Originally posted by jocko_nc
Man, I'm all confused now. Just as well I did not jump on anything too early.
Maybe I should get a nice 300 M 1:4 and a teleconverter? That design will have a large objective lens and let in lots of light for the teleconverter. That way I have a 300 and I have a 500-600. The price will be a bit rough, but it seems there is no free lunch in this league. Is that as handy as a zoom? I don't know. It sucks that the typical 300 M or 300 A does not have a tripod collar.
Otherwise I want a older zoom; long barrel design, multicoated, and with a tripod collar. Thanks for the recommendations, I'm out a lookin'. Not very much available.
I do have a Tele-Takumar in 300. It came without the collar (oops) and is my only M42 lens. I'm not sure why I bought it or what to do with it. I don't think it is any part of the answer. I'm not so sure about adapters.
You could use the old Takumar with an M42 adapter. But you'll lose auto-aperture and would have to close the aperture manually for shooting. But the camera would operate in Av-mode or with M. As Lowell wrote, you could make your own tripod collar for the A 300 - but it is not really necessary. You will be very surprised, when you get that lens, because it is so tiny (I was...) and doesn't necessarily need a collar.
As Lowell's and John's (palmor) experience with the Sigma 70-200/2.8 + 2x Apo tc are so good, I wouldn't hesitate to try this combination. Even if a fixed focal length lens offers a slight advantage in image quality, the advantages of a zoom lens (and with AF) may be more important. It depends on your style of photography and your expectations towards the working speed.
I would not recommend to go for one og these really older zooms 100-500mm and the like. The image quality is mediocre at best. And they combine mostly all the things you woudln't like on fixed focal length lenses and zoom lenses otherwise considered (expect for the tripod collar): they are slow with respect to the aperture and slow to work with, they are very heavy and tend to break in at the longer end, which is the most useful. Also these old lenses may or may not have enough resolution to work with current and future 10-14 MP sensors.
Ben