Back Focal Plane of Objective Lens

[V Hahn]

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Hey,

I am using a Leica HC PL APO 100x/1.40 Oil CS2 Objective Lens, which I want to integrate into a 4f-system. Does anyone know the location of the rear focal plane of this objective lens? Until now I was assuming it is somewhere near the thread, without knowing...

Thanks!

[Benjamin Smith]

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For most objectives, the back focal plane is just inside the back lens.  For example, if you look in the back of an adjustable NA objective, you will see this is where the aperture is.  In general, I've found that if I aim the focal plane at the back lens, then I get no vignetting across the full field of view.  

-Ben Smith

Sent from my iPhone

On Mar 12, 2017, at 1:42 PM, V Hahn <[hidden email]> wrote:

> *****
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> *****
>
> Hey,
>
> I am using a Leica HC PL APO 100x/1.40 Oil CS2 Objective Lens, which I want to integrate into a 4f-system. Does anyone know the location of the rear focal plane of this objective lens? Until now I was assuming it is somewhere near the thread, without knowing...
>
> Thanks!

[Edward Allgeyer]

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Dear Dr. Hahn

I believe Leica uses a letter code on the side of the objective to
designate the back focal plane position. Its not the easiest thing to find
on the Leica website but they have some details here:

http://www.leica-microsystems.com/products/microscope-
objectives/labeling-of-objectives/back-focal-plane/

Hopefully this covers your objective. If not you'll have to get in touch
with Leica.

Best regards,
Ed

On Sun, Mar 12, 2017 at 8:42 PM, V Hahn <[hidden email]> wrote:

> *****
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> *****
>
> Hey,
>
> I am using a Leica HC PL APO 100x/1.40 Oil CS2 Objective Lens, which I
> want to integrate into a 4f-system. Does anyone know the location of the
> rear focal plane of this objective lens? Until now I was assuming it is
> somewhere near the thread, without knowing...
>
> Thanks!
>

[Werner Wittke]

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Dear V. Hahn,
the backfocal plane of this objective is 17,5mm inside the objective measured from the objective shoulder.
Or 27,5mm from object plane.

best
Werner

[John Oreopoulos]

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Hi,

There have been some good responses so far, but practically speaking,  
if you want to put the objective lens into a 4f relay, then one easy  
way to find the BFP is to put a collimated light beam (easiest with a  
laser) into a long focal length lens (something like 200mm focal  
length) and then put the back of the objective at the 200 mm lens  
focus where the light is converging (you can see the 200 mm lens focus  
with an index card moved along the beam path). Then axially translate  
the objective until you see a collimated beam coming out of the front  
end of the objective (find the position of least divergence). In that  
condition, you know you have the BFP of the objective resting at the  
focus of the lens, and you can "look" to see where that is in relation  
to the objective barrel length and where you saw the focus before with  
the index card.

For high NA objectives, you'll find that the BFP exists somewhere  
inside the objective barrel. For low mag, low NA objectives, it  
usually resides near the objective barrel thread / back aperture.

Cheers,

John Oreopoulos
Staff Scientist
Andor Technology
www.andor.com

Quoting V Hahn <[hidden email]>:

> *****
> 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.
> *****
>
> Hey,
>
> I am using a Leica HC PL APO 100x/1.40 Oil CS2 Objective Lens, which  
>  I want to integrate into a 4f-system. Does anyone know the location  
>  of the rear focal plane of this objective lens? Until now I was  
> assuming it is somewhere near the thread, without knowing...
>
> Thanks!
>

[Reto Fiolka]

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Dear all

To add to John's suggestion, to find the plane where your laser focus is (of the lens with a long focal length, say f=200mm in John's example), there is a great trick I learned from Mats Gustafsson:

insert a metal surface into the beampath (say a metal ruler) and watch at some distance the reflected speckle pattern. The coarsest speckle pattern occurs when the metal surface is in the beam waist of the laser focus. Then mark the position of the metal surface on the table.

It turns the problem of finding the laserfocus upside down, instead of finding the smallest spot on an index card (which might be beyond your eye's resolution) you look for the largest speckle structures.

Best,
Reto

[John Oreopoulos]

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Oh, that's a really good trick. Thanks for sharing! You can't find wisdom and lore like that in a textbook.

Cheers,

John Oreopoulos

> On Mar 14, 2017, at 2:40 PM, Reto Fiolka <[hidden email]> wrote:
>
> *****
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> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
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> *****
>
> Dear all
>
> To add to John's suggestion, to find the plane where your laser focus is (of the lens with a long focal length, say f=200mm in John's example), there is a great trick I learned from Mats Gustafsson:
>
> insert a metal surface into the beampath (say a metal ruler) and watch at some distance the reflected speckle pattern. The coarsest speckle pattern occurs when the metal surface is in the beam waist of the laser focus. Then mark the position of the metal surface on the table.
>
> It turns the problem of finding the laserfocus upside down, instead of finding the smallest spot on an index card (which might be beyond your eye's resolution) you look for the largest speckle structures.
>
> Best,
> Reto

[John Oreopoulos]

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Of course, if it's not obvious to you, be laser safe if you're going to use Reto's finding focus trick.

John Oreopoulos

> On Mar 14, 2017, at 2:51 PM, John Oreopoulos <[hidden email]> wrote:
>
> *****
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> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
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> *****
>
> Oh, that's a really good trick. Thanks for sharing! You can't find wisdom and lore like that in a textbook.
>
> Cheers,
>
> John Oreopoulos
>
>> On Mar 14, 2017, at 2:40 PM, Reto Fiolka <[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.
>> *****
>>
>> Dear all
>>
>> To add to John's suggestion, to find the plane where your laser focus is (of the lens with a long focal length, say f=200mm in John's example), there is a great trick I learned from Mats Gustafsson:
>>
>> insert a metal surface into the beampath (say a metal ruler) and watch at some distance the reflected speckle pattern. The coarsest speckle pattern occurs when the metal surface is in the beam waist of the laser focus. Then mark the position of the metal surface on the table.
>>
>> It turns the problem of finding the laserfocus upside down, instead of finding the smallest spot on an index card (which might be beyond your eye's resolution) you look for the largest speckle structures.
>>
>> Best,
>> Reto

[V Hahn]

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John, Retoure, thanks a lot for your tips, didn't hear about the speckled idea before, sounds like a neat idea!

[Nico Stuurman-3]

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On 3/14/17 11:51 AM, John Oreopoulos wrote:
> Oh, that's a really good trick. Thanks for sharing! You can't find wisdom and lore like that in a textbook.

Actually, you can find it in this excellent book chapter by Rainer
Heintzmann (
http://onlinelibrary.wiley.com/doi/10.1002/9783527671595.app1/pdf ),
which I found since you linked to it on this mailing list:
http://confocal-microscopy-list.588098.n2.nabble.com/4f-system-alignment-with-fluorescent-light-td7583200.html,
so all credit should still go to this list!


Best,

Nico

>
>> On Mar 14, 2017, at 2:40 PM, Reto Fiolka <[hidden email]> wrote:
>>
>>
>> Dear all
>>
>> To add to John's suggestion, to find the plane where your laser focus is (of the lens with a long focal length, say f=200mm in John's example), there is a great trick I learned from Mats Gustafsson:
>>
>> insert a metal surface into the beampath (say a metal ruler) and watch at some distance the reflected speckle pattern. The coarsest speckle pattern occurs when the metal surface is in the beam waist of the laser focus. Then mark the position of the metal surface on the table.
>>
>> It turns the problem of finding the laserfocus upside down, instead of finding the smallest spot on an index card (which might be beyond your eye's resolution) you look for the largest speckle structures.
>>
>> Best,
>> Reto

[John Oreopoulos]

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Amazing, I totally forgot about that book chapter, but I don't think I ever read the part about finding a lens focus. That's the problem with electronic versions of a publication: When they're not at your finger tips in a physical form, it's easy to forget they are there and browse them. I probably responded about that book chapter in the previous post because it was fresh in my mind at the time and I had come across the book chapter recently. Since then it remains buried in the depths of my computer directories. Kudos to Rainer (again!). Thanks for helping me re-discover this one, Nico!

John Oreopoulos


On 2017-03-15, at 4:27 PM, Nico Stuurman wrote:

> *****
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> *****
>
> On 3/14/17 11:51 AM, John Oreopoulos wrote:
>> Oh, that's a really good trick. Thanks for sharing! You can't find wisdom and lore like that in a textbook.
>
> Actually, you can find it in this excellent book chapter by Rainer Heintzmann ( http://onlinelibrary.wiley.com/doi/10.1002/9783527671595.app1/pdf ), which I found since you linked to it on this mailing list: http://confocal-microscopy-list.588098.n2.nabble.com/4f-system-alignment-with-fluorescent-light-td7583200.html, so all credit should still go to this list!
>
>
> Best,
>
> Nico
>
>>
>>> On Mar 14, 2017, at 2:40 PM, Reto Fiolka <[hidden email]> wrote:
>>>
>>>
>>> Dear all
>>>
>>> To add to John's suggestion, to find the plane where your laser focus is (of the lens with a long focal length, say f=200mm in John's example), there is a great trick I learned from Mats Gustafsson:
>>>
>>> insert a metal surface into the beampath (say a metal ruler) and watch at some distance the reflected speckle pattern. The coarsest speckle pattern occurs when the metal surface is in the beam waist of the laser focus. Then mark the position of the metal surface on the table.
>>>
>>> It turns the problem of finding the laserfocus upside down, instead of finding the smallest spot on an index card (which might be beyond your eye's resolution) you look for the largest speckle structures.
>>>
>>> Best,
>>> Reto

[Steffen Dietzel]

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Am 16.03.2017 um 05:31 schrieb John Oreopoulos:
> *****
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> *****
>
> Amazing, I totally forgot about that book chapter, but I don't think I ever read the part about finding a lens focus. That's the problem with electronic versions of a publication:

Hint: The paper version is available at your local book store (or at
least at an online book store) for around 95 Euro (in Germany).

;-)

And just now while checking the price I see that there is a 2nd edition
announced for 17. Mai 2017 for 120 Euro (amazon.de) or April 2017 for
144 Euro (publisher's web site). The major chapters seem to be the same,
except for a new "Appendix B: Matrices and Images". More information is
not yet available.


Steffen


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