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 Canon ELPH 150 IS and Pentax K-500 side-by-side from the front, back and top in their relative dimensions. Canon ELPH 150 IS has external dimensions of 95 x 57 x 24 mm (3.74 x 2.24 x 0.94″) and weighs 142 g (0.31 lb / 5.01 oz) (including batteries). Pentax K-500 has external dimensions of 130 x 97 x 71 mm (5.12 x 3.82 x 2.8″) and weighs 646 g (1.42 lb / 22.79 oz) (including batteries).
Below you can see the front-view size comparison of the Canon ELPH 150 IS and the Pentax K-500. Canon ELPH 150 IS is clearly the smaller of the two cameras. Its body is 35mm narrower, 40mm shorter and 47mm thinner than Pentax K-500. As you can tell, actually this is not a fair size comparison since Canon ELPH 150 IS has a built-in lens but Pentax K-500 doesn't. Once you put a lens on K-500, its thickness will increase significantly.
Now lets look at the top view comparison of Canon ELPH 150 IS and Pentax K-500.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Canon ELPH 150 IS is significantly lighter (504g ) than the Pentax K-500 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 K-500, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Canon PowerShot ELPH 150 IS (IXUS 155) nor Pentax K-500 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 DSLR Cameras with Weather Sealing
LCD Screen Size and Features
Pentax K-500's 3.00" LCD screen is slightly larger than Canon ELPH 150 IS's 2.7 screen.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.