Groove and Stylus Inspection Optics

[jesusfwrl]

Having personally experienced how difficult it can get to find decent optics for the inspection of grooves and stylii, I embarked on a journey to find what is actually available on the market, what can be bought off the shelf and what needs to be custom made.

The goal is primarily to fit my own lathes with a high quality groove inspection microscope, and to put together a second microscope for stylus inspection and alignment.

As a secondary objective, I am investigating the possibility of offering such systems as a commercially available product. Since most parts would need to be custom-made, it might make sense to make more than the two or three systems that I will be needing for my own purposes.

Thus far, among us in the Magnetovolt team, we have used pretty much everything remotely suitable: From vintage Leitz and Spencer microscopes to cheap plastic Chinese toys, magnifying glasses of different qualities, Japanese lenses as well as Soviet industrial and medical/biological microscopes...

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There is an enormous availability of products, new and used, but most of them leave a lot to be desired.

The requirements are as follows:
1) Adequate magnification for the required purpose
2) Adequate illumination options
3) Adequate support and adjustment facilities
4) Large enough working distance between objective lens and object (for safety and illumination)
5) Solid construction
6) Adequate depth of field
7) Excellent image quality without distortion
8 ) Easy to read reticle and crosshairs
9) Operator Comfort
10) Reasonable cost (hahaha)

Anyone having ever looked through more than one type of microscope will probably be able to tell they are not all made equal! As such, their prices vary as much as their quality does.

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While we have been unable to find an off-the-shelf microscope ideally suited to groove or stylus inspection, we have found currently manufactured lenses which will do the trick, while the body can be a custom affair along with the supporting structure and adjustments.

Unfortunately, there is no currently manufactured match for the first lenses we have come across for groove inspection, so our search is far from over.

Suffice it to say that this lens has never been used on a disk mastering lathe, to the best of my knowledge, and while it is probably overkill, it offers an unsurpassed amount of visual detail of the groove walls.

I will be updating this thread with more details on our findings and progress.

[Soulbear]

Hi Jesus,

Having personally experienced how difficult it can get to find decent optics for the inspection of grooves and stylii

You and Me Both!!

Groove Inspection 'Scopes.jpg

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I will be updating this thread with more details on our findings and progress

I'll be looking forward to that with Great Interest, Te He!
Regards Soulbear

[jesusfwrl]

Haha, thanks, Soulbear, I feel less alone now.
Nice collection...

[Soulbear]

Hi Jesus,

Nice collection...

That's not the end of it. During my own Web Searches, I landed on an U.K.-based "Educational Equipment" Supplier who gave an effusive account, glowing with unrestrained enthusiasm, about the "Capabilities" of this U.S.B. Microscope :-

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Accepting at "Face Value" that the "Higher Price" would ensure that it would be of "Better Quality" I duly paid out around £60/€80 for it (My Dumb Ass!!). It is emphatically NOT of "Better Quality" I can assure you of that, the exact same item, in different packaging, is available via the Bay for as little as £10!! :-

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This image is the first one I made using this item, and the Software that came with it, subsequent images I made (Which I've now somehow deleted), were a great improvement on this one, and showed much more detail. I think Lathe Trolls member "Victrolaguy" has also made some posts about using these Inexpensive U.S.B. Microscopes, and said he was getting "Good Results", (Sorry I don't know how to Link to the Thread) He also made a great and inexpensive "Mounting" for it, I recommend that you check that thread out, to see his results. Just don't pay out €80 for a €12 'Scope !! Te He.
Regards Soulbear

PRESTO 6D / MICROSCOPE HAS ARRIVED / 12 bucks

Unread postby THEVICTROLAGUY » Wed May 04, 2016 9:34 pm

[Sillitoe]

Pretty good value for money with this Oitez DP-M17.

Damaged diamond

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[Fela Borbone]

Hi!
I the microscope is a difficult thing. Maybe an electronic microscope is the answer(except form the money and room question ) I had this usb too , and pixels are too big but the software can allow measurenents, for that money it was wothy. Inusable for stylus inspection but for grooves can help. Then i bougth a more serius optic one and a camera on it and is muvh better. But the problem, maybe is the same you experimenting, when we are dealing with 3D things to see, is not easy to focus the whole groove under big magnification. Or the surface or the bottom. Is there any trick or lens able to focus both?

[jesusfwrl]

Fela, You have hit the nail on the head.

This is probably one of the most frustrating aspects of finding a suitable microscope. The record groove and the stylus are both 3D objects and you ideally need to be able to see the whole of them clearly without having to adjust the focus wheel until your fingers hurt.

This all has to do with the construction of the optics and the particular property you are referring to is the depth of field, in practise related to the aperture. In simple terms, this factor effects the actual depth of an object or a record groove for that matter, which would still remain in focus when the top of it is in focus. All microscopes have some amount of this, but if this is very small, you will only be able to see a micrometer or so above and below to focal point, meaning that if you focus on the top of the groove (disk surface) the bottom will look blurry.

A related aspect is also what is known as the working distance: The distance between the object and the objective lens when the object is in focus.
For a lot of applications, especially those with illumination from underneath this does not have to be more than 0.5 millimetre or so. But if you try focusing a microscope objective lens only 0.5 mm above a surface of a lacquer disk, you will soon find out how easy it is to keep on accidentally ramming the objective lens into the lacquer disk while trying to focus. Also, it is almost impossible to shove enough light through that tiny gap, especially considering that the light source should really not heat up the disk.
There are certainly lenses available with a big enough depth of field and a large enough working distance, but they tend to be far more expensive to construct, and tend to be of lower magnification. Naturally, the larger the magnification, the smaller the depth of field and working distance, which means that you would most likely be needing an eyepiece of large magnification to go with it.

Add to that equation that you also need the optics to be constructed in a way that does not induce severe optical distortion (typically noticeable as curving of the image towards the edges of the field, as beautifully demonstrated on one of this photo below of a magnifying glass), no unnecessary darkening or blurring of the image, the ability to also give you a sharp and bright image of the measurement reticle, and a large enough ocular lens with a comfortable geometry that does not give you eye strain when you need to check over a master you just cut.



The best one I found had a working distance of 9cm and a huge depth of field, so that I haven't been able to find a record with grooves deep enough to be blurry at any point.



the picture above shows my favourite objective lens next to a more or less standard objective as you can see, the large objective is massive in size (49mm diameter, more like an SLR camera lens) and very heavy. Very unusual design for a microscope but mind blowlingly effective!

In addition, a true stereoscopic microscope will present a true 3 dimensional image of the groove, and if given a big expensive objective lens with a huge depth of field, it feels like you have just turned into a tiny microbe walking inside the record groove, almost being able to touch the groove walls. Truly impressive.
I am a bit old fashioned with my optics (still using film SLR cameras), so I definitely want a purely optical microscope as standard. The ability to also mount a camera (film or usb digital camera) might be a bonus as additional feature. An old fashioned camera with a composite video output would also give you the bonus of being able to display the image on a TV monitor much to the amusement of your guests, but my primary inspection instrument will be glass based.

[Soulbear]

Hi There,

I had this usb too , and pixels are too big but the software can allow measurenents, for that money it was wothy.

The software for this PCE-MM200 USB 'Scope has a great measurment feature, a scale that can be overlaid onto any images that are captured. I've just taken these images :-

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They're of an early 6T's Chubby Checker record, I think I'd need to Play Around with the Software some more to learn how to "Scale" things propperly. As a quick means of checking that any cutting is not going "Awry" I think it's OK. Now whether it's "Up to Snuff" for Groove Analytics, remains to be seen. It doesn't appear to have the Crystal Clarity of the U.S.B. 'Scope that James recommends, but because the category of the images are different, this may be making comparison more subjective, and less objective.
Regards Soulbear

[Sillitoe]

Nice one Soulbear,
I want to get something like this for my 5DMK2... Eventually.
http://www.lmscope.com/produkt22/lm_photo_microscope_en.shtml

[Fela Borbone]

Depth of field, thanks Jesus,
The software of this usb are usefull( cooltech) i use it with the other scope and is double good...but the original have to be plugged to start the software and then can change to the other or import pics
To check the point of stylus I used time ago no microscope, but a regular usb cámera.I removed all lenses and leave the cmos chip uncover. Placing the stylus on it ,the shape can be seen on the computer screen
Not all cameras work the same and higher resolution ones have larger chips so the resolution is the same after all.
Cheap fun!

[Soulbear]

Hi James,

Nice one Soulbear,
I want to get something like this for my 5DMK2... Eventually.
http://www.lmscope.com/produkt22/lm_pho ... e_en.shtml

That Kiddy looks like the "Mutts Nuts" or the "Dogs Bollocks" as we Un-sophisticated Yokels are fond of saying. Reading the Specifications, it really does look the "Poodles Privates" not cheap, but then the "Good Stuff" rarely is. Back in the day when I used to imbibe a "Snifter or Two" of my favourite Malt Whiskey, the price of some of those, could bring a Tear to my Wallet too, Te He!
Regards Soulbear

[Sillitoe]

Haha, yep they're exxy for sure.

Here's some grooves with that digital scope.
Tells me that the channel separation in my handmade head could be better, but my ears already told me that!
Stylus wasn't straight either.. I've designed a stylus changing station/ head mount platform but haven't had one built yet.

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[Gus]

[YouTube2]https://www.youtube.com/watch?v=GuCdsyCWmt8[/YouTube2]

[jesusfwrl]

e2]https://www.youtube.com/watch?v=GuCdsyCWmt8[/YouTube2]

Tempting...Maybe one day...

As for the DSLR microscope attachment posted above (http://www.lmscope.com/produkt22/lm_photo_microscope_en.shtml) by Silitoe, the objective lens used has a working distance of only 10mm. This is still very small for my standards, and this design will most likely not offer adequate depth of field capabilities.

The manufacturer states that it comes with a motorised focusing assembly so you can shoot many pictures at different focal plane settings and combine them in software to get a single image with adequate depth of field.

This will certainly work, but why bother when for the same or less money you can get a complete microscope with glass objective lens and measurement reticle included, with an objective lens having a much larger working distance and an adequate depth of field on the first place?

A big portion of the cost of this product is the mounting structure, which would of course need to be modified to fit on a lathe.

The problem with a shallow depth of field and small working distance is that you also don't have much of a tolerance for focusing errors. Swinging a heavy microscope assembly 12" or more away from its stand, with a mechanism that allows it to slide along the radius of the record on the platter, poses significant mechanical challenges. Apart from having to engineer the slide assembly to be perfectly parallel to the record surface along the entire travel, you also need to make sure that the structures are rigid enough so it doesn't vibrate or shake during operation. This is close to impossible to achieve, and gets even harder the heavier the microscope assembly is and the greater the tolerance requirements are.
A more forgiving microscope assembly would remain in focus even with an error of +/- 0.001mm on the supporting structure. I don't think anyone will make a supporting structure better than that for a lathe, so the microscope should be chosen appropriately to not be too sensitive to such tolerances. The image should remain in focus while you are inspecting the disk, without blurring out every time you breath to heavily or every time you slide the microscope a bit further.
It should also be able to keep the entire groove in focus, within the range of groove depth and width that can be cut on that lathe.

This is all definitely achievable within this budget, but you need to chose carefully.

[Sillitoe]

Hi Jesus,

The link I posted to states "Since the working distance is much shorter (about 10 mm with the LM microscope 80x) than with conventional stereo microscopes, a significantly higher numerical aperture can be achieved. As a result, the image resolution is markedly increased."

Higher numerical aperture= More stuff in focus... Lots of trade offs in this game, good luck.

Cheers
Sillitoe

[jesusfwrl]

There is a difference between lateral plane resolution and vertical plane resolution.

The depth of field has to do with vertical plane resolution. As a general rule, the higher the numerical aperture, the smaller the depth of field. It is the small numerical aperture values that offer the desired depth of field for record grooves.

The mathematics behind this are quite simple, and widely available on the internet. Calculate it and see for yourself.

It all depends on what you are trying to observe... while higher numerical aperture values can be desirable in certain applications, for record grooves, it is the smaller values that are most desirable.

Not only can you see better what you want to see, but you will also have fewer incidents of ramming the microscope into the lacquer and less chance of overheating the blank while trying to illuminate it.

[Sillitoe]

Hi Jesus,

I've just contacted the company asking for some single images of vinyl grooves at higher magnifications.
Hopefully they'll get back to me and if they do I'll post the images here.

We shall see!

Cheers
James

[Sillitoe]

Here's the reply

"Dear Mr. Sillitoe,

thank you for your interest in our products.

If you send us a sample of your preparation, we can make demonstration pictures. We can use different optical methods and focusing techniques.

This service costs € 380 exkl. VAT"

Interested to see what you come up with Jesus (go for the electron microscope )

Cheers
James

[Sillitoe]

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Here are a couple of quick shots of dirty discs captured with the USB scope using an additional light source.

Cheers
James

[grooveguy]

Hey, thanks to all you guys for compiling this history of failures and successes. Well done! Indeed, a good 'graven image' of the fruits of our recording labors would be nice to have. I recall that the little Spencer (I think it was) microscope on the school's Presto lathe, with its pre-focused flashlight-bulb source, looked awfully good, but to replicate that with eBay optical devices would probably give a dismal showing. Results posted here from USB microscopes looks to be the best alternative, with the further advantage of keeping our clumsy heads and hands away from the engraving area. So please post pictures of final installations, etc., along with images obtained.

Actually, the USB microscope idea reminds me of Howard Holzer's (HAECO) demonstrations at AES shows in the '70s. His lathe had a microscope coupled with a vidicon TV camera, the first time that most of us saw grooves on a video monitor. Lots of 'ohs' and 'ahs'.

In my own experiments, I find myself looking more for groove-to-land observations than for short wavelength irregularities, my blank lacquers are from various time periods and manufacturers. If I could manage a proper mounting arrangement, it seems that for me, anyway, an optical "triplet" and an LED light source that would display an area maybe half an inch diameter would be very useful. And something like that does not require getting down and peering through an eyepiece. Rather, the virtual image should be quite visible from several inches.

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