Last night I decided to exercise my Canon EF-S 18~55mm kit lens with using the onboard flash. Everything came out underexposed. I had the camera set to 1/10s, F5.6 fastest setting and pushed ISO to max., @6400. I could not get any photos properly exposed. I then inserted the Canon EF-S 55~250mm lens and no problem getting very good exposures.
I should have mentioned earlier that with the kit lens, I noticed through the viewfinder that the onboard flash generated a very weak beam. I just now went ahead and cleaned the contacts on the bottom of the kit lens. With the shutter at 1/60s, F/5.6 and ISO @ 200, I took two shots and they both turned out very good. The only difference is that it is currently 1:49 in the afternoon with plenty of sunshine coming through the same room. Just to make certain, I will wait until this evening and try it again in low light conditions. If anyone has had similar experiences, I would like very much to hear about them. Thanks,
I also failed to mention that I am using a Canon EOS Rebel t5.