[3dem] FEI LowDose over-exposing film?

[Bullitt Esther]

Hi,

The way that we check for this problem is by the curvature of the film  
-- the side with the emulsion is slightly concave, so if you find  
films where the curvature is wrong-way-round (that is, convex with the  
notch in the upper right corner), throw them out before putting them  
into the cassette.

-Ester
On May 14, 2012, at 7:32 PM, Gabriel Lander wrote:

> Thanks to everyone for your responses,
> John Rubinstein brought up an issue that had not crossed our minds -  
> as it turns out, some (but not all) of the films in our batches of  
> SO-163 have the emulsion on the WRONG side relative to the notch.  
> With the emulsion side down, the backscattered electrons from the  
> metal film holders are resulting in this over-exposed appearance.
> We are using film purchased from Ted Pella in late 2010/early 2011.  
> If anyone else has noticed this issue and remembers what batches of  
> film had this problem, please let me know.
> There are two ways to test if the emulsion is on the correct side:
> One way is to try scratching off the emulsion with a razor after  
> it's been developed. It should scratch off easily and be clear  
> underneath if you are scratching the emulsion side.
> The other way (this is how we plan on checking that each film is  
> emulsion side up when loading plates in the future) is to gently  
> slide a gloved finger along a corner of the film. The plastic side  
> will squeak, while the emulsion side does not.
> Thanks for the advice John,
> -gabe & greg
>
>
> On May 14, 2012, at 3:46 PM, Wim Hagen wrote:
>
>>
>> On May 14, 2012, at 10:55 PM, 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_______________________________________________
>>> 3dem mailing list
>>> 3dem at ncmir.ucsd.edu
>>> https://mail.ncmir.ucsd.edu/mailman/listinfo/3dem
>>
>
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---
Esther Bullitt, Ph.D.
Dept. of Physiology & Biophysics
Boston University School of Medicine
700 Albany Street, Room W302
Boston, MA  02118-2526

Email:      bullitt at bu.edu
Telephone:  617-638-5037
Facsimile:  617-638-4041
http://www.bumc.bu.edu/phys-biophys/faculty/bullitt