Hi i m new at photography. I have just bought a Nikon d80 + nikkor 18-135 1:3.5-5.6 lens. I m trying to learn my camera by taking photos. But my problem is; i set everything to manual mode lens : M ( not A) camera : M ( not AF ) setting : M ( manual / not auto ) but unfortunately i can't take photos when the aperture is 3.5. Sometimes when there is enough light it allows me to change it to 3.5 and i can take photos but when the light is not enough after that, it AUTOMATICALLY changes it to 5.6 which i dont want. I asked my friend who is using SLR and he said "it's nonsense, in manual mode you can control everything". So my question is, is there anything i m missing ? Why it does not let me to use 3.5 whenever i want ? is there any setting to turn it off for camera not to change it automatically ? Thank you in advance for your help.