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 Nikon D3S and Pentax E90 side-by-side from the front, back and top in their relative dimensions. Nikon D3S has external dimensions of 160 x 157 x 88 mm (6.3 x 6.18 x 3.46″) and weighs 1240 g (2.73 lb / 43.74 oz) (including batteries). Pentax E90 has external dimensions of 102 x 59 x 25 mm (4.02 x 2.32 x 0.98″) and weighs 145 g (0.32 lb / 5.11 oz) (including batteries).
Below you can see the front-view size comparison of the Nikon D3S and the Pentax E90. Pentax E90 is clearly the smaller of the two cameras. Its body is 58mm narrower, 98mm shorter and 63mm thinner than Nikon D3S. As you can tell, actually this is not a fair size comparison since Pentax E90 has a built-in lens but Nikon D3S doesn't. Once you put a lens on D3S, its thickness will increase significantly.
Here is the back view size comparison of the Nikon D3S and Pentax E90.
Now lets look at the top view comparison of Nikon D3S and Pentax E90.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Pentax E90 is significantly lighter (1095g ) than the Nikon D3S 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 D3S, the total kit will weigh much higher.
Weather Sealing
With its weather-sealed body, we believe that the D3S has a big advantage over the E90 which doesn't provide any kind of environmental sealing.
LCD Screen Size and Features
Nikon D3S's 3.00" LCD screen is slightly larger than Pentax E90's 2.7" screen.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.