But there is a small limitation that you should know and consider before buying:
The bag is quite small.
It is indeed offered specifically for the Nikon D 3100, however, the camera will adjust only "lying on its side" with the "small" 18-55mm lens in the main compartment of the bag.
Will looking at the camera lying down "right", they bulge out of the bag easily (ie camera located on the outer walls with pressure, there is no more free space available), so it is protected only by the cushioning against impact damage.
The entrainment of a larger objective is, if this is to remain mounted on the camera, questionable and the additional entrainment of another lens for Nikon D 3100 (or a comparable SLR) is not possible in this case.
It is also questionable whether the driving of an external flash is also possible, as this would have to be accommodated in the side pockets (which, depending on the size of the flash is difficult or even impossible).
But.. If you only want the camera with a lens mounted on an excursion or similar carry, so this bag is perfect.
It protects the camera against light shocks, dust, moisture and sand, is processed stable and has a shoulder strap that is long enough that larger / stronger people can reassign the pocket in case of emergency "cross". The size of the bag also makes sure that you can carry it comfortably on a trip, etc. with it without the pocket one is constantly in the way.
The side pockets and a small front pocket offer enough space to carry extra memory cards, filters and one (or more) replacement batteries.
When you're ready, every time you pack the camera in your pocket, remove the lens, then should in the main pocket also the body and two lenses can be accommodated (I have not tried yet), but I personally feel that as to laboriously.
I personally use this bag as described above, and should I have to take more material / want, I take a larger bag.
Conclusion: strong buy recommendation, but considering the size of the bag.
Addendum:
I gave it a try and unfortunately have to tell that this bag is definitely too small for the entrainment of another objective. Even if you want to wrap up both lenses from body separated, fits all not in this bag.
The Nikon 3100 also does not fit with the "big" "Nikon AF-S DX Nikkor 55-300 mm - lens" in this case mounted on the camera regardless of whether or separated.
Accordingly, I do not believe that the Nikon 3100, together with the little (but not much) smaller "Nikon AF-S DX Nikkor 55-200mm - Lens" fits into this bag.
Camera + Nikon AF-S DX Nikkor 18-105mm - Lens I have not (yet) tried.
So, as I said, a great little pocket, but considering the purchase size.
