Shooting an impromptu product coverage in the shop one morning meant making an improvised scoop out of a roll of Ilford printing paper. It's good paper, and gives a spotless finish.
To get a neutral white balance in the mixed shop lighting I used the Custom White Balance provision on my Fujifilm X-T10 camera to reset it in one go. Lots of cameras have this same feature - you point the lens at a plain white surface that is illuminated like your subject and the camera measures the colour temperature with one shot. If you say OK to the result you have a steady basis to shoot from, colour-wise.
Only trouble is when I shot I had a real spot - obviously my sensor had picked up a lugie the size of a Volkswagen and when I stopped down to f:14 it showed up something terrible. Well, I opened the lens a little, put on flash, and resigned myself to cloning it out in the finished products - I didn't have time to wait for a sensor clean.
That's the three choices you have; clean, clone or claggy pictures.
After I got home I decided to see if I could clean the sensor myself with a puff of air - I wouldn't touch the filter in front of a sensor with anything else - I leave that to the staff at Camera Electronic when it gets really bad - but figured a puff from a blower would be fairly safe. As the spot was in the upper left of the picture the offending dirt must have been in the lower right area - I puffed carefully all round the place and then took another diagnostic picture of a clear blue sky and small aperture.
No good. Still spotty. Puff again. Still spotty. Then I happened to glance at the rear element of the lens.
The spot. Sitting there. One puff and it was gone, and with the last photo....voila:
This is the wide angle/short focal length trap that has got me before. When you use this sort of gear and then stop down to f:11-22 you run a risk of picking up dark spots from gunk on the rear elements of your lenses or light spots from the front elements of filters in front of the lenses. It can be deadly if you are firing a flash at a subject against a dark backdrop.
The answer, as Ernest our technician says, is to take as much care with the element surfaces as you are urged to do with the sensor - and to make sure that you are not re-contaminating everything
each time you heave a lens on and off. Clean out the camera bag, make sure your clothing is not shedding itself into the camera.
And when you are next in the shop, whack out some cash for a Camera Electronic lens cloth
or some packets of Hoodman Lens Cleanse wet wipes. The money is little enough and the time you take clearing the optical pathway will be repaid 100 x over in not having to clone stamp every darn file you make.