I don't have experience of conventional lenses longer than 300mm, so take what I say accordingly.
A mirror lens is different to handle. In the 500mm focal length range, it is certainly likely to be lighter to carry around, which sounds like it would be a plus for your situation. But not all mirrors are equal. I have a Russian MTO 1100mm mirror that doesn't see a lot of use because it's a heavy pig, and is hard to use without a tripod. I prefer hand held shooting, so that puts it lower on my "what willI shoot with today?" list.
But a mirror lens, unless you're shooting with a Minolta AF mirror lens or its Sony derivative, is also manual focus. This may change what you're able to shoot.
The fixed f8 aperture common on many 500mm mirror lenses makes it slower and dimmer than many conventional telephoto lenses of similar focal length. Combine that with MF, and again, there's likely going to be an impact on what you're going to be able to shoot. Faster moving subjects are going to be harder to capture quickly.
Donut bokeh, comes with the territory, but its impact can be reduced by careful selection of background. This is not always possible of course. We usually have to go where our subjects are and put up with whatever they happen to be in front of at the time. We don't always have the luxury of being able to choose a backdrop less likey to provoke donuts. If the subject is interesting, and the image well focused and composed, the presence of mirror lens bokeh shouldn't make or break an image. I can live with it if the final image is still sufficiently compelling. Unless you point it out, many viewers, particularly those who are not as photo-technically inclined, might not even notice it.
I usually have to bump contrast and brightness in post, but it's not a big deal.
I try to keep some guidelines in mind when I shoot with mirror lenses. Not that I haven't broken or ignored them, but when I do, it usually shows.
As much as possible, fill the image with your subject. A tight crop of a bird that was small to start with is unlikely to result in a satisfactory final image.
Shoot in bright light. Even with the excellent high ISO performance of recent cameras, cranking up the sensitivity too much to make up for poor lighting, is going to give you less than stellar pictures, with details lost to high ISO grain. Find your own ISO limit, and shoot within it. You can use faster shutter speeds like 1/800, or 1/1000 or faster (see below), but nice bright light is recommended. There's no free lunch.
Never having had a long conventional lens like your 150-500, I can't make a direct comparison. I've never really done a "scientific" comparison to see if my 55-300 cropped to the same FOV as my 500 mirror gives similar, better, or worse results. I usually have one or the other, not both, if I'm shooting tele in that range. I don't doubt that a fixed 300, or longer/better zoom would likely give better images than my 500 mirror, but I can't use what I don't have. I try to work within the limitations of the tools at hand. As I'm not likely to be soon (or ever) able to afford a better tele lens, I'm content to live with what I've got. When things work out, I'm happy with what I get. And for memories and record-keeping, sometimes a bad picture is better than none at all. So be it.
Many posts and articles online tend to scoff at mirror lenses, and certainly a bad mirror lens is not going to do you any favours. But, contrary to what some would have you believe, not all mirror lenses are bad. Looking at the best of the shots by mirror shooters in this thread can give you a taste of what's possible. As for my own recommendations, I've used the Tokina 500mm f8 and the Tamron 55BB 500mm f8 mirrors most extensively. My Russian mirror is a hangar queen, quietly sitting in its wooden box, awaiting the signal to scramble, which does not often sound. Of the two mirrors I've used most, I would give the Tamron the edge. There have been times when I have been truly, pleasantly surprised by what it can deliver. Here are a few examples I'm particularly pleased with, which I've posted previously, just so you can see what sort of result I'm happy with:
K-S2, 1/1000 sec, 200 ISO
K-S2, 1/1000 sec, 800 ISO
All of the following were taken on a KP at 1/2000 sec, 800 ISO:
100% of above:
100% of above:
The thing to figure out is if this move is going to be right for you. If you go in aware of a mirror lens's limitations, and you're willing to work within them, accepting whatever changes to shooting technique and subject matter it imposes, you're good. If you don't feel that any of these represent too much of a sacrifice, then I would certainly invite you to take the plunge. A good mirror lens is probably going to be cheaper than a good conventional telephoto, too. If it turns out that it doesn't give you satifaction, you haven't likely spent that much, though "that much" is going to vary for each of us. (If you go for a Tamron Adaptall, the fixed aperture means you can stick with a plain PK mount and not worry about looking for the pricier PK-A one.) In the end, if you're happy with the pictures you get, and it keeps you shooting, that's all that's important.
I hope you find this helpful, keeping in mind that free advice is often worth exactly what you paid for it!
Good luck with your research and decision.
Bruce
|
