Re: Need advice regarding Watson metallurgical microscope

On Jan 29, 2:06 am, Christopher Tidy <cdt22NOS...@xxxxxxxxxxxxxx>
wrote:
Kevin Cunningham wrote:

Hi Kevin,

Thanks for your thoughtful response.

A power supply can be found else were, either on e-bay, your local
dealer or from Ludl, you don't need a Watson. Now, the reason that
metallographs were wade with single objective mounts is to maintain a
very good control on parcentricity. Later on, in the late '70's,
makers could manufacture very parcentric nosepieces. I wouldn't
change this.

So would you often unscrew the lens with a specimen on the table? I'm a
little surprised by this, but possibly only because I've never done it
before. It seems it would be very easy to knock the specimen
accidentally. Also, with higher magnification lenses I doubt there would
be enough room between the focused lens and specimen without raising the
lens and losing your focusing, but I guess this wouldn't be a problem if
you're only worried about parcentricity.

Actually the parcentricity on the Watson microscopes I have seems pretty
good. Using a crude visual estimation with low to medium power lenses,
it looks close to perfect. I can't test the high power lenses as none of
my microscopes have complete condensers, and there's not enough space
between a x50 lens and a specimen to light it with a torch beam. This is
one of the reasons why I want a proper reflected light microscope.

However the parfocality seems a long way out. I tested x4, x8 and x10
objective lenses with x10 eyepieces. The x4 and x10 objectives are made
by Watson. The x8 is Russian. The eyepieces are either made by Baker,
Brock or don't carry a name. Any combination of these lenses needs
approximately a 1 mm carriage movement to focus after a lens change.
This is more than the fine focus adjustment can provide. The presence of
a cover glass slip doesn't correct the issue.

If the parfocality is due to inaccuracies in the turret, I believe these
inaccuracies must have been present since manufacture. I have three
microscopes and they all behave in the same way. The turrets are also
very sturdy. At their thinnest point they are 0.15" thick. They look
accurately manufactured and the two mating parts are both numbered.
There is also a bearing surface around the circuference, so it seems
unlikely that the turret would have been damaged by winding the lens
down into the table.

Incidentally, what does the marking "PARA" mean on a lens? Is it
anything to do with parfocality or parcentricity?

What ever you do, don't think you can get high quality results from
conventionally mounted metal specimens with a biological, cover glass
corrected objective. Metal specimens conventionally have no cover
glass and that makes a whole bunch of difference. The higher the NA
the more important it is to have the correct cover glass or lack of
cover glass. It is conventional in metallurgy to not use oil so NA
stops at 0.95 usually. Some makers during the 160mm days used a
longer correction length for metallurgical objectives. Nikon, for
instance, used 210 mm since metallurgical beam paths were longer since
you had a reflected illuminator.

As at test, I looked a wooden ruler using a Watson x10 NA 0.28 objective
and a Baker x10 eyepiece. I lit the ruler from the side using a Maglite
LED torch. The ruler was flat enough for most of the image to be in
focus at once, and the grain provided plenty of fine detail. I looked at
the ruler under a glass cover slip and without. I looked carefully but
couldn't see any loss of detail without the cover slip. In fact, I
thought the image looked better without the cover slip, as the
brightness and contrast were higher.

Have you tried using transmitted light lenses without a cover slip and
found the results unacceptable? If so, do you remember what lenses you
used? I ask because it has a strong bearing on whether or not I want to
buy this Watson microscope. I just wonder from the test I did if the
cover slip only really matters in the most high performance
applications. There are plenty of Watson transmitted light lenses on the
market, but I've never seen a Watson reflected light lens. I don't know
if Watson ever made them, and I don't think Watson are in business any
longer.

Since I'm in America I doubt I'd buy a Watson unless I wanted to
collect. As a user 'scope here they are incredibly rare. If your in
England, there a bit easier to find but there still not my first
choice for a metallograph. When you need objectives, etc. they can
be a bit difficult to get.

There are many Watson microscopes in England. They're one of the most
common quality microscopes on the used market.

Many thanks for the help.

Best wishes,

Chris

Chris, Parfocality requires the that the eyepieces be made by the
manufacturer. There are way to many problems is you use some one
elses eyepieces. When examining an objective turret you have to use a
precentered objective and eyepiece or spend some time with a set
specimen and a set field diaphragm, the variance for a bad 'un is way
to small, a few microns between two positions.

Geez, yes, sometimes a cover glass corrected objective is used on non-
cover glassed specimens and if the NA is above 0.25 the results are
quite bad. You get tons of hazy and lots of fun with non-corrected
problems that would be corrected by using the right cover glass. Now
for obvious reasons metallurgists don't use cover glass and they do
use reflected light. If you need these two things then a metallograph
is for you. If your not looking at prepared metal specimens then you
just don't need a metallograph. Remember the prep these instruments
are designed to use looks like a hockey puck.

Thanks, let me know what you do!

Kevin Cunningham
SMS
.