Doug Kerr
Well-known member
Richard Dickins, on the Pro Photo Home forum, has just concluded a long investigation of a peculiar phenomenon he reported with his EOS 5D Mk II. He reported "ghosts" on the image, and with great prescience, said they looked like reflections of camera internals.
He underwent a very lengthy diagnostic process, and has just reported the conclusion. I'll make a long story short.
The metal bar on the lower edge of the reflex mirror (actually part of the mirror "frame", I think) (this is the edge that is toward the lens when the mirror is raised for exposure or live view) has a matte black finish (for the same reason as for everything inside the mirror box - to avoid any path for out-of-frame off-axis rays to reach the sensor).
Presumably to avoid the possibility that, during handling of the mirror, this matte finish would be "scuffed" (thus leading to somewhat-shiny places on it), it is protected by a temporary plastic strip (such as we find on LCD displays, equipment front panels, and so forth during shipping).
Evidently in the case of this particular camera, the protective plastic strip was never removed. It was of course shiny enough to provide a reflection path to the sensor for off-axis rays emerging from the lens.
This may well be a one-in-a-million flaw. But I thought it was worthwhile for us to be alert to the possibility.
The thread is here:
http://www.prophotohome.com/forum/c...-eos-5d/81508-5dmkii-reflections-picture.html
It includes a wonderful photo showing the shiny bar and the reflection it causes on the sensor (before Richard realized why the strip was shiny).
Overall, great diagnostic work, and a good conclusion.
Best regards,
Doug Kerr
73 years old today
He underwent a very lengthy diagnostic process, and has just reported the conclusion. I'll make a long story short.
The metal bar on the lower edge of the reflex mirror (actually part of the mirror "frame", I think) (this is the edge that is toward the lens when the mirror is raised for exposure or live view) has a matte black finish (for the same reason as for everything inside the mirror box - to avoid any path for out-of-frame off-axis rays to reach the sensor).
Presumably to avoid the possibility that, during handling of the mirror, this matte finish would be "scuffed" (thus leading to somewhat-shiny places on it), it is protected by a temporary plastic strip (such as we find on LCD displays, equipment front panels, and so forth during shipping).
Evidently in the case of this particular camera, the protective plastic strip was never removed. It was of course shiny enough to provide a reflection path to the sensor for off-axis rays emerging from the lens.
This may well be a one-in-a-million flaw. But I thought it was worthwhile for us to be alert to the possibility.
The thread is here:
http://www.prophotohome.com/forum/c...-eos-5d/81508-5dmkii-reflections-picture.html
It includes a wonderful photo showing the shiny bar and the reflection it causes on the sensor (before Richard realized why the strip was shiny).
Overall, great diagnostic work, and a good conclusion.
Best regards,
Doug Kerr
73 years old today
