What a photon really is:
fitz
pent...@yahoo.com
I'm refurbishing a microscope with an assortment of old
microscope objectives in the range 1.5" (!) to 2 mm. Some state
tube length 200mm but for most, tube length is not stated.
How critical is tube length and how does one discover
whether the working tube length is too short or too long?
Is the right length more important for short or long focal
length objectives? Usually short focus systems are more difficult
but the 2mm objective is working so near its infinity focus, the
tube length could be less critical.
pentagrid
Bob May
Standard design puts the focal plane of all of the eye lenses for the
system at a particular lenght also. As such, there needs to be a spec for
the distance between the two lens systems and, on a lot of microscopes,
that is often something like 200mm. for the tube to eyelens mounting face.
--
Bob May
rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net
Joseph Gwinn
pent...@yahoo.com wrote:
Depending on the make and how old the microscope is, there may or may
not be a standard tube length. Threads were also standardized in
stages. The original standards were established by the Royal Society in
the UK, if I recall.
Tube length *is* critical, as the lenses are optically corrected for the
stated tube lengths. One can focus with other tube lengths (within
reason) and have usable images, but full optical resolution may not be
achieved. How important is this?
What make and model is this microscope? Someone will know its details.
Joe Gwinn
RCM co-religionist.
pent...@yahoo.com
The microscope is made by Vickers Instruments model number
unknown. All that is left of it is the fairly elaborate lower
half. The main microscope tube and angled eyepiece assembly is
missing. I am fabricating replacement parts.
The basic question that I'm asking is - is there any better
way of determining optimum tube length other than just suck it
and see?
pentagrid
jeff
> unknown. All that is left of it is the fairly elaborate lower
> half. The main microscope tube and angled eyepiece assembly is
> missing. I am fabricating replacement parts.
>
> The basic question that I'm asking is - is there any better
> way of determining optimum tube length other than just suck it
> and see?
>
One way would be to use a filar micrometer and measure a known artifact
at the image focal plane, adjusting tube length until the correct
magnification is achieved. You should be able to cobb something up with
a set of verniers, and an eyepiece, but make sure the eyepiece is one
with an external field stop as this is necessary to achieve focus on
both the artifact and verniers concurrently. Also, as a point of
reference, I have an old B&L toolmakers microscope and the tube length
is 160mm.
--
Jeff Lowe
Joseph Gwinn
pent...@yahoo.com wrote:
It turns out that Vickers has a fan club. Here are a few examples:
<http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-
uk.org.uk/mag/artdec01/vickers.html>
<http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-
uk.org.uk/mag/artsep98/cts.html>
<http://www.york.ac.uk/inst/bihr/guideleaflets/Vickers/Vickersfrontpage.h
tm>
There are enough pictures and descriptions that you may be able to
identify the model.
I would assume that Vickers has multiple patents, and general technical
details are often included in such patents. It's probable that Vickers
had a standard "barrel length", for interchangeability. Or one standard
length per product family.
If the objectives have magnifications engraved into their barrels, as is
typical, one can measure the barrel length needed to achieve the stated
magnification, as mentioned by another poster. Without an optical
bench, this may be hard to do all that accurately, but will certainly
get one into the ballpark. One can cobb together a good enough bench
for this one use, however.
Joe Gwinn
Louis Boyd
eyepiece camera instead. Ronchi screens (black and white stripes) would
be suitable as a target and they are available in a wide range of line
widths. The eyepiece cameras have no lens and the microscope objective
just forms an image on the CCD chip so it's just a matter of knowing the
two image scales and one distance to determine the objectives "power"
and focal length. Even cheap CCD cameras have precisely spaced
pixels. Many image display programs allow measuring images in pixels.
The CCD manufacturers datasheet gives the precise pixel spacing.
Edmund Optics sells Ronchi screens and many other precision targets.
pent...@yahoo.com
<joeg...@comcast.net> wrote:
>In article <th36k5h3uouehulp5...@4ax.com>,
> pent...@yahoo.com wrote:
>
snip
The microscope looks like an update of the Vickers Patholette
design but with vernier scaled X and Y movements added to the
focussing stage/substage assembly. All are mounted on a
substantial rectangular base with built in power transformer and
lamp assembly.
The objectives are all non Vickers so I'm making the
tube length variable between 160mm and 200mm and hoping for the
best.
pentagrid
gr
With lower power objectives (10x and below) the tube length is not that
critical because the NA limits what differences you are likely to see.
This is similar to the question that comes up with microcircuit lenses
(which are largely based on microscope objective design); "How far from
the designed reduction ratio can I use this lens?"
A 20xR lens would perform at full capacity in a range from about 17xr to
25xr and near full from 15xr to 30xr. The outer edges of the image
suffer most as you get away from the design conjugates.
For tube lengths in the range of 160 to 200mm the resolution loss will
be quite small, except for high mag, high performance lenses.
gr
Joseph Gwinn
pent...@yahoo.com wrote:
This may be a toolmakers microscope of some kind.
> The objectives are all non Vickers so I'm making the
> tube length variable between 160mm and 200mm and hoping for the
> best.
It's likely that they were made to Vickers' specs though. But that
variation range sounds likely to work.
Joe Gwinn