Backlash in image shift movement?
Added by Anchi Cheng over 13 years ago
From Nicolas Coudray
I have another question, this time concerning the type of movement before acquisition:
I noticed that if I choose "image shift" (for instance, or "image beam shift"), then, the image shift is indeed done, but, after this and before the acquisition of the image, it also moves the stage (looks like the backlash correction), even though the movement is not "stage position". Is it normal? Is there a way to avoid moving the stage when "image shift" or "image beam shift" movement is chosen for a given magnification?
Thanks in advance...
Replies (2)
RE: Backlash in image shift movement? - Added by Anchi Cheng over 13 years ago
In Leginon, we went back and forth and decided a long time ago that the stage position could not be assumed to be at where it needed to be when image-beam shift was applied. For example, the user might have paused Leginon, and moved the stage somewhere else to do something themselves before continuing with acquiring an image that used "image shift" or "image beam shift". Therefore, at a lower level, the stage position is still set even if you use "image shift" or "image beam shift".
On the pyscope side, we avoid the backlash problem you mentioned in this situation in tecnai.py by defining a minimal movement below which value the stage would not go through the backlash routine, and therefore not moved if it is really there.
Looking in the code, your jeol1230.py do not use such algorithm to avoid the extra move when it is already there. You should compare setStagePosition function in tecnai.py and jeol1230.py and add such backlash prevention in your code, then it will not do backlash "correction" when it does not need to move.
Hope our reasoning make sense to you.
Anchi
RE: Backlash in image shift movement? - Added by Nicolas Coudray over 13 years ago
Yes, it makes sense, thank you for the answer...
Nicolas