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 400D and Leica V-Lux 3 side-by-side from the front, back and top in their relative dimensions. Canon 400D has external dimensions of 127 x 94 x 65 mm (5 x 3.7 x 2.56″) and weighs 556 g (1.23 lb / 19.61 oz) (including batteries). Leica V-Lux 3 has external dimensions of 124 x 81 x 95 mm (4.88 x 3.19 x 3.74″) and weighs 540 g (1.19 lb / 19.05 oz) (including batteries).
Below you can see the front-view size comparison of the Canon 400D and the Leica V-Lux 3. Leica V-Lux 3 is 3mm narrower and 13mm shorter than Canon 400D but it is also 30mm thicker. As you can tell, actually this is not a fair size comparison since Leica V-Lux 3 has a built-in lens but Canon 400D doesn't. Once you put a lens on 400D, its thickness will increase significantly.
Now lets look at the top view comparison of Canon 400D and Leica V-Lux 3.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Leica V-Lux 3 is 16g lighter than the Canon 400D but we don't think this will make a significant difference.
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 400D, the total kit will weigh much higher.
Unfortunately neither the Canon EOS 400D (EOS Digital Rebel XTi / EOS Kiss Digital X) nor Leica V-Lux 3 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 DSLR Cameras with Weather Sealing Top Bridge Cameras with Weather Sealing
LCD Screen Size and Features
Leica V-Lux 3's 3.00" LCD screen is slightly larger than Canon 400D's 2.5" screen.
Moreover, Leica V-Lux 3 sports a Fully Articulated screen
which you can change the angle and position of the screen almost freely, making it possible to shoot from waist or over-the-head levels, and especially very useful for shooting selfies and video. On the other hand, Canon 400D has a fixed type screen which provides almost no flexibility in shooting positions compared to V-Lux 3.