Yes, it is much too wide a field for absolute rules.
Much will depend on what is easily available and accesible to OP.
When it comes to stereomicroscopes quite a lot can be told by looking at
optical quality throughout the field of vision. Lots of the cheaper
instrument have the picture blurring towards the edges, and this is not hard
to spot when one knows what to look for. A complete newbie who does not know
what to look for will be in trouble.
PvR

+ + +
Aaron schreef I would not like to have what I posted
taken as an absolute rule.
However, my advice,comes from experience with many insruments. It is
good advice for a newbie. Everyone is free to comment..

The issue of microscope quality is often reduced to provanance alone.
Its snobbish and that is not my position. The issues are materials,
design and workmanship. All the makers including the big four make
low cost entry scopes for routine lab work and student use.. Here the
technical genius of these large companies is directed to minimizing
the cost instruments for routine laboratory work. Their aim is to
make it as cheap as they can to attract price buyers and still feel
okay with their name on the product.. Again, these are not great
instruments. There is a difference between routine microscopes and
research level instruments. I am appending an article that I wrote
and posted to sci.techniques.microscopy some time ago that expands
this theme..

Fine optics require expensive exotic glasses and very accurate precise
manufacture to get the lens profiles. (Coatings are important but the
fundamental accuracy of the lenses is more so. Remember the original
defect in the Hubble telescope mirror.). Also the internal metal
parts of a microscope require lots of high precision machine work to
provide the proper orientation of the lens elements and accurate
durable focusing,, especially in zoom stereo microscopes. Materials.
workmanship and strict quality control are not cheap, even in the
thrid world. There is no "free lunch." An experienced microscopist
will spot quickly the absence of the atributes. My point is that a
good industrial quality instrument has a very low price for the
quality abailable because others have withstood the depreciation..

It is easy for a new buyer to be fooled because the new imports look
slick on the outside. It takes a few hours spent using an instrument
for eyestrain and headaches to develope. These symptoms are related
to poor focus and alignment of the optics. It also takes experience
with many different instruments to recognize a quality image. A quick
look down the eyepieces is not going to reveal the truth. New buyers
are going to be impressed with any view because the initial response
to any magnified images is so positive.

However, you do raise another point. Not everyone needs or
appreciates top level quality. So whatever meets your needs is fine
as long as you are happy. That is why microscopes of every
desctiption, quality and price are being sold today..

Aaron

Appended post from sci.techniques.microscopy:
(Sorry for any redundencie)

This question (new versus old microscopes) appears on this NG
regularly from novice buyers who are
tempted to purchase one of the new off-brand microscopes that are
imported from Japan, China, India, the old Communist block countries
Russia, etc. The price gets their attention and the scope looks
slick. The older name brand microscopes cost as much or more than
these "new" scopes. It is clear the questioners have neither the
background to evaluate an "older" microscope for inherent value, nor
assess a new scope for optical quality Hence the question.

Successfully purchasing a microscope (new or old) requires
considerable background knowledge which can't be provided in brief
comments. However I hope the following helps.

The top four old line manufacturers still making high quality new
microscopes are Zeiss, Olympus, Nikon and Leica. The new off-brand
microscopes vary in performance from "yuk" to quite good. Are the
best of these equal to the top four. In my opinion, no. They may
look like modern microscopes but the necessary precision in
manufacturing the optics is not quite there.

I think it is now necessary to generally define terms age and quality.
First, the word "older" as I want to use it refers to scopes 10 to 25
years old, but no more than 50. Quality microscopes younger than 10
years are difficult items. These are still in their prime and
generally in the possession of the original purchaser. If you do
happen to pick one up, parts are scarce and very expensive purchased
new. Starting in the mid 1950's binocular and trinocular designs
became more common and focusing was achieved by moving the stage
rather than the optical tube. These changes produced the greatest
improvement in ergonomics. Subsequent inovations are to raise the
height of the eyepieces to avoid stuping and lower the controls to
make them easier to reach . These last improvements can be aproximated
by raising the scope to eye level, using an adjustable height chair
and providing rests to bring your hands closer to the controls.

With respect to quality there are routine laboratory scopes and more
elaborate research instruments.

The major manufacturers market routine laboratory scopes with
inexpensive achromat objectives and simple eyepieces. They are not
great optical instruments, however ergonomic and slick looking they
may be.. These are the most numerous microscopes available. Many
older bright field / dark field microscopes equal and exceed the
performance. The ergonomics of new and old scopes are not so different
for this type.

The quality of objectives and eyepieces is the most important
characteristic separating routine scopes from research scopes.
Planachromat and especially flourite and plan apochromat objectives
are much higher optical quality and cost more both for the number of
individual lens elements and the choice of exotic materials that go
into a single objective. Phase contrast, Differential Interference
Contrast (DIC), epi-illumination, powerful lamps, high NA turret
condensers, and elaborate mechanical stages are other typical
components of research level microscopes. So quality has two
dimensions. One is the precision in manufacture. Second is the
complexity of the components.

The price for a given quality of optics is much less for an older
scope than the corresponding newer microscopes. Microscopes are much
worse than cars considering initial depreciation. Buy a new scope,
any new scope, and especially the high end research scopes and you
will be very hard pressed to resell it for anywhere near the original
cost. Generally speaking and recognizing a few exceptions, a well
cared for microscope will retain almost all of its optical performance
over time. There is an excellent supply of high quality microscopes
retired from industrial and academic institutions which are excellent
for hobbyists or others with a restricted budget. I believe these
scopes are the real bargains if properly evaluated for parts and
condition.

Is a new Zeiss, Olympus, Nikon, Lica research scope easier to use and
does it posses outstanding quality in the optics? Yes!! But the
prices of the new microscopes are between 4 and 15 times the same
quality scope that is 15 to 25 years older. Today, older
top-of-the-line microscopes sell on eBay for $1,000 to $4,000 dollars
that cost as much as $20,000 purchased in 1975 dollars. Premium grade
objectives, for Zeiss, Nikon, Olympus and Leica scopes, which cost
several thousand dollars new, go for a few hundred dollars in good
optical condition used. Going back as far as the 1950's Bausch and
Lomb, AO and other companies manufactured excellent quality compound
microscopes that are now available for $500 or less. The B & L line
of stereozoom microscopes are very available and popular in the $300
to $700 range. Greenough stereo scopes go for $100 to $250 depending
on condition and features. These are all excellent scopes.

The new research grade equipment from any of the four major
manufacturers is typically in the $15,000 to $80,000 range today as
you choose the best grade of objectives and add phase contrast, DIC
and epi illumination and other choice optional components.

So my personal preference is to purchase very high quality research
grade equipment that is 10 to 30 years old in as near to pristine
condition as I can find. It is used and there will be some traces of
wear and tear, but the performance will be far beyond what the same
dollars could purchase in new equipment.

Aaron