03-05-2018 03:07 PM
I would not buy that lens. It is a cat lens. It is manual everything. Unless you know what you are doing this lens will be difficult to use.
However it can be done. Lots of folks do use them. IQ will be poor but that is almost a given with its price point.
Save your money for one of the Sigma or Tamron 150-600mm super zooms. Even look used if money is too tight.
If you just want a prime look at the Canon EF 400mm f/5.6L USM Lens. It is light-years better than the one you are considering. Fantastic IQ and auto everything. It is a super popular lens so the used market on it is great. Way better idea.
That's absolutely true... but they are cheap. So if you wanted the cheapest way to get to 500mm to image distant objects... it would be an inexpensive option.
My other concern is that at high focal lengths, if an object in flight (such as a bird or plane) gets out of the frame... it can be very difficult to get it back in the frame fast enough (before it's gone). Sometimes a long focal length lens is not the best option.
Considering these mirror lenses are completely manual focus... that would be especially challenging. It would work for the moon because the moon isn't racing across the sky and you can take all the time you need to focus. For an airplane... you'd be trying to track the plane and keep in the frame of view WHILE trying to focus at the same time and THEN try to grab a photo before it's gone. That's quite a challenge and likely to result in mostly a lot of out of focus or missed shots where the plane wasn't in the frame.
03-05-2018 05:21 PM
"My other concern is that..."
The extremely ugly bokeh. Its great if you love donuts!
IMHO, absolutely a poor option, except for the price it has nothing going for it. The Bower 500mm f/8 Manual Focus Telephoto T-Mount Lens is, again, light-years better choice. Best choice is to find a used, even a very used, ugly rating, Canon EF 400mm f/5.6L USM Lens. You will be well better off.