Entrance Pupil Microscope Objective
B. Gambier
More or less same question:
Can such an objective be considered telecentric in object space?
Now I am specifically referring to the very long working distance objectives
made by Mitutoyo.
Are there other microscope objectives with equally or comparably long
working distances available on the market these days.
My info is a bit dated :-)
Thanks
BG
Helpful person
I assume that the Mitutoyo objective you are using is corrected for a
long conjugate of infinity. Most superior modern objectives are
infinity corrected.
All proprly designed microscope objectives are telecentric in object
space. This ensures that the image size does not change with defocus.
To ensure telecentricity, the aperture stop is internal to the
microscope objective.
Juan Rayces
Oooops! Mr. Gambier is asking where is the entrance pupil of a
microscope objective, not where is the aperture stop. The correct
answer is: the aperture stop is at infinity in object space. Mr.
Helpful Person is right, then, in saying that the well-designed
objective is telecentric in object space. Sorry I have no idea who is
Mr. Mitutoyo, I cannot help with that. J. Rayces
DonJan
DonJan
Mitutoyo is the manufacturer of a line of huge infinity corrected
microscope objectives. They typically have working distances of 34 to
6mm with 25mm entrance apertures (NA 0.06 to 0.7). Costs range from
$500 to $8000. Some are even corrected for VIS/NIR. They are
remarkable.
I've searched the patent literature but have not been able to get an
example of a design. If anyone has a design, I'd love to see it.
Another remarkable commercial lens are the three 1:1 Printing Nikors.
They are near diffraction-limited and corrected for 400 to 800nm (150,
105 ,95mm EFL) and cost $15,000 to $6000. This is another lens that
I'd love to see the design.
Helpful person
> microscope objective, not where is the aperture stop. The correct
> answer is: the aperture stop is at infinity in object space. Mr.
> Helpful Person is right, then, in saying that the well-designed
> objective is telecentric in object space. Sorry I have no idea who is
> Mr. Mitutoyo, I cannot help with that. J. Rayces
I (probably incorrectly) asumed that B. Gambier understood that
telecentric meant that the pupil was at infinity. Thanks for the
clarification.
B. Gambier
"Helpful person" wrote
Juan Rayces wrote
Thanks very much for yr collective answers.
I am aware that telecentricity means that the entrance pupil is at infinity.
So concerning metallographic microscope objectives I am very happy to hear
that this is indeed the case, at least in object space.
I had more or less assumed that this was true as this assumption made my
life much easier.
But I needed some reassurance from the experts as I am not a lens
designer...
I would guess that the Mitutoyo and Nikon / Nikkor designs are patented, in
as much as a patent reveals the truth, the whole truth and nothing but the
truth.
Lambda Research (Oslo, Trace Pro) sells an optical data base that should
include all lens design patents since the inception of the USPTO until the
present.
Pls see their site for more details. Japanese and European Patents may also
be included.
The author / compiler of this DB is Brian Caldwell.
Objectives externally identical to the Mitutoyo objectives appear to be
sold under different names.
I love'em, they are superb, apo and all and the extra long working distance
is soooo niiiice.
Thanks again.
Bertrand Gambier
Helpful person
>
>
>
> Objectives externally identical to the Mitutoyo objectives appear to be
> sold under different names.
>
> I love'em, they are superb, apo and all and the extra long working distance
> is soooo niiiice.
>
> Thanks again.
>
> Bertrand Gambier
I too like the Mitutoyo objectives. I haven't formally measured their
performance but the long working distance is especially nice fo many
applications. I wasn't aware that they made apochromatic versions of
their objectives.
B. Gambier
" B. Gambier" <Para...@Nowhere.Com> wrote in message
> Where is the entrance pupil of a microscope objective (metallographic)?
>
> More or less same question:
>
> Can such an objective be considered telecentric in object space?
Objective telecentric in object space indeed, thanks for your answers.
Now what about the condenser?
What are the consequences of this fact for the illumination?
I mean for Koehler illumination.
Must the condenser be somehow telecentric also?
I would think so, but how?
And where could I find the schematic of such a condenser?
Thanks.
GB
Andrew Resnick
Hang on there a second: a condenser for a metallographic microscope?
Those use reflected light, correct?
Here's my take on microscope optics- consider just the condenser, the (
2D)sample, and the objective (transillumination).
For either critical or Kohler illumination, both lenses are focused on
the sample. In critical illumination, the source is imaged onto the
sample by the condenser lens, while for Kohler, the Fourier transform of
the sample is imaged onto the sample by the condenser. That is, for
Kohler illumination, the source is at minus infinity as far as the
condenser lens is concerned. This is immaterial to the lens being
telecentric or not.
Infinity-corrected means something different than telecentricity (
although I don't know specifically about the Mitutoyo lenses). Infinity
corrected objectives put the image at plus infinity, but the exit pupil
is located at or near the back surface of the lens (at least they are
for Leica objectives). The entrance pupil should be located at the
sample, as can be inferred by maximizing the light-gathering efficiency
of the system. The front focal length of infinity corrected lenses
seems, AFAIK, to be defined by a tautology: the magnification is defined
in terms of a ficticious tube length, and so the front focal length is
likewise defined in terms of this fiction.
Or am I missing somthing?
--
Andrew Resnick, Ph. D.
National Center for Microgravity Research
NASA Glenn Research Center
Helpful person
Koehler illumination images the light source at the microscope
entrance pupil. As the entrance pupil is at infinity, the light
source is focused at infinity.
B. Gambier
"Andrew Resnick" wrote
B. Gambier wrote:
> >> Where is the entrance pupil of a microscope objective
(metallographic)?
> >>
> >> More or less same question:
> >>
> >> Can such an objective be considered telecentric in object space?
> >
> > Objective telecentric in object space indeed, thanks for your answers.
> >
> >
> > Now what about the condenser?
> >
> > What are the consequences of this fact for the illumination?
> >
> > I mean for Koehler illumination.
> >
> > Must the condenser be somehow telecentric also?
> >
> > I would think so, but how?
> >
> > And where could I find the schematic of such a condenser?
> >
>
> Hang on there a second: a condenser for a metallographic microscope?
> Those use reflected light, correct?
Right, so the objective is the last component of the illumination system.
Perhaps not a true condenser in the conventional sense therefore.
However there is a beam splitter above the objective.
Between the objective and the so called tube lens.
Before the beam splitter there are additional optics and finally the light
source.
So perhaps the illumination system, again while not a true a condenser, has
to
fulfill the expected role of a condenser.
> Here's my take on microscope optics- consider just the condenser, the (
> 2D) sample, and the objective (transillumination).
>
> For either critical or Koehler illumination, both lenses are focused on
> the sample. In critical illumination, the source is imaged onto the
> sample by the condenser lens, while for Kohler, the Fourier transform of
> the source is imaged onto the sample by the condenser. That is, for
> Koehler illumination, the source is at minus infinity as far as the
> condenser lens is concerned. This is immaterial to the lens being
> telecentric or not.
>
> Infinity-corrected means something different than telecentricity (
> although I don't know specifically about the Mitutoyo lenses).
OK, telecentricity in object space appears to be a property of all
microscope objectives where as infinity correction refers specifically to
metallographic objectives.
> Infinity
> corrected objectives put the image at plus infinity, but the exit pupil
> is located at or near the back surface of the lens (at least they are
> for Leica objectives). The entrance pupil should be located at the
> sample, as can be inferred by maximizing the light-gathering efficiency
> of the system. The front focal length of infinity corrected lenses
> seems, AFAIK, to be defined by a tautology: the magnification is defined
> in terms of a ficticious tube length, and so the front focal length is
> likewise defined in terms of this fiction.
>
> Or am I missing something
I am a little lost here...
OK but the tube length is not really fictitious, as a tube lens becomes
necessary.
This tube length brings the image (originally at infinity) provided by the
objective to a focus where it can be observed.
So the tube length is replaced conceptually by a tube lens whose focal
length is generally more or less equal to the tube length.
At least that's my understanding.
>
> Andrew Resnick, Ph. D.
> National Center for Microgravity Research
> NASA Glenn Research Center
Thanks
BG
B. Gambier
From: "Helpful person"
>
> Koehler illumination images the light source at the microscope
> entrance pupil. As the entrance pupil is at infinity, the light
> source is focused at infinity.
OK, I get it.
Thanks to everyone.
BG