Nikon 50X objective with iris

[dtrinh]

Hi everyone,
I found this Nikon 50x objective online. It has an iris to change the numerical aperture from 0.5 to 0.85. It also says Oil.
My question is, does it need oil at all NA value? I thought oil immersion is only needed when an objective have high NA?
Thank you!

[PeteM]

The objective is designed to use oil immersion, regardless of the iris setting. The iris makes this an excellent objective to use with a darkfield condenser - just close the iris a bit to get the best image.

For brightfield you'll see deeper under the cover slip than a 100x oil objective and still have a very sharp .85na resolution objective with the iris wide open..

[LouiseScot]

Hi

I think they are no-coverslip objectives

Louise

[dtrinh]

The objective is designed to use oil immersion, regardless of the iris setting. The iris makes this an excellent objective to use with a darkfield condenser - just close the iris a bit to get the best image.

For brightfield you'll see deeper under the cover slip than a 100x oil objective and still have a very sharp .85na resolution objective with the iris wide open..

Thank you for the info. very interesting. It is difficult to make a dark field stop for objective above 40x; this objective solves the problem then.
Bests,

[dtrinh]

Hi

I think they are no-coverslip objectives

Louise

Hi,
It is written 160/-, so I guess it can be used both with and without coverslip?

[BramHuntingNematodes]

Immersion oil has the same ri as the slip so as long as you have the working distance you can use or not use

[LouiseScot]

Hi

I think they are no-coverslip objectives

Louise

Hi,
It is written 160/-, so I guess it can be used both with and without coverslip?

Yeah, I was thinking the '-' meant NGC (that would be 0) but I presume there's no value as it's adjusted/determined by the correction collar?

Louise

[LouiseScot]

Hi

I think they are no-coverslip objectives

Louise

Hi,
It is written 160/-, so I guess it can be used both with and without coverslip?

Yeah, I was thinking the '-' meant NGC (that would be 0) but I presume there's no value as it's adjusted/determined by the correction collar?

Louise

[Scarodactyl]

- just means it doesn't matter. A max 0.85 n.a. oil objective will not care one bit about the difference between coverslip glass and oil.

[LouiseScot]

- just means it doesn't matter. A max 0.85 n.a. oil objective will not care one bit about the difference between coverslip glass and oil.

But that would depend on the mounting medium? If it was an aqueous sample a cover glass would be needed and the cover glass thickness would matter? I have a feeling these objectives might have been made for viewing dried blood films with oil immersion. Correct me if I'm totally wrong!

Louise

[ldflan]

It's identified in the literature as designed for doing blood cell counts under darkfield illumination, hence the iris. Hemacytometers use a very thick cover glass (0.4mm), which may also explain "-" designation?

[LouiseScot]

Ah the objective is actually mentioned here https://www.microbehunter.com/microscop ... 739#p87739

I would check with the seller that the iris is in good working order...

Louise

Edit: The Nikon CF brochure is a useful resource https://krebsmicro.com/Nikon_CF.pdf

[Scarodactyl]

But that would depend on the mounting medium? If it was an aqueous sample a cover glass would be needed and the cover glass thickness would matter?

Not particularly. It doesn't matter how thick or thin the glass above the aqueous sample is since the remaining space is filled with equivalent oil. Honestly even on my 60x/1.40 which is rated for a 0.17 cover slip I can still get fairly great results without a cover slip. Whether you can look all the way down into an aqueous sample with good image quality is a different issue, but a 0.85 objective should be pretty tolerant of medium mismatch.

[apochronaut]

Plus the iris diaphragm allows for a slight tweak in order to increase the depth of field. With iris diaphragms there is seldom any noticeable resolution loss with iris closure up to a certain point but you can gain depth of field somewhat.

[dtrinh]

Thank you all for very informative inputs. I have ordered one, mostly to have the dark field capability.
Best regards.

[LouiseScot]

Thank you all for very informative inputs. I have ordered one, mostly to have the dark field capability.
Best regards.

Do post a review - and some images, if you can

Louise