http://confocal-microscopy-list.275.s1.nabble.com/objective-focal-length-tp1588271p1597895.html
Thank you for that pointer. I agree, and the consensus seems to be that
something has not been reported properly in the paper. When I am puzzled about a
paper, I assume that I probably made a mistake. However, all of the responses
> The paper says it is a Zeiss Planachromat 25x/0.5 objective. I searched
> for such an objective and the only I found was the Zeiss Jena
> GF-Planachromat shown at
>
http://cgi.ebay.de/Zeiss-Jena-GF-Planachromat-Phv-25x%2F0,50-Phako--neu-_W0QQitemZ380085053453QQcmdZViewItemQQimsxZ20081127?IMSfp=TL0811271110001r39141
>
>
> It's easy to see by the diameter of the front lens (<5mm) alone that
> this objective cannot possibly have a working distance of 11m at an NA
> of 0.5. So it seems very likely that the specs given in the paper are
> simply wrong.
>
> Beat
>
>
>
> At 18:39 29-11-2008, Aryeh Weiss wrote:
>> Content-Transfer-Encoding: 7bit
>>
>> The problem is that an infinity corrected 25x lens with a 25mm focal
>> length should require a tube lens with a 625mm focal length (25x25).
>> Does such a microscope exist?
>>
>> --aryeh
>>
>>
>> Patrick Van Oostveldt wrote:
>>> Dear Arey,
>>> Not being an expert I should say: if the tube lens forms an image at
>>> 245mm (=focal length) and if the lens magnification is 25x the
>>> objective should have a focal length of 9.8mm. The working distance
>>> is smaller than this, but is not directly predictable.
>>> However the magnifcation inscribed on the lens (25X) is dependent on
>>> a specific focal length of the tube lens. For Nikon objectives it is
>>> 200mm for Zeiss it is 164.5nmm. Probably this can be the point of
>>> confusion.
>>> Best regards
>>> Patrick
>>> Quoting Aryeh Weiss <
[hidden email]>:
>>>
>>>> That is also how I understand it. So I assume that the distance between
>>>> the tube
>>>> lens and the intermediate image plane is the focal length of the
>>>> tube lens.
>>>>
>>>> Best regards,
>>>> --aryeh
>>>>
>>>> Guy Cox wrote:
>>>>> I am absolutely not an optics guru!
>>>>>
>>>>> But, as I understand it, an infinity corrected objective will form
>>>>> an image
>>>>> at 'infinity', so the distance from the principal plane to the
>>>>> object will be
>>>>> the focal length. But where the image is formed after the tube
>>>>> lens will
>>>>> depend on the focal length of the tube lens and we have to know
>>>>> this to make
>>>>> any useful calculation.
>>>>>
>>>>> It was all so much simpler in the days of 160mm tube length!
>>>>>
>>>>> Guy
>>>>>
>>>>> -----Original Message----- From: Confocal Microscopy List
>>>>> [mailto:
[hidden email]] On Behalf Of Aryeh Weiss
>>>>> Sent:
>>>>> Friday, 28 November 2008 7:20 PM To:
>>>>>
[hidden email] Subject: objective focal length
>>>>>
>>>>> I am confused with regard to the front focal length of objectives.
>>>>> I thought
>>>>> that the magnification of an infinity corrected objective will be the
>>>>> distance between the tube lens and the intermediate image, divided
>>>>> by the
>>>>> front focal length of the objective (which is where I expect the
>>>>> object to
>>>>> be). Since the objective is not really a thin lens, I can
>>>>> understand that the
>>>>> actual working distance may be less than the focal length, since
>>>>> the focal
>>>>> length may need to be measured from inside the objective casing.
>>>>>
>>>>> However, I have a paper that describes a 25x/NA=0.5 air objective,
>>>>> which has
>>>>> an 11mm working distance, as having a 25.1mm focal length, while
>>>>> the distance
>>>>> from the tube lens to the intermediate image is 245mm. This has me
>>>>> confused,
>>>>> and I realize that I do not understand something fundamental here.
>>>>>
>>>>> So, I turn to the optics gurus on the list to clear this up, with
>>>>> many thanks
>>>>> in advance.
>>>>>
>>>>> --aryeh -- Aryeh Weiss School of Engineering Bar Ilan University
>>>>> Ramat Gan
>>>>> 52900 Israel
>>>>>
>>>>> Ph: 972-3-5317638 FAX: 972-3-7384050
>>>>>
>>>
>>
>>
>> --
>> Aryeh Weiss
>> School of Engineering
>> Bar Ilan University
>> Ramat Gan 52900 Israel
>>
>> Ph: 972-3-5317638
>> FAX: 972-3-7384050
>
>