[LRflex] Bluedot Frustration...An Update.

All:
Whether the "Blue Dot" is caused by light bouncing off the sensor, and then being reflected back to it again, off the rear element of the lens, or whether it is a reflection between internal lens elements, under certain conditions, I am not sure.
It is not, as Philippe suggested, flare being reflected off the metal bits of the lens. There was no flare. The photos were taken, indoors, in the shade, on an overcast day, with the lens hood in use. 

Slobodan Dimitrov (LEG) proffered:


Possible reflection of the rear element on the sensor.
I had that problem with a 60mm Elmarit-R and the old Canon EF
35-350mm f/3.5-5.6 USM L.
This is now being addressed by various manufacturers with the
refiguring of ghost free coatings, or "Ghostless coating".


and later:
It's more prone to happen in the close focus range. Not all lenses will respond the same way. Outdoors, I had very bad flare racked out at 250mm and over. Canon finally redesigned the lens with new coatings, and reduced that particular model to 300mm.
This seems to be it. When I checked back, when it has happened it has always been with the 80~200/4 Vario, though it has been a very rare event, until this last series of close-ups. However, it has occurred, in outdoor shots. I'd upload one, and show you, but my ISP is having problems, today, and nothing will upload for me! (My BluDot.htm page, posted Saturday, is gone, too!) Perhaps tomorrow I will be able reload it, and some more.
Meanwhile, I changed to the 50mm Summicron for the closeup work, using either an ELPRO or Doug's universal extension tube (very slick!) for the job. Not a problem in sight!
For those who've followed the Beauty Six saga, the closeups are for a 1923 DeBrie Sept 35mm Cine/still camera and a Birnbaum (Prague) Nova Perforetta.
The Sept can be seen at: http://www.camerapedia.org/wiki/Debrie_Sept (all photos taken with the 50 Summi, as above.) 

The Birnmaum page will be along, in the fullness of time.

In future, will forgo the convenience of a zoom, for close-up work!

Cheers!
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David Young,
Logan Lake, CANADA

Wildlife Photographs: http://www.furnfeather.net
Personal Web-pages: http://www3.telus.net/~telyt
Stock Photography at: http://tinyurl.com/2amll4

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