Not for the first time, I wish we could post diagrams to the list! What Eric says is obviously correct about the area we illuminate. But illuminating an area doesn't mean that we can see it. In transmission microscopy we are accustomed to setting the field diaphragm to make the illuminated area match the visible area. A high-class epifluorescence system will let us do exactly the same thing. We tend to be slack about this since (unlike the transmission case) the illumination is automatically in focus so resolution is not affected. Can I suggest to Eric (and anyone else who wants to get to grips with such issues) that he takes a simple, cheap, student microscope and swaps through all the available eyepieces without changing anything else? That way he will understand how an eyepiece determines the field of view.
Guy
Guy Cox, Honorary Associate Professor
School of Medical Sciences
Australian Centre for Microscopy and Microanalysis,
Madsen, F09, University of Sydney, NSW 2006
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From: Confocal Microscopy List [mailto:[log in to unmask]] On Behalf Of Eric Laloum
Sent: Wednesday, 5 March 2014 7:09 PM
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Subject: Re: Is field of view of objective constrained by field number of microscope?
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One point raised by Guy Cox left unanswered, regarding factors affecting field number. To my understanding field number is mostly linked to the objective lens and maybe constrained by microscope, but is not related to the eyepiece.
For instance, in the cases where we need to estimate irradiance onto the sample (photons / sec / m²) in wide-field epi-fluorescence microscopy ; we need to divide total light power on sample plane (as measured by power meter) by illuminated area ; and the illuminated area is calculated with objective field number (and magnification).
It's just my own guess and I haven't investigated it furher, so don't hesitate to comment t correct ...
Eric Laloum
Paris
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De: "Guy Cox" <[log in to unmask]>
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Envoyé: Samedi 1 Mars 2014 12:40:29
Objet: Re: Is field of view of objective constrained by field number of microscope?
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I may be missing something here but I thought the field number was largely a property of the eyepiece. A WF eyepiece uses a field lens to reduce the final magnification a bit but in the process substantially increase the FOV. Of course the actual diameter of the tube has to allow this and that is why most manufacturers went to 25mm lens mounts rather than RMS when they went to infinity correction. In this regard the old East German Zeiss lenses were better than the West German ones. But of course after German reunification the West German company could not possibly accept that the East German company actually did some things better.
Guy
Guy Cox, Honorary Associate Professor
School of Medical Sciences
Australian Centre for Microscopy and Microanalysis, Madsen, F09, University of Sydney, NSW 2006
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From: Confocal Microscopy List [mailto:[log in to unmask]] On Behalf Of Kurt Thorn
Sent: Saturday, 1 March 2014 5:39 AM
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Subject: Re: Is field of view of objective constrained by field number of microscope?
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Hi Shalin -
I've done some qualitative investigations of this on our microscopes, and you can access information beyond the nominal field number of the microscope. The vignetting seems to mostly occur in the C-mount and camera adapter, so if you remove these you can get a bigger image. See
http://nic.ucsf.edu/blog/?p=108 for some details.
However, there's no guarantee what the performance of the objective beyond the nominal field number will be. In particular, the NA may be lower, there may be problems with field curvature and there will likely be aberrations. In fact, even at the periphery of the nominal objective FOV the point spread functions are more aberrated - see
http://nic.ucsf.edu/blog/?p=770
I hope that helps.
Kurt
On 2/28/2014 9:22 AM, Shalin Mehta wrote:
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> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> Hello,
>
> I have a question about the maximum usable field of view of commercial
> objectives, if the only constraint is the mostly-flat field of view.
> We would like to find a commercial low mag, high NA objective and
> extract as much field of view as possible.
>
> Is the usable field of view of an objective constrained by the field
> number of the microscope? i.e., if the field number of the microscope
> is 26 mm, is the diameter of the field of view constrained to 26mm/mag
> of the objective?
>
> Are there stops in the objective that enforce this specification? If
> we are to use a tube lens of same focal length as the commercial
> microscope, but larger diameter, can we have a field of view larger
> than specified by the field number? Having a flat field of view will
> be great, but slight imperfection is not a problem.
>
> Thanks
> Shalin
>
>
--
Kurt Thorn
Director, Nikon Imaging Center
http://nic.ucsf.edu/blog/
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