An Astrophotography Primer Part 1

Astrophotography 101 A primer

Astrophotography 101 A primer

I've had many requests for me to write an article on how I take the photo's I take. Let me first state I'm not an expert on the subject, more like a student of the craft. Secondly, this isn't intended to be a end all be all article. The subject matter is vast, and volumes have been written on it. My hope is to give you a general overview and point to some good resources on the web if you care to learn more.

1. The first item needed is a telescope of some type with good optics. Any of the major brands will work, like Meade, or Celestron, just to name 2. My choice was the Meade LX-90. It is a 8" Schmidt Cassegrain design with a good solid tripod and a goto mount with reasonably accurate tracking capabilities. Buying a scope is a whole article unto itself. Just stay away from the department store variety and you should be OK. IMHO the LX-90 is about the best bang for the buck out there today, as it's turned out to be quite a nice imaging platform.

2. A camera helps :>). The simplest way to get started is with a digital camera. Features to look for are: A manual mode where you can control expose times and apature. It's also best if the lens is threaded. This makes coupling it to the scope very simple. Look for a lens that zooms internal to the lens housing. Another words, the lens itself doesn't move when zooming in and out. The Nikon CP995 is a very popular choice. I personally use the Sony DSC-F707. Exposure times aren't as important if you're only wanting to take pictures of the moon or planets. Just about any camera will have exposure times long enough for that. If you're interested in shooting Deep Sky objects then look for exposure times of 30 seconds or longer. It's also best if you can adjust the ISO setting. All of my deep sky shots use ISO400.

3. Coupling the camera to the scope. The most common way to hook a digital camera to a scope is called afocally. This is where a telescope eyepiece is attached to the camera lens and the whole unit is mounted to the eyepiece holder on the scope. The eyepiece focal length is usually in the 25 to 40mm range and the 2 glass surfaces kept as close as possible to minimize vignetting. There are numerous ways to accomplish this. If the lens on your camera is threaded, you can buy step rings and adapters. The product I use is made by a company called Scopetronix. For full details you can visit their web site at www.scopetronix.com They sell adapters for just about every camera made. I'm in no way affiliated with the company other than a satisfied customer, and I have some of my photo's displayed there. They have some excellent tutorials on their site dealing with astro imaging.

4. Scope alignment. In order to take photo's with nice round stars, you need to have a good alignment on your scope. There are 2 methods of tracking stars on the LX-90. You can use the Polar mode, in which you need a wedge mount or you can use the ALt/AZ mode. I've found the Alt/Az mode to be quite good when your camera is limited to 30 second exposures or less. The only draw back to this method is you'll have to deal with what's called field rotation when aligning your images. More on that later. For details on how to align your scope consult the owners manual. The bottom line on scope alignment is this: The better job you do on alignment the better your images will turn out.

5. Taking the photo's. Rule number one: take lot's of shots. If photographing the moon you may get by with just one good image for a final product. The trick is getting that one good image. There are several variables affecting image quality. The biggest is called "seeing". The upper atmosphere plays a big part in how sharp your images are in any given time period. Just like the heat waves off a hot road distorts distant images, the atmosphere causes similar effects on sky images. This is what causes the stars to appear to twinkle. BY taking lots of images you greatly increase your chances of getting a sharp image between the shifting layers of atmospheric currents. The other variable is called transparency. This is the amount of dust and water vapor in the air. It acts as a filter reducing the amount of light reaching your lens. Rare are the nights when both conditions are at a minimum.

When shooting deep sky objects, rule number one really applies. Deep sky objects are very faint. By using a technique of layering or stacking images you can greatly increase the signal to noise ratio and produce images like those taken by more expensive CCD imagers or 35mm long exposures. OK, well not quite as good but pretty darn close, and for a fraction of the cost. By taking say, 20 30 second images and then aligning and adding them together, you've created a 10 minute exposure.

I'll cover this topic and what to do with your images after you've taken them and image processing software in part 2. Hope you found this article helpful.

Two great places to hang out and gain a lot of knowledge are the Yahoo group called Digital_Astro and the web site www.arksky.org. Thousands of folks taking great photos of the universe. Maybe I'll see you there. Now get outside and take some photo's and most importantly have fun.

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