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the aspiring film astrophotographer understands some of the basic
requirements for longer (15 minutes or more) prime focus (at the
focal plane of the optical system) guided exposures, you may wonder
where to start and what do I need? What follows are my thoughts
based on over 32 years of deep-sky film astrophotography.
During the period from 1973 to 1978 I formulated the basic framework of the astrophotographic techniques I now employ. Simply put, it would be to use methods and equipment that give consistent, reliable and usable results, and apply them to the complete range and classes of objects requiring long exposure film photography. I will not delve too deeply into any one of these topics, as many of them have been discussed individually in magazine articles, books, and web pages like this (I have included a few links to personal web pages, many of which have outstanding 'how to' articles).
Telescope/Optics - Almost any optics can be used. The focal length and speed of your system will probably dictate what types of objects will be best suited to your system (a 30 arc second Planetary Nebula will be unrecognizable in a 3 degree field of view). I believe that the variances of seeing, focus, guiding and Murphy (as in his 'Law') will equalize most differences in optical quality between types of optical systems during 60-minute plus exposures. I used a 'common' 1972 vintage Celestron 8 (C8) for years, and now use both 8 inch and 14.5 inch classical Newtonian reflectors, both with f5 primaries. As attested to in the pages of the magazines and numerous web sites, almost any system can work, using the proper techniques. Do not succumb to "aperture fever" without exploring the capabilities of what you already have. I used the orange tube C8 for 12 years, selling it only to finance the 14.5", NOT because it wasn't still useful. In these days of available 'astrographic' mounts and drive systems (and autoguiders!!!), an f/10 system is a very powerful photographic tool.
Mount - Probably THE single most important equipment
change you can make to your system for long exposure photography.
Look for rock-like stability and smooth tracking. I use my system
exclusively in the field, where it can very often be windy. My
14.5" cannot normally be used in the field in winds over
about 10-15 mph. If conditions dictate, I use the 8", being
able to photograph in almost anything short of gale force winds.
Since the 8" and 14.5" are better suited for different
types of objects/fields, I make two lists of objects to shoot
(see PREPARATION/List...). I never want to waste a CLEAR night just because
its windy! The more stable the mounting the better. Stability
includes the base, pedestal or tripod, not just the equatorial
head or fork base. My tripod (based on Kim Zussman's implementation
of Bill Schaefer's design) alone weighs at least 70 pounds and
is as stable as many permanent piers. The amount (usually in seconds
of arc) of periodic error in the tracking system may not be as
important as its regular occurrence, which can be corrected (manually
or autoguided). Since all drives will have some periodic error,
look for a smooth, regular deviation, as caused by the rotation
of the main worm.
Polar Alignment - Not equipment; but an important procedure to assure your mounting tracks properly in declination. Very important for extremely long (over 2 hours) exposures, or for those that use wide angle systems. Even perfectly guided photos can be compromised by field rotation; that is, the rotation of the photographic frame around the star you are guiding on! I use the 'declination-drift' method to align, generally taking 45 to 90 minutes to align properly. A careful alignment will let you (or your autoguider) concentrate on seeing and Right-Ascension irregularities.
Film - My film of choice has always been a black and white panchromatic emulsion. I prefer to avoid the controversies associated with the presentation of a color image. Kodak Technical Pan 2415 is the best current all around choice for amateur deep-sky astronomical photography. It can be developed to various levels of contrast for photography of the moon, planets and deep sky objects. Since most deep-sky objects are very faint (or have very faint outer sections), hypering Tech Pan 2415 is a must. For best results, hyper, develop and print your own film. I use a Lumicon model 300 hypering kit (no longer available from Lumicon), but your own hypering chamber can easily be made. Consistency is the key. When out in the field, you want to know the film you're using will be properly sensitized for your needs. The length of time you hyper, the temperature and vacuum, along with the development time, will effect the sensitivity of your film. Kodak D-19 seems to be the best high-contrast developer for 2415. I prefer a development time of 6-8 minutes for my negatives. If you use a faster system than f5 you may prefer a little less speed (and less hyper/development fog) by developing 4-5 minutes, while users of slower systems may prefer more film speed by developing 8-10 minutes. The key here is to find what works for your system/needs, and stick with it!
Accessories - A Lumicon Coma Corrector (for f4 to f6 Newtonians) improves the stellar images at the corners of the negative, thereby increasing the usable field. I guide off-axis using a Lumicon Newtonian off-axis 2-inch guider. Off-axis guiding eliminates most flexure problems, but can make finding a guide star harder than in a separate guide scope. I use a knife-edge system to focus my camera body to assure precise and consistent focus (check out here for Chuck Vaughn's instruction / theory of a knife-edge focusing device). Several commercial knife-edge type systems are now available. Using a high power ground glass magnifier also works well. A high power magnifier can be home made using the top of an old eyepiece (10 - 20mm) or an old finder scope (I understand that 6 x 30's work well). An autoguider ( I have been using the ST4 from SBIG Santa Barbara Instrument Group since August 1995) can improve your chances of a successfully guided longer (60 minutes or more) astrophoto. Though not necessary for successfully guiding an astrophoto, this is one accessory many people can not do without. After using an autoguider for ten years now, I can say that an autoguider guides no better than my manual guiding, but it sure saves you neck, or back or whatever ails you (not to mention the chance to stay out of the cold). Autoguiders also make very long exposures (2 hours or more) as easy [sic] to take as a 30 minute photo. Click here to see Philip Perkins' article on the use of the ST-4 autoguider, or here to see instructions by James J Janusz.
Read/Listen - I am often asked how I choose/find some of the objects I shoot. If you have the hardware capable of delivering crisply focused, well guided astrophotos, why shoot M 42 or M 31 every time they're up? Since I enjoy photographing all kinds of objects, my ideas come from all kinds of sources. I subscribe to a number of amateur astronomy publications. Unfortunately, some of the best for covering faint, obscure, hard to find and unusual objects are no longer published (such as Dave Eicher's landmark 'DEEP SKY MONTHLY', and 'THE OBSERVER'S GUIDE', which was published by Astro Cards). My first start at shooting unusual (non-Messier / non-NGC) objects came from supplying Dave with illustrations for his magazine. Reports in observer specialty publications can give a good feel for the relative visibility/placement of objects in a given field. Professional pictures used in the magazines as illustrations of an object or field are also sources of potential targets. The Web is now an incredible resource. See my Links page for a glimpse of resources available. Remember, we all have access to the same sky. Chances are your local astronomy club has members interested in observing/photography. Discussions at local and regional astro-meetings are great places to talk with people that are already active in photography; most are more than willing to share their thoughts on target selection.
Atlases/Guides - When I started serious photography my sources were occasional magazine articles, a photocopied Messier list and a 1964 edition of "Norton's Star Atlas". Since the release of the classic three volume "Celestial Handbook", by Robert Burnham, Jr., there has been quite an increase in resources available to the amateur. The Uranometria 2000.0 (along with the companion "Deep Sky Field Guide") has the best scale and range of objects plotted for a starter set of a wide variety of objects to shoot (now the Millennium Star Atlas is out with more stars, but not more non-stellar objects). Without mentioning all available atlases and guides, let's just say there's plenty of sources around. Computer databases and atlases are now available for those with a computer. My favorites are the Arizona Database v9.0 (Dark Sky), which lists data on over 61,000 objects and allows you to keep extensive observers notes and conduct exhaustive searches by object type, size, magnitude, etc., and Megastar, which uses the Hubble 'Guide Star Catalog Version 1.1' to plot stars to 15th magnitude and uses a wide variety of catalogs showing over 208,000 non-stellar objects. The newer electronic bases/drives also can be equipped with extensive non-stellar databases, including the ability to slew the telescope to the object.
Everything there/work? - Few things are more frustrating than setting up at a remote site and discovering some critical component is missing or doesn't work. This could be anything from forgetting a cable to your power supply to the film advance lever of your camera not working, or anything in between. I check key system components either before leaving, or after returning from an outing in the field. I store all accessories relating to operations in the field in a series of toolboxes that are organized by accessory type. Drive corrector, power cables and fuses, etc. in one box; off-axis guider, coma corrector, T-rings etc. in another, and so on. When loading the vehicle for a night out, I simply put all boxes/cases in the vehicle and am assured of having everything I need at my remote site.
Backups/Spares - If something can break, burn out, or run down - it will! Try to have a replacement on hand. I try to keep extra cables releases, bulbs, batteries, charts and so on with me. Bring some simple tools with you. Screwdrivers, pliers, tape, odd nuts and bolts are sometimes lifesavers at a remote site. Remember, you want to maximize your chances of being able to take photographs from a site where you may be alone and/or not able to control circumstances.
Site - Only some thoughts here, as not everyone has access to a mountain top "Mecca"! The site I most frequented in the past is the parking lot at Mt. Pinos, California. Located about 65 miles northwest of downtown Los Angeles, at an elevation of about 8300 feet, this site is easily accessible year round. A drive of just under two hours gets me a fairly dark sky (naked eye around 6.0+ most of the time, I'm told) that is normally free of haze and moisture. The Bortle Dark-Sky Scale for Mt Pinos would normally be about 4 (Rural/Suburban transition) to 3 (Rural sky) on a good deep marine layer night. The past three to four years I have been going to Figueroa Lookout (Bortle scale 3) in Santa Barbara county, which has a similar sky to Mt Pinos, but is not normally snowed in during the winter and is much less crowded during new moon weekends. In general, get as far from cities as you can. A level, clear area is desirable. If you are to shoot specific targets, make sure they are visible from your site. Pavement is not necessarily detrimental to the local seeing. MANY people use the paved parking lot at Mt. Pinos and seem to get acceptable results.
List what you want to shoot - I find it very important to make a list of what objects I intend to shoot on a given night. Once you have the knowledge of what and where to find objects, you'll find the nighttime skies of any season are crammed with things to shoot. I make my decisions on what objects, and in what order to shoot them, in the comfort of my home in the days before I go out. Since I may have to use the 8" because of windy conditions, I make a separate listing for each telescope. The 40 inch focal length of the 8" is best suited for larger emission nebula, dark nebula, open clusters and fields that contain a combination of objects scattered across a couple of degrees. The 14.5" is best suited to close-ups of galaxies, planetaries and other smaller objects.
Creature comfort - This could be considered using proper equipment. The Fall/Winter temperature at Mt. Pinos can easily drop into the teens or single digits (Fahrenheit). I have seen many an amateur astronomer come from the 60+ degree Los Angeles basin and be turned away by the bitter cold of an early Winter evening. When I was still manually guiding all my astro photos, it was essential that I stay as warm and alert as possible throughout the night. Dress as warmly as you can, in layers. Good down jackets and pants are lifesavers if you have to stand (or sit) at your telescope for hours at a time. Wear a hat (ski cap or such) and gloves. I bring hot coffee and high energy munchies. Use what suits you best. I normally move immediately from shooting one object to the next, and don't take time out to 'warm up', rest or otherwise take a break (waste of shooting time!!!). Do whatever you can to make your time profitable.
Take a chance - One thing that I have learned through the years is not to take as gospel the data published in astronomical catalogs. Many professional surveys we now have access to were done as quick and dirty classifications of non-stellar objects. The size/magnitude data are very tentative for many objects. Many PK planetaries or Sharpless emission nebula are no more difficult to photograph than many of the NGC cataloged objects. I have shot many, many objects that were not visible through in my camera viewfinder or telescope eyepiece. With today's combination of filters, films, mounts and autoguiders, you need not skip over all those oddly named and plotted squiggles, circles and squares in today's atlases.