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 Olympus 7040 and Olympus E-P3 side-by-side from the front, back and top in their relative dimensions. Olympus 7040 has external dimensions of 95 x 56 x 26 mm (3.74 x 2.2 x 1.02″) and weighs 144 g (0.32 lb / 5.08 oz) (including batteries). Olympus E-P3 has external dimensions of 122 x 69 x 34 mm (4.8 x 2.72 x 1.34″) and weighs 369 g (0.81 lb / 13.02 oz) (including batteries).
Below you can see the front-view size comparison of the Olympus 7040 and the Olympus E-P3. Olympus 7040 is clearly the smaller of the two cameras. Its body is 27mm narrower, 13mm shorter and 8mm thinner than Olympus E-P3. As you can tell, actually this is not a fair size comparison since Olympus 7040 has a built-in lens but Olympus E-P3 doesn't. Once you put a lens on E-P3, its thickness will increase significantly.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Olympus 7040 is significantly lighter (225g ) than the Olympus E-P3 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 E-P3, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Olympus Stylus 7040 (mju 7040) nor Olympus PEN E-P3 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 Compact Cameras with Weather Sealing Top Mirrorless Cameras with Weather Sealing
LCD Screen Size and Features
Olympus 7040 and Olympus E-P3's LCD screens have the same diagonal size of 3.00 inches.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.