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Guy has explained it very clear. ONe thing to add: you may want that the
eyepiece image at the same focal distance with your confocal, so the
position of objective is fixed. If you only consider doing a z-section
within a few hunderds of microns, then you will find that the telescope
composed by the tube lens and the scan lens will give you such tolerance
(depth of focus) for you to do so, especially if you take the compromise
between the two close-by galvos.

Cheers,
Peng Xi
Ph. D.    Associate Professor
Dept. of Biomedical Engineering, College of Engineering
Peking University, Beijing, China
Tel: +86 10-6276 7155
Email: [log in to unmask]


On Thu, Jul 25, 2013 at 7:53 PM, Guy Cox <[log in to unmask]> wrote:

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>
> José,
>
>            You are quite right about the problem.  You just have to decide
> what compromises to make.  Ideally both X and Y scan mirrors should be
> imaged on the BFP of the objective and several manufacturers have achieved
> this by appropriate optics, while others have just opted to have them
> close-coupled and accept the compromise.  If you are now going to focus by
> moving the objective rather than the stage the risk of vignetting obviously
> increases.  On possible 'solution'  (or compromise) would be to introduce
> intermediate optics to make both scan planes telecentric  so that then the
> objective movement is the only problem.  I think you could get away with
> this in most cell biology cases.
>
>                                                                  Guy
>
> -----Original Message-----
> From: Confocal Microscopy List [mailto:[log in to unmask]]
> On Behalf Of DINTINGER José
> Sent: Thursday, 25 July 2013 6:32 PM
> To: [log in to unmask]
> Subject: design of XYZ scan system
>
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> Dear all,
> I'm currently working on the design and fabrication of a cheap compact
> confocal microscope and I have a question regarding the design of the
> scanning system. For practical reasons, the ideal solution for me would be
> to keep the sample stationary and scan the laser beam focus in the XYZ
> directions.
> After looking through the literature, I was thinking to use the standard
> design consisting of  2 closely spaced galvo mirrors for the XY scan , and
> move the objective in the axial direction for the Z stacks. However I am
> not sure whether these 2 approaches are compatible; from what I read it
> seems this is the case but there is a point that confuses me.
> Indeed, the proper positioning of the galvo mirrors requires that their
> pivot point is imaged on the back focal (telecentric) plane of the
> objective via a scan lens and tube lens, meaning that the distance between
> the mirrors and the back focal plane of the objective must remain fixed. On
> the other hand, if I move the objective (independently) to adapt the
> Z-position of the focus, it would mean that the mirror-objective distance
> is changed...
> I hope my question makes sense and I'd really grateful for any help.
> Many thanks,
> José
>
> José DINTINGER
> Research scientist
> BioMEMS Section
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> CSEM Centre Suisse d'Electronique et de Microtechnique SA Jaquet-Droz 1 |
> Case postale | CH-2002 Neuchâtel www.csem.ch
>