At 01:55 PM 12/9/2001 +0100, Thomas you wrote:
A little more technically, every light source is a source of waves and
it's only by catching *all* the light that a lens can reproduce a perfect
picture of the source itself. By using obstacles of different shapes you
are in fact choosing what kind of information to include in the picture,
and therefore also which imperfections to be stuck with in the image.
The mathematics behind this is definitely not suitable for ASCII
communication.
For my part then, I'm grateful for ASCII limitations! but also for your
attempt to provide an explanation for someone who didn't even take HS physics.
The sun star diffraction seems almost by definition to occur only in
photographs of light sources.
The diffraction occurs everywhere in photography, every point your lens is
imaging is smeared in the same way. It is however very weak, and it's only
in these special circumstances (very bright sources on dark surroundings)
that you'll be able to see it directly. Take a look at Gary Reese's lens
tests, and you'll see that as lenses are stopped down their contrast will
suffer. Guess why...
I hadn't put that together at all. When people say, as I have sometimes
heard, that the 75-150/4 is flare-prone, I guess I should truck out this image.
I've added another image with sun stars to the page I posted earlier:
http://soli.inav.net/~jdub/sunstar.html
The new image is the first one on the page. This is a sunset image in
which there are two sets of sun stars created by the sun itself. I
didn't take the photo with any notion that I would get sun stars. Rather
I was hoping to catch the beams breaking through the clouds. I got a bit
of that and a bonus with the sun stars, I think.
This is interesting but not different from the previous examples. You have
a cloud in front of the sun, effectively dividing the sun into two light
sources. You'll see that both sources have their own "sun stars", or
diffraction stars.
Yeah, I was just wondering if what John refers to as the "glory" light or
beams is also a species of diffraction, but one happening "in front of the
camera" -- like light breaking over a cloud as light "breaks" over the
diaphragm. "Diffraction" literally means "breaking apart." (I'm a little
better linguist than a physicist, but not very good at that either.)
A bad lens will degrade images of everything, but a SC lens won't smear
your "sun stars" more than it will smear your clouds, rocks, or whatever.
Lens construction could possibly play a role, but that has to do with
placement of the aperture, definitly not with coatings.
Keep shooting these great pictures, don't worry about the lenses.
Regards,
Thomas Bryhn
PS! Have you ever tried squinting at the sun?
Squinting at car headlights more. (Is that what you're getting at?) I
sometimes do that to accentuate the star effect, and other times put on
glasses to sharpen it up or reduce it. Is squinting the equivalent of
stopping down the lens? Is that why you're supposed to stop down in order
to get this effect better?
The genesis of all these questions is a comment/critique from my brother
about the smallness of the sun star in my Lake of the Clouds photo. I was
wondering if some lenses make bigger sun stars because of their
formula. Henceforth, I'll assume not.
Thanks again for your explanations, John Lind also you for yours, and Mark
M-L for your explanation and links. (I'll let you and John settle the glory
business!)
Cheers to all,
Joel W.
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|