I just got a Canon 70D off eBay and have been taking night pictures and things were ok. Then, without warning, the lights in my pictures got blurry and hazy, maybe overblown. It's happened with both my lenses. 50mm and 28-135mm. We don't have a good camera store nearby. I have no idea where to start. Please help?
It might have been slight condensation on the lens if it was perfectly fine and then "without warning" things got hazy. I don't know what the temperature /humidity was like but on clear nights things exposed to the night sky can cool by radiating their heat to said sky. If the temperature falls below the dew point condensation will form. This is a known phenomena for astrophotographers and astronomers. Try it again on a clear night that's relatively warm and dry (or an overcast night) and see if it repeats.
This has to do with your aperture. If you close down your lens to a narrow aperture you will get a sharper crisper edges to the lights and even a star like effect. If you widen your aperture you will get a soft glow like in your picture. Take the same picture at f/16 or f/22 and the softness will go, take it at f/2.8 and your haziness will return.