Have to say that unless there's a fault, it looks worse than the vignetting with my ancient FA PZ 28-105/4-5.6 @ 28mm and f/4 on my K-1. It's probably worse than my FA PZ 28-80/3.7-4.5 but I don't have that to hand. It may be easy to correct in post but I'd rather not have to.

Pentax need to get the bread and butter stuff covered first, this 70-210 is one if the more useful new lenses (not huge & heavy and reasonably priced). I'd expect you'd also need a wider option for weddings, putting this 70-210 on your spare body gives you good twin lens options.

My current goto lens in this range is the M80-200/4.5, this might replace it on the K-1 (my film cameras still need aperture rings).

Presumably you're using it on a body that supports SDM? Some of the early ones didn't or needed firmware updates.

Presumably you've tried cleaning the contacts...

Edit: Have you tried this: https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/300459-found-c...

IIRC there used to be a strap contraption that attached to the top of a monopod and reached the floor. The idea bring you stood in the strap and braced the monopod with it. I have no idea how well it worked.

Edit: Is this the shoulder brace (looks like goes on the monopod);
https://www.wexphotovideo.com/manfrotto-361-shoulder-brace-mn361-11046/

There are various foot attachments available too.

Back to the original subject, a quick check of SRSs used stock shows it missing, presumably sold...

If you have an AF lens attached to this converter, does it pass the focal length back to the camera of can you set it manually like a manual focus lens?

Despite these prices, I won't be selling mine.

Edit: Then again, um blimey: link

The f/2.8 limit is likely related to the original SAFOX as present in the SFX & SF7 bodies (which probably had an AF minimum of f/5.6).

Modern DSLRs are likely to have much more sensitive AF (and much faster/powerful screwdrive motors).

Thanks for the comments. Previously. The real benefit of the GR is it's a shirt pocketable camera with a fantastic lens and a large sensor. I might pair it with my MX-1 for tele shots, both of these will easily fit inside the shoulder bag I usually use (which is usually stuffed full of other holiday stuff).

In APS-C I only really have the DA17-70/4 (bought years ago, I might go for something with WR today). It's my 'just-about' lens: just about wide enough, just about long enough, just about fast enough and just about compact enough.

In FF/135 (not forgetting film) I don't have a modern do-it-all zoom, my Tamron AF 24-135 is the closest option but I rarely use it. The FA20-35/4 almost lives on the K-1 with an FA50/1.4 and either M135/3.5 or M80-200/4.5 for tele. After years of using the 20-35, a 28-xx zoom just doesn't cut it (not wide enough).

I still shoot film with mechanical cameras, so any lenses (apart from the DA17-70) need to have aperture rings and I can't justify buying an expensive lens if it doesn't.