Twofer question re: Teleconverter and mirror lens

First, I was wondering what the difference is with a mirror lens (let's say a 800mm) opposed to a regular prime lens? Any advantages or disadvantages of one over the other.

Second, I read someone asking about buying a 400mm or simply buying the new Canon EF 2x III teleconverter for his 70-200mm lens. Which would be a better option?

Thank you

Hmmm don't know anything about mirrored lens, I supose its uses mirrors to magnify focal length ?? I know they are reputated to have poor IQ compared to a regular lens of the same lengths......
As for 400 V 70-200 with 2x TC, I can't imagine the 70-200 with the TC beating a 400mm prime's AF. From what I have seen so far, the bare 400mm beats the shorter focal length with the TC in image quality too...... But I'm here to be convinced otherwise

Having played with both, I can probably have a go.

Mirror lenses have some things going for them - they are inexpensive, compact, light. On the other hand they tend to have poor-to-indifferent optics, they are optically slow and have fixed apertures. The bokeh - particularly on highlights - looks like a donut. Some like it, some do not.

I have a Celestron 500mm f/5.6, a 1980's derivative of the C90 spotting scope. On the whole it's better than not having a 500mm lens, but it suffers from chromatic aberration. Provided I get the focus right, I can usually fix this in post processing.

A slow, fixed aperture lens means that you may not have enough light in the viewfinder to focus easily.

On the 70-200/2.8 + 2x teleconverter.
You will find that this combination is a long way from either the 400/5.6 prime or the 300/4L + 1.4x tc. I've tried all combinations and found that the 400/5.6 was sharp and quick to focus (but it was impossible for me to use because of camera shake.) The 300/4L + 1.4x tc worked well - the IS makes the combination less user hostile than the 400/5.6L. Finally, it seems that almost every lens suffers when a 2x converter is attached.

Last thought - you could also consider the 100-400 - it's a decent lens indeed.

a mirror lens is basically a telescope design, light goes in, bounces off a mirror, which bounces off another mirror and out the lens.

Because there is a small circle in the way of the light (one of the mirrors), mirror lenses tend to create odd donut shaped bokeh.

Also, there are no aperture blades, so you can't change the aperture...and normally, that aperture is rather slow.

IQ wise, the teleconverter may be the better option (not completely sure though), especially where bokeh is concerned. some people really hate that donut bokeh (it can be rather distracting).

on the other hand you can get mirror lenses for kinda cheap, so that's a plus.

oh yeah, you normally can't autofocus w/ the mirror lenses either...although you might not be able to autofocus w/ a teleconverter, depending on your camera body and lens you use (aperture may not be fast enough for AF).

here's a thread to look at about mirror lenses. https://photography-on-the.net/forum/showthre​ad.php?t=971172