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 Pentax RZ10 and Olympus E-P1 side-by-side from the front, back and top in their relative dimensions. Pentax RZ10 has external dimensions of 97 x 61 x 33 mm (3.82 x 2.4 x 1.3″) and weighs 178 g (0.39 lb / 6.28 oz) (including batteries). Olympus E-P1 has external dimensions of 121 x 70 x 36 mm (4.76 x 2.76 x 1.42″) and weighs 355 g (0.78 lb / 12.52 oz) (including batteries).
Below you can see the front-view size comparison of the Pentax RZ10 and the Olympus E-P1. Pentax RZ10 is clearly the smaller of the two cameras. Its body is 24mm narrower, 9mm shorter and 3mm thinner than Olympus E-P1. As you can tell, actually this is not a fair size comparison since Pentax RZ10 has a built-in lens but Olympus E-P1 doesn't. Once you put a lens on E-P1, its thickness will increase significantly.
Here is the back view size comparison of the Pentax RZ10 and Olympus E-P1.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Pentax RZ10 is significantly lighter (177g ) than the Olympus E-P1 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-P1, the total kit will weigh much higher.
Weather Sealing
With its weather-sealed body, we believe that the RZ10 has a big advantage over the E-P1 which doesn't provide any kind of environmental sealing.
LCD Screen Size and Features
Olympus E-P1's 3.00" LCD screen is slightly larger than Pentax RZ10's 2.7" screen.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.