objective choice

[Stephan Speier]

Hi,

We are want to purchase a motorized fluorescent stereomicroscope with
camera for surgeries and tissue sample documentation, thereby using
fluorescence whenever possible.
The objective will be 1x (because we need the working distance and view
field) and the zoom ratio about 1:10. We will end up with a max
magnification of about 80-100x.

Two of the 4 "big" vendors suggest an achromat objective because it
collects more
fluorescence light (less glass in the objective), which is important due
to the big
working distance and more important than the corrections at this low
magnifications.
The other two vendors suggest an plan apo objective. They reason the
benefit from the better correction will overcome the light loss and that
the correction is as important at low magnifications.

Any opinions?

Thanks,
Stephan

[Craig Brideau]

Have you looked at 'machine vision' style lenses?  Basically they are
objective lenses meant for assembly line inspection and the like.
They often feature flat field and good color correction.  Regarding
your lens choice, your best move would be to arrange to demo a variety
of lenses.  The manufacturers can make all the claims they want about
their lenses but you really won't know how they will perform for your
specific application until you try them.  Insist on a demo before you
buy.
Mitutoyo and Edmund Optics make some good low-mag inspection lenses.

Craig


On Mon, Jan 18, 2010 at 11:44 AM, Stephan Speier <[hidden email]> wrote:

> Hi,
>
> We are want to purchase a motorized fluorescent stereomicroscope with
> camera for surgeries and tissue sample documentation, thereby using
> fluorescence whenever possible.
> The objective will be 1x (because we need the working distance and view
> field) and the zoom ratio about 1:10. We will end up with a max
> magnification of about 80-100x.
>
> Two of the 4 "big" vendors suggest an achromat objective because it
> collects more
> fluorescence light (less glass in the objective), which is important due
> to the big
> working distance and more important than the corrections at this low
> magnifications.
> The other two vendors suggest an plan apo objective. They reason the
> benefit from the better correction will overcome the light loss and that
> the correction is as important at low magnifications.
>
> Any opinions?
>
> Thanks,
> Stephan
>

[James Pawley]

>Hi,
>
>We are want to purchase a motorized fluorescent stereomicroscope with
>camera for surgeries and tissue sample documentation, thereby using
>fluorescence whenever possible.
>The objective will be 1x (because we need the working distance and view
>field) and the zoom ratio about 1:10. We will end up with a max
>magnification of about 80-100x.
>
>Two of the 4 "big" vendors suggest an achromat objective because it
>collects more
>fluorescence light (less glass in the objective), which is important due
>to the big
>working distance and more important than the corrections at this low
>magnifications.
>The other two vendors suggest an plan apo objective. They reason the
>benefit from the better correction will overcome the light loss and that
>the correction is as important at low magnifications.
>
>Any opinions?
>
>Thanks,
>Stephan

Hi Stephan,

While it is true that Plan-Apo's tend to have more elements, and
therefore more surfaces to reflect (and lose) light, modern
multicoating reduces this effect a lot.

I would say, check the NA. All objectives have an NA, even those on
stereoscopes. However, you must remember that on stereoscopes with a
single objective, each eyepiece uses only part of the NA (Sometimes
only 2 small circles worth of it, located either side of the axis.
Other times, about one half of the circular field.) and you are
probably most interested in the NA "as seen from the Camera/CCD port"
(which may be the same as that from one eye or may be different).

Higher NA should give you more light at a given magnification.
However, it will also give you less depth of field.

Another major variable is the excitation illumination. You can
compare this by masking the sensor of some photometer (even a
"Solar-Cell" hooked to a voltmeter) so that its sensitive area
approximates the area of the specimen that you plan to view. To
measure the relative intensity of the excitation light in different
scopes, place the unmasked area where the specimen would normally be.

Cheers,

Jim Pawley
--
               **********************************************
Prof. James B. Pawley,                          Ph.  608-263-3147
Room 223, Zoology Research Building,              
FAX  [phone]
1117 Johnson Ave., Madison, WI, 53706  
[hidden email]
3D Microscopy of Living Cells Course, June 12-24, 2010, UBC, Vancouver Canada
Info: http://www.3dcourse.ubc.ca/             Applications due by March 15, 2010
               "If it ain't diffraction, it must be statistics." Anon.

[Peter Gabriel Pitrone]

Have you thought about a macroscope, instead of a stereoscope? With only one light path a macroscope would be better for photography. A stereoscope has two light paths off set from each other by about 15 deg, or 7.5 deg off the axial for each path. Nikon makes a good macroscope capable of DIC at low magnification, and they have good objectives. Although I must say that I'm not trying to advertise for them (we don't even have one)!

Pete

P.S. No commercial interest!


On Jan 18, 2010, at 19:44 PM, Stephan Speier wrote:

> Hi,
>
> We are want to purchase a motorized fluorescent stereomicroscope with
> camera for surgeries and tissue sample documentation, thereby using
> fluorescence whenever possible.
> The objective will be 1x (because we need the working distance and view
> field) and the zoom ratio about 1:10. We will end up with a max
> magnification of about 80-100x.
>
> Two of the 4 "big" vendors suggest an achromat objective because it
> collects more
> fluorescence light (less glass in the objective), which is important due
> to the big
> working distance and more important than the corrections at this low
> magnifications.
> The other two vendors suggest an plan apo objective. They reason the
> benefit from the better correction will overcome the light loss and that
> the correction is as important at low magnifications.
>
> Any opinions?
>
> Thanks,
> Stephan

[Glen MacDonald-2]

We went through this process several years ago when purchasing the first of our several fluorescent dissecting microscopes.  Without sufficient NA you will not deliver enough excitation from your source and not collect enough signal, as Jim says.  The actual type of lens seems less important.   Ask to compare the Achro and Plan objectives in your preferred and "tolerable" working distance range.  It will help if the demo is using an optimal filter set for your specimens rather than some generic filter the vendor is using out of convenience.  Of course, there are more options for excitation sources and some improvements in filters and optics for the modern instruments, so you might get by with a lower NA than previously possible.  

Regards,
Glen
On Jan 18, 2010, at 10:44 AM, Stephan Speier wrote:

> Hi,
>
> We are want to purchase a motorized fluorescent stereomicroscope with
> camera for surgeries and tissue sample documentation, thereby using
> fluorescence whenever possible.
> The objective will be 1x (because we need the working distance and view
> field) and the zoom ratio about 1:10. We will end up with a max
> magnification of about 80-100x.
>
> Two of the 4 "big" vendors suggest an achromat objective because it
> collects more
> fluorescence light (less glass in the objective), which is important due
> to the big
> working distance and more important than the corrections at this low
> magnifications.
> The other two vendors suggest an plan apo objective. They reason the
> benefit from the better correction will overcome the light loss and that
> the correction is as important at low magnifications.
>
> Any opinions?
>
> Thanks,
> Stephan