Noise spots on long exposures
Long time reader, first time poster... with a big thanks to the community.
I own a Sony Nex 6 and noticed that long exposures show blemishes that are not visible on short exposures (see picture). I don't know when this started, but it wasn't always the case. Also, I'm quite sure it occurred with several lenses, so the issue seems to be with the camera. I used the built in sensor cleaning function, but to no avail. Any ideas as to the reason and what I could do about it? Going for a short trip to Acadia this Sunday and hoping to have it fixed by then.
Here's an example - you'll see it especially in the sky:
|Thunderheads With Egret by Buzz Lightyear|
|Double Rainbow; Abiquiu, NM, USA. by abiquiuense|
from After the Rain
|White Tern-2289 by vbuhay|
from A Whiter Shade of Pale