Too small?

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MicrobeGazer45
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Too small?

#1 Post by MicrobeGazer45 » Mon May 25, 2020 9:39 pm

The smallest bacteria are about 500 - 200 nm, the ebola virus is 600 - 1400 nm . Could it be seen with a light microscope? If so, at what magnitude? If not, other bacteria would be too small for the light microscope, wouldn't they?

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Re: Too small?

#2 Post by Hobbyst46 » Mon May 25, 2020 10:02 pm

Wikipedia mentions that the width of the ebola virus is 80nm. If it looks like an open string and not as a compact 3d body (like a "wool ball"), it will not be visible in light microscopy, since 80nm is considerably below the resolution limit.
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Re: Too small?

#3 Post by MichaelG. » Tue May 26, 2020 7:11 am

A quick rule of thumb:

Short wavelength visible light has a wavelength of about 400nm

It is therefore possible to detect points which are about 200nm apart
... BUT no detail which is smaller than that will be visible.

Nyquist [sampling] theory explains why, in digital terms
Abbe, Airy, and Rayleigh illustrate how, in analogue terms

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Re: Too small?

#4 Post by 75RR » Tue May 26, 2020 7:23 am

MichaelG. wrote:
Tue May 26, 2020 7:11 am
A quick rule of thumb:

Short wavelength visible light has a wavelength of about 400nm

It is therefore possible to detect points which are about 200nm apart
... BUT no detail which is smaller than that will be visible.

Nyquist [sampling] theory explains why, in digital terms
Abbe, Airy, and Rayleigh illustrate how, in analogue terms

MichaelG.
One can take photos using 400nm light but you do not want to stare into it!
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Re: Too small?

#5 Post by MichaelG. » Tue May 26, 2020 9:51 am

75RR wrote:
Tue May 26, 2020 7:23 am
MichaelG. wrote:
Tue May 26, 2020 7:11 am
A quick rule of thumb:
[…]
One can take photos using 400nm light but you do not want to stare into it!
Very true ... but my point was that it sets the lower limit of all visual observation.
[ in white light, the longer wavelengths make no further contribution to that limit ]

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Re: Too small?

#6 Post by 75RR » Tue May 26, 2020 10:59 am

MichaelG. wrote:
Tue May 26, 2020 9:51 am
75RR wrote:
Tue May 26, 2020 7:23 am
MichaelG. wrote:
Tue May 26, 2020 7:11 am
A quick rule of thumb:
[…]
One can take photos using 400nm light but you do not want to stare into it!
Very true ... but my point was that it sets the lower limit of all visual observation.
[ in white light, the longer wavelengths make no further contribution to that limit ]

MichaelG.
It was a caution for the OP ;)
Last edited by 75RR on Tue May 26, 2020 11:08 am, edited 2 times in total.
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Re: Too small?

#7 Post by Hobbyst46 » Tue May 26, 2020 11:03 am

75RR wrote:
Tue May 26, 2020 10:59 am
MichaelG. wrote:
Tue May 26, 2020 9:51 am
75RR wrote:
Tue May 26, 2020 7:23 am


One can take photos using 400nm light but you do not want to stare into it!
Very true ... but my point was that it sets the lower limit of all visual observation.
[ in white light, the longer wavelengths make no further contribution to that limit ]

MichaelG.
It was a caution for the OP ;)
Given the title subject, 400nm light would be of the least concern...
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Re: Too small?

#8 Post by MichaelG. » Tue May 26, 2020 2:28 pm

75RR wrote:
Tue May 26, 2020 10:59 am
It was a caution for the OP ;)
... and a very wise one too.

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Re: Too small?

#9 Post by wporter » Tue May 26, 2020 4:44 pm

the ebola virus is 600 - 1400 nm . Could it be seen with a light microscope? If so, at what magnitude? If not, other bacteria would be too small for the light microscope, wouldn't they?
To clarify for the OP, actually, using darkfield, they might be 'seen', although maybe not very recognizable or identifiable. Some cutting-edge microscopy these days relies on just detection and image reconstruction from point sources, from fluorescence or darkfield techniques, below the Rayleigh limit.

Here's a quote re classic darkfield:
Simultaneously, even smaller particles (detectable solely by their ability to scatter light) now diffract enough light to become visible and suspended particles can be seen even when their diameters are smaller than 40 nanometers, which is about one-fifth the 200 nanometer resolution limit with oil immersion objectives of the highest numerical aperture. In biological applications, the movements of living bacterial flagella that average about 20 nanometers in diameter (too small to be seen in brightfield or DIC illumination) can be observed and photographed using high numerical aperture darkfield condensers.
from https://micro.magnet.fsu.edu/primer/tec ... field.html


Not darkfield, but for an interesting read, circa 2000:

True optical resolution beyond the Rayleigh limit achieved by standing wave illumination
Jan T. Frohn, Helmut F. Knapp, and Andreas Stemmer

from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC16528/

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