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 E-PM1 and Nikon P510 side-by-side from the front, back and top in their relative dimensions. Olympus E-PM1 has external dimensions of 110 x 64 x 34 mm (4.33 x 2.52 x 1.34″) and weighs 265 g (0.58 lb / 9.35 oz) (including batteries). Nikon P510 has external dimensions of 120 x 83 x 102 mm (4.72 x 3.27 x 4.02″) and weighs 555 g (1.22 lb / 19.58 oz) (including batteries).
Below you can see the front-view size comparison of the Olympus E-PM1 and the Nikon P510. Olympus E-PM1 is clearly the smaller of the two cameras. Its body is 10mm narrower, 19mm shorter and 68mm thinner than Nikon P510. As you can tell, actually this is not a fair size comparison since Nikon P510 has a built-in lens but Olympus E-PM1 doesn't. Once you put a lens on E-PM1, its thickness will increase significantly.
Here is the back view size comparison of the Olympus E-PM1 and Nikon P510.
Now lets look at the top view comparison of Olympus E-PM1 and Nikon P510.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Olympus E-PM1 is significantly lighter (290g ) than the Nikon P510 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-PM1, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Olympus PEN E-PM1 nor Nikon Coolpix P510 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 Mirrorless Cameras with Weather Sealing Top Bridge Cameras with Weather Sealing
LCD Screen Size and Features
Olympus E-PM1 and Nikon P510's LCD screens have the same diagonal size of 3.00 inches.
On the other hand, Nikon P510 features a
Tilting screen where you can change the angle of the screen to make it easier to shoot from waist or over-the-head levels whereas the Olympus E-PM1 has a fixed type screen which provides less flexibility in shooting positions compared to P510.