I don't know, i'm sorry, cause i don't have a canon.
If your camera have a shutter position marked "B" or "OPEN" (probably are available in the "manual" mode only), then you probably can do it (need to check on your user manual) ..... and about the diaphragm, it's dependingg from your objective ..... it's the "f" value, (or "stop" value, in some countries) ..... more the value is low (2, 3.5, 5.6 .....), more the diaphragm is opened, more the value is high (16, 22, 32), more it's closed.
You probably need to made some experiments, before to find good values, but, if your machine have a manual mode "B" position for keep the shutter opened, you can try start experimenting with diaphragm on f22 or f32.
Anyway, remember that, for these experiments, you need a stand (tripod), very stable, and preferably a remote control (wired or wireless don't care), for the shoot button, cause any movement or vibration of the camera will ruin your image.
EDIT: sorry, i just found some technical specification for the A95 camera, and no, it's not a type of camera that you can use for this type of images, sorry ..... you need a semi-professional camera, at least, "reflex-type" model and with "manual" modality, and the A95 one don't have it ..... sorry for have to say that .....