Pentax have always maintained that they will not produce a full frame DSLR, so where is the surprise, and which lenses do you perceive as being wasted?

Watch the auction sites for a Vivitar 283. They generally go for a similar amount to your budget.

My local retailer has 28 of these in stock . . . nothing else . . . just 28 of these.

If it's being modelled by the installer, I'll have gazillions . . .

Let's not forget the 1.5x crop factor. The DA* 300mm lens has a film equivalent FOV to a 450mm lens (close enough to 500mm for me).

Add to that a 1.7x T/C and you have a 765mm equivalent lens.

There was a super-telephoto lens planned, it used to be on the roadmap. I haven't looked lately.

I was referring to the bird's wing from it's own perspective. It's on the bird's left side, therefore it's the bird's left wing, or the right as we see it in the image.

But then . . . you knew that

When buying new lenses, you gets what you pays for.

If it's new, and cheap, it's cheap for a reason. Do you really think that if a lens produced first rate, top notch, world beating images at 500+ mm with a decent wide aperture, that it would sell for peanuts?. . . No? Neither do I.

Oh, and 3000 satisfied customers CAN be wrong.

My own criteria is:-

Sturdy enough to hold my K20D + grip + SMCP 500mm lens.
Light enough to make me decide to take it with me, rather than leave it behind.
Must have the ability to spread the legs flat and have removable centre column to hold the camera at (or very near) to ground level.
Must have a facility (hook) to add weight for stability.
Must have the option of metal spiked or rubber feet.
Must have a ball-head with independent horizontal and vertical controls.

My choice:-

Manfrotto 055PROB and 488RC2 head.

Don't worry about the hot pixel George. It's actually a navigation beacon, you just happened to catch it when it was on.

PS: It's on the underside of the bird's left wing.

There's one here at https://www.pentaxuser.com/forum/topic/sigma-50-500mm-for-sale-14905

It's probably what you'll end up buying as it seems to be the best of the bunch. Not a lot of use in low light though, apparently.