Natural Science Forum / Physics / Optics / March 2007

Hello,
         Kevin is correct that Phase and DIC are 'industry standards'
but cell biologists are usually more interested in counting cells,
looking for contamination of cultures, and assessing viability of
cells than particular features of cell morphology. Phase and DIC are
rather expensive, and fickle - you really DO need the hardware
manufactured by the maker of your microscope for best results. Mix and
match it definitely ain't.
Darkfield can be done quite well at magnifications up to x400 with
ordinary objectives, and pushing it to x600 if you have really good
x15 eyepieces. You need lots of light, a bit of cardboard and some
scissors.but you do not need a special condenser for darkfield. You
will not be able to use a x100 objective unless it has a built in iris
to reduce the N.A. to about 0.8. May I suggest you start with homemade
darkfield patch stops at first. I made a whole lot of them with an
acetate sheet, a circle cutter, and some wide pvc tape or cardboard.
Experiment with different sizes around 12mm-18mm diameter.  Suggest
you look at the relevant articles on Micscape, which cover the topic
in some detail. It is worth playing with, just for the images which
can be breathtakingly beautiful - I was looking at an amoeba the other
night and it looked like a river of gleaming jewels. Good luck to
you ; there's a lot of fun in this and it can be very rewarding, but
you do not really need to buy a df condenser to explore the technique.
hugo johnson

Kevin:

Are you again bashing DF for biological applications? :-)

Dan might be talking about the one depicted at
http://www.tfttools.com/BM100FL.htm

This scope isn't exactly what you would use for "scientific" work. But then
again, what is "scientific" work? If that's the scope in question, we can
forget about adding Phase or DIC.

You are talking about the "standard for researchers" without being too
specific. I know that you only refer to biological applications (e.g. life
cell analysis). But you may want to clarify this in your next conquest
against DF.

Regarding the resolution advantage of DF vs. DIC and Phase, I completely
disagree. It does not only depend on the size of the subresolution particle
but also on the fact that you can detect them at all. DIC is useless with
any cell tissue that is birefringent (e.g. nerve cell cultures). That's why
Zeiss introduced a newly improved interference technology to capture this
very important market segment. Phase has limitation in resolution. DF can
easlily accomplish a resolution of up to NA 1.10. With Phase, the maximum
obtainable NA is around 1.15 (assuming NA(obj) = 1.40 and NA(cond) = 0.90).

It really does not matter how many times you have sold a DF setup. You told
us this already several times. Ironically, Nikon still offers DF components
for their new Eclipse series scopes. Maybe they are just catering to some
life blood vampires out there. Maybe you were just in the wrong market
trying to sell DF.

Anyway, I use DF almost everytime I need to get some answers from certain
samples (...yes, they are not biological samples).

BTW, why do you think that most "researchers" are using DIC instead of
COL? - Because, they don't know how to setup proper oblique illumination.
The same applies to DF. Most people fail misearbly because they just don't
have the skills. But then again, why sell a $300 COL setup when we can sell
a $6000 DIC setup? - DIC is good for business.

Cheers,

Gregor