Re: Increase depth of field without reducing aperture?


"Phil Hobbs" wrote

> There is a direct tradeoff between resolution and numerical aperture in
> any linear imaging system: the focused spot size goes as lambda/NA, and
> the DOF goes as lambda/NA**2 until you get to near NA=1, where it gets a
> bit more complicated.

In microscopy you can have NA larger than 1 with immersion! ;-)

OT

Incidentally immersion is now the latest rage in microphotolithography with
water as the immersion liquid with an index substantially larger than 1, for
the time being.

Other fluids with higher indices are under investigation.

Which is why in the not too distant future lines as fine as 50 nm will be
possible.

In fact immersion microphotolithography (under the name of splash & flash)
has pretty much displaced the competition as the technology of the future
(e.g. x-rays). "Conventional" optics wins the day!



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