Yes, cleaning sensors can be very disconcerting.
The A77 and other A mount cameras have an anti-aliasing filter in front of the sensor, so you are actually cleaning that, not the sensor. However damaging the filter is as bad as damaging the sensor. All the A mount cameras have a mirror in front that can gather dust that would otherwise go onto the sensor and cleaning that can often solve the problem. Proper cleaning will usually require that you clean both. Note that the A77 has a removable translucent mirror that is very fragile and does not flip up out of the light path like DSLR mirrors, thereby providing a small amount of additional protection to the sensor. In the event that you damage the translucent mirror, it is much cheaper and easier to replace than the DSLR mirror. Most A mount cameras have a setting that vibrates the sensor to automatically remove dust. In my experience it does not work unless it is just dust bunnies. Other dust, like pollen, can bake onto the sensor and require more force to remove, not easy!
Imagine the chance of getting dust on the A7 series cameras which have no mirror at all. In addition, the A7R and A7RII do not even have the anti-aliasing filter.
« Last Edit: October 01, 2016, 02:29:58 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.