100X Dry Objective Working Distance

[mike42]

What is considered to be the minimum safe working distance for 100X dry objectives. I'm referring to a working distance which results in not having to be concerned with the objective coming into contact with the slide or cover slip.

[Greg Howald]

You may need a long working distance objective. They are available from what is called the big four manufactures. Nikon sells them.
Greg

[viktor j nilsson]

A 100x dry LWD is a pretty limited objective. A regular (short working distance) 100x dry would be limited to a NA of less than 1.0, which is already a disappointing low resolution for that magnification. Long working distance always comes at the expense of NA, so a LWD dry 100x will have an even lower NA. In the finite Nikon CF range, there's a CF N plan achromat 100x dry LWD which has a NA of 0.8 and 0.66 mm working distance.

At such low NA, you are probably better off using a good 40x and cropping or using higher magnification eyepieces.

[mike42]

LW Scientific makes a 100X dry objective with 0.85 NA and .72mm working distance. Promotion photos look pretty good. Tried to attach photos but files too large. Google LW Scientific 100X Dry Objective if you wish to see them.

[viktor j nilsson]

https://www.lwscientific.com/products/1 ... -objective

Our new 100x DRY Infinity PLAN objective will bring a radical change in the world of microscopy. With clarity, resolution, and flat-field-of-view that rivals the best 100x OIL Infinity PLAN objectives. Why use oil?

That doesn't exactly inspire confidence.

[MichaelG.]

It’s worth looking at the Specification sheet [on Dropbox], which is linked from this page:
https://www.labessentials.com/products/ ... -objective

The two notes labelled TIP: seem honest enough.

MichaelG.

[viktor j nilsson]

Yes, that note is correct, but the pictures (where the 100x dry looks as good as, or even better, than the 100x oil) is flat out misleading or even consciously deceptive.

[charlie g]

Hi mike42, happy new year all. I totally agree that to flat out state: 'why use oil' regards to 100X objectives is a deliberate microscopy performance mistatement....frankly a marketing hollow ploy.

I enjoy my Nikon Plan 100X dry, NA 0.90 , 160/ 0.14-0.20, correction-collar objective...under very specific circumstances...I observe live freshwater pondlife using coverslip-wetmount slides.

I would never, never waste my time , 'playing chickie with disaster' of crushing a preserved -fix mount slide...be it diatoms, radiolarians, mold spores, etc., etc., I never employ my Nikon 100X dry objective with costly and dear to collect fixed-slides.

My suggestion to you, mike42, is that it is never about the 'specs listed for a dry/non correction-collar 100X finite objective'...it is about defining on your specific slide, on your microscope ...the total optical thickness of the 'sandwich '..of your slide+media enclosed specimens+cover slip....defining/ determining if you can even attempt to use a non-correction collar/Plan 100X dry objective. That brochure for the dry 100X you have interest in...totally avoids this aspect of the use of their optic for sale.


With my wet mount slides...the fluid depth under the coverslip..can be lowered to a 'sweet spot' thickness permitting use of my Plan 100X dry, NA 0.90 objective.

So for me...the Plan 100X dry ,NA 0.90 correction-collar objective please only with wetmount slides...I choose cover-slip thickness, I control fluid thickness under that cover slip.

Please for yourself define what type of observing enjoyment , you consider with a Plan 100X dry objective...please don't crash and ruin cherished fix-mounted slides with a Plan 100X dry objective.

thanks for a great post, I learn from all who participated in your thread. charlie guevara, finger lakes/US

[Hobbyst46]

From the specs and the manual of the 100X0.85 dry objective from LW per the above link:
1. The example photos of (presumably) blood cells are irrelevant to high resolution as claimed in the link.
2. The objective is marked as infinity/0.17, and (accordingly...) the manual recommends to cover the specimen with a coverslip.
3. The first instruction in the manual seems to be "remove all immersion oil from your lab". This is not precaution, but more like panic.
4. Apparently, under the thick fog blanket of coronavirus, present knowledge about refractive indices has become obsolete and the Abbe theory is no longer valid...

[mike42]

All comments thus far have been very helpful. My initial concern was over-cranking the objective into the slide/coverslip, and wanting to learn if there was a certain working distance which would preclude the chance of that happening when using a 100X dry objective. My near vision hasn't been the best after cataract surgery, and it's very difficult for me to tell when an objective is getting too close. I do know that a lot of quality objectives are spring loaded which helps to prevent damage.