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Cyclops



Joined: 05 Aug 2006
Posts: 2968
Location: North East of England

PostPosted: Wed Oct 11, 2006 1:49 pm    Post subject: For Charles Krebs Reply with quote

Hi Charles,I was just perusing your website and I came across an item in Gallery 2, and I was just wondering what it is?
Is it an alga or a cilliate, or both? I notice they seem to form colonies, but not quite the same as Volvox.

http://krebsmicro.com/webgal2/File077.jpg

Excellent site by the way!
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Charles Krebs



Joined: 01 Aug 2006
Posts: 5803
Location: Issaquah, WA USA

PostPosted: Thu Oct 12, 2006 7:46 pm    Post subject: Reply with quote

Larry,

It's a Synura colony. This page has some pretty good info.

http://silicasecchidisk.conncoll.edu/LucidKeys/Carolina_Key/html/Synura_Main.html
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Cyclops



Joined: 05 Aug 2006
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Location: North East of England

PostPosted: Fri Oct 13, 2006 3:25 pm    Post subject: Reply with quote

Thanks Charles.
Some neat pics on that site, but what really amazed me were the pics taken with a SEM. How on earth do they coat something so small with gold!
Think
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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Fri Oct 13, 2006 5:28 pm    Post subject: Reply with quote

Cyclops wrote:
How on earth do they coat something so small with gold!

One method is a vacuum deposition process called "sputtering". See http://en.wikipedia.org/wiki/Sputtering.

--Rik
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Cyclops



Joined: 05 Aug 2006
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Location: North East of England

PostPosted: Sat Oct 14, 2006 6:48 am    Post subject: Reply with quote

Cool,if rather heavy, stuff!
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rjlittlefield
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PostPosted: Sat Oct 14, 2006 9:19 am    Post subject: Reply with quote

The newer ESEM's (Environmental Scanning Electron Microscopes) don't require coating at all, even for non-conductive specimens. See http://www.calce.umd.edu/general/Facilities/ESEM.pdf for explanation.

There are also other coating materials with advantages over gold. One interesting coating is "amorphous carbon", which is optically transparent like diamond. As with the gold, it's laid down one atom at a time using one or another thin film coating process like sputtering or chemical vapor deposition.

--Rik
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Cyclops



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PostPosted: Sat Oct 14, 2006 9:36 am    Post subject: Reply with quote

I know all too well that the limit for an optical microscope is about 2000X(mine goes to 1,250) but why is this so?
Would a higher M require too small an aperture in the objective to form an image, or would the objective need to be too close to the subject to be practical?
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Charles Krebs



Joined: 01 Aug 2006
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Location: Issaquah, WA USA

PostPosted: Sat Oct 14, 2006 10:51 am    Post subject: Reply with quote

It has to do with diffraction and the wave nature of light. I'll let Rik provide the math Wink

Check out:
http://www.microscopyu.com/articles/formulas/formulasresolution.html
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rjlittlefield
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PostPosted: Sat Oct 14, 2006 11:22 am    Post subject: Reply with quote

Charles Krebs wrote:
I'll let Rik provide the math Wink

There's a time for math. This isn't it. Very Happy

Cyclops, a handy analogy is to think about determining the shape of something by feeling it with a stylus.

If the stylus has a small tip, you can detect fine detail; if the tip is large, you can't.

Using visible light is like using a stylus with a tip that's at least 0.2 micron radius, and more like 0.4 microns with most setups.

Magnify that by 1000X, and you're talking about a stylus whose tip appears to be 0.2-0.4 mm radius. That's already larger than the detail you can see by eye at normal viewing distance, so increasing the magnification any farther just gets you a bigger blur, no more detail.

Pushing the analogy even farther, using light to image a virus whose diameter is 20 nanometers = 0.020 microns, is like trying to determine the shape of someone's hand by feeling it with a beachball. You can maybe tell it's there, but the shape is a mystery.

Electron microscopes have a lot higher maximum magnification because they're effectively using a lot smaller stylus.

--Rik
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Cyclops



Joined: 05 Aug 2006
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Location: North East of England

PostPosted: Sat Oct 14, 2006 11:30 am    Post subject: Reply with quote

Yea I get it now. Its to do with the size of the waves of light and resolving power. Its kinda like a film camera where the film is quite grainy. If the film grains are bigger than fine detail in the object being photographed then that fine detail cannot be resolved.
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