I saw some remarks about an F 2.8 lens not being a good combination with an APS-C camera because it is big size. Of course I could go for a F 4.0 or F 5.6 lens ... but what would that do to image quality? I am not a pro, but I was under the assumption that a F 2.8 lens catches more light in darker situations and that it produces a nicer (blurred) background than a F 4.0 lens. Is this true? Because that is my main reason to look for a F 2.8 lens.
In your original post you wrote:
I want to buy a new camera to expand my hobby. I would like to go to cities and take pictures of buildings and street life. And also I would like to photograph nature, like landscapes, trees and lakes.
Faster lenses gather more light, allowing you to shoot at faster shutter speeds. This is mainly useful when shooting people, sports or any action where you want to reduce subject motion blur. It used to also be important for avoiding camera shake (when shooting handheld) but this is less an issue with image stabilization.
Faster lenses allow you to shoot with less depth of field. Good when you want blurred backgrounds.
But your described uses don't really scream "shallow depth of field" and you might end up going from one extreme (HX99) to another (big camera with multiple big lenses) in pursuit of something you don't need and end up with a camera you hate to carry and use. (I'm not predicting this - just suggesting things to watch out for). That Fujifilm X-S1 shot you linked in your OP was shot at f/5.6 on a 2/3" sensor (though at a long focal length).
I use a Nikon Z5 with multiple lenses, but one consideration in choosing my current kit is that I like to go out with one - or at most two - lenses most of the time. My every day lens is the 24-200 which covers a lot of ground (and can get blurred backgrounds in some situations, but otherwise, that's its weakness). I plan on picking up the little 40/2 to carry with that when I travel - small, fast, handy for low light (indoors, etc). I have the 50/1.8 which I use around the house. The 105 for macro or portraits. And I'll end up with a long tele for backyard wildlife (currently using an older camera for that).
That's one approach. I have the RX10 III and it's an extremely capable camera. Image quality is very good, but I just find something slightly lacking compared to the APS-C photos I've been shooting for almost 20 years now. That said, it's good enough that if it were a more enjoyable camera to shoot, I'd be sorely tempted to just throw in the towel and use it for most everything (maybe with a small camera & fast normal prime for low light). I found it handy when I used it for travel, but too frustrating to use it instead of the cameras I've been using for years.
The RX100 series is excellent as well. The newest models with long zooms are supposed to be excellent. I have the 'I' (with 28-100 equivalent) and always liked it. The 24-70 equivalent lens on some of the models is supposedly excellent, but you probably won't want to be restricted to that range.
I looked at m43 as a compact alternative to Z, but the 12-100/4 is as big as (and more expensive than) the 24-200 I bought. There are other lenses that are smaller, but equivalence means you're giving up something (range and/or speed) so it's a good system if compactness is your goal, but if you're trying to balance compactness with lens speed, then most options are going to be roughly similar in size.
There are no easy answers - good luck with your decision!
