[QUOTE=marciofs;1495939]This two images were taken with a 0.420mm pinhole and the same time exposure 25min.
Do you think the flare is actually UV light. If I use UV filter does it solve this flare problem[QUOTE]
My first guess would be light reflections inside the camera. Did you paint the inside matt black and cover the metal of the pinhole with black tape?
Or did you take the photo into direct sunlight? I supose you don't have light leaks?
* "So much time and so little to do. Wait a minute. Strike that. Reverse it. Thank you." (the original Willy Wonka: Gene Wilder, 1971)
* My favorite cameras: Leica SL, Leica M7, Russian FKD 18x24, Bronica SQ-B and RF645, Rolleiflex T2, Nikon F4s, Agfa Clack and my pinhole cameras
I don't know. I have seen something like that when the sun reflected into the pinhole. One of my cameras has a 1/4" drilled hole in the side of a can, and the pinhole is taped inside the can. The edges of the 1/4" hole are shiny, and a glint of sun can reflect directly onto the pinhole. It causes something similar.
The exposure in the 2nd one looks very good.
I like UV reflection in the air or mist, but I don't think it could be that strong.
Because pinholes are so small it is easy to improvise a very efficient "lens" hood for them. This should eliminate most flare problems when there is a lot of sky around the subject or when the sun is just outside the picture area.