Black-drop - is it real?

On Wed, 09 Jun 2004 19:03:45 GMT, nobody wrote:

For my money, the black drop appears to be substantially caused by the
eye's own optical illusion, and is dependant upon the image scale of the
eyepiece (the effect was more pronounced at what experience tells me is
medium magnification and wasn't noticable when the Venus image was very
small (zooming out the Photoshop image greatly) or very large (highly
zoomed in.)

Thus, in addition to the eye playing tricks, the magnification, quality
of the optics and the seeing most likely contribute to the effect,
positively or negatively.

The problem is that for all theories at the moment, I'm hearing
examples of images taken with equipment/conditions that counter each
theory.

Despite the massive number of images taken of the event, I've had very
few equipment/conditions/black-drop (y/n) reports sent in yet [HINT
HINT!].

Unless there's data to back it up, theories will simply stay as
theories.

For my part, I believe it's caused by equipment quality and the
contrast of the image that is being observed. However, I'd dearly
like to gte some proof.

--
Pete Lawrence
http://www.pbl33.co.uk
Most recent images http://www.pbl33.fast24.co.uk/recent_images.html

For my money, the black drop appears to be substantially caused by the
eye's own optical illusion, and is dependant upon the image scale of the
eyepiece (the effect was more pronounced at what experience tells me is
medium magnification and wasn't noticable when the Venus image was very
small (zooming out the Photoshop image greatly) or very large (highly
zoomed in.)


Thank you ! I concur with this. I purposley made hi magnification
images and kept them slightly dark to Verify this effect . In Dayton
Ohio Seeing was Fantastic and the Disc of venus exibited No Black drop
shape that I could image. my pics at :

http://home.woh.rr.com/directoryww/0...itOfVenus.html

Woody AKA (disposable Spambait E-mail)

"Pete Lawrence" wrote in message
...
On Wed, 09 Jun 2004 14:35:13 GMT, Sam Wormley
wrote:

I didn't see a hint of it in the first hour of the transit--looking via
web cams and nasa tv. Got clouded out for the direct observation. :-(

Bad news Sam - I'm sorry you missed it

A lot of solar projection observations mention the black-drop effect.
Was there anyone out there that saw the transit with a projection
arrangement but didn't see the black-drop?

I used an 8'' Newt projected on to a piece of paper. I am a newbie so my
quality is not great. In this pic,
http://www.darofamily.com/jeff/files...s/p1010065.jpg, I believe
there is some black drop.

BV.

"Pete Lawrence" wrote in message
...
On Wed, 09 Jun 2004 19:03:45 GMT, nobody wrote:

For my money, the black drop appears to be substantially caused by the
eye's own optical illusion, and is dependant upon the image scale of the
eyepiece (the effect was more pronounced at what experience tells me is
medium magnification and wasn't noticable when the Venus image was very
small (zooming out the Photoshop image greatly) or very large (highly
zoomed in.)

Thus, in addition to the eye playing tricks, the magnification, quality
of the optics and the seeing most likely contribute to the effect,
positively or negatively.

The problem is that for all theories at the moment, I'm hearing
examples of images taken with equipment/conditions that counter each
theory.

Despite the massive number of images taken of the event, I've had very
few equipment/conditions/black-drop (y/n) reports sent in yet [HINT
HINT!].

Ellicott City, MD (just south of Baltimore, MD)
8'' Hardin Optical Newt on a Dob mount
Eyepiece was the lower power of the two that came with the scope, not sure
of mag. off the top of my head
Image projected on to Staples Printer Paper
Images taken with Olympus C-320 digital cam

I believe this image hints at the effect,
http://www.darofamily.com/jeff/files...s/p1010065.jpg. I can make
full-res versions available if requested.

Disclaimer: I am a newbie hack, so I am not sure if this data is even
helpful. Flame not.


BV.

Again, I'm very interested to have others try my Photoshop experiment,
to see if my results are duplicated. This experiment eliminates all
other factors - it is solely the eye looking at a flat image field
simulating the image field at focus.

Interestingly, last night, I perused the seemingly myriad animations now
available of this transit and noticed that some clearly show the effect
and some do not. Notice that I use the word 'effect' as opposed to
'phenomenon'.

FWIW,

Bart Fried

Pete Lawrence wrote:

On Wed, 09 Jun 2004 19:03:45 GMT, nobody wrote:


For my money, the black drop appears to be substantially caused by the
eye's own optical illusion, and is dependant upon the image scale of the
eyepiece (the effect was more pronounced at what experience tells me is
medium magnification and wasn't noticable when the Venus image was very
small (zooming out the Photoshop image greatly) or very large (highly
zoomed in.)

Thus, in addition to the eye playing tricks, the magnification, quality
of the optics and the seeing most likely contribute to the effect,
positively or negatively.


The problem is that for all theories at the moment, I'm hearing
examples of images taken with equipment/conditions that counter each
theory.

Despite the massive number of images taken of the event, I've had very
few equipment/conditions/black-drop (y/n) reports sent in yet [HINT
HINT!].

Unless there's data to back it up, theories will simply stay as
theories.

For my part, I believe it's caused by equipment quality and the
contrast of the image that is being observed. However, I'd dearly
like to gte some proof.

On Thu, 10 Jun 2004 13:03:34 -0400, "Benign Vanilla"
wrote:


"Pete Lawrence" wrote in message
.. .
On Wed, 09 Jun 2004 14:35:13 GMT, Sam Wormley
wrote:

I didn't see a hint of it in the first hour of the transit--looking via
web cams and nasa tv. Got clouded out for the direct observation. :-(

Bad news Sam - I'm sorry you missed it

A lot of solar projection observations mention the black-drop effect.
Was there anyone out there that saw the transit with a projection
arrangement but didn't see the black-drop?

I used an 8'' Newt projected on to a piece of paper. I am a newbie so my
quality is not great. In this pic,
http://www.darofamily.com/jeff/files...s/p1010065.jpg, I believe
there is some black drop.

That's a really nice pic, and for a newbie, ou should be pretty proud
of it!

Like a number of other pics I've had, the black-drop appears to be
'stimulated' in pics like this from a degree of chromatic fringing
around the dark edges. What eyepiece (fl + type) were you using?
What were your sky conditions like?


--
Pete Lawrence
http://www.pbl33.co.uk
Most recent images http://www.pbl33.fast24.co.uk/recent_images.html

On Thu, 10 Jun 2004 17:57:44 GMT, nobody wrote:

Again, I'm very interested to have others try my Photoshop experiment,
to see if my results are duplicated. This experiment eliminates all
other factors - it is solely the eye looking at a flat image field
simulating the image field at focus.

Interestingly, last night, I perused the seemingly myriad animations now
available of this transit and noticed that some clearly show the effect
and some do not. Notice that I use the word 'effect' as opposed to
'phenomenon'.

I've been like a zombie over the last 2.5 days due to lack of sleep on
Monday night (well - no sleep!). However, my brain is now starting to
reactivate.

When I get the webpage up and running would you like to submit your
experiment for inclusion? If so - send me an email privately so I can
contact you direct (unless your header email is for real). For
convenience, my email is pete dot lawrence at pbl33 dot co dot uk.

--
Pete Lawrence
http://www.pbl33.co.uk
Most recent images http://www.pbl33.fast24.co.uk/recent_images.html

"Pete Lawrence" wrote in message
news snip
I used an 8'' Newt projected on to a piece of paper. I am a newbie so my
quality is not great. In this pic,
http://www.darofamily.com/jeff/files...s/p1010065.jpg, I believe
there is some black drop.

That's a really nice pic, and for a newbie, ou should be pretty proud
of it!

Like a number of other pics I've had, the black-drop appears to be
'stimulated' in pics like this from a degree of chromatic fringing
around the dark edges. What eyepiece (fl + type) were you using?
What were your sky conditions like?
snip

Forgive my ignorance, but the best answer I can give is that it was the
lower powered plossel that came with the scope. I think it may be a 25mm, at
48x mag I guess? Sorry. Still amazed at what I can see with the scope, so I
have not focused on "how" it is letting me do it yet. It's a Hardin Optical
8'' Dob.

On to my next area of ignorance. I do not know how to report on my seeing
and clarity in the area. I can say, I was shooting just off the edge of my
neighbors house, but I don't think the roof heat was a problem as it was
early in the morning. We had some light haze and lots of moisture in the
air. No clouds at all, and the disc of the sun was clearly visible. Just as
the sun crested the trees, I briefly looked over and was able to see venus
naked eye but just for a second. So I think seeing was a close to perfect as
it could have been.

BTW, thanks for the compliments. I appreciate. The pics most of you post
astonish me. I have to say my favorite pic that I took that day (and I have
no idea why) is the one showing the trees. I stepped partially in front of
the scope and that image got reflected from the primary on to my arm. It
looked cool, so I refocused it on some paper and took that snap.

http://www.darofamily.com/jeff/files...s/p1010035.jpg

Now on to the black drop. I have no knowledge of why or if this happens, but
I believ that I can see it in the picture I mentioned in the original post.
To me, it looks like that old illusion of the white lines criss crossing on
the black background. The intersections all look grey.

BV.

(wingsnaprop) wrote:

http://home.woh.rr.com/directoryww/0...itOfVenus.html

Your images are underexposed. Take the 10th from the bottom and
adjust the levels. A "black drop effect" (or at least what other
people have posted as "black drop") appears.

nobody wrote:

Again, I'm very interested to have others try my Photoshop experiment,
to see if my results are duplicated. This experiment eliminates all
other factors - it is solely the eye looking at a flat image field
simulating the image field at focus.

Since the effect can be photographed, it isn't an "optical illusion".

A more germane PhotoSlop experiment: make a large white area on a
black background. Put some small black areas on this white piece, at
various distances from the edge.

Engage the gaussian blur tool and watch as "black drop effects" appear
and disappear as you wiggle the radius of the blur around.

www.google.com: "point spread function"