Nidelva river through Trondheim Norway

Nidelva river through Trondheim Norway
by Saaru Lindestokke                

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The large and nearly perfect circle(s) often found in photos taken with an IR filter are often referred to as "hotspots", and they are mostly caused by internal reflections in the lens and filter combination. To my eye, the most obvious spots in your example image are these sorts of hotspots. The internal reflections are not absorbed by all len and barrel ...


I have seen the same issue and found that sealing the filter to the filter folder (Lee in my case) made the spots go away. I think that because the IR filter stops so much light and therefore the expose time is so long then any light creeping in through tiny gaps between the filter and its holder will allow any small specks of dust on the back of the filter ...

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