>>3598435I don't have experience with any of them other than the Opteka one, but I do have experience with it on bellows and other extension. Also, are you referring to the "Rokinon f/8.0" one? If so, it is evidently much better than the Opteka for use and IQ. Otherwise, the f/6.3 one should just be a rebrand of the Opteka. All the 500mm f6/3 mirror lenses from Rokinon, Opteka, Lightdow, Bower, Pomya, Bewinner, Phoenix, etc are all rebrands of the same lens. Sometimes you'll even find one that has "Nikkor" on it, but that is of course fake. You can tell because it will look exactly like the OP in color and style, but with a different name on the gold name plate. There are also a ton of them on Amazon with the name on the lens marked out.
>>3598441You'd probably need to contact one of the owners like on that forum and give them a hunk of cash.
>>3598444Because, mirror lenses are low contrast by their very nature. That vid was taken before I bought a velvet-lined lens hood (95mm dia) for it. I have some press-fit flocking and will be making an extension for that lens hood. The lens hood helps it gain noticeable contrast. Since these are 500mm you can put an amazingly comically long lens hood on them if you wish and get very good contrast. Some people take the lens barrel apart and add flocking to everything they can, which also helps.
In post, the photos are easily corrected without causing problems.
