Maximum number of magnifications for a microscope

[meteor]

Don't know where to post this, I hope is in the right place. What's the maximum number of magnifications that a microscope (of any class) has achieved to date? I want concrete ciphers.

 

[mfb]

"Number" as in different magnification steps? You can magnify an image as much as you want, that is not the relevant quantity. The resolution is the interesting property, it is generally limited by the wavelength of the light or particle used to make the image: Visible light won't resolve structures smaller than ~200 nm, UV can resolve smaller structures but is likely to destroy chemical bonds. Electron microscopes can image individual atoms.

 

[TeethWhitener]

As @mfb mentioned, the important quantity in microscopy is resolution. Standard microscopy is diffraction-limited, meaning that the smallest resolved feature is on the order of the wavelength. In the case of visible light, this is about 200 nm. In the case of electrons, this can be angstroms.

However, the diffraction limit is a far-field effect (where the distance between the sample to image and the objective is large compared to the wavelength), and there are several techniques in existence nowadays for going beyond it ("superresolution microscopy"). These generally fall into 2 camps (below). The resolution for each is on the order of single nanometers when using visible light as the source.

The first is to use a near-field probe, where the distance between sample and objective is on the order of the wavelength or less. This is an active field of research and has only recently become feasible, mainly because Maxwell's equations in the near-field are much more complicated than in the far field (the desired information is contained in non-propagating evanescent surface waves), and their solution requires a fair degree of computational power.

The second technique is to use far field imaging along with some clever way of localizing light sources. The two most famous examples of this technique--awarded the Nobel Prize in Chemistry in 2014--are PALM (photoactivated localization microscopy) and STED (stimulated emission depletion). The techniques differ in their details, but both are based on the idea that a fluorescing molecule will display its light according to a predictable point spread function. If the point spread functions of two closely (sub-diffraction limit) spaced fluorophores can be distinguished, their most likely positions can be computed and an image can be built up. PALM does this by using different fluorophores of different colors, while STED does this by using partially overlapping lasers: one to excite a group of fluorophores and one to de-excite part of that group.

 

[Andy Resnick]

Don't know where to post this, I hope is in the right place. What's the maximum number of magnifications that a microscope (of any class) has achieved to date? I want concrete ciphers.

As a rule of thumb, the maximum 'useful magnification' in light microscopes under standard widefield conditions is approximately 1000 x (numerical aperture). For electron microscopes, the accelerating voltage is used instead of numerical aperture, and from what little I understand, the maximum useful magnification is about 1000 x (accelerating voltage)