Size and weight are big decision factors when you are trying to find the ideal camera for your needs.
In this section, we are going to illustrate the Sony A57 and Nikon S5100 side-by-side from the front, back and top in their relative dimensions. Sony A57 has external dimensions of 132 x 98 x 81 mm (5.2 x 3.86 x 3.19″) and weighs 618 g (1.36 lb / 21.80 oz) (including batteries). Nikon S5100 has external dimensions of 97 x 57 x 22 mm (3.82 x 2.24 x 0.87″) and weighs 132 g (0.29 lb / 4.66 oz) (including batteries).
Below you can see the front-view size comparison of the Sony A57 and the Nikon S5100. Nikon S5100 is clearly the smaller of the two cameras. Its body is 35mm narrower, 41mm shorter and 59mm thinner than Sony A57. As you can tell, actually this is not a fair size comparison since Nikon S5100 has a built-in lens but Sony A57 doesn't. Once you put a lens on A57, its thickness will increase significantly.
Now lets look at the top view comparison of Sony A57 and Nikon S5100.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Nikon S5100 is significantly lighter (486g ) than the Sony A57 which may become a big advantage especially on long walking trips.
Again, this comparison may not be very useful in real life as we are comparing the weight of a camera with a built-in lens to the body-only weight of an interchangeable lens camera. Once you put a lens on A57, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Sony SLT-A57 nor Nikon Coolpix S5100 provides any type of weather sealing in their bodies, so you have to give extra care especially when you are shooting outdoors. If weather sealing is a must-have feature for you, check these sections: Top DSLR Cameras with Weather Sealing Top Compact Cameras with Weather Sealing
LCD Screen Size and Features
Sony A57's 3.00" LCD screen is slightly larger than Nikon S5100's 2.7 screen.
Moreover, Sony A57 sports a
Fully Articulated screen which you can change the angle and position of the screen almost freely, making it possible to shoot from waist or over-the-head levels, and especially very useful for shooting selfies and video. On the other hand, Nikon S5100 has a fixed type screen which provides almost no flexibility in shooting positions compared to A57.