School of Life Sciences

The Sussex Centre for Advanced Microscopy

Use of the Transmission Electron Microscope (TEM)

Astigmatism Correction

N.B. I usually carry out astigmatism correction on my sample but, if you prefer (and you might find it easier), there is a 'holey carbon' grid in the small petri dish by the TEM for you to use. Please replace this after use!

(a) Correcting astigmatism on your own sample

	Obtain a focused image (at the highest magnification at which you wish to acquire an image)
	Looking through the binocular, find a roughly spherical feature in your sample
	Pull down the cover of the panel at the lower left of the TEM and the 'OBJ STIGM' adjustment controls are immediately to your left
	Initially, flick the 'RESET' button downwards
	Now adjust the X and Y knobs one at a time until you achieve the sharpest image *all around* the feature
	Now re-focus the image if necessary and repeat the latter

(b) Correcting astigmatism using the holey carbon grid

	Obtain a focused image (at the highest magnification at which you wish to acquire an image)
	Looking through the binocular, find a small spherical hole in the film
	Now turn the 'Focus' knob clockwise from true to slightly over-focus and you will see a 'fringe' appear around the hole
	Pull down the cover of the panel at the lower left of the TEM and the 'OBJ STIGM' adjustment controls are immediately to your left
	Initially, flick the 'RESET' button downwards
	Now adjust the X and Y knobs so that the fringe is of uniform width all around the hole
	Gradually focus the image to true focus and the fringe will narrow further.
	If the fringe is now not of uniform width, repeat X and Y knob adjustments so that it is
	Focus the image to true focus and check that the edges of the hole are all sharp and there is no residual astigmatism (if there is, repeat the last two steps)