3m-5a zm-5a 8/500 teleconverter

[djronbxs]

Hi,

I have the 3m-5a zm-5a f8 500mm and a russian 2x teleconverter. Now i would like to increase the magnification. What do you think is the best way to do it:

Buy another 2x and stack them to together for a 4x ?
or
buy a barlow lense ?

thanks
ronald

[WolverineX]

stacking teleconverters is not a good idea, especially with mirror lenses, because image in viewfinder will become too dark because of loss of light and mirror lenses are already slow lenses. what you might get in magnification you'll lose in ability to focus correctly with too dark image in viewfinder.
also most teleconverters tend to downgrade image quality

[djronbxs]

so barlow lense would be a better choice ?