http://confocal-microscopy-list.275.s1.nabble.com/Astigmatism-aberration-as-a-function-of-distance-tp7582827p7582839.html
I will check how tight I mounted the mirrors. For the fringes things, I
will look into it. And I don't have a DIC wedge in the system. Now I am
simple system, i.e. fiber+collimation lens+imaging lens+camera. I will
8 St. Mary St., Boston, MA, 02215
> *****
> 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.
> *****
>
> Hi Lu
>
> A mirror can produce astigmatism -if it is bent by pressure from the
> mount. The amount of astigmatism may not depend on distance -depends on
> where it is arising -for sure if you have to move an alignment tilt screw
> when moving an optic along the axis you have something off axis.
> Astigmatism is most easily produced by a surface that does not have equal
> radii of curvature in two orthogonal directions this could be a tilted
> spherical surface or a bent plane and you don’t need much to see the effect
> -just a one wave error in the wavefront will do… That you lost the
> astigmatism when you substituted a 150x objective suggests to me that you
> look at the collimator. Have you considered looking at fringes to help you
> decide what the error is? Look at some of the telescope literature on the
> web to see how to do this.
>
> As a last thought, you don’t by any chance have a DIC wedge in the system
> do you and you are not seeing an eyepiece problem?
>
> And a beam diameter of 5mm sounds a bit small to fill the rear aperture of
> most objectives...
>
> HTH
>
> Mark
>
>
> a cylindrical lens -which is what you get of you go off axis
> On 5/11/2014, at 9:08 am, Yan, Lu <
[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.
> > *****
> >
> > Hi Kyle, Mark,
> >
> > Thanks for your suggestions. Regarding to Kyle's comments/questions:
> >
> > 1) my beam splitter is those cube beam splitter. I should have mentioned
> > that even without beam splitter, when I imaged the collimated beam
> through
> > a lens far away from the collimation lens [between two lenses are just
> two
> > mirrors (1 inch Thorlabs silver protected mirror)], I got similar amount
> of
> > astigmatism. [To Mark: would mirrors usually also cause astigmatism in
> > microscopy? Then does that make sense to use larger mirrors? my beam
> 1/e^2
> > size is about 5 mm in diameter.]
> >
> > 2) the fiber is single moded, and I have tried imaging is using a 150X
> > Nikon objective lens (single lens imaging), and it does not have higher
> > order mode, pretty Gaussian. BTW, imaging with 150X obj. did not give me
> > astigmatism as I moved the fiber (or the camera) back and forth.
> >
> > Besides these, I have another question about astigmatism. Supposed that I
> > have an off-axis lens for the collimation of my Gaussian illumination
> beam,
> > does the amount of astigmatism I will get depend on the distance after
> > which I will image the Gaussian beam?
> >
> > Thanks,
> > Lu
> >
> > -----------------------------------------------------
> > Lu Yan
> > Nanostructured Fibers and Nonlinear Optics Laboratory
> > Electrical and Computer Engineering
> > Boston University
> > 8 St. Mary St., Boston, MA, 02215
> > (617)353-0286
> >
[hidden email]
> > -----------------------------------------------------
> >
> > On Wed, Nov 5, 2014 at 3:04 AM, Mark Cannell <
[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.
> >> *****
> >>
> >> I agree, it could be the mirrors -are they pinched in some way or else
> you
> >> have a lens/source off axis.
> >> HTH
> >>
> >> Mark
> >>
> >> On 5/11/2014, at 7:56 am, Kyle Douglass <
[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.
> >>> *****
> >>>
> >>> Hi Lu,
> >>>
> >>> On 11/05/2014 05:36 AM, Yan, Lu wrote:
> >>>> Hi folks,
> >>>>
> >>>> I am building a fiber based confocal microscopy setup (with sample
> stage
> >>>> scanning). But I always got some astigmatism aberration in PSF
> >> measuremnts.
> >>>> The similar aberration was there even I replaced the objective lens
> >> with a
> >>>> regular lens and imaged my illumination beam through that lens with a
> >>>> camera. I got elongated beam 'spot' on both sides of the focal plane,
> >> and
> >>>> the orientation of the two 'spot' were orthogonal. I think that is
> >>>> astigmatism aberration if I am not mistaken. I draw a schematic in
> >> Evernote
> >>>> so I can include it here. Here is the link:
> >>>>
> >>
>
https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe> >>>> (copy and paste if the link does not work in email)
> >>>>
> >>>> I tried to adjust both lens in xy to avoid off-axis incident, but the
> >>>> aberration would go away. So I got confused where they came from. I
> hope
> >>>> someone here could lead me a direction to further look into it.
> >>>>
> >>>> Thanks very much,
> >>>> Lu
> >>> Here are two quick checks that came to mind. Maybe you've tried them,
> >> but it's still good to check all the possible sources of the problem:
> >>>
> >>> 1) Is the beam splitter really a glass cube as it's drawn, or one of
> the
> >> thin dichroic-like beam splitters? Sometimes the thin dichroics are
> >> slightly warped in one direction and can introduce astigmatism after
> >> reflection.
> >>>
> >>> 2) When you illuminate a flat surface or white piece of paper with
> light
> >> directly coming from the single mode fiber, do you see a smooth,
> >> homogeneous intensity distribution or some other kind of structure? I've
> >> noticed that one can occasionally get a weak first-order mode coming
> from
> >> the fiber if the wavelength is close to the multimode cut-on. It may not
> >> necessarily lead to astigmatism, but it's still good to check.
> >>>
> >>> Good luck!
> >>>
> >>> Dr. Kyle Douglass
> >>> The Laboratory of Experimental Biophysics
> >>> EPFL, Lausanne, Switzerland
> >>
> >> Mark B. Cannell Ph.D. FRSNZ
> >> Professor of Cardiac Cell Biology
> >> School of Physiology & Pharmacology
> >> Medical Sciences Building
> >> University of Bristol
> >> Bristol
> >> BS8 1TD UK
> >>
> >>
[hidden email]
> >>
>