLR need "Live View" for pities sake? You can see the picture you're going to take in the viewfinder, that's what an SLR's all about! You look through the viewfinder, see the frame is set up as you desire, make sure the area of interest is in focus and that the depth of field is satisfactory, and press the shutter release button. The only reason I could figure why the Canon 5D MkII had a live view LCD screen was for those coming to DSLR photography via a point and shoot digital camera, or because its handy when capturing a video sequence.
The Sony a900 has neither live view, nor video capture. It's a stills DSLR aimed at stills SLR camera users. It has a superior higher resolution cmos sensor, of Sony's own creation, the 24.6Mp Exmor cmos-T4 sensor, with a good low light capability. It produces very high resolution images, far higher than those produced by my film SLR's even using fine grain black & white films such as Kodak TP2415 technical pan. By the same token I soon discovered it needed lenses of a far superior nature to those I'd thought were excellent on my film SLR's. Fortunately Sony have produced a range of "G" class Fx format aspheric apochromatic lenses, and Zeiss make a series of Sonnar aspheric apochromatic lenses. The range though is limited compared to Canon & Nikon.
So at last I've moved into the C21st, albeit about a decade after everybody else. And it is now time to play catchup. I've written two articles about my encounters with my Sony a900 which are posted on my website's logbook page. So I'm not going to repeat them here. In summary what I learned before I attempted to take a photograph of the Moon was that focussing a DSLR is far harder than focussing an SLR, and that mastering the plethora of functions on a DSLR takes a lot of practice, and awful lot of practice. I forget how many times I've read and re-read sections of the 174 page manual.
After I'd acquired all the salient accessories needed for photographing the Moon through my 5.5-inch apo-refractor, my first and so far only opportunity arose in September 2009. We had a long spell of sunny dry days and clear nights. I set up my telescope on the back lawn and left it outdoors for well over two weeks.
My first attempt was on the 9th September, Moon Age 20 days, waning gibbous. I set up the DSLR at the f/7 prime focus and tried to focus the image with a x2 right angle viewfinder attachment using the "aerial" technique. When I checked the exposed image on the 3-inch LCD view screen at x19 it wasn't quite focused. I used the rackmount's fine focus knob and trial and error, hunting for the true focus. I made a long series of exposures, with the shutter speed set manually, based on the time honoured method of calculation given in Roth's book, rather than trusting the camera's auto-exposure 40 segment metering array. I succeeded in capturing some well exposed and sharply focused images. But at f/7 the image size was only 9mm. Nevertheless, when viewed on the LCD view screen @ x19, the detail recorded was remarkable. Far more detail than I'd ever captured on slide film or TP2415 at similar image scales.
I was better prepared on the 11th. I decided to fit my TCFS digital focuser and a 2x TeleVue Big Barlow, to enlarge the image to 18mm. With the increased projection distance the image size was actually 26mm. I used the aerial focusing technique to get approximate focus, and then the fine focus knob to home in on it, and the digital focuser to hunt down true focus and then hopefully follow it as the temperature fell. Over a three and a half hour imaging session the focus shifted inwards by a tenth of an inch. The depth of focus was critical, only 5 wavelengths of yellow light, or about 100 micro-inches. The seeing was excellent, and the detail I was able to record went down to less than a mile. For instance the straight wall could be easily seen, and the small rhille near Birt, Rima Birta, just made out on some of the raw images. I was well chuffed. What also amazed me was the subtle colourations of different parts of the Maria, something I'd never captured on colour slide film.
My next session on the 13th was a disaster, I could not eliminate shutter vibration (I was using mirror lock-up), and it turned out the telescope was way out longitudinal balance, following an all day H-alpha bino-viewing session. By the time I'd discovered the cause my remote release batteries were all flat.
And so to the final session on September 15th, the 26 day old crescent Moon in a slightly hazy sky and poor seeing. I flattened all my batteries but got some excellent pictures of Earthshine with exposures up to 2 minutes. Never before have I seen a colour Earthshine image that reveals the bluish caste to the Moon's Ashen Light, caused by the blueness of the Earth illuminating its dark side.
My Sony a900 when shooting raw, produces big file sizes, a single raw frame is 35Mb. When converted to a 16 bit tiff LRGB file, 140Mb. Downloading a 16Gb Extreme IV UDMA card using a USB CF card reader took about 7 hours! (I now have a Firewire 400 CF card reader). And where to put all the image files? Would my G4 PPC Mac be up the task of processing these image files?
Well I have to confess that my poor old Mac is groaning under the strain, but standing its ground. What I really need is a G5, but it will have to wait. What I did get was a LaCie 1Tb external Firewire / SATA hard drive to store all the image data. How long it will take to fill it I know not. But I'll just have to start burning archival quality DVD's of the selected raw and processed files. Hopefully they'll last longer than some of my slides and negatives. most of which have deteriorated over the decades.
I also decided I needed a better printer than my 8-bit Canon S900, so I invested in a Canon Pixmar iP4700 14-bit printer, which can handle 16-bit tiffs sent to it by Photoshop CS4. The print quality is superb, and it uses less ink than the S900.
All I've done so far is process selected single raw images. With Pete Franklin's helpful assistance I've also managed to blend my Earthshine image and the crescent image taken on the same night, and I have to say it does make a very attractive print.
I also tried to photograph the Sun in H-alpha, but without much success. The image on the LCD view screen in daylight is too dim to tell if its correctly focussed. Later this spring I'll try focusing the camera remotely using my PC laptop in my garden shed, where I can judge focus in the shade. There was another strange phenomenon too. When I tried processing the sharpest H-alpha image, it revealed Newton rings. Presumably these are produced by the etalon which has a very narrow passband of only Å0.25. They aren't visible visually, but when I enhanced the image contrast in photoshop, out they popped, plain as day.
What I have yet to try is image stacking. Most image stacking software is written for Windows, not MAC OS X. There is one programme called Keith's Image Stacker, which the author tells me can handle big DSLR files. Whether my G4 can handle them is another matter. Mind you it did blend a pair of 140Mb tiffs without any trouble, and it did it within a few seconds. So it may be up to stacking the raw images.
This page was created by SimpleText2Html 1.0.2 on 13-Jul-2009