CTFFIND3 and SPIDER :astigmatism and astigmatism angle and tilt angle
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Hi
my questions are regarding conversion between the values from CTFFIND to the ones that I should use for TF C (CTF correction)in Spider,
first, if I understand correctly I should use the average of DFM1 and DFM2 as the defocus value
but then,
should I use the value of the following difference as astigmatism?
(DFM2 - DFM1)
or should I use (DFM2 - average)
according to TF C command in SPIDER the astigmatism is :
the defocus range due to axial astigmatism. In the example the value given indicates a defocus range of +/- 400A around the nominal value as the azimuth is varied.
The last sentence sound to me as the difference between the any extreme and the average ("nominal")
I am confused because there is another page in spider where the astigmatism definition reads: magnitude: the difference between the highest and lowest defocus.
Do you know either which one is correct? or how can I tested it?
Regarding the astigmatism angle
If (DFM1 - DFM2) > 0 , the angle is angle_spider = angle_ctffind + 45.0
If (DFM1 - DFM2) < 0 , the angle is angle_spider = angle_ctffind + 135.0
is that the correct conversion?
Finally what is the correction between the tilt angle from CTFTILT and the one used in SPIDER?
thanks a lot in advance,