Well ever since I purchased my FS700 second hand, the camera arrived with some marks on the sensor (not enough to effect my filming as I always shoot on low apertures).

But me being OCD, I used a wet sensor cleaning swab off ebay today.

BIG MISTAKE. It left some nasty smear marks which initially made my heart skip a beat.

I went through 3 wet swabs to finally clean the sensor well enough so that the smear marks left were absolutely minimal.

I then couldn't resist and used a microfibre cloth that I have to clean my lenses with and used it on the tiny smear marks left on my sensor to rub it off.

It hasn't left any scratches as far as I can tell, even after putting a torch light in there for a closer look. However, it does have a few micro dust still. It isn't 100% cleaned. But cleaner than when it arrived. It's not visible when you plain look at it, but when a light is on the sensor you can see it.

My question is ... can the sensor actually EVER be 100% clean? it can't can it? as soon as you clean it, another spec goes on there!

Not going to bother doing it again unless it's really dirty and effecting my images produced.

I also noticed, that the REAL sensor is all the way at the back, in front of the real sensor are the built in ND's and the actual piece of glass I have been cleaning is just another element? What is it?

First, be thankful that there's glass there protecting the actual camera sensor.
I'm not really sure, but that glass may also be acting as a 4K-optimized anti-aliasing filter to help minimize 'jaggies' and other artifacts.
The fact that there's some spacing between the glass and the sensor behind it also means that any slight dust specks will tend to show up less.
In terms of 'absolute clean' - think about it this way -- if you're in a real clean room environment than there won't be dust particles in the air to settle on surfaces (such as a sensor cover glass). To help minimize dust in the workshop run a couple of air filtration systems 24/7 - and clean their capture filters frequently.
Of course when changing lenses on location, try to minimize the amount of time that the lens port is open - keep it covered whenever there's no lens on it!

I have a couple of dust specs on the sensor that I can't get rid with a blower, any good recommendations on what to do? Touching the glass seems a bit risky to me...

Sami

Well after sort of having a rant on this thread, I did some proper research via Google.

I found the best way to clean the sensor and the camera in general. Using Methanol (Eclipse drops), Sensor Swabs and Pec Pads (Lint Free Tissues).

And as Dave pointed out. It's not the sensor we are cleaning at all. It's a anti aliasing filter or something along those lines that we are cleaning. It's glass and fairly robust. Unless you rub it aggressively you won't scratch it. But if you don't use the correct materials (like I didn't ... my fake £5 swabs off ebay didn't have methanol) you will leave a foggy smudge on the sensor.

I've just spent £20 and ordered myself some of the cleaning products above. Should allow me to clean the sensor and repeat the process as and when I need to do it again in the future. I also use a few other NEX cameras that I can use the cleaners on if needed.

i've cleaned sensors, actually the low pass filter I think, on my stills cameras over years, before the so-called self-cleaning systems were developed, the dust was pretty noticeable and that's what I used - pec pads a 35mm spatula and the eclipse fluid.
Even at that you need to have as near to as possible cleanroom conditions as you can inttroduce other contaminants and stuff if your not careful, also be aware that the fluid evaporates very quickly, only use the one side of pad once turn it over and use then discard! it will only re-deposit dust back again if you do!

On the FS700 the *only* thing you have access to / can touch is a piece of optically clear glass protecting the very fragile ND filters. The FS700 is nearly unique among all digital cameras in this respect. You could clean this chunk of glass with Windex if you wanted, although obviously Eclipse fluid and lint free swabs are the way to go.

The actual sensor is behind the ND filters. In sensor design, if any type of anti alias filter is used, it is always bonded directly into the "sensor sandwich", never mounted at a distance away from it. The raw silicone of the sensor's photo-diodes are never exposed in any sensor design.

Since the glass protecting the ND filters is a distance away from the sensor, any dirt on it must be rather large to show up. Dirt on a sensor shows up because it is normally sitting fractions of a millimeter above the photo-diodes, casting a very sharp shadow. In the FS700, dirt on the glass protector will cast a very diffuse shadow.

However, using the FS700 in dirty environments, and taking poor care of the camera could potentially lead to dust ingress behind the ND filters. My first FS700 came from the factory with 3 specs back there. In this case your only choices are 1) return the camera, 2) send it to Sony for repair, and hope it comes back better than it was, or 3) ignore it.

While I don't like the idea of there being dust back there, I chose option 3, knowing there was no chance I would ever shoot at an aperture which would reveal it.

Thank you for such a thorough explanation. Learnt something new.

I should mention that front glass is spotless after using the proper tools for the job. The key is to use 1 or 2 drops of the eclipse fluid on a lint swab and then give it a single stroke back and forth and discard of that swab. Do this once, or twice and the glass becomes spotless. In my case any way. My sensor or should I say the optical glass looks spotless now. Looking forward to cleaning it again now that i'm confident doing it.