Hi, that's really quite under exposed, not always a bad thing but a camera should produce a reasonably accurate representation of the subject is photographs and that isn't. Put another way if your computer screen or printer gave a darker version of everything you would find a way to fix it.

If it’s any help I had two perfect examples shot with Nikon D200s over the weekend so with attention to every variable it is possible. A catch light on the card will throw the results out so make sure it’s not reflecting a brighter light than the whole and is evenly lit.

Secondly you might get better results with more settled artificial light indoors - light can vary quite a bit for instance with changes in cloud density between shots. This is a precise, almost scientific, test so you do need to remove all variables and a cloud going across the sun or twenty seconds passing between your initial reading and the last of your shots can make the whole process meaningless.

If you are going to use a low energy bulb for instance I would turn it on about half an hour before I took the pictures as these get progressively lighter after a short period of use.

If you do in the end discover that your camera is under exposing by a half stop or so then you can apply exposure compensation in future – that’s what we’ve been doing with film for years – pro films even come with the ‘real’ ISO printed on the batch and a good photographer would never simply trust the manufacturer’s figures.