Lights….. Camera….. Action…….
Getting Started in Astrophotography
By Clayton Kessler
Astrophotography does not have to be a big "production". You can take very satisfying, very professional looking, astrophotos with fairly minimal equipment. If this is a part of the hobby that interests you I urge you to take the plunge!
Let me give you some background. I have been in the hobby of astronomy for about three years. I don’t make any claim to be some kind of "expert", I am just an average schmoe with less than average patience. I did, however, have a driving force. Ever since I was a child I have been fascinated by the astrophotos taken by observatories and placed in magazines. I did not realize that many amateur astronomers were getting similar results, and getting published, using equipment available to us all. I will let you in on a little secret, many of the photos that I see, in magazines, are piggyback exposures through regular camera lenses. Secret #2 – piggyback astrophotos are relatively easy to take! In piggyback photography you take pictures through a camera lens – not the telescope. The telescope is used to make "guiding corrections" or correct any errant drifting of the stars by watching a star through a crosshair eyepiece.
What is needed to take astrophotos? Well….. a camera, of course, and you need to be able to hold the shutter open for a length of time. This means the camera should have a "bulb" or "B" setting. An older Single Lens Reflex (SLR) is perfect. You also need a cable release, if you touch the camera to trip the shutter you will blur the photo. You also need some kind of mount that will track the stars. This is not as difficult as it seems. Look at your telescope, is it a fork mounted SCT?, a newtonian on a german equatorial mount?, does it have a motor drive? If so, you are golden. You just need to attach your camera to the telescope, OR THE MOUNT, and start to take photos. The mount, you say? How come? Well a lot of scopes, notably 4.5" reflectors, come with a small GEM and a motor drive is a frequent accessory. This small mount is fine for visual work but somewhat light duty to drive both the telescope and the camera. The solution? Remove the telescope! This takes enough strain off of the motor that you can use the mount for photography with shorter focal length lenses. Without a telescope you cannot guide the mount but this is not so critical with a short focal length lens.
Ok, you have a camera and a motorized equatorial mount – now what? Well, we need to attach the camera to the mount. Many mounts or telescopes have the facility to attach a "piggyback camera mount" and these are available from scope dealers. The cost for a piggyback mount runs from 30 to 50 dollars and they will support a camera and up to a moderate telephoto lens. When you are just starting don’t use more than a moderate telephoto (135mm or so). If your scope does not have any way to attach a piggyback mount there are other ways…….
You need to look at the mount and be creative. Often there are screw holes that can be used to attach a "ball swivel camera mount" available from a camera store. Every mount is different so take a look. If you see something that you think will work try it! You can even use a piece of wood, a ¼-20 screw and a roll of duct tape (or "Doug" tape at the NCO). Attach the camera to the wood with the ¼-20 screw (sink the screw head into the wood so it will not scratch anything). Duct tape the wood to your telescope tube near its’ balance point. Take astrophotos. Is this an elegant solution? Heck no! Does it look good? Heck no! Will it take astrophotos? You Betcha!!!
What else do you have to do? When you set up you have to POLAR ALIGN your mount very carefully. Polar alignment is critical to good astrophotos – especially if you want to use that 500mm telephoto. Polar alignment means you are going to adjust your mounts’ polar axis parallel with the axis of the earth. If your scope has a polar alignment finder scope this is easy. If not you may have to rough align with a compass and protractor and do a drift alignment to perfect your alignment. The method for drift aligning a scope is written up in many reference books far better than I could here. If I could give you a hint, find someone at a star party that is proficient in this and have them teach you. It is not hard and takes around 20 minutes or so. If this seems hard, don’t worry! It is not difficult and if you are going to take photos with short focus lenses (35mm, 50mm, 100mm) just set north with a compass and set your latitude with a protractor. Sight on Polaris through your finder scope and start shooting!
OK, we have a mount, a camera and a cable release. We have duct taped our camera to the scope. What else do we need? How about film! It must take some special kind of high speed scientific film to take astrophotos, doesn’t it? Nah, you don’t need any special film, the ones available from your local drug/department/camera store are fine. What kind do I recommend? Well – stay away from black and white. It is hard to get developed, most places have to send it out. You really don’t need Tech Pan 2415 that has been hypered for this kind of astrophotography. Leave that to the "pro-amateurs" that get published in the national magazines. Color film is much more impressive! There are lots of colorful things in the sky that are so dim we see them as shades of gray. Color film, however, shows lots of red emission nebulas and blue reflection nebulas. In addition, stars themselves have lots of color variation and look great on color film. I can recommend several common color print and slide films that should be easy to get a hold of. Kodak sells Royal Gold 400, Max 800, Ektachrome Elite II 200 and Ektachrome 1600. The Ektachrome films are slide films. Fuji also has several very good films that you can get anywhere. Fuji Super "G" 400 and Super "G" 800 are getting hard to find but are great films. They are being replaced with Superia 400 and Superia 800 X-tra. There is both bad news and good news here. The Superia 400 started as a great Astro film – so naturally the formulation has been "improved". This "improved" Superia 400 has been TERRIABLE for astrophotography! The good news is that the Superia 800 X-Tra is a WONDERFUL film that is very commonly available. In general start out with about an ISO 400 - 800 speed film and you won’t go far wrong.
How long do you expose the film? This depends upon sky conditions and the "speed" of the camera lens. Generally speaking, the darker the sky – the longer you can expose the film. I can give you the rule of thumb that I use from "moderately dark" (Boon on a mediocre night) skies.
Camera Lens Speed: Exposure Time:
f 2.8 10 minutes
f 3.5 20 minutes
f 5.6 30 minutes
f 8 45 minutes
Another hint I can give is to "stop down" your 50mm lens to at least f2.8. This will reduce or eliminate the coma that is present in all camera lenses. This coma does not show up in terrestrial subjects but stars are pinpoints and they show aberrations that would otherwise not be noticed.
So! You took some photos – now what? You have to get them processed. Color print films can be processed at your favorite "One Hour Photo" joint. But be prepared for some more work when you get them back. Many photos will be very washed out looking, or they may be a strange green color. This is quite normal, your photos have to be "color balanced". Most automatic processing systems have no idea what an astrophoto is, and neither do most processing machine operators. If you have the necessary computer hardware and software to do this yourself that is wonderful, but most people do not. This is where a good photo processor is a jewel. Cultivate your local shop, bring your stuff in at a non busy time and schmooze. Ask what they can do to darken the background and bring out details. Bring in magazine pictures and show them what you want. Most places like happy customers and will make the adjustments necessary to make your photos look their best. Before I became computerized with this stuff I had a great deal of satisfaction with Quicksilver Photo in Plymouth and Photo 1 in Cadillac. Both shops have done a very fine job with my astrophotos but it took communication to let them know what I wanted.
Well, we didn’t talk about how to take astrophotos if you have a dobsonian, or how to take prime focus astrophotos or where to take astrophotos. Maybe some future articles there. Go out, set up, take astrophotos and show them off!