Among other things, Darren New saw fit to write:

> Except that back-scattering off the atmosphere provides a much larger
> area of light. Contrast the sky with the moon vs the sun, both of which
> are about the same size. It's difficult to even look close to the sun on
> a clear day.

So similar are their sizes, indeed, that we can experience both total and
anular eclipses... I find that amazing.

-- 
light_source{9+9*x,1}camera{orthographic look_at(1-y)/4angle 30location
9/4-z*4}light_source{-9*z,1}union{box{.9-z.1+x clipped_by{plane{2+y-4*x
0}}}box{z-y-.1.1+z}box{-.1.1+x}box{.1z-.1}pigment{rgb<.8.2,1>}}//Jellby

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Tek wrote:
> The reason it's hard to look at the sun is it's brighter than the moon. 

Right. I meant, it's difficult to even look within about 5 degrees of 
the sun. I think the disk that's projecting light is a lot larger than 
0.5%. Of course, in POV you have to do things somewhat differently to 
get the same effect.

-- 
   Darren New / San Diego, CA, USA (PST)
     His kernel fu is strong.
     He studied at the Shao Linux Temple.

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"Darren New" <dne### [at] sanrrcom> wrote in message 
news:46225066$1@news.povray.org...
> Tek wrote:
>> The reason it's hard to look at the sun is it's brighter than the moon.
>
> Right. I meant, it's difficult to even look within about 5 degrees of the 
> sun. I think the disk that's projecting light is a lot larger than 0.5%. 
> Of course, in POV you have to do things somewhat differently to get the 
> same effect.

I'm not sure I follow. The sun's disk is 5 degrees in radius from earth, the 
brightness of it doesn't make it any larger (like I say you can use a filter 
to see that all the suns direct light comes from that disk). Povray can 
simulate a circular area light of the same angle and brightness. The only 
reason I'm using a larger one is because I'm taking some artistic license, 
in truth a small ball on a table would have an almost perfectly sharp 
shadow.

-- 
Tek
http://evilsuperbrain.com

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Tek wrote:

> I'm not sure I follow. The sun's disk is 5 degrees in radius from earth, the 
> brightness of it doesn't make it any larger

The sun might appear as a larger apparent "disk" of brightness
due to directional scattering in the atmosphere. In fact, compare
the two attached WIP images. The sun really appears quite small
in the version without scattering (and that was already 4 times
larger than physically correct).

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Attachments:
Download 'beach-320.jpg' (10 KB) Download 'beach-scatter-320.jpg' (10 KB)

Preview of image 'beach-320.jpg'

Preview of image 'beach-scatter-320.jpg'

Tek wrote:
> Any suggestions on how I can make this more real?

I think my biggest problem is the reflection in the sphere is perfectly 
focused, but then so is the sphere itself. With a short focal length, 
only one should be in focus as you're either focused the (very short) 
distance to the sphere, or the (very long) distance to the trees behind you.

Cheers!
Rick Measham

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Actually because it's a curved reflective surface the reflection will tend 
to appear very sharp. What you said is certainly true of flat mirrors but 
the distortion in a convex mirror makes the image appear sharp (because the 
image appears much smaller than in a flat mirror, so the blur is relatively 
unnoticeable).

Here's a great example google image search found: 
http://colourblind.ca/images/20050807233841_shiny_sphere.jpg
You'll notice the background is blurry but both the ball & reflection appear 
sharp.

In any case, I'm using focal blur when rendering now, and pov's simulation 
is good enough to accurately apply focal blur to reflections.

-- 
Tek
http://evilsuperbrain.com

"Rick Measham" <ric### [at] diespammerdieisitenetau> wrote in message 
news:462### [at] diespammerdieisitenetau...
> Tek wrote:
>> Any suggestions on how I can make this more real?
>
> I think my biggest problem is the reflection in the sphere is perfectly 
> focused, but then so is the sphere itself. With a short focal length, only 
> one should be in focus as you're either focused the (very short) distance 
> to the sphere, or the (very long) distance to the trees behind you.
>
> Cheers!
> Rick Measham

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"Jellby" <me### [at] privacynet> schreef in bericht 
news:nkc### [at] badulaqueunexes...
> Among other things, Darren New saw fit to write:
>
>> Except that back-scattering off the atmosphere provides a much larger
>> area of light. Contrast the sky with the moon vs the sun, both of which
>> are about the same size. It's difficult to even look close to the sun on
>> a clear day.
>
> So similar are their sizes, indeed, that we can experience both total and
> anular eclipses... I find that amazing.
>

It is one of those random chances that nature offers us  :-)
If I am correct, we are also at the right time too, while the Moon is slowly 
receding. So there might come a moment when only anular eclipses will happen 
I believe. The astronomers among us can tell.

Thomas

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Tek wrote:
> Actually because it's a curved reflective surface the reflection will tend 
> to appear very sharp. What you said is certainly true of flat mirrors but 
> the distortion in a convex mirror makes the image appear sharp (because the 
> image appears much smaller than in a flat mirror, so the blur is relatively 
> unnoticeable).


Bah! I sat here thinking about it before I posted that. Decided I was 
right and hit the "Send" button. Now I regret it. Of course you're right.

Cheers!
Rick Measham

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Tek nous apporta ses lumieres en ce 15-04-2007 13:09:
> "Darren New" <dne### [at] sanrrcom> wrote in message 
> news:46225066$1@news.povray.org...
>> Tek wrote:
>>> The reason it's hard to look at the sun is it's brighter than the moon.
>> Right. I meant, it's difficult to even look within about 5 degrees of the 
>> sun. I think the disk that's projecting light is a lot larger than 0.5%. 
>> Of course, in POV you have to do things somewhat differently to get the 
>> same effect.

> I'm not sure I follow. The sun's disk is 5 degrees in radius from earth, the 
> brightness of it doesn't make it any larger (like I say you can use a filter 
> to see that all the suns direct light comes from that disk). Povray can 
> simulate a circular area light of the same angle and brightness. The only 
> reason I'm using a larger one is because I'm taking some artistic license, 
> in truth a small ball on a table would have an almost perfectly sharp 
> shadow.

The Sun's real apparent radius is 0.5 degrees. It's extreem brightness does make 
it look much larger, as even with a very small amount of scettering, that 
scattered light is still blinding.

-- 
Alain
-------------------------------------------------
I can read your mind, and you should be ashamed of yourself.

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Nonetheless we're not discussing how it looks, rather how to simulate it 
with an area_light. The majority of the light comes from the sun itself, not 
the scattering (since if you look at the sun through a filter you can see 
it's disk clearly), hence I'm using a lightsource to simulate the sun and 
radiosity from the HDR dome to simulate scattered light from the sky.

-- 
Tek
http://evilsuperbrain.com

"Alain" <ele### [at] netscapenet> wrote in message 
news:4623e6d1$1@news.povray.org...
> Tek nous apporta ses lumieres en ce 15-04-2007 13:09:
>> "Darren New" <dne### [at] sanrrcom> wrote in message 
>> news:46225066$1@news.povray.org...
>>> Tek wrote:
>>>> The reason it's hard to look at the sun is it's brighter than the moon.
>>> Right. I meant, it's difficult to even look within about 5 degrees of 
>>> the sun. I think the disk that's projecting light is a lot larger than 
>>> 0.5%. Of course, in POV you have to do things somewhat differently to 
>>> get the same effect.
>
>> I'm not sure I follow. The sun's disk is 5 degrees in radius from earth, 
>> the brightness of it doesn't make it any larger (like I say you can use a 
>> filter to see that all the suns direct light comes from that disk). 
>> Povray can simulate a circular area light of the same angle and 
>> brightness. The only reason I'm using a larger one is because I'm taking 
>> some artistic license, in truth a small ball on a table would have an 
>> almost perfectly sharp shadow.
>
> The Sun's real apparent radius is 0.5 degrees. It's extreem brightness 
> does make it look much larger, as even with a very small amount of 
> scettering, that scattered light is still blinding.
>
> -- 
> Alain
> -------------------------------------------------
> I can read your mind, and you should be ashamed of yourself.

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