Word & Pictures Joe Roberts
Taking pictures of the night sky can be a fascinating experience and you don't have to own a telescope to begin. Here are your basic needs:
The best type of camera to use for astrophotography is a manual 35mm SLR camera and the following features are a must:
- The camera should have removable/interchangeable lenses (most SLRs meet this requirement).
- It should be one that allows the shutter to be operated in all modes (time exposure mode especially) even with the battery removed!
- The camera must have the ability to do long time exposures (usually the 'B' setting).
- It should be able to accept a remote shutter release cable.
- The camera should have a tripod thread.
- Don't worry if your camera has a broken exposure meter - you don't need it for astrophotography.
There are many cameras available that meet the above criteria and in my opinion the best SLRs for astrophotography are often the simple, low end models. One such example is the Pentax K1000 that can be picked up for around 100. It's a basic model that fits the bill perfectly and has been around for a long as I can remember. Other cameras that I found are good for astrophotography include the Pentax ME Super, Canon FT and Nikon FM, but there are many more. A high end Nikon or Canon isn't likely to take an astrophoto that is any better than one taken by the budget Pentax K1000. It's the lens quality that matters most
For basic astrophotography, a standard 50mm lens is a great place to start and most 35mm cameras have one in their range. Such lenses sell for between 50 and 100. Another lens that is good for a beginner is a 28mm wide-angle which allows you to photograph a larger area of the sky in one shot.
Many camera outfits come with a zoom lens with a range of say 28mm wide-angle to around 70 or 80mm mild telephoto. Zoom lenses typically have more optical elements than their fixed focal length counterparts and are therefore more susceptible to aberrations. For this reason I prefer fixed focal length lenses, but don't let this discourage you from experimenting with zoom lenses. Many will allow you to take decent astrophotos.
For even the most basic astrophotos, you need a tripod. The tripod does not have to be too expensive, it just has to be able to hold the camera steady. This is because many astrophotos require exposures of 30 seconds or more. The tripod should have a head with enough degrees of motion to allow you to easily point the camera at any portion of the sky.
This is necessary to take photos without vibrating the camera and ruining the photo. A cable release can be picked up at most any camera store for around 6 preferably the locking type. Try to get one with a long cable (several feet is ideal). Shorter ones are OK if you are extra careful not to vibrate the camera while the shutter is open.
Choosing the proper film is probably the single most important variable for beginning astrophotographers. I tend to use negative film and found the following films are excellent for those just starting out: Kodak Royal Gold 1000, Kodak Royal Gold 400, and Fuji Super G800. For B&W prints, try Kodak T-Max 400. All are commonly available at most camera shops. If you use the Kodak colour films, buy Royal Gold, not the 'plain' Gold! It costs a little bit more, but it really is better for astrophotography.
To time your exposures you'll need a stopwatch (a wristwatch with a second hand is fine). Having a pad and pen to keep records of the work you've done is a good idea too. Your notes will help you to later sort out what you've taken, as well as what worked well and what didn't.
A 15 second exposure of Venus, Jupiter and Mercury taken 2 March 1999 looking over Horse Pond in Salem, CT on Kodak Gold 200 film. Mercury's reflection off the water is very prominent.
Your first astrophotos
Start by shooting an easy target such as a constellation using the Wide Field Fixed Tripod method. You don't need a telescope, just the items listed above for this type of astrophotography.
- Load the film (I recommend colour film for your first shots) into the camera and advance it to the first frame.
- Mount the camera on a tripod and attach the cable release. Set the aperture on your lens to around f/2 or f/4 (but do keep notes) and set the focus to infinity!
- Aim your camera at a part of the sky where there are the most bright stars visible - Orion is an excellent target if you are starting in autumn or winter. Try not to aim the camera in a direction where there is a lot of skyglow (caused by light pollution); in addition, make sure that no streetlights are shining directly on the camera lens (otherwise 'ghosting' and poor contrast images might result).
- With the camera set on B, fire and lock the cable release and begin timing your exposure.
- At the 15 second mark, end the exposure, advance the film and take another shot of the same area, but this time make the exposure 30 seconds.
- Try another exposure at 60 seconds. Do the same thing but try a different aperture setting.
Repeat this procedure for different areas of the sky. Be sure to try and take at least a few shots of the polar region!
For one shot, set the lens f/stop to around f/8, and take an exposure of an hour or so (this will result in a very interesting effect due to the Earth's rotation).
Here is a shot of circumpolar star trails as seen from my backyard in Oakdale. This is about a two hour exposure with a bright Moon in the sky (to the south, out of the picture). The film was Kodak PMZ-1000, the camera was a Canon FT with a Canon 28mm f/2.8 lens set to f/11. The object at the upper left of the image is the edge of the roof of my house. The dotted lines in this image are due to airplanes flying over (I count five visible airplane trails in this image).
Once you have finished the roll of film, you need to consider where to get it processed. Your local one-hour photo processor is a good place because you are able to personally give instructions for processing to the person who will do the actual developing & printing of the film. If you send a roll out to a mail order house, the chances are that your written instructions will be lost and something bad will happen. When you bring the film in for processing, tell the machine operator that the photos on your roll of film are astrophotos. Also mention that many (if not all of them) will be very dark compared to regular shots; tell them to print every exposure (regardless of what the machine thinks), and tell them not to cut the film (negatives)!
The reason for requesting that the negatives are not cut is that the borders between the frames of astrophotos are often hard to detect at a casual glance, and the operator may inadvertently slice an otherwise very good shot in half. This has happened to me. More than likely, the prints you receive will not be perfect the first time around. Some will probably need darkening or lightening, and they may need some colour balance. Once you do have a good shot, keep it handy as a reference to show the operator what the photos should look like in general. Most of the one-hour photo shops I have dealt with have been very cooperative and are often willing to do corrections for no extra charge.
Here is a shot of the constellation Orion taken with the lens intentionally thrown out of focus. This astrophotography 'trick' can be used to clearly reveal star colours. Orion shows a beautiful variety of star colours. From Red Giants to Blue-White 'superstars' and red nebulae, Orion has it all. This was a 30 second fixed tripod shot using Kodak Royal Gold 1000 film in a Pentax K1000 camera and 50mm f/2 lens. The processing lab's auto splicer could quite easily have cut this through the middle.
Your processing options are limited if you use B&W film, unless you have a home darkroom. The reason is that few (if any) one-hour processing shops do B&W on site and the majority send out to commercial processing houses. In my experience film is processed in a generic way and is not suited to astrophotography. If you have a home darkroom, you have much more control over the final result and it's well worth trying B&W astrophotography.
Assessing the results
Your first roll may not be perfect, but chances are there will be at least a few decent shots. Do you notice that the stars appear as tiny streaks even on the short exposures? Although it does not seem to, the Earth really does rotate enough to leave a short star trail even on a 30 second exposure! Notice also that the longer exposures may have recorded more stars (especially if the camera was aimed at the polar region and/or your sky is very dark).
- Do you see unexplained 'ghosts' in your images?
This can be caused by stray light (from nearby streetlights or floodlights) that is scattered by the camera lens. The remedy is to be sure that your camera is completely shielded from stray light sources.
- Are your photos washed out to the point where it looks like they were taken in twilight? Light pollution in your area may be the problem (you'll have to get to a dark sky area to eliminate this problem).
- Do you see the various colours of the stars? If you took a photo of the constellation Orion you should see both red and blue stars. Film is great for capturing star colours as compared with the human eye.
Comet Hale-Bopp sets over a field. Taken from Rt 82 in Salem, CT USA, 50mm f/2 lens, 30 sec exposure on Kodak Royal Gold 400.
This shot was taken from my backyard in Oakdale, CT on 14 April 1997; a fairly fat Moon was in the sky at the time. 30 second fixed tripod exposure on Kodak Royal Gold 1000 film, 50mm f/2.0 lens on a Pentax K1000 camera.
Comet Hyakutake taken from Lebanon, CT, March 1996. A five minute exposure using a 28mm f/2.8 lens.
About the Author
Joe Roberts is an electronics engineer primarily involved in sonar work for the US Navy. One of his greatest interests is amateur astronomy, an activity he has been involved with since 1973 when, at the age of 12 he bought his first Tasco 60mm telescope. Joe also has a strong knowledge of observational astronomy and fellow observers often use him instead of 'go to' on their telescopes. He has dabbled in CCD imaging and hopes to become much more involved with this field in the near future. Joe has a web site Amateur Astronomer's Notebook, that he runs with co-partner Peter Chapin. Joe tries to observe the stars and planets whenever the weather (and his schedule) allows.