Using a brush often will not get rid of all the dust. If you have pollen or anything that was damp when it got on to your sensor it will need to be remove using a Sensor Clear type cleaner. The a77 is not prone to dust on the sensor due to the mirror never moving out of the light path. It can happen, but usually it gets caught by the mirror.
It may be dust in your lenses, although that is even rarer than above.
« Last Edit: July 31, 2014, 04:21:48 AM by AScot »
Sony A7, A850, A77, A700 || Sony>> 70-300G, 28-75 f2.8 SAM, 16-80CZ, 50 f1.4, FE 28-70 OSS, FE 24-70CZ f4 OSS, LA-EA4 || Minolta>> 300 f4 G HS, 200 f2.8 G HS, 100 f2.8 (D) Macro, 50 f1.7, 28 f2.8, 28-135 f4-4.5, 70-210 f4, 500 f8 Reflex, TC x 1.4 HS, TC x 2 HS. || Sigma 21-35 f3.5-4.2. || Tamron SP 24-135.