In article <3c73c919$1@news.povray.org>, "Greg M. Johnson" <gregj:-)
565### [at] aolcom> says...
> "John Bradshaw" <joh### [at] nospamhotmailcom> wrote in message
> news:3c72e14a@news.povray.org...
> > Also, would like comments on the scanning electron microscope effect. It's
> > not quite where I want it to be, but getting there. (see previous post SEM
> > texture)
> 
> I reviewed that teapot image with an SEM expert and these were our comments
> there, many of which would apply to your image...
> 
> An SEM has a detector off to one side.  So in effect surfaces which face the
> detector will be brighter (higher collection yield) than those which face
> away. Your image gives the feeling that the detector is in the center of the
> sample, if there's not multiple light sources.
> 
> The image rightly shows how surfaces which are normal to the "camera" ie.,
> incident beam are brighter. Again, the secondary electron detection yield is
> higher as well on these surfaces.   This is a good *pigment*, FWIW.
> 
> It looks, however, as if it were stainless steel, with very little beam
> penetration into the sample.  Contrast this with "record 22 of 700; Title:
> 'Blood cell' " in the image gallery at.
> http://www.uq.edu.au/nanoworld/images_1.html
> 
> For an organic, low-atomic-number sample, I'd expect there to be some
> translucency, almost a 'media' effect, as in that blood cell image
> 
> The "etched steel" effect in your texture normal is a bit troublesome.  Here
> the concern is not so much with SEM physics but with the intuitive feel of
> cells: things should be more round, even like "Lung surface: image 39 of
> 700" at that gallery.
> 
> 
> _________
> Greg M. Johnson
> 10-yr SEM user
> 
> 
> 
It is true that a SEM has a detector somewhere to one side, but this 
doesn't mean in any way that the resulting image can be compared to an 
object illuminated by the detector as the light source! 

The secondary electrons that make up the SEM image can very well 
originate at the opposite side of the object. These electrons are low 
energy particles and travel slowly, so their paths are easily bent. 

And what i really miss in these images is the so-called "Kanten Effekt" 
characteristic to SEM images. In short this means that thin and sharp 
parts of the object show up much lighter than the more even and smooth 
parts.

In general the image looks a bit like an SEM image...  :))
-- 
Regards, 
Sander (who spent half his working life behind an SEM!)

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