At the 600mm range a scope is far more “profitable” than a lens, no doubt. But even at 400mm I think a scope is very worth it.
I started using scopes with a 400mm F/5 scope I had, and it had more resolution than any lens I ever had. Even my fine Nikkor 300mm F/4 ED IF isn’t as good, and I had a few other teles in that range, pretty much everything I could mount on my Nikon bodies. Of course that scope was quite bad in CA, but it was an achro, with todays prices on shorter APOs, EDs , etc, you can find better than a lens for a much cheaper price.
Like Mark said the Equinox 66 (400mm F/6) or other clones, that cost less 280€ are quite good, and I’m betting capable of better results than any tele bellow 800€ or more, if you’re willing to cope with the manual focus. Also considering it’s a scope, it’s light transmission it’s a bit higher than a lens at the same aperture, so we’re looking at least for a 400mm F/5.6 or faster.
The “problem” with these scopes may be the focuser, at 1.25” it’s doubtful that it would fully illuminate an APS-C sensor…I don’t know this for sure, but I’m almost sure it wont.
Also, if one is willing to buy used, several good MF lenses can be found for more or less the same price, for example a Nikkor 300mm F/4.5 AIS ED (300€), or a 400mm F/5.6 AIS (500€)...or my 300mm F/4 AF witch I'm selling for 500€ |
| ...also they’re smaller, have aperture control and focus much closer. A 300mm F/4.5 is perfect for dragons and butterflies.
JMHO on the matter, don’t want to argue with anyone