Very nice but the slight green tinge in 1 and 4 is a little off-puting for portraits.

If you need the flexibility of a zoom, prefer FF compatibility and don't mind the size & weight then a 70-200mm makes sense. Many people prefer a small prime not just because of the size & weight but also because it allows for a more relaxed subject, which tends to happen when you're not pointing a bazooka lens at them

If you go for a 50-135mm f/2.8, by all reports optically superb, then make sure it comes with a guarantee whether you buy it new or used. SDM failure is a very real problem.

The DA 70mm f/2.4 lens is superb and I believe can cover the FF image circle, plus of the traditional portrait range it's the best compromise (105mm equivalent in FF terms), but that won't be the case on FF. The 77mm f/1.8 would be the safer bet and is designed for a FF image circle, a little faster and maybe with better out-of-focus areas, but you might find it a little short on FF, depending on the circumstances under which you shoot.

I like Flickr a lot - I get a large amount of free storage (I'm currently on 2.4% and have just over 5000 photos there) which can be used to link to external sites such as this forum and there's a decent social side in the groups. I hope none of that changes but until it does I won't worry about it.

The change from KAF3 to KAF4 is the electronically controlled aperture. There's no mechanical lever to stop down the aperture, it's done instead with a motor or solenoid inside the lens, making it functionally equivalent to the more modern mounts like EF, m4/3, Fujifilm X etc

At least in Pentax gear, Spain is usually around 20% more expensive for everything. The price may be higher for Pentax mount due to it being a special run. I agree Sigma would do well to move what little they produce for Pentax over to KA4 mount and that would make things easier for them and maybe we'd see more lenses for Pentax mount.

I posted this over on the US forum but I know there are plenty of wildlife photographers here who may be interested.

I don't really keep up with the super-telephoto news as it's not my thing but I thought this might be of interest to some. Apparently the Sigma 50-500 had been discontinued in the K-mount but according to this page (in Spanish) sent to me by a Spanish Pentax online dealer, a limited run is to be produced soon. The price in Spain is 1379.00€, no idea what it would be elsewhere.

Sigma 50-500mm para Pentax: una oportunidad quizás única

I'm amazed this is still here - I picked up a Sigma 17-50/2.8 (same model as here) last year and have been amazed by how good it is, so much so that it pains me to see this one stay "on the shelf" so long. Here's a link to my album of photos from it, if that helps to tempt any buyers https://www.flickr.com/photos/69424694@N06/albums/72157688496630782

It doesn't have OS, that was removed as unnecessary in the Pentax mount. Saves some weight I suppose.

I have heard that the A is much better than the K and I've seen a lot of great photos with 50/1.2s in the last few years, but then good photographers (or at least those with perseverance) will probably be drawn to such a lens anyway. But then I've seen great stuff with 50/1.7s too...

No-one needs a 1.2 but everybody wants one. I'd love to have one but get the impression that it's a steep learning curve due to the razor thin depth of field at 1.2, but if you don't use it wide open then why are you buying it? No-one needs a 1.2 to stop it down to f/8.

Having said all that, I have four different 50/1.4s and I don't think I ever use them wide open.

In summary - get it and sell it on if you don't get along with it.

Just as well, I was getting tired of resisting.

If the conference is at the conference centre then you could head down to Dalry (past Haymarket taking the left fork heading out of town). It's a little run down but with lots of character (at least to my taste) and some mildly grubby tenement buildings. The New Town (on the north side of Princes St a few blocks down the hill) has nicer buildings but less character while still being a good place to get some interesting shots. On the same side of town you'll also find Stockbridge, a lovely area with interesting shops and buildings and some nice back-streets and quaint alleys to explore. It's one of my favourite parts of town and when I head back these days I'll always look for an AirBnB in that area.

Personally I'd avoid the Royal Mile and Grassmarket but maybe that's because I've been there so many times that I see them as the more touristy/stag do areas and I prefer going off the beaten track.

The museum in Chambers street was done up a few years back and the main entrance hall, which is glass-covered, has the most beautiful light, especially if you're lucky with the weather. It's worth a look even if you're not photographing. It's also free to get in (but feel free to leave a donation).

As already stated though, it's hard to think of any area that you couldn't get good photos of near the centre. If you let us know where you're staying or where the conference is then maybe I can suggest some good areas close by.

Oh - and in case you feel the urge to look for any interesting film gear, check out http://www.cameratiks.co.uk/ at the top of Morningside. They're not the cheapest place and the owner's a little surley but what they have is good and there's plenty of it, and they don't seem to mind people browsing. Half the stuff's in the windows so you can do a lot of browsing (and drooling, ha ha) without even going in.