*****
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.
*****
Andrew,
the Res = 1.22 lambda / 2NA is based on the Rayleigh criterion and that
makes sense for self-luminous objects, so it is good for fluorescence
and dark field microscopy. Or for observing stars, which I believe was
what it was originally described for: How far have to points to be away
from each other... The 0.61 is the radius of the first ring minimum of
the diffraction pattern, 1.22 the diameter. In any case, the condenser
has no influence on this.
Now, if you use a condenser, then you are obviously up to transmission
microscopy. In this case, my understanding is that the Abbe equation is
more appropriate, which assumes a line pattern: How far do the lines in
a grid have to be apart from each other, such that you can resolve them
(i.e. catch the first ring maximum of the diffracted light). Abbe is
usually cited as d=lambda/2 NA. However, more precisely is the following:
d = lambda /(NAobj + NA condenser), where NA condenser must not equal or
smaller than NA objective. So, if NA condenser is bigger than NA
objective, then the formula falls back to d=lambda/2 NAobjective.
While Rayleigh is sort of a convention (why not use Sparrow?) the Abbe
limit is absolute. One condition seems to be that the light is coherent,
which is apparently fulfilled since the light comes from (only) one source.
In summary, I don't think Res = 1.22 lambda / NA (obj) + NA (condenser)
or a derivative form make sense, since it mixes Rayleigh and Abbe. But I
have seen this formula before and I definitely could be wrong, and I am
sure other listers have figured it out :-)
Steffen
Am 02.02.2017 um 22:53 schrieb Andrew Barlow:
> *****
> 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.
> *****
>
> Dear Confocal list,
>
>
> I'm about to roll out an update for my Android app, "Resolution", which some of you were kind enough to download when I published it late last year.
>
>
> The original version was really designed around fluorescence microscopy, it only gave the user the option to enter a single NA, and it calculates resolution using the following version of Abbe's equation:
>
>
> Res = 1.22 lambda / 2NA
>
>
> I thought it would be helpful to add the ability to characterise a transmitted light objective, with a distinct condenser NA and objective NA, and to calculate resolution based on the following version of the equation:
>
>
> Res = 1.22 lambda / NA (obj) + NA (condenser)
>
>
> My original thought was to just implement this version of the equation exactly as it is, a let the user freely enter the two NAs, and do the calculation. However, my understanding is that this version of the equation really only applies when the NA of the objective and the NA of the condenser are equal. Under circumstances in which they are unequal, the true resolution would be:
>
>
> Res = 1.22 lambda / 2 NAmin
>
>
> Where NAmin = the smallest NA of the condenser and objective. In such cases resolution is constrained by the smaller of the two NAs.
>
>
> This is pretty much what I've implemented, but I don't have the confidence to release this without first checking with this list that this is the right approach.
>
>
> If you could share your thoughts on this I'd be very grateful.
>
>
> If anyone would be interested in taking a look at the beta of the next version I'd be happy to share it with them.
>
>
> Many thanks,
>
>
> Andy Barlow
>
--
------------------------------------------------------------
Steffen Dietzel, PD Dr. rer. nat
Ludwig-Maximilians-Universität München
Biomedical Center (BMC)
Head of the Core Facility Bioimaging
Großhaderner Straße 9
D-82152 Planegg-Martinsried
Germany
http://www.bioimaging.bmc.med.uni-muenchen.de
|
