Cleaning the matrix is a vital necessity. Below are examples of a dirty matrix not for the faint of heart who suffer from heart disease, please do not read further.

Matrix cleaning. Article from Radozhiva.
One of the disadvantages of modern digital SLR cameras compared to film, is that camera sensor gets dirty over time. In film cameras, a new piece of film is allocated for each frame, so there is simply no problem with pollution for the film.
How to check the matrix of the camera for contamination?
Very simple. For this you need take a picture on the closed diaphragm of a plain background... The easiest way to do this is to put the camera in aperture priority mode (mode A or Av on the mode dial). Set the minimum allowable aperture value, this means that the F number should become the maximum, most often F16, F22, F32, F36. Turn off auto ISO and set the minimum allowable ISO value: most often it is ISO 50, ISO 100, ISO 200. After that, just take a picture.
Please note that the focal length of the lens does not affect the check of the dirtiness of the matrix. A solid background should be photographed only to make it easier to notice dirt on the matrix. When the aperture is closed, it will be long excerptIt’s best to mount the camera on a tripod or on a stationary object. Length excerpts does not affect validation. If there is no tripod, you can simply take off the blue sky.

Dirt on the matrix
In the photo above, I made the settings ISO 100, F16, 50mm. In order to more clearly see all the fear and horror of a dirty matrix, you can set the maximum image contrast in the program editor. See below.

Dirt on the matrix
By arrows I showed the dirt that I had on Nikon D200, my camera Nikon D200 not cleaned for more than a year.
Attention: Do not be afraid of a dirty matrix. At open apertures (at apertures up to F / 8.0), dirt will hardly affect the quality of pictures. You can shoot your whole life on F1.4-F4.0 and not worry at all about the cleanliness of the sensor.

Contrast enhancement to see dirt
Do I need to clean the matrix?
Everyone decides for himself. I need a clean matrix, as I earn money for a living by photography. I often have to shoot scenes with a closed aperture (group portrait, landscape, photo for reviews), so I monitor the cleanliness of the matrix and try to take my cameras every 6 months to clean the matrix. Cleaning the matrix costs from 40 to 100 cu and takes 1-2 days. It is quite expensive, and the cleaning result does not always suit me. Therefore, I decided to do this business myself. For a more or less reasonable price of 60 cu I came across the Green Clear Sensor Cleaning System (Non full frame Size) for DSLR Cameras. The system allows cleaning about 80 times with a bottle and 3 times with special cleaning mop brushes.
Integrated matrix cleaning systems
Now it has become very popular to install matrix cleaning systems in CZK (digital-mirror cameras). My practice shows that such systems cannot completely protect the matrix from dirt. Basically, cleaning systems are based on the fact that the matrix vibrates and shakes off the dust. But dirt is not only dust, it can be streaks from condensation or something else. Cleaning systems simply cannot cope with this. On my Nikon D90 with the cleaning system I had to take it to the service after a year of use and the active cleaning function. I often fall into the hands of cameras with cleaning and I always see dirt on the matrix. So, cleaning systems for 2012 cannot provide the quality of cleaning that is so strongly advertised by manufacturers.
For owners of CZK Nikon will be useful article about the software method of combating dust and dirt on the matrix.

Green Clear Sensor Cleaning System (Non full frame Size) for DSLR
How I cleaned the matrix:
The Green Clear Sensor kit includes a can of some kind of gas, three dust suction tips and three sets of mops for cleaning. You need to read the instructions for the Green Clear Sensor or watch the training video. I also had a small Russian-language instruction in the kit. Most of all, it was difficult for me to install the valve on the cylinder - you first need to strangle it, and then tighten it.
- I collected a vacuum pump. By simply attaching a valve to the cylinder, to the valve an extension tube, to the tube one of the cleaning tips.
- Set up the camera in order to clean it.
- With the help of a pump, I sucked up dirt.
- Using a mop, I cleaned the sensor.
In fact, it’s a little scary to go to the matrix of the camera, but when you do this often, all fear disappears.

Before and after cleaning
Attention: I advise you to read the instructions for your camera. In order to clean the matrix of the camera, you need to raise the mirror in front of the matrix. There is a special function for this, usually called “mirror up” or “mirror up for cleaning”. On Nikon, when this function is activated, when you press the shutter button, the camera raises the mirror and remains in this position until the camera is turned off. If the battery charge is less than 60%, the mirror up function will be disabled. Do not use slow shutter speed to clean the sensor. My friend was cleaning the matrix on shutter speed at 30s and got carried away, the camera lowered the curtains and the mirror - nothing good came of it. Also, in the specialized mode, the camera does not take a picture - no voltage is supplied to the matrix, which also reduces the risk of damaging something.
Conclusions:
Sometimes you need to check the camera matrix for contamination and take the camera to a service, or clean the matrix yourself. Self-cleaning is 3-4 times cheaper for after-sales service. Built-in systems for cleaning the matrix from dirt can only postpone serious cleaning of the matrix in time.
Thank you for attention. Arkady Shapoval.
contacted the service here https://comp-service.kiev.ua, cleaned and put in order
Good afternoon, I want to understand how the aperture can affect the visibility of dust on the matrix? In my opinion, the dust on the matrix lies directly on the photocells (directly in contact with the photocells or microlenses of the photocells). In this case, the dust is always more than one pixel. Whether the light comes from one source or not does not matter in this case. Now, if the dust lies at some distance from the matrix, then yes, due to a non-point source, light can bypass the dust speck. It is interesting from a purely educational aspect. Thank you in advance.
A point on the matrix is formed by a set of rays from the rear lens of the lens. The narrower the beam of these rays, the less contribution is made by the obliquely incident rays, which means they are able to pass by the debris on the glass of the matrix. The smaller the aperture, the narrower the cone that forms the image of the point. You must also understand that in fact the garbage lies directly on the photocells of the matrix, and on the glass that covers these elements.