62 PART IV Digital Documentation
make compromises. For sure! But here are some general questions that can help
you decide on the right microscope camera:
✔✔Are you working with fluorescent, colored or stained samples?
✔✔Do you need a certain resolution and a specific field of view for
your application?
✔✔Do you need a sensitive low noise camera for work with
sensitive living cells?
✔✔ Is your sample alive and kicking? Moving fast? Very bright?
CCD, CMOS – What the Hell? Physical
Things You Should Know
This question is aimed more or less at the technical fans among you. Whether you
go for one or the other sensor type may influence the resolution and speed of the
camera. And that’s why this section is a little technical.
CCD means Charge Coupled Device. So far, so good … The image acquisition
principle is based on the conversion of light (photons) into
an electrical charge signal (electrons). We are really lucky that silicon
is a perfectly suited material to do this conversion in the visible
light spectrum as silicon can be processed nowadays at high quantities
and qualities.
By the way, this “inner photoelectric process” was explained by Albert
Einstein, who received his Nobel Prize for explaining this effect
in 1921. And in 1970, the first working CCD sensor was presented.
Willard Boyle and George E. Smith were awarded the Nobel Prize for
the invention of the Charge Coupled Device in 2009. The CCD sensor
consists of a lot of small, light-sensitive individual segments or
buckets, also known as pixels (picture elements), which are arranged
in a rectangular matrix (the image area of the sensor). When you
acquire an image, it is projected onto the sensor image area. During
the exposure time, the sensor converts the amount of light arriving
at each pixel into a number of electrons (charge) per each little image
spot and holds them in the pixel. You can imagine these photons
as raindrops collected in buckets. The efficiency - how many incoming
raindrops (photons) are caught in these buckets - is called quantum
efficiency. After the exposure time is over, these charge packets