A few weeks ago I attempted to take some photos of the moon with my 300mm lens. The results were pretty good, but I wanted more, more, more! At 300mm, the moon is still quite small in the frame, and the photo I just linked was cropped a fair bit to “zoom in” some more.
The trouble is, telephoto lenses are expensive. I looked at various options and eventually got an excellent deal on an Opteka 500mm f/8 mirror lens.
Using a lens with a focal length of 500mm (or 1000mm with supplied teleconverter) was never going to be easy. At such a huge zoom, the tripod needs to be rock-steady, otherwise the image will move all over the place.
The Opteka 500mm lens was manual focus, like most (all?) mirror lenses. In principle this didn’t bother me, since I frequently use manual-focus Canon FD lenses. But in touching the barrel of lens, no matter how lightly, you send the moon ricocheting wildly around the viewfinder. You have to wait ten seconds for it to stop wobbling to see if your focus adjustment was any good.
Which brings me onto my next point. The focus ring is extremely sensitive. Even for an infinitely-distant object such as the moon, moving the focus ring just a millimetre sends the image to a blur. It’s a bit like using a rangefinder – when not perfectly focussed, there are two ghost images that slide past each other as you adjust the focus. I never managed to make them line up properly with this lens because it was too sensitive.
After an hour with the lens and camera on a tripod, I hadn’t managed to get a well-focussed picture of the moon. And in cases where I had got the focus not too far off, the general image sharpness was terrible, and there was considerable chromatic aberration. The following image is the best I got out of the mirror lens in an hour of shooting.
That could have been a really nice image, as the moon almost fills the frame.
I won’t give up just yet, but I’m reasonably confident that I won’t be able to improve on that picture. I might do better to buy a Canon 2× teleconverter to make my 300mm lens into a 600mm. I guess the L-series glass is a little out of my league for the time being 🙁
So, to answer the question in the title…
No. Mirror lenses are not worth it.