http://confocal-microscopy-list.275.s1.nabble.com/Astigmatism-aberration-as-a-function-of-distance-tp7582827p7582835.html
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...
> *****
> To join, leave or search the confocal microscopy listserv, go to:
>
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy> Post images on
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> *****
>
> 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]
>>