Size and weight is a big decision factor when you are trying to find the ideal camera for your needs.
In this section, We are going to illustrate FujiFilm S2800HD and Sony A390 side-by-side from the front, back and top in their relative dimensions. FujiFilm S2800HD has external dimensions of 110 x 74 x 82 mm (4.33 x 2.91 x 3.23″) and weighs 437 g (0.96 lb / 15.41 oz) (including batteries). Sony A390 has external dimensions of 128 x 97 x 86 mm (5.04 x 3.82 x 3.39″) and weighs 549 g (1.21 lb / 19.37 oz) (including batteries).
Below you can see the front view size comparison of FujiFilm S2800HD and Sony A390. FujiFilm S2800HD is clearly the smaller of the two cameras. Its body is 18mm narrower, 23mm shorter and 4mm thinner than Sony A390. As you can tell, actually this is not a fair size comparison since FujiFilm S2800HD has a built-in lens but Sony A390 doesn't. Once you put a lens on A390, its thickness will increase significantly.
Here is the back view size comparison of FujiFilm S2800HD and Sony A390.
Weight is another important factor especially when deciding on a camera that you want to carry with you all day.
FujiFilm S2800HD is significantly lighter (112g ) than the Sony A390 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 A390, the total kit will weigh much higher.
Unfortunately neither FujiFilm FinePix S2800HD (FinePix S2900HD) nor Sony Alpha DSLR-A390 provides any type of weather sealing in their body, 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 Bridge Cameras with Weather Sealing Top DSLR Cameras with Weather Sealing
LCD Screen Size and Features
FujiFilm S2800HD's 3" LCD screen is slightly larger than Sony A390's 2.7" screen.
On the other hand, Sony A390 LCD screen has a Tilting feature
where you can change the angle of the screen to make it easier to shoot from waist or over the head levels. On the other hand, FujiFilm S2800HD has a fixed type screen which provides less flexibility in shooting positions compared to A390.