Hi folks, to Antoine Couett, regarding latest Ocean Nav Prob, I got N20 08.5,W64 24 not exactly three star pinwheel fix.
I think there's been some confusion about these midnight Sun pictures.
Perhaps. Can only hope you haven't augmented the supply ...
It's not necessary for there to be "distortion", as such, for the image of
an object subtending a constant angle, such as the Sun, to vary in size
when projected on to a flat plane, such as a photographic plate.
Which is why its important to make the distinction between apparent distortion, referring to a natural visual effect, and distortion which could, for example, be caused by some aberration of the lens.
A perfect lens, presenting no distortion whatsoever, will project the image
of a rectangular object filling the field of view (such as a large sheet of
graph paper or a squared-up office block) on to a rectangular film as an
exactly similar rectangular image. A pinhole acts as such a perfect lens; a
small thin lens will approximate it.
A pinhole is far from being a "perfect lens", as each point of light it projects is diffused. That's its main drawback. The other quite significant apparent distorting effect any imaging machine will show, when reproducing your graph paper or office block, is when both the lens and the film plane are not parallel with the subject. If they are not, then the resulting apparent distortion is simply an effect of perspective. A photo of train tracks converging into the distance, or fence posts receding in size as they get further away, are examples of this which can be visually pleasing. However, when the camera close to the ground is tilted up to get that office block into frame, the same effect of perspective is perceived as displeasing visually; the building appears to be leaning backwards. For this, and other reasons large-format plate cameras have independent lens and film planes that can be adjusted in all planes; this apparent distortion can be corrected.
Having said that, while in our sun pic the camera was pointing upwards the result would be smaller suns as their altitude increases, not larger. So this is not the answer.
A distorting loptical system would show either "pincushion", or "barrel"
distortion, depending in the way that it reshapes such a rectangle, but we
can concentrate on a non-distorting pinhole.
Why? Was the sun pic taken with a pinhole camera?
The question is simply one of mapping. A pinhole maps such a flat-plane
object undistorted on to a flat-plane film, but cannot do so with the
spherical sky. It's just the same problem as mapping the polar regions of
the Earth.
Now you're cookin' with gas. Yes, an arc is being "distorted" onto a plane. As I already said, perhaps with inadequate clarity.
Another possibility (but not for
the likes of us) would be for a CCD sensing array to be produced on the
inside of a sphere rather than a flat plane; I wonder if that's been tried?
Leaving aside "the likes of us", a baffling concept, yes of course its been tried. Panoramic cameras, whose lenses rotate around an arc, project their image onto a curved film plane. This avoids that apparent distortion of wide angle lenses we have been discussing. However, if the resulting photograph is viewed as a plane, which is usually the case, apparent distortion is evident, that disappears when the photograph's edges are brought together to approximate the same arc as was recorded.
Sun images on any photo are ALWAYS vastly overexposed. I will believe that
a Sun image is not overexposed, when someone shows me sunspots on such an
image: so far, nobody has.
Why would the earlier and later suns be significantly brighter than the one in the centre? For our practical purposes the exposure is fine if the edge of the sun is clear and crisp. Nope, don't think this idea is helpful.
The Sun disc edge-contour extends outwards to
the radius where the overexposure ends. Any haze surrounding the Sun
diffuses the light such as to increase the radius of that contour. That
seems to have happened in the photograph, with increasing haze as the
morning progressed, particularly in the last picture taken at 1:20 am.
But BOTH the earlier and then later suns show similar diffusion. Why should it be so?
The New Busy think 9 to 5 is a cute idea. Combine multiple calendars with Hotmail.
