Hi Beat,

The info is from a paper by Ovryn and Izen, JOSA A/vol 17, No 7, p. 1202 (july 
2000), in section 3. A colleague asked me for some help, and since I dont 
understand it, I turned to the list.

Best regards,
--aryeh



Beat Ludin wrote:
> Hi Aryeh
> 
> Maybe the tube lens is not the original one, so that the "25x" objective 
> really functions as a 10x in this setup?
> Can you give us more info about the setup. A 25x/0.5 air objective with 
> a 11mm WD must be pretty big...
> 
> Beat
> 
> At 09:20 28-11-2008, you wrote:
>> 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
> 
>