The Canon 100-400mm L IS II zoom lens is perhaps the best lens, not designed for close-up work, ever put on the front end of a Canon camera.
Canon 100-400mm Zoom Lens
The Canon 100-400mm L IS II zoom lens is perhaps the best lens, not designed for close-up work, ever put on the front end of a Canon camera. It may even replace some normal lenses, not just astrophotography ones. It focuses close enough to replace a macro, and a 70-200mm zoom lens (yes, you lose a little on the close side, but 70mm vs 100mm isn't that much). Plus the reach at the 400mm end is substantial, and well worth the slight loss of the 70-100mm range. It's ultra-sharp, has a fluorite element, focuses incredibly fast (more so if you use the limiter switch), and auto-focus works with Canon Extenders. As if that isn't enough, it has one of Canon's best Image Stabilization setups which can easily help you get 4 or even 5 stop faster action by eliminating camera shake. Set your camera to ISO 400 and you can hand-hold this baby all day long. Or at least, until the 3.5 pound weight makes your arms hurt. In short, this is an incredible lens.
I count myself lucky that I was able to secure one used in pristine condition for a great price. You may have to hunt for yours, since they are so fabulous that they rarely show up on the used market without commanding premium prices. But if you are as lucky as I was, you'll want to throw it on your Time Machine and aim it at the stars almost as much as you'll want to take wildlife and portrait photos in daylight. On an APS-C crop sensor camera like the Canon 450D or Canon 80D, it has almost the same reach as my main SV503 100mm/f7 imaging rig.
Here's a comparison from Astronomy Tools in Imaging Mode. If you don't know about this web site, you should bookmark it now. The field of view calculator lets you compare different scopes, cameras, barlows, and other items to see how it will effect your shot on solar system objects, Messier objects, and basically anything in the sky. Since it's a web page, you can run it from anywhere you have a network connection. Here's what it shows the FoV would be for my normal AP rig, taking pics of the Moon. This is a 102mm/f7 scope with an ASI2600 camera on it and a 0.8x flattener/reducer.
Now compare this to my Canon 100-400mm zoom on the front of a Canon 80D with no other optics:
Yes, they're not quite the same, but consider that I have to turn on the mount, get it tracking, and do everything with a heavy, equatorial, semi-permanent rig if I go with the first option. With the Canon, I can just pick it up, hand-hold it while I aim it at the Moon, and get a picture like this:
Imagine how much better it would be if I actually put it on a tripod, focused properly, and used a cable release? This is the ideal portable astrophotography rig! Plus, if I need to switch to something more wide-field, I can pop off the 100mm-400mm zoom and put on an 85mm or a 24mm or even a 10mm and capture almost the entire visible sky.
More to come as I explore this lens, but I'm very happy to have been able to secure it as part of my collection!