Is Slide thickness critical?

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75RR
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Is Slide thickness critical?

#1 Post by 75RR » Mon Apr 19, 2021 4:53 pm

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It suddenly occurred to me that though I do take into account cover slip thickness I have not done the same with slide thickness.

Both my slide boxes have 1.0/1.2mm written on them. Though I have not measured the slides. Is there an ideal thickness?
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BramHuntingNematodes
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Re: Is Slide thickness critical?

#2 Post by BramHuntingNematodes » Mon Apr 19, 2021 5:23 pm

I believe for immersion that slide thickness is a consideration. I have an achromat condenser with a large thickness requirement that might be difficult to focus properly with a very thin slide. Maybe you could do it with some more viscous immersion oil though. I have three darkfield condensers that have different thickness requirements as well. For general non-immersion brightfield or even phase it has not been important.
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75RR
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Re: Is Slide thickness critical?

#3 Post by 75RR » Mon Apr 19, 2021 5:47 pm

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Thanks

Found this in Fundamentals of light microscopy
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Re: Is Slide thickness critical?

#4 Post by Hobbyst46 » Mon Apr 19, 2021 8:39 pm

I believe that exact slide thickness in an upright microscope is important for optimal illumination, since the condenser top lens is usually very close to the slide bottom.
And perhaps important also for inverted microscope, if a slide were placed on the stage, coverslip on top - not sure since I only used the inverted with Petri dishes.
Optimal slide thickness (I think) is 1.05-1.1mm.

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Re: Is Slide thickness critical?

#5 Post by 75RR » Mon Apr 19, 2021 9:28 pm

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Thanks Hobbyst46, looks like I am going to start measuring slide thickness as well now.

Found this in Light Microscopy by Murray and Robinow page 15
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Re: Is Slide thickness critical?

#6 Post by apochronaut » Mon Apr 19, 2021 10:10 pm

Currently, a slide thickness of 1mm is considered optima for most applicationsl. In the past, thicker slides were more often used, ahout 1.2mm. The thickness of the slide does not affect the performance of the objective lens directly but does indirectly by affecting the performance of the condenser. If you look at the slide as being the coverslip of the condenser, the same rules that govern objective coverslop performance apply to the condenser slide relationship. This is why manufacturers instead of saying, just go ahead and use a 1.25 N.A. condenser dry, manufacture actual dry condensers, because an oil immersion condenser used dry will suffer from spherical aberration, just like an oil immersion objective does when used dry. Fortunately, spherical aberration in a condenser is not as devastating to the image as it is in an objective. Anyone who has adjusted a condenser for any of the contrast enhancement techniques will know the effect of s.a. through a condenser, though.

So, slide thickness is more relavent when air is the immersion medium. DF condensers used to be marked with the optimum slide thickness ; very important since a fairly precise angle is required in order to reduce loss of light due to transmission through the slide surface, instead of tir. It also will have some effect on the working N.A. of the condenser, so where one is utilizing a high N.A. objective, there could be a slight loss in resolution with a thicker slide.

With an oiled condenser and an oiled objective, as long as the slide has a refractive index that maintains homogeneity of the system , a few tenths of a mm aren't going to do too much. If it was a quartz slide for instance, the situation might be a little different.

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