Visual observing through my CPC-800 was inspiring. But I soon wondered if I could take pictures through it? After a research I decided that a DSLR camera would be a good way to start, and a DSLR is great for everyday use. But DSLRs are expensive and I was unwilling to spend another one to two thousand dollars on equipment.
So I turned to eBay. I’m not nuts about shopping on eBay (that’s another story), but I found a canon 20D camera for about $60 and was tickled pink when it arrived! It was in terrific shape and was just as described by the seller. That and a few accessories and I was on my way! A T-Adapter allowed attaching the camera to the telescope in place of an eyepiece.
I took a few shots and soon discovered that this stuff was tricky! For one thing focus is critical for astrophotography and the 20D wasn’t well suited for this usage. DSLR cameras normally use an auto-focus lens. But my telescope isn’t an auto-focus lens and focusing on stars through the viewfinder was difficult. Tediously taking trial and error shots got me closer but wasn’t very accurate.
This was such a problem that I ditched the Canon 20D. What I needed instead was a camera with “live-view”. Live view lets you view images on its LCD monitor while focusing – pretty much like every point-and-shoot in existence, but is an unnatural feature for early DSLR cameras. I found another eBay bargain, a Canon 40D for about $130. I resold the 20D for close to its initial cost.
My research suggested that astrophotography would be tough without an equatorial mount or wedge. The altazimuth mount of the CPC-800 is not well suited to astrophotography because it must move in both altitude and azimuth simultaneously to follow the ecliptic (the apparent motion of stars and planets as planet Earth rotates beneath them). This leads to rotation of the image as shown in this short clip:
Field rotation in these sequential images of comet 41P.
I generated the clip from sequential pictures of comet 41P which can be seen moving across the field.
An equatorial mount gets aligned to the Polaris and slews the telescope along the ecliptic while requiring motion in only one axis, and alleviating the field rotation issue.
A wedge angles your telescope to that of your geographical latitude. This gets you closer to the capabilities of an equatorial mount. But a wedge is another thing to setup and align on my outings so I decided to stick with the easy altazimuth mount for now. (I did eventually start using a wedge, see below.) Plus, the wedge costs about $400 and this thing is essentially just a few (well machined) hunks of metal and a hinge!
I eventually got some shots of the moon, the Orion nebula, and a couple of galaxies. They’re far from perfect but have given me a taste for more. The Orion nebula is a beautiful object when photographed. Colors jump out – colors that you can barely see through an eyepiece. This nebula is bright enough to produce decent results from short exposures – short enough to avoid field rotation and star trails.
I’ve taken 30 to 180 second exposures of various objects, but longer exposures start becoming a problem. Taking multiple short exposures reduces or eliminates star trails, and the pictures can be post processed to combine (or stack) the images. Field rotation can be removed as well. This common technique is done using software such as Nebulocity. Learning this technique is time well spent, as the process is useful at more advanced levels of astrophotography too. I’m still working on this and will let you know when I’m good at it!
Update, September 2017.
Well, I’m getting better at it. I built a wooden wedge to experiment with and finally decided to order a Celestron wedge. See the September blog entry for more details
The Neophyte Astronomer 