20x and 50x shootout - Phono Stylus Images

[ray_parkhurst]

One last post to show a stylus shot with the Nikon 10x BD. I shot it at the same 45-deg orientation as the others, but the stylus is a line contact type (Sumiko Andante P76) with a very short contact length, and is an example of how resolution at the tip is insufficient to make an accurate contact length measurement. However, the larger depth of field allows a practical shot of the whole stylus tip as well as the end of the cantilever, a "glamor shot" if you will:
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[rjlittlefield]

a "glamor shot" if you will

It is a lovely shot!

example of how resolution at the tip is insufficient to make an accurate contact length measurement

I've probably overlooked this in earlier postings, but is there some specific amount of accuracy that you need?

--Rik

[Sym P. le]

A good work up on stylus geometry / contact dimensions -> https://www.sound-smith.com/articles/st ... nformation.

More technical -> https://orbray.com/en/product/jewel/product/stylus.html or -> https://orbray.com/magazine_en/archives/223

Exotic stylus shapes are laser cut and worn out at 500 hrs. Set your budget accordingly.

Thus ends our reading for today.

[ray_parkhurst]

I've probably overlooked this in earlier postings, but is there some specific amount of accuracy that you need?

When new, a line contact stylus like the one above has a contact length of approx 0.12mil (~3um). Sonic degradation begins when the contact has widened to approx 0.25mil (~6um). At 10x this gives a range of 30-60um on sensor, or around 6-13 pixels on the HRT2i or 8-15 pixels on the A7Rm4. But at 10x and NA 0.25 the edges are blurry. At 20x and NA 0.4 I get 12-26 (or 16-30) pixels and a sharper edge, so it's much easier to estimate the length. At 10x I think I get +/-25% accuracy, while at 20x I think I get +/-10%, which is a typical minimum I'd strive for.

As an example here is a broken-in AT-8008 stylus shot with both 10x and 20x BD objectives. Single images with contact in critical focus. Sharpened. Full views:
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And here is a 100% crop of the contact patch from each. I measure the contact length at 12 pixels on the 10x image, or 4.6um , and 27 pixels on the 20x image, or 5.13um.
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[ray_parkhurst]

An eBay seller was selling some new LU Plan 20 ELWD objectives for a good price, and I picked one up. Same time another seller had some Thorlabs mounted achromats, a 200mm and 250mm, also for a good price. Tried the 200mm together the LU in comparison with the finite BD Plan 20 shooting a Denon DL-103 stylus with known 500-hour play time. Interesting results! Let me know any comments:

BD Plan 20 ELWD
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LU Plan 20 ELWD
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Note that the LU Plan forced me to build a ringlight that would fit around the objective. I made it with adjustable height, so I could vary the lighting angles. I could do the same with the BD Plan but am showing it with the coaxial system. The variable height is interesting, though the max height is only a bit higher angle than the BD Plan, so not a huge advantage. Biggest advantage I see is the improved CA performance. Seems the Thorlabs achromat is working fine with the objective to give overall a better CA response than the BD Plan.

I think I have a new stylus imaging objective!