Tuesday, May 4, 2010

THE SPOT by Anonymous

What is the spot? Historians of camera optics, can you help us?

The facts are these:

1. The spot is always centered horizontally and vertically.
2. The spot is basically a nice disc, but it can be slightly incomplete or irregular.
3. The spot is white, but it can be transparent to one degree or another.
4. The spot never appears in color photos and rarely in photos later than 1950 or so.

The evidence seems to show that the spot is an optical phenomenon and not (for example) something in front of the lens or a chemical accident at the darkroom stage. But at some point something in camera design changed to eliminate the spot forever. What was it?


  1. Orbs as we would say in the parnormal world!!!!
    Ghost Hunter Glenn!

  2. It must be light leaking from the iris when the blades don't close completely.
    I would bet that this fenomenon only happened to cameras that had s behind the lens shutter.

  3. Domenico, what do you mean by this phenomenon only happened to cameras that had s behind the lens shutter? My friend who wrote this sent me an email and asked "One problem that comes to mind is that the effect is sporadic. For example, the balloon girl came with some others taken within a few minutes that didn't have the spot."

  4. A shutter behind the lens is created by many blades that create a circular aperture. Now, looking at the pictures, the white spot is always centered and that suggests me that the problem is very likely to be the shutter that doesn't close itself completely at all times.
    These were rudimentary mechanisms and it's possible that this problem wouldn't be present consistently. Capisci?

  5. Ok, my friend responded and says "Capisco, but doesn't the iris hypothesis predict spots of all sizes, down to a point? I don't think that's borne out. Normalized to the dimensions of the photo, the spot is about the same size in all the examples I have. And, more fundamentally: the iris is already open to take the picture, no? The picture is a controlled light leak through the aperture. Is Domenico's idea that iris and shutter are the same in this camera and the spot represents an exposure before or after the iris reaches its proper size to take the picture?"

  6. My hypothesis is based not in the diaphragm, but on the leaf shutter, that probably doesn't close at all times completely.
    The diaphragm is a different component of the lens assembly. As you say the diaphragm is regulated at different aperture sizes to regulate the depth of field and the amount of light reaching the film.
    The leaf shutter, which I mistakenly called behind the lens shutter(but that in reality is between the two lens groups), is another component of the lens mechanics which determines the speed of the exposure.
    This, as I said, could have been the culprit of the problem, by not closing completely at times, hence allowing light leaks reaching the film.
    There are other kind of light leaks possible in a camera, from bellows leaks to part of the body, but the nature of the ghost image suggests strongly that is coming from the mechanism which is supposed to regulate the times of exposure (shutter).
    If I am right you owe me an espresso.

  7. Stacy, this is for Domenico:

    Another question is how many of those early snapshot cameras had leaf shutters. I believe Brownies, for example, had some sort of curtain shutter. But I bet Domenico is right. I make a pretty good espresso.

  8. It's possible that the ruby fell out of the camera back. Then if the camera is left out in the sun the light eventually leaks through the paper backing and creates the perfect white spot. I say this, because it looks more like a contact thing than an optic thing.