[3DEM] Jamming of FEI low-noise film holders

[John Rubinstein, U of T]

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Dear 3DEM list users,

With our new FEI F20 microscope we selected low-noise film holders for 
our plate camera system.  These holders do not have a metal back and 
consequently do not produce backscattered electrons that can fog the 
film (this topic has been discussed previously on the 3DEM mailing 
list).  The advantage of these holders seems well established at 300 keV 
but I have not seen measurements of film fogging by backscattered 
electrons at 200 keV.  Thinking there was no disadvantage in using these 
film holders, I selected them for our 200 keV instrument.  There was 
some delay in getting the low-noise film holders and in the meantime we 
borrowed conventional holders and cassettes without incident.

When we started using the low-noise film holders, we ran into some problems:

1) The low-noise film holders require different camera cassettes (with 
springs set for the weight of the film holders).  While the old FEI 
camera cassettes dropped right into position to engage film inserting 
rod, the new cassettes are a much more snug fit and needed to be pushed 
down into the microscope to engage the connection.  This difference led 
to a couple of plate jams before we learned that the cassettes need to 
be pushed firmly into the microscope.

2) Film holders occasionally jam in the top half of the cassette (in our 
local terminology, the 'donator' part of the cassette).  As the stack of 
plates is lowered (by gravity) during a session on the microscope, one 
plate will occasionally jam in the donator and all subsequent 
'exposures' are taken without film.  Our engineer has looked at the 
cassette and can not see why these jams occur.

Has anybody else experienced this second problem?  Has anybody 
determined the reason why these jams occur or found a solution for it?

Any information would be greatly appreciated.

Best regards,
John


-- 
John Rubinstein
Molecular Structure and Function Program
The Hospital for Sick Children
555 University Avenue, Rm. 3330
Toronto, ON
Canada
M5G 1X8
Tel: (+001) 416-813-7255
Fax: (+001) 416-813-5022
www.sickkids.ca
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