recording data on plate
Added by Anonymous over 18 years ago
Hi, we have collected succesfully some data on plates. However, the the negatives seem to be underexposed. I only changed the exposure preset to "use plate", the dose was similar to what we normally use for manual data collection. The exposure time was set to 1 sec in the exposure preset, low dose was off. Are there any other parameters, which can be changed by leginon, e.g. plate delay time, pre-exposure time, etc. Does leginon also use the CCD exposure time from the exposure preset for plates?
Thorsten
Replies (1)
- Added by Jim Pulokas over 18 years ago
Leginon will use the same exposure time with the film option turned on or off. The film exposure function is actually doing a CCD exposure. The sequence is sort of like this:
- insert plate
- take CCD exposure
- take out plate
The reason for doing a CCD exposure is just to get the shutter open and closed with the right timing. Since the plate is inserted, the CCD image comes out all dark and we just throw it away. There are no other options for controlling the shutter timing in Leginon, but depending on which camera you have, there may be options somewhere else. For instance, we have a Tietz camera that can be configured to have a pre-exposure, but this is not set up in Leginon, it has it's own configuration tool. Likewise, there may be some configuration options in Digital Micrograph that alter the behavior of the Gatan camera.
In any case, the exposure time set up in your exposure preset should produce the exact same amount of exposure on either film or CCD. You can usually confirm that the proper exposure time is being used by watching the lights on the camera control box turn on and off during an exposure. When doing this with film, it is also important that the film is completely inserted before the exposure starts, and that the exposure is done before the film is removed. This can be verified by listening for the plate to go in and watching the shutter lights. This has always been working for us, but let us know if something seems strange. There could be some variation in how different systems behave.
When comparing a film exposed with Leginon to a film exposed manually with the Tecnai exposure button, are all other parameters the same (spot size, intensity, defocus, magnification, etc.)? To be sure, you can load your preset into the Tecnai low dose exposure mode and then take a film exposure with both Leginon and manually using the expose button. Just remember that when using Leginon, the exposure time is taken from the preset, but when doing a manual film exposure on Tecnai, you have to enter in the exposure time into the Tecnai interface (which you will want to be the same as in Leginon).
Jim