may you point me to the right direction how to clean it? Will it be adequate by using the camera sensor cleaning thing?
There are several methods you can try. For each of these methods I have read people saying that they don't work, and have read people saying they do work. To see what a variety of opinions there are you can search on this site for "sensor cleaning" and find threads like
this one for example.
1. You can try to blow the dust off with a blower like
this.
2. You can get a sensor cleaning brush, like
this.
3. You can get a special (and really expensive) sensor cleaning brush
like this that charges up with static electricity that attracts dust particles.
4. You can get sensor cleaning kits
like this. You put a little fluid on one of the pads and wipe it across the sensor.
5. You can get a sensor loupe
like this to let you see the dust spots on the sensor. If you don't have this you have to capture images of a blank wall or piece of paper with a small aperture (e.g. f/22) to see if there are still any dust spots after you have tried cleaning the sensor.
6. You can pay £50 or more to have the sensor cleaned.
I would suggest trying #1 and/or #2 first, and then #4 if that doesn't work.
The rest of this is just my experience, which doesn't seem to be typical, so to be honest is probably best ignored. I just include it so you know where I'm coming from on this subject.
I have had terrible problems with dust spots. It is a real problem for me because I do use very small apertures quite a lot.
#1 I have a blower. It hasn't worked for me.
#2 I haven't tried a sensor cleaning brush.
#3 I have only just found out about this. I'm not ready to spend that amount of money yet, especially when I read that if the brush touches the edge of the sensor it can pick up grease with can then make matters worse. The thing is, the spots on my sensor are often very near the edges.
#4 I have used several of these kits. With ten pads in each, that means I have tried 30 or 40 times to clean the sensor this way. (Yes, I have lost count). I have thought a couple of times that the sensor really was clean, but each time I pretty soon realised that it wasn't. I am awaiting delivery of yet another of these kits.
Sometimes the pads seem to leave quite large "hairs" on the sensor - I assume they are fibres that come off of the pads, which result in really nasty marks like the one here on the left of this crop.
Fibre on sensor - IMG_5723 Crop by
gardenersassistant, on Flickr
In this case I think the fibre must have been left in the camera after one of the cleaning attempts, but wasn't on the sensor when I took the final f/22 test shot of a blank piece of paper, and then a bit later when I was using the camera normally it moved on to the sensor.
#5 I have just ordered a sensor loupe (I have only just found out that they exist). I intend to use it in combination with the cleaning pads. If that doesn't work I may try #3. Or I may just give up.
#6 I have been very dubious about trying this as I suspect that either it won't be completely effective or, if it is, I'll quite soon get some more dust spots, for example if I change the lens on the camera. And keeping paying £50+ and not having the camera for a couple of weeks each time doesn't appeal to me at all.
I got so frustrated with all this that I recently considered getting rid of the Canon 70D. I have changed lenses plenty of times with my Panasonic G3 and never had any problems with dust, and I got some lovely flower pictures with it. But after trying my Panasonic G3 again I realised just how much I do like using the 70D for flowers, and how much I like the results (apart from the dust and fibres on the sensor). I then tried an extreme manoeuvre
which I strongly advise against trying as it could well damage your camera (but I was desperate and was ready, quite literally, to throw the camera in the bin at that stage if I did damage it). I used our vacuum cleaner to try and suck the dust out of the camera. I actually got the best results doing that, but I still couldn't get it completely dust free. It is an ongoing story.