[3dem] FEI LowDose over-exposing film?

[Bob Grassucci]

Hi All,
The drained battery would explain things if they were using auto 
exposure rather than manually setting the exposure time which is what 
low dose does.  Another time the auto-exposure flakes out is when the 
wire leading from the fluorescent screen gets frayed and/or broken 
because this is what carries the current to the ammeter that determines 
the current hitting the screen.  The battery is part of that circuit.
Bob

On 5/16/2012 8:51 AM, werner kuehlbrandt wrote:
> Hi Gabe,
>
> Can I add another aspect to the discussion of over/under-exposed films on your (non-Krios) Titan?  We were puzzled by a similar effect with our Falcon CMOS camera (so no film involved) on our new Titan Krios, where images were randomly over- or underexposed.  After about three months we discovered that the electron dose meter returned random readings.  Apparently the battery was empty. No-one at FEI had noticed or bothered to check. It would be interesting to know if this explains your problem.
>
> Werner
>
>
> ************************************************
>
> Werner Kühlbrandt
> Max Planck Institute of Biophysics
> Max von Laue-Str. 3
> 60438 Frankfurt am Main, Germany
>
> Tel  +49-69-6303 3000
> Fax +49-69-6303 3002
>
> ************************************************
>
>
> On 14 May 2012, at 22:55, Gabriel Lander wrote:
>
>> We are encountering a serious issue collecting film using our Titan (not Krios) with the Tecnai low dose kit. Certain images appear to be severely over-exposed, while others appear to be normal, high quality, low-dose exposures.  Here are two examples of images collected during the same session, from the same cartridge of film, one right after another.
>> http://www.ocf.berkeley.edu/~glander/pic/img001_FFTs.jpg
>>
>> The top image is of good quality, exhibits Thon rings to around 5Å, while the one below it has no discernible Thon rings, and is overall much darker in appearance.  We can only assume that this is due to overexposure of the film to the beam, but not to the extent that we see obvious radiation damage to the sample (no bubbling). We've monitored the blanker during the exposures, and according to all the readouts in the Tecnai software it is working properly. The film is inserted into the microscope and waits for 10 seconds before exposing the film. Multiple users are having this issue.
>> Also, we never seem to have this problem when collecting CCD images.
>> If anyone has ever experienced this issue or has any insights into what is happening, we would be most appreciative.
>> - Gabe Lander&  Greg Alushin, Nogales Lab_______________________________________________
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>> 3dem at ncmir.ucsd.edu
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