20x and 50x shootout - Phono Stylus Images

[ray_parkhurst]

I've tried quite a few objectives over the last few years shooting phono styli, both with small ringlights as well as BD illumination. My most recent (failure) was a 20x Mitty BD, which was quite a disappointment. I have not tried replacing it, so this shootout only includes the following:

Bausch & Lomb 20x BD
Nikon 20x MM with ringlight
Nikon 20x ELWD BD
Olympus 20x Neo Splan ELWD
Nikon 40x ELWD BD
Nikon 50x MM with ringlight
Mitty 50x M Plan Apo BD

I did not include lower power objectives though I have used these in the past, in particular the Nikon MPlan 10 and 10x BD objectives, because they don't give comparable resolution vs the 20/40/50x in this shootout. I only included the B&L since it is 20x with long enough working distance to work. Its contrast is compromised by the design of the BD system, but could be improved with some work if only the resolution was supportive.

The key to my method of stylus imaging is to place the contact patch(es) in a plane parallel to the sensor, and illuminate it with a ringlight either from a BD or ringlight source. This creates a dark contact patch surrounded by a bright ring of light where the light reflects directly to the sensor. The angle of the ringlight vs the contact surface varies among objectives and you can see that variation in the apparent size and contrast of the contact patch.

Here are the images:

20x Bausch & Lomb BD

20x Nikon MM with ringlight

20x Nikon BD ELWD

20x Olympus Neo SPlan ELWD

40x Nikon BD ELWD

50x Nikon MM with ringlight

50x Mitutoyo BD Plan Apo

I have not yet decided which gives the best performance. The Mitty has best resolution and CAs, but the Nikon 40x has better contrast on the contact patch, which is important for the application. I thought the 20x Oly may win this shootout, but I am not leaning that way. It is not as clear cut as "the sharpest one wins" or "the one with best CAs wins" because the application is sensitive to lighting angles and resulting contrast.

Note that I'm presenting at 100%, but would publish at 50% or smaller.

Comments welcome.

Edited to add: Sorry, the 50x images are not 100%. They are reduced to approximately match the 20x.

[rjlittlefield]

I don't know anything about this application area, so I am curious.

When you publish, what sort of message is supposed to be conveyed by the images?

Among the better objectives, would the nod go to the one that best conveyed the message, or do aesthetics count too?

What exactly would "best conveyed" even mean?

--Rik

[ray_parkhurst]

I don't know anything about this application area, so I am curious.

When you publish, what sort of message is supposed to be conveyed by the images?

Among the better objectives, would the nod go to the one that best conveyed the message, or do aesthetics count too?

What exactly would "best conveyed" even mean?

--Rik

The reason for doing these images is to determine the amount of wear present on the stylus tip. In an actual measurement I would shoot both contacts (by flipping the stylus 90deg to the other contact) and measure the size of both contact patches. I will often also shoot a front view of the stylus which shows if contacts have formed "flats". Here is a graphic I made a while back to show the basic concept, and also a composite showing projections of the contacts vs the front view, for this particular stylus.
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There are (at least) two issues with these images and measurements:

1. If the stylus tip is new, and no contact flat has formed, the visual size of the contact is ambiguous and depends on the angle of the light cone
2. If contact flats have formed, the contrast between flats and their edges is visually important in order to make an accurate measurement

In the first set of images the light cones vary as to width and angle, causing a variation in perceived size and contrast of the contact patch. This stylus has a well-formed contact, and the light angles of the objectives are all optimized and/or selected for best contrast in this application, so the variation is subtle. I need to do a similar shootout with a new stylus to make a final decision on which objective will give the best overall contact patch discrimination. I will likely do this on a new stylus of the same type as this one so I have a good comparison for the decision.

[Sym P. le]

Contact patch aside, a penny for my thoughts?

• The Mitty clearly wins on all points.

• The Nikons all suffer from C.A.'s, the 20x BD being the most severe.

• A high N.A. 50x objective will out resolve a lower N.A. 20x objective any day of the week, so even the idea of comparing a 20x Oly to a 50x Mitty is a clear win for the Oly.

[ray_parkhurst]

Contact patch aside, a penny for my thoughts?

• The Mitty clearly wins on all points.

• The Nikons all suffer from C.A.'s, the 20x BD being the most severe.

• A high N.A. 50x objective will out resolve a lower N.A. 20x objective any day of the week, so even the idea of comparing a 20x Oly to a 50x Mitty is a clear win for the Oly.

For sure from CA and resolution perspective the Mitty is superior, but as I stated above that is not the whole story. I hope the Mitty comes out on top overall but I will only be able to tell once I image a new stylus to see how the un-worn area is resolved and presented.

[Scarodactyl]

If you want to look at flat spots in particular coaxial illumination might be the weapon of choice, though it adds a lot of complications to a photomacro setup.

[ray_parkhurst]

If you want to look at flat spots in particular coaxial illumination might be the weapon of choice, though it adds a lot of complications to a photomacro setup.

The "traditional" way to do this work is with the "Shure" technique. Shure Bros made a stylus evaluation microscope that used (I believe) a 20x objective with 10x eyepieces to look straight down on the tip of the stylus. Illumination was by 2 lights, one on each side, pointing horizontally at the stylus. The 45-deg contact flats reflected the light up to the objective and created a bright spot on either side. It was up to the user to interpret the size of the bright spots to determine the level of wear. See diagram below for the concept.

I have tried this method, but the bright spots are difficult to analyze. You can qualitatively see differences between a worn and new stylus, so for the purposes of evaluation for replacement the method works OK, but I was looking for a more quantitative outcome that could be used for experimentation and correlation. The biggest advantage I saw with the Shure method is it allows both contacts to be viewed simultaneously.

I also briefly tested an axial approach, but it gave a "too bright" reflection spot similar to the Shure method. I could reduce exposure to view just the spot, but then the rest of the image was too dark to see what was going on with the rest of the stylus, ie orientation, etc. It might be workable, but with the convenience of the BD objective or small ringlight illumination, which gives a nice illumination to the overall stylus while giving good contrast between the contact patch and the "ring" around it, I have never looked back to other methods.

[Scarodactyl]

The strength of direct reflections from coax illumination has to be controlled with polarizers. There should be a fixed analyzer and the input polarizer should be rotatable so you can adjust it. Unfortunately that isn't always standard on microscope illuminators even though it's really a bare minimum requirement for happy imaging imo.

[rjlittlefield]

As a very general rule, I figure that if I want to emphasize a feature then I should use highly directional illumination at some suitable angle, but if I want to clearly resolve a feature, I should use diffuse illumination and look closely. It's basically a tradeoff between boldness and resolution. I get worried any time I see strong diffraction fringes, like around the edge of the contact flat in some of the images above.

So I wonder, what does the camera see from a tip view, if the stylus is surrounded by a diffusion cylinder that illuminates from everywhere that is not physically blocked?

Unrelated, I find myself puzzling over this snippet

shoot both contacts (by flipping the stylus 90deg to the other contact)

I have the impression that the contact flats are on opposite sides of the stylus. Is that wrong? Or if it's right, then why 90 degrees and not 180?

--Rik

[ray_parkhurst]

As a very general rule, I figure that if I want to emphasize a feature then I should use highly directional illumination at some suitable angle, but if I want to clearly resolve a feature, I should use diffuse illumination and look closely. It's basically a tradeoff between boldness and resolution. I get worried any time I see strong diffraction fringes, like around the edge of the contact flat in some of the images above.

So I wonder, what does the camera see from a tip view, if the stylus is surrounded by a diffusion cylinder that illuminates from everywhere that is not physically blocked?

Unrelated, I find myself puzzling over this snippet

shoot both contacts (by flipping the stylus 90deg to the other contact)

I have the impression that the contact flats are on opposite sides of the stylus. Is that wrong? Or if it's right, then why 90 degrees and not 180?

--Rik

In this case I want to emphasize the contact flat using directional illumination. The ability to resolve the flat effectively depends on the contrast between the edge of the flat and edge of the body of the diamond that has not been worn. In this case that edge is close to the direct reflection angle of the light from the BD or ringlight illumination. The result is a dark flat with no reflections going toward the objective, surrounded by a bright ring of direct reflections.

I'm not sure what you mean by diffraction fringes. Can you elaborate, or are you interpreting the direct reflections as diffraction fringes?

Regarding a tip view with diffuse illumination, check the first image in this thread:

https://www.vinylengine.com/turntable_f ... 19&t=92996

This was a very worn stylus that imaged well with such illumination. The contact is gigantic as the stylus was played far too long. A few later images show similar illumination but with much smaller contacts, and I found them difficult to work with, hence the use of the 45-deg technique.

Regarding the angles of the contact flats, indeed they are on opposite sides of the stylus tip, but they are perpendicular to each other. This is the case because the vinyl groove they are meant to play is cut at a ~90-deg angle. Thus if you are looking directly at one contact flat parallel to the sensor, you would rotate the stylus 90-deg to move the other contact flat into same position. Both of my graphic drawings show the contact flat orientations on the tip of the stylus, though only on the second graphic are they specifically pointed to and emphasized.

[rjlittlefield]

I'm not sure what you mean by diffraction fringes. Can you elaborate, or are you interpreting the direct reflections as diffraction fringes?

At the arrow, the effect that looks like ringing is one that I associate with illumination that is too hard and can cause resolution to be lost. Stuff like this appears frequently in bug eyes if the illumination is not diffused.

A few later images show similar illumination but with much smaller contacts, and I found them difficult to work with, hence the use of the 45-deg technique.

OK, thanks.

Thus if you are looking directly at one contact flat parallel to the sensor, you would rotate the stylus 90-deg to move the other contact flat into same position.

Got it, thanks. Somehow my head was stuck doing the rotation around the axis of the cone. Too many balls in the air...

--Rik

[ray_parkhurst]

I'm not sure what you mean by diffraction fringes. Can you elaborate, or are you interpreting the direct reflections as diffraction fringes?

At the arrow, the effect that looks like ringing is one that I associate with illumination that is too hard and can cause resolution to be lost. Stuff like this appears frequently in bug eyes if the illumination is not diffused.

This effect is only showing up on the edge where the diamond is polished. Polished diamond is a very tricky thing to image. Notice those anomalies don't show up in the areas of the diamond that are rough.

[rjlittlefield]

This effect is only showing up on the edge where the diamond is polished. Polished diamond is a very tricky thing to image. Notice those anomalies don't show up in the areas of the diamond that are rough.

Yep, that's definitely the appearance. But if you think about Fourier and friends you have to wonder, is the same sort of thing actually happening all over, and we're just not seeing it because we don't know what the surface would look like without that effect?

I am reminded of this discussion from a few years ago: viewtopic.php?p=164914#p164914 .

--Rik

[colohank]

These are perhaps silly questions, but why would a hard diamond stylus ever show any signs of wear, even after tracking innumerable miles in relatively soft vinyl grooves? Is "wear" actually an accumulation of micro fractures along cleavage planes induced by tiny impacts as the tip bounces from side-to-side in the groove at audible frequencies? Induced point-pressures at impact could be significant. If wear is indeed a manifestation of fracturing, would a diamond stylus tend to fracture more quickly at low frequencies (fewer but heavier impacts) or high frequencies (more but correspondingly lighter impacts)? Given that diamonds have a hexagonal closest-pack molecular structure, do stylus manufacturers bother to orient diamond tips on their holders such that their cleavage planes are least vulnerable to side impacts?

[ray_parkhurst]

These are perhaps silly questions, but why would a hard diamond stylus ever show any signs of wear, even after tracking innumerable miles in relatively soft vinyl grooves? Is "wear" actually an accumulation of micro fractures along cleavage planes induced by tiny impacts as the tip bounces from side-to-side in the groove at audible frequencies? Induced point-pressures at impact could be significant. If wear is indeed a manifestation of fracturing, would a diamond stylus tend to fracture more quickly at low frequencies (fewer but heavier impacts) or high frequencies (more but correspondingly lighter impacts)? Given that diamonds have a hexagonal closest-pack molecular structure, do stylus manufacturers bother to orient diamond tips on their holders such that their cleavage planes are least vulnerable to side impacts?

Here's the seminal report on diamond styli from 1950. I think it answers the major questions:

https://www.aes.org/aeshc/pdf/how.the.a ... stylus.pdf