Posted by
Guy Cox on
URL: http://confocal-microscopy-list.275.s1.nabble.com/magnification-of-digital-microscopes-tp3989284p3990612.html
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
______________________________________________
Phone +61 2 9351 3176 Fax +61 2 9351 7682
Mobile 0413 281 861
______________________________________________
http://www.guycox.net
-----Original Message-----
From: Confocal Microscopy List [mailto:
[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?
No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 9.0.702 / Virus Database: 270.14.50/2481 - Release Date: 11/11/09 06:56:00