A77 and dust in sensor

Looking at the pigeon picture and my own A77 photos the size of the spots seems to be typical for small point-like dust particles. (The size of the spots/shadows is related to the thickness of the sensor stack, including the AA filter "cover glass", but probably also to lens telecentricity.)

I usually has less than 5 such spots several months after a cleaning.

Some dust particles may come from the camera itself, especially the focal plane shutter. No matter how excellent they are made, metal parts are moving at high speed and cause slight grinding and dust. (If you think this sounds unlikely, take a close look at some door hinges in your home. Focal plane shutters are made of hinged metal blades.)

The bayonet mount and aperture mechanism also produce some dust.

All DSLR style cameras (including SLTs) needs sensor cleaning from time to time. A blower (rocket blower or rubber bulb syringe) is a first measure. But often there are some stubborn dust particles that won't go away, so you need to add a few tools. This is a very low cost alternative:
- Glasses, about +3 stronger than your normal. (Glasses may be easier to use than a magnifying glass/loupe.)
- A small pointed paintbrush.
- Lens cleaning tissue (very cheep on ebay).
- Some drops of clear alcohol (disinfection type mixture of about 70% with just ethanol and isopropyl works ok).

Wrap the tissue on the small paint brush and secure it (with tape or a twist tie). Point a spot lamp on the sensor. Wearing magnifying glasses you should now clearly see any major dust. Remember the image is projected upside down on the sensor. Dust spots near the top of a picture will come from dust near the bottom of the sensor. To make the dust stick to the cleaning tissue you can carefully breathe to let water condense on the sensor or moisture the tissue tip with a drop of alcohol. Change the tissue often (don't put dust back on the sensor).

Edited by amrep - 21 October 2018 at 12:56

Γεια σου! If a blower won't do the job, I would recommend a good cleaning kit. It's scary, but following closely the instructions will do the job fine. And the more you do it, the better you will get at it. The cleaning kit should come with distilled water and sealed (one use) fiber-less brushes.

When I accidentally spat into my a77 sensor (eh, don't ask...), I used this kit successfully.

One thing to note for a77 (and other SLT cameras) is that the dust can also accumulate on the translucent mirror, so it may need cleaning too (both sides...). Just be very, very, very careful (as careful as you are with the sensor) because the mirror is actually a very thin and stretched membrane: it's very easy to warp or tear it! So apply as little pressure on the mirror as possible.

Good luck and all the best.

Here's a whole article on sensor cleaning from a few years ago

Still a very useful resource