http://confocal-microscopy-list.275.s1.nabble.com/Power-at-Immersion-Lenses-tp7589305p7589313.html
the smaller aperture lenses. This will cause a great deal of apparent power
lenses. He also nicely explained the point about not focusing on the sensor
surface that I tried to get at earlier. Thanks!
> *****
> To join, leave or search the confocal microscopy listserv, go to:
>
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> *****
>
> A few quick notes:
> 1) Be careful comparing between objectives. Not only is the transmission
> efficiency different, but the area of the back aperture is also different,
> meaning the amount of light going into an objective also varies. Also,
> unless the light intensity profile at the back aperture is a perfectly
> uniform top hat, the difference in light going into an objective won't be
> as simple as the ratio of the back aperture areas.
>
> 2) With high NA objectives, you run into an additional problem of
> increasing amounts of light reflecting off of the power meter (think
> Brewster's angle). As such, a lot of the marginal photons will reflect,
> reducing the overall measurement.
>
> 3) As already mentioned, the back reflection due to the glass-air interface
> at the objective lens will also reduce the amount of transmitted light
> compared to a glass-oil interface, and even more so if the objective lens
> is scratched or dirty.
>
> 4) Power meters can saturate and become non-linear if all the light is
> shined on it in a very small area. Ideally, you will want to cover as much
> of the sensor as possible, especially at higher intensities.
>
> With this in mind, a quick and dirty solution would be to get the objective
> as close to (if not lightly touching) the sensor area as possible, and then
> gradually increase the light intensity until you get a stable measurement.
> Then gradually pull the objective away until you reach a peak power
> reading. The objective may need to be able to get within a millimeter of
> the sensor to have the marginal rays stay within the sensor area. Due to
> the issues stated above, this will be a slight underestimation, but it will
> definitely get you in the ball park.
>
> If you need a much more accurate measurement, an oil immersion compatible
> power meter seems the best (although fairly expensive) option:
>
https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_ID=2191>
> One other option that comes to mind would be if you had an oil immersion
> condenser, you could use it to recollimate the light from the first
> objective, and then place the power meter at the back aperture of the
> condenser. With everything lined up correctly, and without any scattering
> material between the objective lenses, the losses from the condenser should
> be purely transmission losses, allowing you to accurately back-calculate
> the intensity at the sample plane. Obviously, make sure the aperture stop
> is wide open.
>
> Cheers,
> Ben Smith
>
>
>
> On Fri, Mar 15, 2019 at 12:14 PM Jim Haley <
[hidden email]> wrote:
>
> > *****
> > To join, leave or search the confocal microscopy listserv, go to:
> >
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy> > Post images on
http://www.imgur.com and include the link in your
> posting.
> > *****
> >
> > Are you trying to measure relative light output at the various
> > proximities or absolute light output in terms of units such as Lux?
> >
> > Thanks And Have a Great Day!
> >
> > Jim Haley
> >
> >
> >
> > ******************************
> >
> > Jim Haley
> >
> > Applications Engineer
> >
> > MVIA, Inc.
> >
> > P.O. Box 161
> >
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> >
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> >
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> >
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[hidden email] <mailto:
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> >
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http://www.mvia.com/>
> >
> > Digital Microscope Cameras from MVIA <
> >
http://www.mvia.com/Digcams/dig_cameras.html>
> >
> > Image Analysis Software from MVIA <
> >
http://www.mvia.com/IASoftware/ia_software.html>
> >
> > ******************************
> >
> >
> > On 3/15/2019 11:08 AM, Claire Brown, Dr. wrote:
> > > *****
> > > To join, leave or search the confocal microscopy listserv, go to:
> > >
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy> > > Post images on
http://www.imgur.com and include the link in your
> > posting.
> > > *****
> > >
> > > Hello All,
> > >
> > > We are trying to measure the power of a light source through a 63x oil
> > immersion lens. With the short focal distance the power we measure is
> > highly dependent on the position of the sensor relative to the lens.
> > >
> > > Can the power be measured this way or do we need to get a sensor that
> we
> > can put oil on and use oil immersion to really get a proper measure of
> the
> > power at the sample?
> > >
> > >
> > > Sincerely,
> > >
> > > Claire
> > >
> >
>
>
> --
> Benjamin E. Smith, Ph. D.
> Imaging Specialist, Vision Science
> University of California, Berkeley
> 195 Life Sciences Addition
> Berkeley, CA 94720-3200
> Tel (510) 642-9712
> Fax (510) 643-6791
> e-mail:
[hidden email]
>
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http://vision.berkeley.edu/>
>