Re: Are lower magnification objectives brighter?

Posted by Christoph Ruediger Bauer on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Are-lower-magnification-objectives-brighter-tp7592013p7592014.html

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Hi,

I teach my students that light gathering power of an objective depends on the NA raised to the power of four divided by its magnification squared. I think the concept comes from Shinya Inoué probably in his book "video microscopy" if I remember correctly.
Not sure if the confocal setup is changing this principle as it may not always make full use of the NA (for example when using a beam expander).
Best regards,
Christoph


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-----Original Message-----
From: Confocal Microscopy List <[hidden email]> On Behalf Of Andreas Bruckbauer
Sent: 22 March 2021 17:28
To: [hidden email]
Subject: Are lower magnification objectives brighter?

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Dear all,
Are lower magnification objectives brighter than higher magnification ones when they have the same NA, e.g. a 40x NA 1.4 objective compared to 63x NA 1.4? I mean for confocal microscopy.

Confocal.nl stated this is a recent webinar and on their website:
“A lower magnification allows for a larger field of view and brighter images, since light intensity is inversely proportional to the magnification squared”https://www.confocal.nl/#rcm2

I would think that this is caused by less light going through the smaller back focal aperture when the illumination is held constant? Most of the light is clipped as explained in fig 1 of  https://www.nature.com/articles/s41596-020-0313-9
So, the microscope manufacturer could adjust the illumination beam path and laser powers to best suit the objective?Or are lower magnification objectives really brighter?  

The field of view will obviously be larger for the 40x objective, but I am more interested to understand the claimed benefit in brightness. 

best wishes

Andreas