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Alright, suppose the light source is incoherent then. There are a few ways to achieve this. Would then the mirror test be equivalent to the fluorescent microbead test?

Also, I should have mentioned that the handbook is very clear about using a coverslipped mirror surface with the correct immersion medium between the coverslip and the mirror to avoid spherical aberration.

John Oreopoulos

On 2011-07-03, at 1:15 PM, Lutz Schaefer wrote:

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> John,
> 
> obviously there is a difference. Besides the different wavelengths, when using a mirror the image formation in the detection path is almost coherent. With a fluorescent object on the other hand, it is incoherent. The difference between these two forward problems lies in the way how the final intensities on the camera are produced. In the coherent case, (complex) amplitudes of elementary sample waves add up (causing the typical constructive/destructive interference) before they become subject to convolution with the observation PSF. Finally, the camera will sense the absolute intensity. In the incoherent case, no interference takes place. The forward problem can be modeled as the sum of the intensities before convolution. This is the fundamental difference! In practice you will also see that the mirror images will show depth varying transverse fringe patterns when your mirror has a good quality, indicating partial coherence. This is clearly not the case when you are using a SIP chart. To me, adding amplitudes and adding intensities are different quantities after convolution that you can't really compare against each other better than approximately. On that subject is plentiful literature available, one contribution that comes immediately to mind is Norbert Streibl's thesis from 1984.
> 
> Best Regards
> Lutz
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> --------------------------------------------------
> From: "John Oreopoulos" <[log in to unmask]>
> Sent: Sunday, July 03, 2011 12:25
> To: <[log in to unmask]>
> Subject: Using a mirror for axial resolution testing
> 
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
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>> 
>> I have a question regarding the use of a mirror for measuring the axial resolution of a confocal imaging system (laser scanning or spinning disk).
>> 
>> Jim Pawley's handbook has a chapter that describes a few useful tests that can be done across different wavelengths to assess your microscope's axial resolution using a mirror. I have wondered for quite some time if there is any difference between using a mirror and the excitation wavelengths or a fluorescent object (microsphere) to test axial resolution. I could only find one posting on this in the archive:
>> 
>> http://lists.umn.edu/cgi-bin/wa?A2=ind0106&L=CONFOCALMICROSCOPY&D=0&P=8438
>> 
>> So I'm curious, what is the consensus out there right now? Is there a difference or not? I haven't actually had a chance to test it yet and see if the results obtained with a mirror (with laser illumination) match those obtained with a sub-diffraction sized fluorescent microbead.
>> 
>> John Oreopoulos
>> Research Assistant
>> Spectral Applied Research
>> Richmond Hill, Ontario
>> Canada
>> www.spectral.ca=