What is the technical explanation behind good resolution at high magnification works very well at low magnification too in SEM, but not in TEM??
Hi Pranay.
I believe in some cases you do actually do this with the TEM also, however with the TEM as the magnification is increased it will actually switch over to a different lens system at some point. So unless the TEM beam has been very well aligned and set up, you will have to fine tune the focus again after the lens switching.
Hi Pranay.
I believe in some cases you do actually do this with the TEM also, however with the TEM as the magnification is increased it will actually switch over to a different lens system at some point. So unless the TEM beam has been very well aligned and set up, you will have to fine tune the focus again after the lens switching.
Dear Gandharapu
In both SEM and TEM, to obtain optimum focusing, you need to focus at higher magnification, and then reduce the magnification to the desired value. But I think finding the image at higher magnification in TEM is so difficult (without step by step increasing the magnification). So you need to increase the magnification step by step, and focus at every step. When you reached at desired magnification and focused on the image, you need to focus at higher magnification, focus on it and then reduce the magnification to the desired value.
Like Phil already mentioned, there are few different lens settings used in TEM, each for certain magnification range. For JEOL you'll have low-mag mode (objective mini lens is used to form an image on the selector aperture) for range of ~150-3000× , then in normal mode the ranges are as follows: 3k-40k, 50k-120k, 130k - 800k, 800k-1.2M. With each setting also the excitation of the lenses is different, whereas some are switched on or off. There is no TEM with "continuous" magnification from few-1000 mag. to million and more...
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