Question about No Cover Glass Objectives

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Antartica
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Joined: Wed Mar 04, 2020 4:52 am

Question about No Cover Glass Objectives

#1 Post by Antartica » Sun Mar 22, 2020 5:04 pm

What are the benefits of using no cover slip objectives? When do you use them? Online I can only find mention of using them with blood smears. Is that it?

Also, why aren't ALL objectives of type: no cover glass? With the different thicknesses of cover slips, which can cause poorer visual results, why even bother with that? Wouldn't it be better to NOT use cover slips at all?

P.S. I guess they offer some protection from wetting the objective in case you accidentally get too close. But is that the only benefit?

PeteM
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Joined: Tue Dec 06, 2016 6:22 am
Location: N. California

Re: Question about No Cover Glass Objectives

#2 Post by PeteM » Sun Mar 22, 2020 5:40 pm

The higher the magnification, the less depth of field.

So, the specimen needs to be in a flat plane, sometimes flat and within something like .10 mm from the objective.

Cover slip offers at least two advantages. First, a specimen can essentially be flattened or even attached on the underside of a cover slip. An objective designed to see through that .17mm cover slip can then see another .10mm into the specimen at high magnification.

Second advantage is that it protects the specimen and allows permanent mounting.

If you have a specimen that is dead flat and super thin and doesn't care about exposure to air, moisture in the air etc. then something like a NC objective and a thin smear will be fine.

Scarodactyl
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Joined: Sat Mar 03, 2018 9:09 pm

Re: Question about No Cover Glass Objectives

#3 Post by Scarodactyl » Sun Mar 22, 2020 6:14 pm

Most non-coverglass objectives are used for metallurgical/general industrial examination of surface textures, not for biological work. They are nice for doing reflected light photography of more three-dimensional subjects if they have sufficient working distance (many do not as they're meant for coaxial illumination, bf df or epi dic).

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