What is a good mirror lens for my Nikon D5200? I love taking wildlife pictures and need a better telephoto lens. I am using a Nikkor 55-300 AF and it works well, but I need about twice that power. I take a lot of late afternoon pictures and need something that will allow me to take them in low light. Will a mirror lens work well in low light? Camera will use both lens, with or without autofocus.
The other thing which might be an option is a 2x converter/extender? I know you can get them for Canon, so I assume they're available for Nikon gear also.
Low light - You're going to lose light with both the 2x and a mirror lens. Mirror lenses are usually f8 as others have mentioned. A 2x on a 300mm f5.6 will become a 600mm f11. You will lose light no matter how you do it (the laws of physics/optics are against you unfortunately) unless you happen to have a whole bunch of money lying around to buy a 600mm f4 prime lens, which like the rest of us you probably don't...
So, yes, mirror lenses are good for wildlife photography, they are certainly a cheap option to get nice long focal length. You may struggle in low light, depending on how low we're talking.
Find a lens you like the look of, look at the max aperture of it (probably f8) and try shooting at that aperture for a test. That way you'll know whether you can get a happy mix of iso and shutterspeed to work at f8 before you spend anything.