random night scenes

[Elysian]

Still, one single question remain; how to get rid of the perspective effect to get the wall (or any other architecture shots for that matter) straight?

Important to know is that the perspective doesn't change which ever lens you use, only the magnification. That is, if you remain at the same shooting distance with both lenses.

The perspective like in your image is created if the angle (A) between the camera and the building is larger or smaller than 90 degrees. What happens if we respect that angle? Then we might not be able to include some of the higher parts of the building. The only way to keep that angle intact is by using a wide angle lens (don't go too low or you'll get barrel distortion) or by finding a higher postion from which you take the shot (holding camera higher, climbing/walking to a higher position, shooting from inside another building, etc)..
Using a wider lens helps you to include the higher part of the building, but it automatically adds lower parts that you probably don't want in your image. Tough one eh? Then it's either cropping the image or considering to move to a higher postion.

All what I said also applies if your intention is to include more of the botom of the building without the perspective. In that case you position your camera lower or you start using a wider lens with of course all risks of including too much at the top of your shot.
Another approach is to take the shot with the 90 degrees angle in mind and to crop both top and bottom the way you prefer it. I know, it isn't always the best solution, but I thought it was still worth mentioning, especially with the increasing image resolutions we've seen over the last few months.
I do hope that you understand what I meant, it's not all that easy to explain in just a few words.

Let's take your image as an example. Your intention was probably to avoid to include too much of the road, so you tilted the camera slightly upwards which introduced the perspective In this particular example you had two choices when you want to keep that 90 degrees angle intact:

a) Find a higher location to shoot from or hold the camera higher. You might even want to try the "lucky" shot approach by stretching your arms and shooting without being able to have a look through your view finder or to have a descent look at your lcd screen.
b) taking the shot with the highest resolution possible and cropping the bottom part.

Let's make it clear though that perspective isn't always a bad thing, it all has to do what you want to express and sometimes you're so restricted at the location where you stand, that you can't avoid perspective.

Let's say that you find some kind of distortion in your image and you want to get rid of it. There are special tools that can correct this. In my attachment you'll see what kind of options you have available in programs/plugins like that. There are also programs that use markers to correct an image, I expect that they can be easier to use, especially when you have more than one distortion in one image that you want to correct.