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I have a Nikon DX (D5100) camera with the two most basic kit lenses: 18-55mm f/3.5-5.6 VR and 55-200mm f/4-5.6 VR. These two lenses cover lots of scenarios, but I'm starting to believe there is more that awaits me. I'm only a hobbyist, so I'm not sure what exactly :). First of all, I don't want to spend a lot of $. So I started checking out the cheap 35mm f/1.8 prime lens. Reviews say that, with the same exposure settings, the image quality of this lens is superior to mine. However, I started doing the math and got confused.
First of all, the advertisement says that VR effectively gives me +3 f-stops. Am I correct in assuming that the +3 f-stop advantage of VR means that eg. a 1/30s exposure will be as stable as one with 1/240s without VR, and it doesn't change anything else? But I guess it has its limits, so I doubt that it can make anything below 1/30s stable.
So let's compare my lens with the prime lens. Let's say that I set my wide zoom lens to 35mm, max aperture is around f/4.5, VR is off, and let's say that this is too slow for me because it's too dark for example. I can turn on VR, I get +3 f-stops. The 35mm prime lens is f/1.8, which is 2.666 f-stops away from f/4.5. It's not that better, or is it?
I know that advertisements can exaggerate, but I trust Nikon that VR is not totally useless at least. So if my math is correct, then the prime lens is not all that better exposure-wise (except for the supposed image quality). What do you think VR actually gives me and what does the bigger aperture prime lens give me?