[3dem] RE: electron diffraction

De Carlo, Sacha Sacha.DeCarlo at fei.com
Fri Aug 23 08:17:47 PDT 2013


Because Philip wrote "and record an image of it" I got confused. Anyway, from the FEI TF 20 literature a Twin lens has a focal length of 2.7 mm, and the angle for a 0.1nm spacing is more or less 40 mrad for a twin lens nomogram @ 200 kV (see attached). So, now you can calculate that distance :)

Best regards,
Sacha



Sacha De Carlo, PhD | Sr. Research Scientist

FEI
Achtseweg Noord 5, 5651 GG Eindhoven, The Netherlands
T +31 6 10810795 E Sacha.DeCarlo[at]fei.com  fei.com

Explore. Discover. Resolve.


-----Original Message-----
From: 3dem-bounces at ncmir.ucsd.edu [mailto:3dem-bounces at ncmir.ucsd.edu] On Behalf Of Terje Dokland
Sent: Friday, August 23, 2013 16:47
To: De Carlo, Sacha
Cc: 3dem at ncmir.ucsd.edu
Subject: Re: [3dem] RE: electron diffraction

As far as I understand Philips question, he is referring to the distance from the optical axis in the back focal plane of the objective lens, thus the projection lenses should not come into the picture.  But it does depend on the focal length of the objective lens, which is ... 1 or 2 mm or so? You can then use Bragg's law to calculate the angle and from there get the distance.  

On Aug 23, 2013, at 9:36 AM, De Carlo, Sacha wrote:

> Sorry Philip,
> 
> A TEM has a projection lens system, thus if you do not specify the camera length, one cannot answer your question.
> 
> Best regards,
> Sacha
> 
> 
> 
> Sacha De Carlo, PhD | Sr. Research Scientist
> 
> FEI
> Achtseweg Noord 5, 5651 GG Eindhoven, The Netherlands T +31 6 10810795 
> E Sacha.DeCarlo[at]fei.com  fei.com
> 
> Explore. Discover. Resolve.
> 
> -----Original Message-----
> From: 3dem-bounces at ncmir.ucsd.edu [mailto:3dem-bounces at ncmir.ucsd.edu] 
> On Behalf Of Philip Köck
> Sent: Friday, August 23, 2013 16:18
> To: microscopy at microscopy.com; 3dem at ncmir.ucsd.edu
> Subject: [3dem] electron diffraction
> 
> Hi everybody,
> 
> I'm looking for a simple estimation that I can't find in any textbook I've looked in, nor on the internet.
> I wonder if anybody can help me.
> 
> If I put a diffraction grating with spacing 1 Angstrom into the specimen holder and record an image of it.
> At what distance from the optical axis will the corresponding diffraction spot (for 1 Angstrom spacing) appear in the back focal plane of the objective lens.
> 
> Assume a TEM with 200 kV and a twin lens, one that's typically used for protein structure determination.
> 
> Thanks,
> 
> Philip
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