Re: magnification of digital microscopes

Posted by Andreas Bruckbauer on
URL: http://confocal-microscopy-list.275.s1.nabble.com/magnification-of-digital-microscopes-tp3989284p3996042.html

Many thanks for the reply, I got the 70 µm from the 1 arc-min resolution for 20/20 vision as given in the Handbook of biological confocal microscopy by Pawley (Chapter the pixelated image). However I wrongly assumed that this would be for a line pair. It seems to be specified for the thickness of a line in the testpattern which is used for eye testing http://webvision.med.utah.edu/KallSpatial.html#introduction. So for one line pair it would be 140 µm. The EM grid has relatively thin lines compared to the test pattern so it might be more difficult to see and he mesh value would also correspond to a line pair. What would one need on the microscope side to make a fair comparison? The Rayleigh limit seems quite arbitrary.

Andreas

-----Original Message-----
From: Guy Cox <[hidden email]>
To: [hidden email]
Sent: Thu, 12 Nov 2009 3:37
Subject: Re: magnification of digital microscopes

The conventional LM recommendation is based on direct viewing through the 

eyepiece.  The human eye is assumed to have a resolution of 200µm, so to get 

200nm to 200µm is a magnification of x1000.  This is about 700 x NA.  You get 

roughly the same with a x40 NA 0.65 objective, which has a resolution of 500nm 

so you need a magnification at the eye of x400.  



If you are making a print on paper at a magnification of x350 your 200nm 

resolution will come out at 70µm, as you say (there's really no need to get 

pixels involved).  This is way below the commonly used value for resolution of 

the eye, hence the lower magnification.  Maybe some very young people with 

perfect eyesight could get to this value.  I've not met many people who can see 

the mesh of a 400 lpi EM grid (63.5µm) though young folk can often see 200 mesh 

(127 µm).  



So the brief answer would seem to be that you are taking a rather optimistic 

value for the resolution of the eye - where did you get that figure from?



                                         Guy 



Optical Imaging Techniques in Cell Biology

by Guy Cox    CRC Press / Taylor & Francis

     http://www.guycox.com/optical.htm

______________________________________________

Associate Professor Guy Cox, MA, DPhil(Oxon)

Electron Microscope Unit, Madsen Building F09,

University of Sydney, NSW 2006

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-----Original Message-----

From: Confocal Microscopy List [[hidden email]] On 

Behalf Of Andreas Bruckbauer

Sent: Thursday, November 12, 2009 8:58 AM

To: [hidden email]

Subject: magnification of digital microscopes



Hello,

somebody asked me about the magnification of our TIRF microscpe, however

this should also apply to confocal systems. I came up with the following:

The optical resolution of a high NA system is about 0.2 micrometer and

applying 2x Nyquist sampling this is about 100 nm for one pixel (on CCD or

confocal). At the end of the image processing pipeline this will be printed

or displayed somewhere at a resolution visible to the eye. This should be

one line pair per 1/60th degree which is about 70 micrometer at 25 cm

viewing distance. Gong from line pairs to pixels would give 35 micrometer

and the magnification would then be 35/0.1 = 350 x (rather low). Of course

one could print it bigger and on a compter screen it would be much bigger

but this would be empty magnification. Is this right? Why is useful

magnification for optical microscopes given as 500 x NA which would be 700x

in the above case? Is this because the fluorescence is so dimm that the eye

achieves lower resolution? 



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