I picked up a Sigma 400mm/5.6 yesterday It's the AF variant listed here
Seems to be in good condition so a real bargain at £15

It's considerably lighter than my other AF options in the same focal range, so it might get to come out with me more often.

Yes all are impressive!
For me 4 & 5 beat 7, but 10 must be the winner are those planes or shooting stars?
They all seem to be coming from a fixed point and there's not the clear pulsing often seen with aircraft lights, but the intensities look fairly even.

I'm sad to say they all put my shots of Cornwall over the summer to shame.

They do need to be taken with more than a pinch of salt.
If contemplating a new lens for IR they may have some benefit, but I've never bothered with them. I've got quite enough lenses in all reality!

I've not noticed any effect from the filter used, but there are certainly a huge number of variables that affect hotspots:
I've had a lens cause them every time with one body, yet never at all with another.
Another lens only seems to give hotspots when focused close
Then we have aperture setting, Direction of lighting...

I wouldn't consider it surprising for a 850nm to be worse than a 720nm - it is after all working further from the wavelengths the lens is designed for!

I got mine for £10, with 2 other CZJ lenses & a body.
Checking at the time suggested the flektogon alone was worth much more than these values, (~£220 IIRC) but maybe I just spotted the f/2.4
I'd consider both to be excellent deals.

Algi is quite right about PK having a shorter flange distance. However it is still possible to use PK lenses without correcting optics, as long as you don't want to focus on more distant subjects. How far away you can focus is a function of the lenses focal length, with wide angle lens it will almost certainly be just macro distances - many long telephotos (which often have focusing rings the turn beyond the infinity mark & are less effected by extension) may still be fairly usable.
If you have to use a Nikon body the Z series can be adapted to quality glass without any issues - I think it's even possible to get a degree of auto focus! (Techart do a nikon Z to Sony E AF adapter & their Techart pro will focus/focus tune any lens that can be adapted to Leica M...) The techart pro moves the entire lens up to 4mm to focus fairly effective on lenses under 50mm, longer lenses can need to be partially focused first in the same way as with the Pentax 1.7 autofocusing teleconverter...

I'd prefer it with a little less cloud (2/3 to 3/4 cloud cover) - but that's the case for so many of my shots too, we have to live with what nature gives us weather-wise.
To some extent I agree with Phillip about the LHS, but the dark band of conifers (?) are currently on the third and that would be lost with cropping, weakening the left so I'm not totally convinced.

How old was the EVF you tried? The early ones were certainly dire
The ones with my 5 year old mirrorless models are pretty good, except perhaps for action shots. I gather they've improved a lot since then.
Having magnified view & focus peaking available in the viewfinder works really well for manual focusing. I've not bothered getting native lenses for one of my mirrorless systems, and I really like the results I get from those tiny Pentax 110 lenses (even though the 18mm doesn't fully cover APSC).

One of my MFT bodies has a touch screen focus - I've hardly ever used it, AF works just like a normal camera but it allows the AF point to be moved simply when I have wanted it for closeups it's been a lot less faffing around than using the buttons to select a different focus point. BTW I am very definitely not a 'phone snapper' rarely even having a phone with me (I probably carry a camera 100 times as long as I do a phone in any given year)...

I do prefer my k5ii to my mirrorless options for motorsprts & airshows, but thats at least in part down to having AF at a much longer focal length (750mm EFL vs 400mm EFL).

In poor light - night, macro & especially infra red - the EVF is a huge advantage over an OVF, so as response times & resolution have improved the benefits of a DSLR have diminshed.

I'd love to have a camera with the features of my old mirrorless bodies, a modern EVF & Pentax ergonomics. Sadly the K-01 had none of these!

The exchange rate doesn't vary that much - if you assume 1:1 and it still seems reasonable, the inevitable reduction from the true exchange rate is only a bonus. Via pay-pal IIRC you'll actually see the rate the transaction happens at before confirming the payment.

I think most of my zoom lenses are shortest at intermediate focal lengths, usually extending slightly for the shortest FL & more for the longest setting. This is certainly the case for at least half a dozen around the 'normal' focal length.

I'm sure it's a consideration that comes quite a long way down the list of priorities in lens design, in fact probably so far down it's not even on the page.