Why this difference? 5d Vs 400d

[DSLR400D]

Hi Guys,

I have started to play with my brand new canon 5d and there are few things (in fact lots of things) that i dont quit understand. For example i took a shot in my house without a tripod this morning. As it is a cloudy day there is not much sunlight, however, its not too dark as well. But i see that there is significant difference in the two snaps, one taken by my 400D and the other by 400D and i just do not understand why is this the case?

Here is my setup:

Set up 1:
Camera: 400D
Mode: Aperture priority (Av)
Av Value: f 2.8
Tripod used: No
Lens used: CANON 100mm f/2.8 Macro USM Lens
Flash used: No

Set up 2:
Camera: 5D
Mode: Aperture priority (Av)
Av Value: f 2.8
Tripod used: No
Lens used: CANON 100mm f/2.8 Macro USM Lens
Flash used: No

I am posting the results below: The first image (IMG_2715.CR2) is from 400D and the second image (IMG_0106.CR2) is from 5D. Can someone please explain why is the snaps taken from 5d much darker as opposed to 400d? even after having the same setup. Please note the distance at which i took the snap is exactly the same may be 2 to 5 cm + or -


Thanks for your comments.

Regards,
D