Here are a few notes on sensor cleaning. This is something I hate to do but is necessary from time to time. There are many tutorials on the web to guide you but I have had some success with this method.
1. To view sensor dust, take a picture of a neutral surface (blue sky) at a small aperture (f/18-f/22). Use Jpeg. Import to Photoshop and adjust the levels until you get an exaggerated image of the dust. If there are only a few spots, leave well alone unless they are easily viewable on a standard exposed image.
2. If there is visible dust on the sensor, start by opening the mirror on the camera and use a Giotto blower (not the Visible Dust blower which is useless). I have a Visible Dust illuminated Loupe which is handy for inspecting the sensor for dust, although it doesn’t show the really small stuff). If this eliminates the dust, count yourself lucky and finish up. If not, go to step 3.
3. Now is the time for wet cleaning. This should be thought of as a last resort. There are multiple choices (Sensor Swabs, Copper Hill Images, Visible Dust). My preference is to use Sensor Swabs with Eclipse Cleaning Fluid (www.photosol.com). The instruction video on their web site recommends a two-pass approach - one swipe across, then swipe back. I found that a single swipe worked better.
Do this: Put three drops of fluid on a sensor swab. Place the swab on the sensor and press down gently until the stem bends slightly. Slowly, & smoothly, move the swab across the sensor until it reaches the othe side. Keep pressure on the swab. Lift the swab carefully and you should be done. Check the image for dust and repeat if necessary. I have noticed that the swab does not completely cover the height of the sensor and some dust can remain at the edges. If this is a problem, Visible dust has Edge Swabs which, with one drop of fluid, can be run around the edges of the sensor before doing the main cleaning. Be careful not to use too much fluid since this can cause streaking.
4. It’s a frustrating process since you can rarely fix things with one cleaning. The first one usually (for me) makes things worse. Then I panic. It’s not unusual to take two or three tries to get the sensor clean. Even then you can never get rid of everything, including some streaking. Just live with it. If it gets too bad and you are not having success, find somewhere that can do it for you, professionally.
5. I also got quite good results (on the Nikon Z7 which is very prone to dust on the sensor) using Visible Dust (green Ultra MXD-100) with VDust Plus liquid. I took one swipe across, turned the swab over and took another swipe, in the same direction. If the results are similar I prefer the SensorSwabs since there are fewer, less confusing options.
Tom Hogan:
https://dslrbodies.com/cameras/camera-articles/image-sensors/cleaning-your-sensor.html
NOTE TO SONY A7II, A7RII, A7SII USERS:
When cleaning cameras with IBIS using a Gel Stick or Sensor Swab, I suggest locking your sensor in place. To do this, simply run a cleaning cycle on your camera:
Menu > Setup > Cleaning Mode > Enter
The Sony a7 Mark II image sensor will shake for about a second. Once it’s done you’ll see this message on the LCD: “Auto cleaning is finished. Turn the power off. You can also clean the image sensor manually if necessary.”
While this message is displayed the sensor is locked in place. This allows you to use a Sensor Gel Stick or Sensor Swab without moving the sensor. Once you’re finished, turn the camera off.