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What microscope for optical surface inspection?

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#1 Fivemileshigh

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Posted 13 September 2022 - 11:13 AM

Hello everybody, as the title suggests, I am looking for a microscope to examine the polish quality on the surface of a lens. These would be lenses from 4 to 25mm diameter, from 6 to 30mm FL.

 

I only have a basic knowledge of microscopes and I am looking for suggestions. My initial thoughts are to get a compound microscope with dark field illumination. Would 400x be sufficient? Would the subject lens itself interfere with the dark field illumination too much?

 

Would the magnification provided by a stereo microscope be sufficient (let's assume a 4.5x objective, 2x barlow and 20x eyepieces, so around 180x) ?

 

Also somewhat related: What is the difference in looking though a 20x objective with 20x eyepieces and a 40x objective with 10x eyepieces?

 

 

Many thanks!



#2 Brianm14

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Posted 13 September 2022 - 12:04 PM

Forgive me if I must burst a bubble or two.  You should read and learn a lot more about microscopes and microscopy before proceeding to spend any money.

 

Your notion of employing 400x with a compound microscope would be far, far too great a magnification for you.  One, you’d have to have the objective of the microscope impractically close to the surface you wish to inspect.  Two, adequate lighting would be problematic if not impossible.   Plus you’d be hard-put to understand what you’d see at such unrealistic magnifications.  Same for a stereomicroscope at 180x.  

 

In short, your proposed magnifications are totally unrealistic.
 

A stereomicroscope with good lighting would be my first choice.  Magnifications of 20x up to 40x probably would be most useful.  But as with the compound microscope, critically lighting the object will take skill, practice, and an understanding of what you are doing.

 

To address your closing question:

 

The objective provides primary magnification of the object being viewed; the eyepiece (ocular) magnifies the image obtained by the objective.  The information gathered by the objective is the principle limiting factor.  Adding magnification at the eyepiece cannot add any additional information about your object, it can only magnify what comes through the objective.  Adding magnification at the objective can, by contrast, give you more data (information) about your object.

 

What you want is good resolution so you can see a useful amount of detail.  Bear in mind, too, that part of the process is learning to see, to observe, just as it is in astronomy.  You’ll also need to learn about optical glass surfaces in order to understand and interpret what you are seeing.

 

Have you considered starting off by obtaining a very good loupe (such as Belomo) offering about 10x magnification ($45 USD)?  Even here, lighting is a critical factor in obtaining a good, detailed view.

 

Sorry to disappoint you!

 

CS and good luck!

 

Brian


Edited by Brianm14, 13 September 2022 - 12:14 PM.

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#3 Fivemileshigh

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Posted 13 September 2022 - 12:15 PM

Thank you Brian, bubble bursting is welcome at this stage. Indeed I found one answer here:

 

https://www.microsco...ification-range

 

"For instance, to achieve a magnification of 250x, the microscopist could choose a 25x eyepiece coupled to a 10x objective. An alternative choice for the same magnification would be a 10x eyepiece with a 25x objective. Because the 25x objective has a higher numerical aperture (approximately 0.65) than does the 10x objective (approximately 0.25), and considering that numerical aperture values define an objective's resolution, it is clear that the latter choice would be the best."

 

I don't believe you fully understood the scenario though. I propose to inspect the surface of an unmounted glass lens. The microscope objective can even be in physical contact with the observed surface, so an oiled objective and oil darkfield condenser are completely doable. I am looking for micro scratches in the object surface left over from the polishing process.

 

Why would 400x not be realistic?

 

Thanks!



#4 aneeg

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Posted 13 September 2022 - 03:45 PM

Brian is correct. The most important part in checking an Optical surface is the direction of the light and the use of polarizing filters. Light at a 45˚ angle is far better than light from 90˚. It is all about contrast and not magnification.

 

Arne


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#5 Brianm14

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Posted 13 September 2022 - 03:53 PM

Brian is correct. The most important part in checking an Optical surface is the direction of the light and the use of polarizing filters. Light at a 45˚ angle is far better than light from 90˚. It is all about contrast and not magnification.

 

Arne

Yes, polarized light would be used.  Thanks, aneeg!



#6 Brianm14

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Posted 13 September 2022 - 04:35 PM

I made an earlier posting based on a complete misreading of part of post #3 (duh -too little sleep last night).   I have deleted it.

 

Fivemileshigh, I just know no experienced microscopist would approach your project this way.  For instance, you place too much emphasis on magnification, per se.  And I cannot envision how (or imagine why) you would employ an oil immersion objective to obtain 400x.  (It’s been done with oil -and water- in other circumstances.). I am very sure much lower magnification, with proper illumination, if it achieved the requisite resolution, would suffice.

 

I hope you succeed!

 

Brian



#7 Fivemileshigh

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Posted 13 September 2022 - 07:47 PM

Fair enough everybody, many thanks for your inputs. As I've been meaning to get a stereo microscope for my watchmaking for a while now, I will just go ahead and get a good one and see how I get along with the lens testing project. Your advice about polarized light is noted too, thanks!


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#8 j.gardavsky

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Posted 14 September 2022 - 03:31 PM

When inspecting the surfaces (optical, polished paleontology samples, ...) I prefer objectives with long working distance, when observing with the oblique incident light illumination.

 

When working with the light condensor, you can also consider the phase contrast objectives (Phaco).

 

Fluoride and APO objectives will always deliver better contrast, and cleaner resolution of the details.

 

Objectives with the magnification factor 10x up to 20x, and eyepieces with the magnification factor of 10x are enough.

 

Best,

JG


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#9 aneeg

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Posted 14 September 2022 - 03:48 PM

A stereo microscope having much better working distance and also better depth of field, combined with oblique incident light, will be the best solution. A larger working distance will also give you the chance to tilt the lens of inspection.

 

Arne


Edited by aneeg, 14 September 2022 - 03:49 PM.

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#10 j.gardavsky

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Posted 14 September 2022 - 04:19 PM

A stereo microscope having much better working distance and also better depth of field, combined with oblique incident light, will be the best solution. A larger working distance will also give you the chance to tilt the lens of inspection.

 

Arne

Yes,

 

I have the choice,

 

https://www.cloudyni...d-leitz-dialux/

 

and the Zeiss (STEMI) eyepieces up to 25x.

 

Best,

JG


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#11 Brianm14

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Posted 14 September 2022 - 04:24 PM

When inspecting the surfaces (optical, polished paleontology samples, ...) I prefer objectives with long working distance, when observing with the oblique incident light illumination.

 

When working with the light condensor, you can also consider the phase contrast objectives (Phaco).

 

Fluoride and APO objectives will always deliver better contrast, and cleaner resolution of the details.

 

Objectives with the magnification factor 10x up to 20x, and eyepieces with the magnification factor of 10x are enough.

 

Best,

JG

Agree on all points!  I have long working distance objectives on my reflected light, surface examination microscope.

 

I was hoping you’d join in, JG.

 

Best wishes,

 

Brian


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#12 j.gardavsky

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Posted 14 September 2022 - 04:40 PM

Hi Bryan,

 

one of my long working distance objectives is the Leitz LL 20x 0,40, but it requires the microscope tube for the infinity correction.

Admitted, I am mostly using it as a high magnification precission loupe.

 

When inspecting the surface blamisches, and microbubbles, the method of pinhole imaging is helpful. Herewith, you will achieve spatially coherent light, and the otherwise hardly visible blamishes on the lens surface, and the microbubbles in glass will light up)*,

 

https://www.cloudyni...-the-eyepieces/

 

Best,

JG

 

)* more precisely, they will "black up"


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#13 aneeg

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Posted 14 September 2022 - 05:57 PM

Zeiss Jena made a catadioptric 40X objektive which was originally developed for AAS use. I bought it for a customer who wanted long working distance, appr. 20 mm, for a microscope designed for laser etching. I made one for him (SINTEF, Trondheim) by using a CZJ Jenavert. I had to saw the stand in two, make a 20 cm intermediate extension. Laser light was sent throug the camera port, focused with the Berec prism down to 5 micron width. Camera was placed in the binocular tube and inspection and operation via monitor. The laser was a 5W one, quiteextraordinary back in the early 1990s.

Lots of fun.

 

Arne


Edited by aneeg, 15 September 2022 - 05:26 AM.

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#14 Fivemileshigh

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Posted 14 September 2022 - 06:57 PM

Actually the Zeiss Stemi is on the short list smile.gif. All your other advice is noted too, thanks! 


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#15 j.gardavsky

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Posted 15 September 2022 - 10:44 AM

Actually the Zeiss Stemi is on the short list smile.gif. All your other advice is noted too, thanks! 

The ZEISS Stemi are not bad at all.

I have one of the first ZEISS West Germany SV4 with the f-stop controlling the depth of field, and have seen in operation one of the modern ones with the integrated CCD camera.

 

Best,

JG


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#16 Oregon-raybender

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Posted 21 September 2022 - 02:14 PM

My first question to you is: are you a manufacturer or customer?  Looking for surface polish of the lenses during processing or quality inspection. There is a big difference. The lenses are ball type, base on your numbers, size and FL. You don't need high power, 30 - 40X is enough. I can state this, well I looked at thousands of lenses under a microscope for quality issues. The radii alone are so curved that depth of focus will be an issue, plus handling under a standard microscope. 

 

I would suggest the following:  Make a fixture that can hold the lenses and be able to rotate and tilt them. Lighting is key, a LED spot light or focused filament lamp. If a fixture is not possible, then you can use a tweezers, with Delrin  tips. Shaped cotton tips, for removing dust and cleaning.

 

Are you looking for polishing pits, orange peel, coating, etc...? 

 

Here are my suggestions:

 

Find a simple low power microscope, 10X to 40X zoom ( or 30x).  It should have a wide working area for handling and tooling. Look for one with lighting built in, or external.

 

You could also use a digital microscope, HDMI or computer screen hook up.  There are simple ones out there. It will help record and issues, plus ease of use.

 

Handling tools, tweezers with plastic tips, or heat shrink tubing attached, to protect the optics. Be aware of 

optics do fly well, if squeezed too hard!

 

I attached a few images that may help. If needed you can PM for details and assistance.

There is a lot to this that can't be simply explained here. Hope this helps you.

 

Starry Nightswaytogo.gif

Attached Files


Edited by Oregon-raybender, 21 September 2022 - 02:15 PM.

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#17 Fivemileshigh

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Posted 21 September 2022 - 03:21 PM

My first question to you is: are you a manufacturer or customer?  Looking for surface polish of the lenses during processing or quality inspection. There is a big difference. The lenses are ball type, base on your numbers, size and FL. You don't need high power, 30 - 40X is 

 

...

 

There is a lot to this that can't be simply explained here. Hope this helps you.

 

Starry Nightswaytogo.gif

Thank you Oregon, that is a very helpful post!!!

 

I am an end user primarily, however if something worthwhile can be gained by polishing the ball lenses a little better than what can be achieved commercially, I'm ready to get my hands dirty. I guess I'm a little bit both customer and manufacturer.

 

I plan on going ahead with this project, so for now the search is on for a quality stereo microscope.

 

Many thanks again!



#18 Oregon-raybender

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Posted 22 September 2022 - 12:36 AM

There are many manufacturers of ball lenses. They are used in fiber optics connections.

 

I would suggest perhaps buying a few to test, or have custom ones made for you.

 

Here are a few suppliers,I know of, these are well known companies. 

 

Hope this helps you, no sense in re-inventing if available off the shelf.

 

Good luck

 

Starry Nightswaytogo.gif

 

https://www.rossopti...ses/ball-lenses

 

https://www.knightop...all-lenses.html

 

https://www.edmundop...s&Tab=Products#

 

https://www.edmundop...l-lenses/12436/

 

https://www.edmundop...ng-ball-lenses/

 

https://www.optosigm...cro-lenses.html

 

https://ii-vi.com/pr...half-ball-lens/



#19 Brianm14

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Posted 22 September 2022 - 01:11 AM

oregon-raybender wrote, “There is a lot to this that can't be simply explained here.”

 

Isn’t that the truth!

 

Brian



#20 vertex2100

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Posted 22 September 2022 - 01:14 PM

Would this microscope listed on ebay be useful for looking at ball lenses? There are more than one of these listed now.Lools like it already has a nice holder for a round lens. 

Screenshot_20220922-211043_eBay.jpg


Edited by vertex2100, 22 September 2022 - 01:15 PM.


#21 Brianm14

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Posted 22 September 2022 - 02:41 PM

Perhaps.  I’d want some written details on operating condition.

 

The objectives appear to be missing.  Does the lamp (light) require a power supply?



#22 Fivemileshigh

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Posted 22 September 2022 - 03:02 PM

That looks to me like it’s meant to measure the radius of curvature, and not necessarily the quality of that surface?
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#23 Brianm14

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Posted 25 September 2022 - 05:06 AM

That looks to me like it’s meant to measure the radius of curvature, and not necessarily the quality of that surface?

As hinted at in the name . . .



#24 Oregon-raybender

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Posted 26 September 2022 - 02:28 AM

Yes, it's a radius microscope for measuring contact lens back radii. It's OK, 40 and 100 X is normally used. The scope projects a target rectile, focus the bottom surface, then focus up to returned image, the distance is the radii.

 

Would it work, maybe, it's just a simple microscope with lamp. You could remove the target to light up the

surface. See Attached

 

Starry Nightswaytogo.gif

 

https://www.youtube....h?v=KO_KRjv2ZPk


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