Blackmagic Forum

I've come across an issue and I'm hoping you all can help.

I switched some things around in my studio today and noticed a lot of spots in the image of my 4k that I've never noticed before. This is a camera that has up until now normally shot quite wide open (f3) and now it's set up pretty closed down (f12-16). I guess those spots have been there for a while and I've just never noticed them until now.

I know what you are thinking and I agree. All signs point to sensor dust. They don't move if I zoom and they kinda disappear when I open up the aperture.

So, planning on getting some swabs and seeing what I can do.

The thing that confuses me though is that looking at the sensor with the bare eye it looks as clean as a whistle yet the image is literally littered with spots. Is this normal? Am I missing something?

If you shoot at those apertures you will never get a spot free image as even microscopic particles on the sensor glass will cause spots. Keep your aperture below 5.6 and you will not see them.

Legion wrote:So, planning on getting some swabs and seeing what I can do.

First try using a bulb blower (never used canned air, it can cause damage). Hold the camera pointing down and keep blowing it out for a good long time, 30 seconds to a minute. That can sometimes do the trick and avoid a wet clean.

Also note that your image may start suffering from diffraction-related softening at those apertures on a micro four-thirds size sensor. It was worse with the original BMPCC (super 16 size sensor); I can't go beyond f8 without noticeable softening and it's pretty much unusable at f16. Less of an issue on the BMPCC 4K but f16 might start to be affected.

I have the same issue with my Pocket 4K. I usually shoot with a wide aperture and compensate with an ND filter.

Air won’t shift sticky dust particles and wet wiping will leave marks or even scratches if the particles are grit. Wet wiping should only be used to remove grease (finger prints) or other liquid / vapour contaminants if you are unlucky or clumsy enough to get these when changing lenses in a difficult environment and leaving the sensor exposed. For simple dust I use a gel stick which leaves no marks or scratches and will pull off even the most stubborn and stuck particles.

Spots on the sensor itself will be there regardless of aperture setting, Wide-open they may be slightly less defined but will remain visible. Spots on the ND filters if they exist in the camera, spots on the IR filter panel or OLPF/IR filter panel are forward of the sensor and will quickly become less defined the wider the aperture of the lens. Likewise, spots caused by marks or dust inside of the rear of the lens itself will become less defined with the wider aperture setting.