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 » 14 Feb 2017 04:50

Very nice ripblade!

I decided to shoot the VN45LT from above but with a single image rather than a deep stack. The focal plane is first contact point, and from this I can calculate the Span at First Contact (SFC) as 0.7mil. Here's the shot:

http://i943.photobucket.com/albums/ad27 ... LV_1V3.jpg

This simple image answers the question about how deep the stylus tip is going into the groove, and coupled with the detailed contact surface shape images, tells most of the story about the health of the stylus and possibly how well it will perform. As it turns out, this stylus is not very worn at all, and in fact may be just past the "break-in" period. Sure sounds sweet! It will be interesting to see how this stylus wears, and what it will look like when it's time to retire it...will be a sad day.

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Re: Stylus Evaluation Imaging

Post by ripblade » 14 Feb 2017 15:45

Interesting shot, Ray....I can still see some texture in the surface of the contact areas, which for me would indicate very little polishing from actual use.

Are you still using the ring light for this last image?

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 14 Feb 2017 16:00

ripblade wrote:Interesting shot, Ray....I can still see some texture in the surface of the contact areas, which for me would indicate very little polishing from actual use.

Are you still using the ring light for this last image?
I'm using a combination of ring light plus side lighting at -90deg and +90deg. The ring light creates the oval highlight around the tip. The highlight is where the angle is just right to reflect directly up to the lens.

I see your image name includes "50x" in the name. What are you using to take the image? I'm curious to determine the actual magnification so I can determine the contact width on your cartridge. What is needed is:

Optical magnification
Original image size (in pixels) after any cropping
Any downsizing resulting in final image size

With the above info it's possible to measure/calculate the contact width.

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Re: Stylus Evaluation Imaging

Post by ripblade » 14 Feb 2017 16:54

I was curious about the ring around the tip...that's why I asked. Still didn't explain how you able to highlight the wear patches as I know you need the side lights for it....now I know, thanks.

Yeah, the magnification is just a guess based on what it looks like optically. I can't tell you what it is, actually.

Here's an image I know is not cropped:
Benz Wood L2 - 50x - 50hrs.jpg
(367.77 KiB) Downloaded 442 times
The camera resolution is 1.3MP (1280x1024) with .37x reduction lens (whatever that means); objective is 10/.25 (40x?)

BTW, the number of hours on this FG (50hrs) is not a guess...it's pretty close give or take a few.

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 14 Feb 2017 19:15

ripblade wrote:I was curious about the ring around the tip...that's why I asked. Still didn't explain how you able to highlight the wear patches as I know you need the side lights for it....now I know, thanks.

Yeah, the magnification is just a guess based on what it looks like optically. I can't tell you what it is, actually.

Here's an image I know is not cropped:

The camera resolution is 1.3MP (1280x1024) with .37x reduction lens (whatever that means); objective is 10/.25 (40x?)

BTW, the number of hours on this FG (50hrs) is not a guess...it's pretty close give or take a few.
The 10/0.25 means it has 10x magnification at rated total extension, with a Numerical Aperture (NA) of 0.25. The NA describes the light gathering ability of the objective. Bigger NA means a wider cone of light goes through the objective. More light also means shallower depth of field. NA of 0.25 for a 10x objective is pretty standard, and is what I am using as well.

Since you're using an objective, and a reduction lens, I assume you have a trinocular microscope? The .37x reduction lens is designed to make the view at the camera similar to the view at the eyepiece. The reduction lens is actually reducing the magnification of the 10x objective to 3.7x. If you remove the .37x reduction lens, you will get full 10x magnification. Not sure if this is a good thing or not, but fewer pieces of glass between stylus and sensor is almost always better.

Given the above I will try to calculate the contact area for your stylus. I think I have enough info.

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Re: Stylus Evaluation Imaging

Post by ripblade » 14 Feb 2017 19:36

Only 3.7x? :shock:

This is just an inexpensive student microscope. The reduction lens is part of the CCD camera, and is used in place of the eyepiece.

If you need more info, I'll do my best to provide it, but as it is, you're already well ahead of me. :(

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 14 Feb 2017 20:47

ripblade wrote:Only 3.7x? :shock:

This is just an inexpensive student microscope. The reduction lens is part of the CCD camera, and is used in place of the eyepiece.

If you need more info, I'll do my best to provide it, but as it is, you're already well ahead of me. :(
Turns out I do need to know the size of the sensor. Most likely it is a 1/2" sensor, so I'll do the calc based on that. 1/2" CCD sensors are 6.4mm x 4.8mm, so if your sensor is 6.4mm wide, then each pixel is 6.4/1280 = 5um wide. For a magnification of 3.7x, this means that the on-subject resolution is 5/3.7 = 1.35um. The widest of your contacts is 9 pixels / 12um / .47mil, while the other is 6um / 8um / .32mil. The Span of First Contact is same as my V15LT at 0.7mil.

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Re: Stylus Evaluation Imaging

Post by ripblade » 15 Feb 2017 00:10

Yes, your estimates for the sensor are just about right on. Sensor size is spec'd at 6.66 x 5.32mm, with pixel dims of 5.2 x 5.2um.

Thanks for doing the calculations....this is very interesting. :)

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 15 Feb 2017 20:32

I have a NOS VN45LT put aside for when the V15LT needs a replacement. Here's what the new one looks like. Contacts are 0.18mil x 0.9mil:

http://i943.photobucket.com/albums/ad27 ... _2R_X1.jpg

http://i943.photobucket.com/albums/ad27 ... _2L_X1.jpg

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 17 Feb 2017 17:23

I found a reference on Shure site for the V15-III stating the distance "between record contact points", what I've been calling the "span of first contact" or "SFC", is 25um (1 mil). I have not seen this spec'd on other cartridges or styli but have not done an exhaustive search. Anyone else seen this spec'd?

http://cdn.shure.com/user_guide/upload/ ... 95_sd_.pdf

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Re: Stylus Evaluation Imaging

Post by ripblade » 17 Feb 2017 18:43

This corresponds with the 0.7mil bearing radius of spherical and elliptical stylii.

(0.7*Pi/2)=1.099

I suspect most needles start as simple sphericals and so to some degree these vinyl first contact points will be fairly typical.

Look here:

https://www.jico-stylus.com/sas.php

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Re: Stylus Evaluation Imaging

Post by ripblade » 18 Feb 2017 17:17

ripblade wrote:This corresponds with the 0.7mil bearing radius of spherical and elliptical stylii.

(0.7*Pi/2)=1.099

I suspect most needles start as simple sphericals and so to some degree these vinyl first contact points will be fairly typical.

Look here:

https://www.jico-stylus.com/sas.php
Never mind the formula above....maths never were my forte. The correct equation would be: 0.7 x √2=0.99

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 18 Feb 2017 21:06

ripblade wrote:
ripblade wrote:This corresponds with the 0.7mil bearing radius of spherical and elliptical stylii.

(0.7*Pi/2)=1.099

I suspect most needles start as simple sphericals and so to some degree these vinyl first contact points will be fairly typical.

Look here:

https://www.jico-stylus.com/sas.php
Never mind the formula above....maths never were my forte. The correct equation would be: 0.7 x √2=0.99
Easier to understand if you say that the SFC is the hypotenuse of a right triangle with 0.7mil sides. Then the hypotenuse is the square root of the sum of the squares, ie SFC = SQRT(0.7^2 + 0.7^2) = SQRT(0.98) = .99

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Re: Stylus Evaluation Imaging

Post by ripblade » 18 Feb 2017 23:51

Yes, I used a shortcut that works if the sides are the same length.

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Re: Stylus Evaluation Imaging

Post by ray_parkhurst » 19 Feb 2017 05:45

I picked up a Shure DT35P that had unknown stylus condition (figuring it was worn/broken/missing). The stylus appeared intact so I cleaned it and imaged it top down and with 45-deg technique. Turns out it's well-worn, but less than expected. I guess this brings up the real question of this thread...when is a stylus "too worn"? The first stylus I showed (the M99E) was pretty clearly beyond its prime. But this DT35P is nowhere near that bad. It shows the "teardrop" shaped wear pattern I saw on my V15LT (and on ripblade's Benz) but the contacts are nowhere near wearing together at the tip. The contacts measure 0.45 x 1.3 mils. The original stylus spec is 0.2 mils wide, so the tip is definitely well-worn. But what would I expect from this stylus, and is it safe to test on a good record? Would like to hear comments before I mount and play it.

http://i943.photobucket.com/albums/ad27 ... 35_1_A.jpg

http://i943.photobucket.com/albums/ad27 ... 2L_A_A.jpg

http://i943.photobucket.com/albums/ad27 ... 2R_A_A.jpg

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