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Is this considered obstruction? (pics inside)

eddiexp

Rough_Rock
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Jun 3, 2011
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41
I've done a bit of searching on the forum and to my understanding, shallow pavilion angles such as 40.6 deg might exhibit a bit of obstruction?

I believe my pavilion angle is 40.6 deg, so naturally I got curious and tried to take pictures to see for myself. The way I took them was by wrapping a piece of paper around the lens to make a tube (roughly 3-4” diameter) and shooting through that from a distance of about 8" all the way down to about 4", the pictures are ordered from furthest to closest.

I did notice that the further away it was the more crisp the arrow heads were, and the closer I got the more crisp the arrow shafts were.

My question is, is this the obstruction issue that I am reading about, or is it just because I am way too close to the lens which seems to cause the "paddling of the arrow heads"(not sure if that’s what you call that)?

To be clear, it is not that I am noticing any visual performance issues with the diamond. It looks great to me from all angles and distances with the naked eye. However, this forum is evil in some ways, it seems like the more I read the more curious I get after the fact, :)

Thanks!

arrows.jpg
 

yssie

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eddiexp|1316290816|3019629 said:
I've done a bit of searching on the forum and to my understanding, shallow pavilion angles such as 40.6 deg might exhibit a bit of obstruction?

I believe my pavilion angle is 40.6 deg, so naturally I got curious and tried to take pictures to see for myself. The way I took them was by wrapping a piece of paper around the lens to make a tube (roughly 3-4” diameter) and shooting through that from a distance of about 8" all the way down to about 4", the pictures are ordered from furthest to closest.

I did notice that the further away it was the more crisp the arrow heads were, and the closer I got the more crisp the arrow shafts were.

My question is, is this the obstruction issue that I am reading about, or is it just because I am way too close to the lens which seems to cause the "paddling of the arrow heads"(not sure if that’s what you call that)?

To be clear, it is not that I am noticing any visual performance issues with the diamond. It looks great to me from all angles and distances with the naked eye. However, this forum is evil in some ways, it seems like the more I read the more curious I get after the fact, :)

Thanks!

"Obstruction" = facets reflecting what is directly in front of them - your face, your body, your hair and hat, or the camera - instead of intaking light from a slight angle (the brightness just above your head, or to the side of your ear).

Some amount of obstruction of the mains (the arrows going dark) is normal - only those facets reflect what is directly in front and perpendicular. As you get closer, more of the stone's facets will go dark when reflecting what's directly in front of them, because you're directly in front of more facets...

Over-obstruction is when too many facets reflect you from a reasonable viewing distance, because of the way they are angled. Exhibit A (my old stone):

WF-First%20(8)_0.jpg

Obviously this is a pretty odious case - it darkened considerably leaning over to admire it IRL too... not all stones are this severe - and if you're blonde you might well find you can tolerate more obstruction than if you're dark haired and dark-skinned, because at close-but-not-too-close distances facets are reflecting peaches and pale colours instead of dark browns and blacks.

Can't go by just the numbers on the GIA (averaged around eight sections of diamond, then rounded) - I use this example a lot: both these stones are reported as 33.5C/40.6P/58T. My stone above, same as earlier

AA.jpg
BB.jpg



In short - no, I don't think your stone shows any signs of over-obstruction.


ETA forgot linky http://www.screencast.com/users/Pricescope/folders/Default/media/64f27d25-9e00-4e29-96e3-e43ebed12a60
 

Karl_K

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40.6 if it is actually 40.6 is rarely a problem.
However 40.6 on a GIA report is averaged then rounded.
So it could be 40.5 where it starts to be more of an issue unless it has a very high crown.
The sign in a optically symmetrical stone of a too shallow pavilion is the arrow shafts stay dark considerably further away from the viewer than the arrow heads making the table dark.
Once it is determined it does then the next question is if its an issue at normal viewing distances which varies person to person.
Shallow crowns can sometimes have the same issue with the arrow heads(also paddling) but it is not as common.

The third picture your way over obstructing the diamond.
 

eddiexp

Rough_Rock
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41
Thanks everyone for the explanation, I guess what I failed to realize is that this issue is to be examined at normal viewing distances? If I am understanding this correctly, the reason the 3rd picture is the way it is, is because I was holding the lens so close to it?

For what it's worth, the specs on the stone are 35.5 crown/40.6 pavilion/55 table/62 depth.
 

KA

Shiny_Rock
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127
Sorry for the threadjack, but I was wondering a similar thing about my diamond. I have noticed that my diamond does go dark when I look at it in some lighting conditions, especially my living room and cloudy days outdoors. Is that normal for the following specs, or am I reading too much into it?

Depth: 62.5%
Table: 56%
Crown Angle: 35.5°
Crown Height: 16.0%
Pavilion Angle: 40.6°
Pavilion Depth: 43.0%
Star length: 50%
Lower Half: 80%

On the other hand, it has amazing colored light return in sunlight and in many other lighting conditions. Even so, it looks dark with flashes of colored light coming off it. I think that is beautiful, but I was wondering if the darkness is because it does have weird depth/obstruction issues. I have tried to understand the numbers and the science behind it by reading this forum, but I am still learning and very curious. I find the whole thing really fascinating.
 

Karl_K

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eddiexp|1316459665|3020831 said:
Thanks everyone for the explanation, I guess what I failed to realize is that this issue is to be examined at normal viewing distances? If I am understanding this correctly, the reason the 3rd picture is the way it is, is because I was holding the lens so close to it?

For what it's worth, the specs on the stone are 35.5 crown/40.6 pavilion/55 table/62 depth.
It is usually identified at closer range but if its not a problem at normal viewing distances and the owner doesn't mind it if they look real close then its not an issue. Every diamond will go dark if you obstruct it enough as you saw in your 3rd image.

a 35.5 crown works well with a 4.6 pavilion.
But if those are gia numbers that is a grain of salt because of the rounding.
 

Karl_K

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KA|1316460265|3020840 said:
Sorry for the threadjack, but I was wondering a similar thing about my diamond. I have noticed that my diamond does go dark when I look at it in some lighting conditions, especially my living room and cloudy days outdoors. Is that normal for the following specs, or am I reading too much into it?

Hard to tell without seeing what you are seeing and how far away you are viewing it.

Depth: 62.5%
Table: 56%
Crown Angle: 35.5°
Crown Height: 16.0%
Pavilion Angle: 40.6°
Pavilion Depth: 43.0%
Star length: 50%
Lower Half: 80%

Its a combo I would consider buying

On the other hand, it has amazing colored light return in sunlight and in many other lighting conditions. Even so, it looks dark with flashes of colored light coming off it.
That is normal in sunlight.
 

KA

Shiny_Rock
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In the shade outside or on cloudy days, it is pretty dark in the center even from arms length (2-3 feet) away if I look at it directly. In my apartment, it is dark from about a foot away. It is very rarely bright in the center (it is in my office and in some other lighting conditions, but usually the table is rather dark). But it has awesome fire. I was just wondering if there was some sort of trade-off between the darkness and the fire, or if it was possible to get both at the same time. If so, what sort of proportions should one look for to get the awesome fire of my diamond, but so it is also not dark. My understanding from reading these forums is that a high crown helps with fire, which mine is at 16%. If I understand it right, just from geometry, for a crown to be high, I imagine that the crown angle must be large, otherwise the table would become too small. How does this affect the pavilion angle so as to keep it all balanced? And this how does it all affect the brightness? It is quite cool that it is all geometry and physics, and I am really fascinated by it.
 

Karl_K

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KA|1316493016|3021166 said:
In the shade outside or on cloudy days, it is pretty dark in the center even from arms length (2-3 feet) away if I look at it directly. In my apartment, it is dark from about a foot away. It is very rarely bright in the center (it is in my office and in some other lighting conditions, but usually the table is rather dark). But it has awesome fire. I was just wondering if there was some sort of trade-off between the darkness and the fire, or if it was possible to get both at the same time. If so, what sort of proportions should one look for to get the awesome fire of my diamond, but so it is also not dark. My understanding from reading these forums is that a high crown helps with fire, which mine is at 16%. If I understand it right, just from geometry, for a crown to be high, I imagine that the crown angle must be large, otherwise the table would become too small. How does this affect the pavilion angle so as to keep it all balanced? And this how does it all affect the brightness? It is quite cool that it is all geometry and physics, and I am really fascinated by it.
You could try and find a bright red colored face mask or make a mask out of bright red paper.
Then put on the same color shirt.
if the darkness turns red then its obstruction.
 

eddiexp

Rough_Rock
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Karl_K said:
You could try and find a bright red colored face mask or make a mask out of bright red paper.
Then put on the same color shirt.
if the darkness turns red then its obstruction.
Now out of curiosity, wouldn't that cause just about any diamond to turn red, no matter how well cut or not?
 

Karl_K

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eddiexp|1316532509|3021338 said:
Karl_K said:
You could try and find a bright red colored face mask or make a mask out of bright red paper.
Then put on the same color shirt.
if the darkness turns red then its obstruction.
Now out of curiosity, wouldn't that cause just about any diamond to turn red, no matter how well cut or not?
Since all diamonds will react to obstruction yes, however the dark areas if they are caused by obstruction will be obvious, then one can play with distances to see if it is a problem.
If you getting large areas of deep darkness/red caused by obstruction at 1/2 and full arm length then I would consider it to be a problem.
 

eddiexp

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Karl_K|1316532975|3021355 said:
Since all diamonds will react to obstruction yes, however the dark areas if they are caused by obstruction will be obvious, then one can play with distances to see if it is a problem.
If you getting large areas of deep darkness/red caused by obstruction at 1/2 and full arm length then I would consider it to be a problem.
Do you mean that it would be a problem only if turns deep red within a reasonable viewing distance, or even if it turns pale red?
 

JulieN

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I think Karl is trying to say that all diamonds have obstruction, only when it is too dark in normal viewing is it a problem. So, YES, you are seeing obstruction. It looks like a very nice diamond.
 

Karl_K

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eddiexp|1316534119|3021382 said:
Karl_K|1316532975|3021355 said:
Since all diamonds will react to obstruction yes, however the dark areas if they are caused by obstruction will be obvious, then one can play with distances to see if it is a problem.
If you getting large areas of deep darkness/red caused by obstruction at 1/2 and full arm length then I would consider it to be a problem.
Do you mean that it would be a problem only if turns deep red within a reasonable viewing distance, or even if it turns pale red?
Its really hard to describe.
When the diamond is close the arrows will be red in this test.
As you move the diamond away they will get less red as the diamond can see more light coming from around the person.
Eventually the red will fade in a diamond without obstruction issues.
With one with issues it stays red further away into normal viewing distances.
If it does then you know the darkness reported is from obstruction.

If it doesn't then there is another cause.
Which one of is the center isn't dark. the outside is just brighter from low angle light sources(green in ASET).
The higher the crown the more pronounced this effect can be.
 

Karl_K

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Here is a virtual image extreme example.......

extreme-example.jpg
 

eddiexp

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Thanks a lot Karl, I think I finally understand what you have been trying to explain to me all along, I really appreciate your patience!!
 

Karl_K

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At 15 inches from the eye these virtual images show a diamond with obstruction issues and one without.
In the real world it would not be this symmetrical.
This one has issues:

obstructionIssue.jpg
 

Karl_K

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This one does not

NOobstructionIssue.jpg
 
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