Saturday 10 September 2016

Spots on my photos

Although a few spots on a photo can be fixed by running the image through your favourite photo editing software, the source of the problem should be investigated.

If you use a DSLR, black spots are most likely caused by dirt directly on the surface of the cameras sensor.

I've noticed this problem with photos taken on my Pentax K-30 during the last few months, but only just found the time to take a closer look.

Initially, I absent-mindedly just took the lens off the camera body and cleaned the mirror.

Then I engaged brain, and realised that spots of dirt on the mirror (while annoying) were not going to produce spots on the final image.

Use test images

Its a really good idea to take a few test images before and during the cleaning process. This is the method I use:-
  1. Place a white card in an evenly lit location (I use our conservatory, because it has a translucent roof).
  2. Use a short focal length lens, stopped right down (e.g. f22) in manual mode.
  3. Adjust exposure via ISO and shutter speed settings for a centred light meter indication.
  4. Now open up by 1 stop (either by doubling the ISO setting or halving the shutter speed.
  5. Take a test photo.
You may find it helpful to increase the contrast of the test photo, which I did by opening the image file in Gimp, then selecting Colours > Levels... > Auto

 Either way, it should now be very easy to see any spots of dirt.

Sensor cleaning

First of all you need to gain access to the sensor. My K-30 has a "Sensor Cleaning"  mode which powers the mirror up, allowing direct access to the mirror.

Initially the camera complained that the battery needed to be fully charged. I guess it takes a lot of effort to hold the mirror up, so I suggest you charge your battery first whether you get a warning message or not.

Here are four sensor cleaning methods. The first 3 are "dry" and the 4th uses a swab on a stick loaded with cleaning fluid. I suggest you work through the 4 methods listed in order, checking for progress with more test photos at each stage.

  1. If your camera has a "Dust Removal" feature, use this first. This just vibrates the sensor to shake off any loose dirt.
  2. If method 1 does not work, try using a "puffer" to blow away the contamination.
  3. If methods 1 & 2 don't work, try a fine camera brush.
  4. If all else fails, try using a swab and fluid kit like this one.

Note that if dirt is removed (or even just moved to a new location) using one of the dry methods, there is no point in using the "wet" method. Only use the fluid for dirt that is stuck to the sensor.

In order to remove the black sticky spots from my Pentax camera sensor, I had to eventually use the swab and fluid kit.

The method is simple:-

  1. Put 2 or 3 drops of fluid on the end edge of the swab
  2. Slowly wipe the sensor with the swap just once, moving from the left side to the right side
  3. turn the swab over and repeat, moving the swab again from left to right

This left me with a couple of dust specks and a short fiber from the swab. However, these were easily removed using a fine brush.

I conducted the cleaning process in my man-cave with the help of my desk illuminated magnifier.

Although my cave is quite dusty, I kept the door and windows closed so as not to kick up the dust. And as soon as I'd finished cleaning or inspecting the sensor, I turned the camera so the optics were facing downwards and refitted the lens.

No more dirty photos!