# Dipping objectives - DI water or PBS?

**URL:** <https://forum.microlist.org/t/dipping-objectives-di-water-or-pbs/856>\
**Category:** Hardware\
**Created:** [February 7, 2020, 5:40am UTC](https://forum.microlist.org/t/dipping-objectives-di-water-or-pbs/856 "2020-02-07T05:40:58Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![adamkglaser](https://avatars.discourse-cdn.com/v4/letter/a/c2a13f/32.png) [@adamkglaser](https://forum.microlist.org/u/adamkglaser)\
**Post date:** [February 7, 2020, 5:40am UTC](https://forum.microlist.org/t/dipping-objectives-di-water-or-pbs/856/1 "2020-02-07T05:40:58Z")

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Hi everyone,  
I was wondering if anyone had experience or knew if water dipping objectives (specifically the Zeiss W Plan-Apochromat) were designed for immersion in DI water or PBS. Or if they have been designed for both refractive indices?  
Thanks!  
Adam

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**Author:** ![Hazen\_Babcock](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.microlist.org/hazen_babcock/32/281_2.png) [@Hazen\_Babcock](https://forum.microlist.org/u/Hazen_Babcock)\
**Post date:** [February 7, 2020, 11:30pm UTC](https://forum.microlist.org/t/dipping-objectives-di-water-or-pbs/856/2 "2020-02-07T23:30:10Z")

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The refractive indexes are very similar, 1.333 (water) versus 1.335 (PBS, according to a Google search for “phosphate buffered saline refractive index”). I don’t think this difference is large enough to be significant from an objective design perspective. However most vendors are happy to let you demo there objectives so you may be able to test it.

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**Author:** ![adamkglaser](https://avatars.discourse-cdn.com/v4/letter/a/c2a13f/32.png) [@adamkglaser](https://forum.microlist.org/u/adamkglaser)\
**Post date:** [February 8, 2020, 5:43am UTC](https://forum.microlist.org/t/dipping-objectives-di-water-or-pbs/856/3 "2020-02-08T05:43:52Z")

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Thanks, I also now see online that PBS should have a RI of 1.335. If this is true then I agree it is a tiny difference. Measuring some PBS in our lab on a refractometer I got a reading of 1.341 which seems like it could start to have an impact. I will try to contact Zeiss and see what they designed the objective for, otherwise I’ll just go with DI water for now!

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**Author:** ![JamesOrth](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.microlist.org/jamesorth/32/153_2.png) [@JamesOrth](https://forum.microlist.org/u/JamesOrth)\
**Post date:** [February 14, 2020, 4:16am UTC](https://forum.microlist.org/t/dipping-objectives-di-water-or-pbs/856/4 "2020-02-14T04:16:30Z")

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I would say it was designed for water, which I assume the ‘W’ in the name indicates. That said, I’ve used lenses with water and then with PBS, directly comparing them, and found no difference. What are the specs of the objective and how deep are you imaging? I have heard a few reps say that water is safer as if the PBS dries (that would never happen), then its possible there could be some concern. Good luck! My experience is mainly with a Olympus XLPLN25XWMP2 NA1.05 WD2.0mm, but also an Olympus 60X LUMPLFLN-W NA1.10 and Nikon CFI SR Plan Apo IR 60XC WI NA1.27.