How is the focal length of an objective calculated?

[ppoonamk]

Hi,

I am using an objective lens to illuminate my object by a collimated beam. The magnification and NA is available on the objective. How can I calculate the focal length from this information? The objective is not infinity corrected. Thank you

 

[Simon Bridge]

IIRC: You need to measure the LDDV.

 

[Andy Resnick]

Non-infinity corrected microscope lenses are typically based on a tube length of either 160mm (RMS or DIN standard) or 170mm (JIS). Of course, just to be different, Olympus used 180mm...

The magnification is (tube length)/(lens focal length). Note the focal length is not the front working distance.

 

[Simon Bridge]

... or you could just know how people build these things :)

 

[ppoonamk]

Thank you for all the answers. Using the tube length in my calculations worked. Thanks :)