Weird leitz objective

[Rossf]

I came across a leitz inverted objective online - an L 25x with a low low N/A of .22-its mentioned in the Diavert manual as possible objective combinations-what would such a low N/A be useful for-I know lower N/A objectives can be advantageous for inverted work for a bit more depth of focus but .22 is very low for 25x-what would that type of objective be useful for? Just curious...
Cheers ross

[MichaelG.]

Ross

I can only assume that the 0.22 NA is necessary to achieve the rather impressive free working distance of 14.8mm

MichaelG.

[Rossf]

Thanks MichealG-didn’t think about the working distance aspect-I’ve got a Leitz L 40x .5 that is just sharp enough for its N/A but nice depth of focus-inverted objectives are a different beast design wise..
Ross

[MichaelG.]

To my astonishment, my Google search* found just one reference:
https://repository.ubn.ru.nl/bitstream/ ... sequence=1

MichaelG
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*
leitz "L25x/0.22" objective

[Scarodactyl]

Usually that kind of extreme NA compromise for working distance doesn't kick in until about 50x. Maybe it is meant for extreme DoF?