Stylus Evaluation Imaging

the thin end of the wedge
ray_parkhurst
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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 23 May 2019 19:04

I purchased an Empire LTD 290 cartridge on eBay. It was listed as "used, excellent condition, low wear, sounds great". When I received it I checked the stylus tip and it was obviously worn out, not as badly as the N99E in my first post on this thread, but pretty far gone.

Recently I've read that the best way to evaluate stylus wear is by viewing the tip from the front. To determine for myself how well this works, I took the LTD 290 and shot it with 3 methods:

1) My "Ringlight" technique, left and right contacts (pics 1A and 1B below)
2) The Shure SEK technique, focus stacked for better clarity (pic 2 below)
3) The "Front View" technique, focus stacked for better clarity (pic 3 below)

Here are the images:
LTD290_3 Methods.jpg
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The "Front View" technique requires that "groove" lines be added to aid the evaluation. I've added these groove lines to the image below:
LTD290_Front2.jpg
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Each of the shots has advantages and disadvantages:

The Front View technique shows the profile of the stylus tip, so if you know what to look for you can identify its type (conical, shibata, etc). This is mostly true for a new stylus, since once the contacts begin to wear, the profile is altered. In the case of this LTD 290, you can see flats worn on each side of the profile, but it is tough to tell how far along the stylus wear has progressed. Once you see these flats, should the stylus be replaced? If we were looking at a line contact stylus, the flats would be even less obvious. What about the distance between contacts at the very tip? It seems like there is still significant distance between contacts, so the tip is not riding at the bottom of the groove like the N99E was, so is this still OK? Or is this stylus worn out based on this Front View pic? It's very difficult with this technique to measure the length of the contact along the major radius, and this technique gives zero information of the contact length along the minor radius.

The Shure technique shows the contacts as two "cat eyes", though in this case they are really big! There is still space between them at the very tip, so it's clear now that the tip is not riding the bottom of the groove. The reflection of light off the polished tips causes the image to be somewhat unclear, so it is hard to determine the exact size of the contacts, but this technique for sure tells you that this stylus is very worn.

The Ringlight technique shows the contacts with good definition such that their lengths along both major and minor radii can be measured. Why is this important? The length along the minor radius is an important factor in determining the trackability of the cartridge. Increased minor radius contact length causes increased high frequency distortion due to inability of the stylus to track the groove. Conical and elliptical contacts continue to grow larger as they wear, and have a gradual increase in distortion as this happens, so it's vitally important to measure their size, and replace them when they grow beyond a certain dimension.

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Re: Stylus Evaluation Imaging

Post by BMRR » 23 May 2019 19:33

ray_parkhurst wrote:
23 May 2019 19:04
I purchased an Empire LTD 290 cartridge on eBay. It was listed as "used, excellent condition, low wear, sounds great".
The description is pretty typical, unfortunately. A lot of sellers believe that as long as the diamond still appears pointy to the naked eye, it has "low wear." Many sellers say things like "the stylus is still sharp" — as opposed to being worn down to a flat nub, I guess..? :roll:

When I sell carts/styli, if I don't know exactly how many hours are on the stylus (I keep records of this for the carts/styli I purchase brand new), I will say something along the lines of "this stylus is preowned and has an unknown number of hours on it. It appears clean when viewed through my 40x loupe, and I cannot hear any obvious problems when I play-test it on my turntable" or "this stylus is quite old and although the diamond is still intact, it likely has more than 500 hours on it; use at your own risk or consider as a candidate for retipping." I never make claims such as "low wear" if I don't know how many hours are on it.

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 23 May 2019 20:49

BMRR wrote:
23 May 2019 19:33
The description is pretty typical, unfortunately. A lot of sellers believe that as long as the diamond still appears pointy to the naked eye, it has "low wear." Many sellers say things like "the stylus is still sharp" — as opposed to being worn down to a flat nub, I guess..?
Yes, I expect this is typical. I've purchased several cartridges now that had glowing descriptions, and worn-out tips. Being able to photograph them to prove they are worn-out has been a big help. A couple of the worn out ones, even one listed as "new", were pretty expensive and I would hate to have been stuck with them, or worse yet to have believed the seller and use them for playing records!

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 26 May 2019 18:54

BTW, contact length in play direction is 0.45 mil. The original spec for the turntable is 0.3 x 0.7 mil (minor x major radius) so in theory this cartridge is not completely worn out, but well on the way.

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 26 May 2019 21:34

I picked up a Sony XL-MC104P HOMC P-Mount. It was listed as "used, low hours" so I took a chance. Turns out it indeed is nearly new! Contact lengths along minor radius are 0.16 mil and the contacts are not yet well-formed, so I'd estimate that this has seen <50 hours of play.

I imaged the stylus using a new objective I just picked up. This objective has a smaller NA versus the one I've been using (0.31 vs 0.4), resulting in acceptable depth of field with a single shot rather than needing to focus stack. The objective is also much smaller in diameter, allowing integration of a very small diameter ringlight. This brings the lighting angle to ~60-deg, which gives a better measure of the actual contact size.
SonyXLMC104P0.JPG
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SonyXLMC104P1.JPG
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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 26 May 2019 21:36

ray_parkhurst wrote:
26 May 2019 18:54
BTW, contact length in play direction is 0.45 mil. The original spec for the turntable is 0.3 x 0.7 mil (minor x major radius) so in theory this cartridge is not completely worn out, but well on the way.
I meant "the original spec for the cartridge/stylus is 0.3 x 0.7 mil". For some reason the forum would not allow me to edit the post...Ray

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 31 May 2019 04:04

I'm still testing objectives with the goal of getting an acceptable single shot of a stylus without having to do focus stacking. I tried a 25x objective that had a lot of promise, but I just found an objective that gives a really good result without stacking, and has good color correction. I shot the Empire LTD 290 left contact using this objective with a tiny ringlight integrated on the tip. Below are two images...first is a focus stack of 12 images showing the full depth of field of the stylus (but not the cantilever)...second is a single image focused on the worn tip...and last is a 100% pixel view of the tip. Would love to hear comments...Ray
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IMG_3406A.JPG
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IMG_3406B.JPG
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Re: Stylus Evaluation Imaging

Post by DeepEnd » 31 May 2019 07:56

Ray,

The single image versions are very good and certainly makes checking the wear pattern/amount of styli possible but I have to say the stacked image is spectacular!!

Having played a bit with macro photography (only up to 1:1) to get images is difficult never mind at the ratio’s you are using for these images.

I have already read a lot of the previous info you have provided so I am interested in what magnification and NA objective you are now using and what working distance you get?

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 31 May 2019 15:03

DeepEnd wrote:
31 May 2019 07:56
Ray,

The single image versions are very good and certainly makes checking the wear pattern/amount of styli possible but I have to say the stacked image is spectacular!!

Having played a bit with macro photography (only up to 1:1) to get images is difficult never mind at the ratio’s you are using for these images.

I have already read a lot of the previous info you have provided so I am interested in what magnification and NA objective you are now using and what working distance you get?
Thanks DeepEnd! For sure it's much more difficult at these magnifications to get good results. I've tried quite a few objectives in my stylus imaging efforts. As you guessed, working distance is always a challenge, especially for the technique I'm using with the cartridge held at 45-deg angle. Most objectives have such short working distances that the objective body interferes with the stylus body and prevents getting close enough for focus. Some of the better images I've taken were with a Nikon BD Plan 20x NA 0.4. The BD objectives have their own integrated light pipes, so have an optimized ringlight capability that makes these "dark facet" images possible even at 20x, but unfortunately the working distance is just a few mm, and not all styli can be imaged with that objective. It can work well with the hybrid Shure technique (since that is with stylus flat, thus WD is not an issue) but I don't find that as useful as my 45-deg ringlight technique.

Many of the images posted in last few months used a different Nikon objective, the 20x MM. It is a truly spectacular objective, with same 0.4 NA as the BD Plan, but it has much longer WD of ~20mm, and is also telecentric. The long WD allows a small ringlight to be integrated with the setup. For comparison, here is the same stylus (Empire LTD 290) imaged with the Nikon 20x MM, both stacked and single:
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IMG_3419B.JPG
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The shallow depth of field of this objective makes single shots more impractical, though if you nail the critical focal plane, it looks very good. The single image above was selected from a stack of 24 used to render the stacked image. This objective is also relatively expensive (~$2k).

The images in my last post were taken with a much more modest 3.5x NA 0.09 objective, operating at ~10x magnification. I found a tiny ringlight which integrates onto the tip of the objective, so even though the WD is only ~9mm, there is room for my preferred lighting technique. The sharpness of the single and stacked images is not as good as the 20x MM, but is still good enough to measure the contacts accurately and determine if the stylus needs replacement. A big advantage of the lower NA is better DOF, so focusing is much easier. I'm trying to put together an economical system for a forum member so he can do ongoing evaluations, and I think this objective will work well for him.

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Re: Stylus Evaluation Imaging

Post by DeepEnd » 31 May 2019 16:12

Thanks for the information, yes the 20x has a bit more “bite” on the stacked image than the 3.5x but as you say the DOF on the lower powered objective it makes single shot images useable and I suspect slightly easier to get in focus.

I managed to pick up a digital microscope from a local pawn shop a “GXM 9063” but the table doesn’t have enough range to get a full cartridge on the table but for only £19 it gives me something to try looking at styli and a 4c 10x and 40x to try if I purchase a set of bellows (perhaps OM) to fit my Olympus m4/3 EM-5.

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 31 May 2019 16:32

DeepEnd wrote:
31 May 2019 16:12
Thanks for the information, yes the 20x has a bit more “bite” on the stacked image than the 3.5x but as you say the DOF on the lower powered objective it makes single shot images useable and I suspect slightly easier to get in focus.

I managed to pick up a digital microscope from a local pawn shop a “GXM 9063” but the table doesn’t have enough range to get a full cartridge on the table but for only £19 it gives me something to try looking at styli and a 4c 10x and 40x to try if I purchase a set of bellows (perhaps OM) to fit my Olympus m4/3 EM-5.
I predict dismal results from the 40x. Even with the Shure method a 40x has insufficient DOF, so the image is just a blurry mess, and using the ringlight technique is virtually impossible due to the short WD. Do try it though and if it works well please publish the results here.

The 10x will probably work well, as most 10x have enough WD. You may want to increase the extension for higher magnification, though your M4/3 camera may do quite well given its smaller sensor and tight pixel pitch. I look forward to any images you can share...

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 03 Jun 2019 03:31

I see an interesting characteristic in the last images of the well-worn Empire LTD 290 stylus. This stylus has not yet worn to the point of hitting the groove bottom, and the contact length (minor radius / record play) has only grown to ~0.3mil at its widest point, but it is clear from the photos that the wear flats have widened to the point of creating a sharp edge that would likely cause damage to the record groove. My ringlight technique causes a maximum reflection at ~45-deg from horizontal, falling off on either side. When an area is dark compared with what is seen at 45-deg, it means it is close to either 0-deg or 90-deg. In the single (non-stacked) photo of the LTD 290, you can see that the regions of brightest reflection form a triangular region on the side of the stylus. I have emphasized this region with white lines in the image below:
Picture0.jpg
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Zooming in, I have extended the white highlight lines beyond the tip to show the edges of the 45-deg regions that existed before the tip was worn. As you can see, there is a dark oval shaped patch (which is the wear flat), surrounded by a narrow bright ring (which indicates the 45-deg boundary of the wear flat), finally surrounded by a bright region above the patch, and dark regions to the sides and below the patch:
Picture1.jpg
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The narrowness of the 45-deg boundary indicates this edge is very sharp, and the dark regions on either side indicate they form a ~90-deg angle. This creates a potential "cutting" surface which could cause damage to the record groove, especially for high frequency and high amplitude modulations. I have highlighted the areas I believe are of biggest concern in red in the image below:
Picture2.jpg
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I would posit that once the wear flats go beyond the 45-deg lines shown, the grooves are in mortal danger! However, this criteria would not bode well for the MicroLine or SAS laser-cut styli, which have a near-90-deg sharp edge for most of their useful life. I am wondering how these styli avoid causing record damage.

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 06 Jun 2019 03:55

In my post above, I made the statement that the stylus tip had not yet worn to the point of hitting the groove bottom. However, this is not an acceptable criteria for ultimate wear on the tip. Due to the RIAA spec of 0.25mil maximum radius (0.2 mil typical), the lowest contacts should have separation of at least 0.4mil. See the graphic below:
Picture4.jpg
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At contact distance less than 0.4mil, the groove modulations are no longer reliable, and the stylus begins hitting the radiused bottom of the groove on some records. On typical records, the distance is 0.32mil.

I re-shot the LTD 290 top-down, but with only the ringlight illumination. This method shows very clearly tip of the stylus, with the sharp transitions formed by the worn contact patches. In this case, the minimum distance between contacts is 0.23mil, well below the 0.4mil worst case and 0.32mil typical needed to maintain proper contact to both sides of the groove without hitting the radiused bottom. See the pic of the LTD 290 stylus tip below:
IMG_0001A.JPG
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This seems to be a much more objective way to determine the maximum permissible stylus wear than other methods discussed. By the RIAA standard, the maximum distance between contacts should be 1mil, and minimum 0.4mil. Beyond 1mil and the stylus loses contact on maximally-modulated grooves. Below 0.4mil and the stylus hits the radiused bottom of the groove.

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 06 Jun 2019 04:21

Adding another top-down view, this time looking more straight-down onto the contacts. This shows the tip as more square, and contacts more like they would be hitting the record groove. Distance is still the same, but this is a better representation.
IMG_0002A.JPG
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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 06 Jun 2019 18:50

Here is yet another top-down view of this stylus, this time using the same hybrid lighting that I used for the very first image posted here of the N99E stylus.
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And here is a detail crop of the tip of the stylus, with a few measurements annotated:
LTD290 Tip Detail.jpg
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1.0 mil is the minimum groove spacing notation per RIAA. This is the maximum contact spacing allowed, and all styli must fit their contact within this distance to guarantee the stylus can track a maximum-modulated groove.

0.25 mil is the minimum contact width for this worn LTD290 stylus. The contact flats have worn down the diamond tip until the spacing between contacts at the bottom of the groove is 0.25 mil. The contacts have not yet merged together as they did in the original N99E stylus, but they have indeed worn to the point of beginning to contact the radiused bottom of a typical groove (0.32 mil between contacts).

I plan to look at a few of my worn styli to see the distance between contacts, and then do some listening tests to see if indeed my proposed criteria of 0.4 mil minimum contact width at the bottom of the groove is reasonable from subjective (listening) and objective (physical measurement) perspectives. Or should the criteria be 0.32 mil? I hope that listening will give the answer, though it may also involve doing a cross-section of the records I listen to in order to measure the groove bottom radii to be sure.

I may start a separate thread to document the results.

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