If you've ever cursed the spots and dust particles on the front element or protective filter on your lens when they suddenly appeared in the viewfinder and began trying to remove them with a shirt-tail or handkerchief so you could continue shooting, you may have also worried that, unless they attached themselves to your lens between shots, these troublesome blemishes might have been there for some time, unnoticed, but nonetheless spoiling previous shots.
That is certainly a possibility, but it is more likely that while the spots were there all along, they didn't appear to foul your scene until you made a wide angle shot with the iris closed way down. The sudden appearance of these spots is likely due to nothing more than your depth of focus zone becoming so large that it even includes the front element.
The solution is simple. Put away the lens cleaning materials and open the iris a few stops; the spots will disappear. Of course your shot will now be overexposed. Unless, that is, you also change the filter to one that allows less light to reach the imaging chips. Now white balance the camera (most cameras remember different settings for each filter) and get back to your shoot.
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