Stigmator - Revision history

Lbochtler: added some info on alignment

2026-02-15T00:17:52Z

added some info on alignment

Lbochtler: added a note

2026-02-15T00:11:00Z

added a note

Lbochtler: added diagrams of the quadrupole and double quadrupole stigmator, added more description in the double quadrupole lens description.

2026-02-15T00:06:11Z

added diagrams of the quadrupole and double quadrupole stigmator, added more description in the double quadrupole lens description.

Lbochtler at 20:20, 14 February 2026

2026-02-14T20:20:38Z

Lbochtler: added quadrupole Stigmator picture.

2026-02-14T20:17:24Z

added quadrupole Stigmator picture.

Lbochtler: added pictures of the 4 polpiece iron Stigmator and Rang electrostatic Stigmator

2026-02-14T19:56:25Z

added pictures of the 4 polpiece iron Stigmator and Rang electrostatic Stigmator

Lbochtler: added text about the basic types of stigmator

2026-02-14T19:32:22Z

added text about the basic types of stigmator

Lbochtler: Created stub for Stigmator

2026-02-14T19:12:03Z

Created stub for Stigmator

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A Stigmator is a variable strength Cylinder lens used to correct Astigmatism in Electron Microscopes, proposed by [[O. Scherzer| Otto Scherzer]] and first implemented in the [[EM8 | AEG / Zeiss EM8]] by [[O. Rang]] in 1948. This device greatly increased the resolving power of the Electron Microscope and reduced the necessity for frequent cleaning of the optics. The device corrected the inevitable asymmetric shape of the lens field caused by manufacturing the optics, and the charging based parasitic lenses caused by contamination buildup in the optics and beampipes. There are many ways a Stigmator can be created, these include Magnetic and Electric types, the first practical Stigmator, as designed by Rang was Electrostatic.

At the time of its first implementation, the EM8 was the highest resolution Electron Microscope world wide, the Stigmator came standard in the subsequent EM8 versions sold. Microscopes like the [[ÜM 100]] from Siemens where retrofitted with Magnetic Stigmators of the Helical Moving Iron type, and where standard in later Iteration of the ÜM 100. Ever since, every Electron Microscope came standard with at least 1 Stigmator for the Objective Lens.

The Stigmator field has polar coordinates, and controls for such where historically in such, these being Amplitude and Angle. This was historically done by use of a [[Sin / Cos Potentiometer]] for the angle, and a linear potentiometer for the amplitude. Other machines like the [[EM 10 | Zeiss EM 10]] featured 2 linear potentiometers controlling the strength of each Quadrupole separately. Most modern machines feature the XY implementation of the Stigmator control.

= Types =

== Electrostatic Stigmator ==
Used in [[EM8 | AEG / Zeiss EM8]].

== Moving Iron Stigmator ==
=== 2 Pol Piece ===
Example [[ÜM 100 | Siemens ÜM 100]] (Objective), [[Elmiskop I | Siemens Elmiskop I]] (Condenser)
=== 4 Pol Piece ===
Example [[Elmiskop I | Siemens Elmiskop I]]
== Quadrupole Stigmator ==
In a Quadrupole Stigmator, a single Quadrupole lens is used as the correcting element, this lens has 2 north and 2 south poles each opposing one another and oriented at 90° to each other, forming a cross shaped structure. This lens Focuses in 1 axis, and defocuses in the 90° opposing axis, thus allowing correction of astigmatism. Since this Aberration is rarely in the exact axis of the Quadrupole, means of rotating this lens are needed. Machines with such a Stigmator have a mechanical Angle control, usually allowing 90° of Rotation, and an electrical control for the field strength. A notable Example of this Stigmator type is the [[BS 242 | Tesla BS 242]].
== Dual Quadrupole Stigmator ==
Example [[EM 10 | Zeiss EM 10]]

@@ Line 27: / Line 27: @@
 In a Quadrupole Stigmator, a single Quadrupole lens is used as the correcting element, this lens has 2 north and 2 south poles each opposing one another and oriented at 90° to each other, forming a cross shaped structure. This lens Focuses in 1 axis, and defocuses in the 90° opposing axis, thus allowing correction of astigmatism. Since this Aberration is rarely in the exact axis of the Quadrupole, means of rotating this lens are needed. Machines with such a Stigmator have a mechanical Angle control, usually allowing 90° of Rotation, and an electrical control for the field strength. A notable Example of this Stigmator type is the [[BS 242 | Tesla BS 242]].
 == Dual Quadrupole Stigmator ==
-[[File:Double Quadropole Stigmator.png|thumb| Principle Diagram of a Double Quadrupole Stigmator, featuring 2 sets of Quadrupole Lenses offset by 45° to one another.]]
+[[File:Double Quadropole Stigmator.png|thumb| Principle Diagram of a Double Quadrupole Stigmator, featuring 2 sets of Quadrupole Lenses offset by 45° to one another. Quadrupole 1 is shown in grey, and Quadrupole 2 in Green. The coils of the same color are connected together electrically and driven by their own power supply.]]
 In the Double Quadrupole Stigmator, 2 Quadrupoles offset by 45° to one another are used to create an electrically rotatable and amplitude adjustable Cylinder lens. This setup is not to be confused with an [[Octopole]] lens which also features 8 pole Pieces. In this setup the Quadrupole field is formed by having 2 sets of poles at various ratios of power next to one another. Thus allowing full 360° rotation of the field. These 2 interleaved Quadrupoles are controlled either by a [[Sin / Cos Potentiometer]] for Angle, and a Linear Potentiometer for Amplitude, or by 2 Linear potentiometers for each Quadrupole. The Angle is produced by energizing the quadrupoles proportional to move the field lines into an orientation more akin to a single quadrupole at an intermediate angle between the 2 quadrupoles, then to continue rotation, the polarity is reversed progressive moving the field further in angle by another 45°.
 Example [[EM 10 | Zeiss EM 10]]
 = notes =
 The diagrams of the quadrupole and double quadrupole have magnetic monopoles shown, this was intended as a visualizing aid, normally dipoles are present. This is partially an oversight on the part of the artist, and will likely be corrected. Think of the poles as bar magnets with the opposing magnetic pole being opposite the ones pointing inside.

← Older revision		Revision as of 00:11, 15 February 2026
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	In the Double Quadrupole Stigmator, 2 Quadrupoles offset by 45° to one another are used to create an electrically rotatable and amplitude adjustable Cylinder lens. This setup is not to be confused with an [[Octopole]] lens which also features 8 pole Pieces. In this setup the Quadrupole field is formed by having 2 sets of poles at various ratios of power next to one another. Thus allowing full 360° rotation of the field. These 2 interleaved Quadrupoles are controlled either by a [[Sin / Cos Potentiometer]] for Angle, and a Linear Potentiometer for Amplitude, or by 2 Linear potentiometers for each Quadrupole. The Angle is produced by energizing the quadrupoles proportional to move the field lines into an orientation more akin to a single quadrupole at an intermediate angle between the 2 quadrupoles, then to continue rotation, the polarity is reversed progressive moving the field further in angle by another 45°.		In the Double Quadrupole Stigmator, 2 Quadrupoles offset by 45° to one another are used to create an electrically rotatable and amplitude adjustable Cylinder lens. This setup is not to be confused with an [[Octopole]] lens which also features 8 pole Pieces. In this setup the Quadrupole field is formed by having 2 sets of poles at various ratios of power next to one another. Thus allowing full 360° rotation of the field. These 2 interleaved Quadrupoles are controlled either by a [[Sin / Cos Potentiometer]] for Angle, and a Linear Potentiometer for Amplitude, or by 2 Linear potentiometers for each Quadrupole. The Angle is produced by energizing the quadrupoles proportional to move the field lines into an orientation more akin to a single quadrupole at an intermediate angle between the 2 quadrupoles, then to continue rotation, the polarity is reversed progressive moving the field further in angle by another 45°.
	Example [[EM 10 \| Zeiss EM 10]]		Example [[EM 10 \| Zeiss EM 10]]
		+
		+	= notes =
		+	The diagrams of the quadrupole and double quadrupole have magnetic monopoles shown, this was intended as a visualizing aid, normally dipoles are present. This is partially an oversight on the part of the artist, and will likely be corrected. Think of the poles as bar magnets with the opposing magnetic pole being opposite the ones pointing inside.

@@ Line 7: / Line 7: @@
 = Types =
 == Electrostatic Stigmator ==
 This Stigmator is the type originally designed by [[O. Rang]] and has 3 sets of electrodes arranged radially around a central bore. 1 set has a span of 90° and 2 sets have a span of 45°. The 90° segments are usually connected to ground, and the 2 sets of 45° segments connected to bipolar power supplies, changing the polarity and the voltage of these segment sets allows the creation of a continually rotatable and amplitude adjustable electrostatic cylinder lens. This type of Stigmator was first implemented in the [[EM8 | AEG / Zeiss EM8]] which allowed this machine to reach the highest resolution achieved at the time.
@@ Line 16: / Line 17: @@
 Example: [[ÜM 100 | Siemens ÜM 100]] (Objective), [[Elmiskop I | Siemens Elmiskop I]] (Condenser)
 === 4 Pol Piece ===
 In the 4 Pol Piece setup, as featured in the [[Elmiskop I | Siemens Elmiskop I]] and [[Elmiskop IA | Siemens Elmiskop IA]], 2 sets of 2 iron pol pieces are mounted on 2 bevel gears, mechanically coupled in such a way, that both can turn together, allowing angle, and both running opposite to one another, thus allowing amplitude control. This setup is placed like the 2 Pol Piece setup, inside the magnetic circuit of the Objective lens (or other lens), where like the 2 pol piece, it is supplied by the flux of that lens.  Maximum Stigmator power is present when both sets of pol pieces are in the same axis, and minimum Stigmator power is present when both sets are at 90° to one another.

@@ Line 23: / Line 23: @@
 == Quadrupole Stigmator ==
-[[File:Quadropole Stigmator Tesla BS242E from Manual.png|thumb|The Quadrupole Stigmator of the BS242 showing its 4 pols mounted on a azimuth bearing assembly controlled by a rod going to an angle scales scribed on the outside of the column. ]]
+[[File:Quadropole Stigmator Tesla BS242E from Manual.png|thumb|The Quadrupole Stigmator of the BS242 showing its 4 pols (A,B,C,D) mounted on a azimuth bearing assembly controlled by a rod (E) going to an angle scales scribed on the outside of the column. ]]
 In a Quadrupole Stigmator, a single Quadrupole lens is used as the correcting element, this lens has 2 north and 2 south poles each opposing one another and oriented at 90° to each other, forming a cross shaped structure. This lens Focuses in 1 axis, and defocuses in the 90° opposing axis, thus allowing correction of astigmatism. Since this Aberration is rarely in the exact axis of the Quadrupole, means of rotating this lens are needed. Machines with such a Stigmator have a mechanical Angle control, usually allowing 90° of Rotation, and an electrical control for the field strength. A notable Example of this Stigmator type is the [[BS 242 | Tesla BS 242]].
 == Dual Quadrupole Stigmator ==
 In the Double Quadrupole Stigmator, 2 Quadropoles offset by 45° to one another are used to create an electrically rotatable and amplitude adjustable Cylinder lens. This setup is not to be confused with an [[Octopole]] lens which also features 8 pole Pieces. In this setup the Quadrupole field is formed by having 2 sets of poles at various ratios of power next to one another. Thus allowing full 360° rotation of the field. These 2 interleaved Quadrupoles are controlled either by a [[Sin / Cos Potentiometer]] for Angle, and a Linear Potentiometer for Amplitude, or by 2 Linear potentiometers for each Quadrupole.
 Example [[EM 10 | Zeiss EM 10]]