Stylus Evaluation Imaging

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

Post by ray_parkhurst » 19 Jun 2019 21:11

I went on a buying spree a week ago, and purchased a V15-HRP, an AT201EP, a TM20H, and a X5-MCP. All were listed as low use, like new, or even NOS. This was about $600 worth of cartridges (eBay pricing). I posted about the X5-MCP above, mainly because it is a rare cartridge with a stylus type I had not yet imaged. But the others are quite common, and NONE of them came even close to being as described. Without a good method of imaging these, I would have essentially been stuck with them, and all were worn to the point of needing stylus replacement. All of them went back to the sellers. One of the sellers was extremely gracious, and apologized for sending the wrong stylus to me. Another seller simply refunded my money, while a third seller gave me negative buyer feedback, saying that I swapped his new stylus for my old/used one! I hate dishonest eBayers. I did not give him negative seller feedback prior to returning the cartridge, but now I may do that. I expect that many eBay sellers are selling cartridges with lots of wear with terms such as "like new" or "low hours". How would I have proven otherwise without being able to image these? Saved me $600.

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Re: Stylus Evaluation Imaging

Post by billshurv » 19 Jun 2019 22:40

Hi Ray,

That's not a good hit rate! I've been luckier (and also buy broken cartridges more than working ones) but it does show that the cost of a basic imaging rig could rapidly pay for itself! Do you still have the TM body? Due to some luck I have ended up with two 30H stylii in new condition.

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 19 Jun 2019 22:51

billshurv wrote:
19 Jun 2019 22:40
Hi Ray,

That's not a good hit rate! I've been luckier (and also buy broken cartridges more than working ones) but it does show that the cost of a basic imaging rig could rapidly pay for itself! Do you still have the TM body? Due to some luck I have ended up with two 30H stylii in new condition.
No, I sent it back already. I do have a TM30H cartridge though. Are you looking for the cartridge for yourself, or to divest your two styli?

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Re: Stylus Evaluation Imaging

Post by billshurv » 19 Jun 2019 23:01

I bought the second one as was convinced the one that came on my SME30H arm would be worn, so when another came up on ebay I had to have it. Dmitry then checked my original and declared it barely used. I don't need two as I have too many cartridges and stylii as it is so if you would like one of them let me know.

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 03 Jul 2019 02:56

I ended up finding an AT312HEP HOMC P-mount for sale, and just received it. It sounds very good, and seemed to require no break-in, but perhaps it will just get better and better! Going to voice it on some favorites.

I took photos of the contacts, as well as the front view. From the front view I measure the distance between contacts at 0.85mil. From the 45-deg views, the contact lengths are equal and 0.13mils across, and show good contrast even though this is a new cartridge, showing that the contacts have been carefully polished. This may be part of the reason for minimal break-in being needed.

The front view is a stack of 36 images with ~5um spacing, while the 45-deg views are single images selected for best focal plane for the contact patches. Here are the pics:
AT312HEP2.JPG
(39.17 KiB) Downloaded 81 times
AT312HEP1.JPG
(43.9 KiB) Downloaded 80 times

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 03 Jul 2019 04:49

Oops, I made the contact length measurement on the 2x downsized image. The contacts are actually 0.26mil across at the widest point, not 0.13mil.

I tried to edit the original but even though I posted it < 2hours ago I could not edit it.

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 03 Jul 2019 22:23

Something to note about the bottom images...the dark areas are not flats, even though they look to have very high contrast. The front view shows that the contacts are not flattened at all, so the dark areas simply represent the surfaces of the tip that are reflecting light away from the camera sensor. They have high contrast because they are very smooth from polishing, so there is no surface roughness to partially reflect up to the sensor.

This is something of a shortcoming of this method of imaging, in that a new stylus can appear to have worn flats. However, these areas are indeed where flats are going to wear, assuming the cartridge is set up with proper azimuth.

The biggest shortcoming is that it's difficult on a new stylus to measure the distance between contacts. Since the dark regions actually represent the curvature of the major and minor radii, the actual contact point is in the center of these regions, but this is not a precise way to measure the distance. In my previous measurements of new styli I measured from the edge of the dark area. This made me underestimate the contact patch distance. By using the front view, I can see that the distance is 0.85 mil. By measuring to the edge of the dark area, the number is only ~0.6 mil. Of course this will indeed be the distance once the dark area has worn to a flat patch, but for the new stylus measuring to the edge of the patch is incorrect.

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Re: Stylus Evaluation Imaging

Post by DeepEnd » 05 Jul 2019 14:51

Ray, had a quick think on the and assuming you are using some form of ring lighting so there will be a fixed area around the lens where there is no light that corresponds to the inside diameter of the light source/diffuser/reflector that is very probably larger than the aperture in the front of the lens.

Even if this is inner diameter of light source is small say 12mm then for a working distance of 10mm (for a typical 10x objective) with say an lens opening of 6mm then I would assume there is something like an 8.35 degree angle where there is no light being reflected into the lens aperture from the light source not just a flat surface.

I would imagine with a 20x objective this angle will be larger due to the reduced working distance assuming the lighting and aperture stay similar.

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 05 Jul 2019 15:27

DeepEnd wrote:
05 Jul 2019 14:51
Ray, had a quick think on the and assuming you are using some form of ring lighting so there will be a fixed area around the lens where there is no light that corresponds to the inside diameter of the light source/diffuser/reflector that is very probably larger than the aperture in the front of the lens.

Even if this is inner diameter of light source is small say 12mm then for a working distance of 10mm (for a typical 10x objective) with say an lens opening of 6mm then I would assume there is something like an 8.35 degree angle where there is no light being reflected into the lens aperture from the light source not just a flat surface.

I would imagine with a 20x objective this angle will be larger due to the reduced working distance assuming the lighting and aperture stay similar.
It's tough to find small ringlights that work with objectives that have short working distances. There are quite a few long working distance objectives available, and these are what I've been using for most of my imaging. My target is a bit higher than 45 deg in order to ensure the contact patch does not reflect to the sensor. For new styli the surface is still rounded, so the contrast at the edge of the patch is much lower. The very center of the patch will still show minimal reflections, especially if the manufacturer polished the tip to remove surface roughness, but contrast is still lower than seen on worn styli. I do see some reflections even at the center on un-polished styli.

The 20x objective I use has very long working distance (~20mm), and I'm using a ringlight with 30mm ID and 40mm OD, so the angle varies from 45 to 53 degrees.

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