I have owned a D3100 for 3 years now but over the last year I have spent a lot of time getting to know everything about the camera. There is one thing I just don't quite get. I normally use a speed light for flash photography but occasionally I don't have it with me and I am forced to use the on-camera flash. I rarely shoot on auto anymore. I mostly use the semi-automatic or manual mode. The problem I am having is getting the built in flash to fire. For example, this morning I was taking some practice shots to mess with them with Adobe Lightroom to improve my post-processing skills. I was in Aperture mode, using an f8 setting with the flash up and ready to fire (ISO 400). When I take the shot, I just get a long shutter speed with no flash. In fact I rarely can get the flash to fire when I use the manual mode or semi-automatic modes (aperture, shutter priority) but sometimes it does. I have tried using matrix metering instead of spot and still get the same result. If I put my speedlight on, it will always fire in those modes (probably because it is TTL). Why is this and how can I force my built in flash to fire if I want it??
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