Best (cheapest?) way to get beyond 200mm?

Kovno wrote:

Thanks for the replies. I hope it doesn't seem to ungrateful to say these weren't really the answers I wanted! It's pretty easy to find a 70-300mm from Tamron or Sigma for £100. Surely they are better options?

I definitely don't want to buy a separate body.

Any other suggestions?

The lenses you mention may be "better" options if you only want to extend to 300mm.

My Tamron 90-300mm f/4.5-5.6 weighs 516gm, my Pentax 100-300mm weighs 613gm, but only the Pentax has an aperture ring. Both of these lenses cost me less than £10

Very many modern lenses don't have aperture rings, so can only be used "wide open" when on an adaptor, which may be artistically or photographically limiting under some circumstances. Especially when using long telephoto lenses with manual focus, I find the "insurance" of being able to "close down" one or two stops can help ensure a sharp image.

Afterthought :

Depending on the nature of the photography you are interested in, it may be worthwhile considering lenses with a built-in tripod mount. Trying to use an extensively front-heavy camera/lens combination with only a tripod screw in the camera can be frustrating, as I discovered once I'd purchased a Samyang 800mm f/8 mirror. The desire for the combination to "nose-dive" if I've failed to lock up the pan head very firmly is extremely annoying There is also the excessive strain on the camera body lens mount to consider.