Getting started

[Jan]

Jan- "Having now all knowledge and understanding"...  Please stop.  Surely you jest.

Mark, yes, it was said jestingly. I know that it is challenging to understand the basics of digital microscopy, namely the limiting factors for resolution. 

My situation is different from yours. The manufacturer of my LCD microscope guarantees that the total magnification 50X means that 1 mm object is shown as 50 mm on the LCD monitor. The other available optical magnifications are 125X and 500X. I do not use digital enlargement.

I do not care too much about the scope magnification because it is given by the combination of the magnification factor of the LCD eyepiece (12.5X) and the magnification of the objective (4X, 10X or 40X).

Nevertheless when I transfer the captured image JPEG file to the computer I am in a similar situation as you are. 

I understand that for you the scope magnification is important. In the past the magnifying abilities of the USB scopes were often overestimated. I am very glad to hear from you that for your scope all is in compliance with spec. 


Jan

[Jan]

What I'm still trying to understand is scaling, either up or down, inherent in displaying an image on a particular physical display device with a physical pixel density and size. 

The pixel size on the CCD is the limit of what you can resolve. You can magnify it all you want, but beyond a certain limit it won't help you identify anything in the image.

You are correct Herman, high magnification without sufficient resolution leads to empty magnification where no additional details about the sample can be seen.

The resolution is expressed in line pairs per millimetre.

Jan

P.S.: Grepper, attached is Leica's definition of magnification for digital microscopy.

[Jan]

I have finally managed to solve the microscope magnification issue for my purposes.  Using the program CorelDraw I have prepared a scale bars of stated length that I superimpose on the image captured by the camera of the scope.

When an image is resized the scale bar is proportionally resized also. 

Attached you can see the edge of a new Morakniv knife of carbon steel taken at magnification 125X and Tormek honing compound taken at magnification 500X.

Jan

P.S.: 0.1 mm = 100 μm ≈ 0.004" 

[Elden]

Good job, Jan. That makes the "road map" have meaning.

[grepper]

Jan-  Thanks for finding that Leica explanation!  That is exactly what I was thinking and wondering about.

It was the pixel size of the monitor with the pixel ratio of the montor/sensor that eluded me.

For example, with digital cameras you could have a 10mp 1/1.7" sensor, or a 1" sensor.  Obviously, either the pixel size and/or density would be different between those two sensors.  Now, transfer that data, 1-to-1 pixel to a 96 PPI LCD monitor.  Then I started thinking there is the lens, (of some magnification?), focusing the optical data onto the camera sensor. It became a real head scratcher.

Anyway, the calibration and display software that comes with my scope, once calibrated, allows me to measure the distance between any two points regardless of all of that stuff.  Really interesting to think about nonetheless.

[grepper]

Attached you can see the edge of a new Morakniv knife of carbon steel taken at magnification 125X and Tormek honing compound taken at magnification 500X.

It would be interesting to see a 500 X magnification of same, so as to compare it to a 500X image of it sharpened with a 1000 grit wheel, and then another honed with Tormek compound.

From your 125 X image it looks pretty toothy, like at the factory it was sharpened with a fairly coarse grit.

This stuff can be a real time killer!

Is there room under your scope to take an edge up image?

[Jan]

Thanks for your responses, Grepper and Elden! 

Leica explanation is the best I have found. Here is the link http://www.leica-microsystems.com/science-lab/what-does-300001-magnification-really-mean/

Grepper, my scope allows observations in reflected light only for 50X and 125X magnification.

I cannot apply a 500X magnification in reflected light, the objective is very close to the object, circa 2 mm and the object is not well illuminated by the incident light.

The magnification 500X I can use only for transparent samples illuminated from bellow (transmitted light). 

May be in the future I will try to dismantle the original scope table and modify the stage (mechanical desk with nonius) for knife edge observation purposes.

Jan

[grepper]

Thanks for that link.  Amazingly appropriate.  You da man, Jan!

[Jan]

You are welcome, Mark! 

Jan

[grepper]

My USB microscope took a self portrait!

Whenever I look at this I feel the urge to say, "Open the pod bay doors please, Hal".

[Jan]

Definitely better incident light illumination than I have! 

From the true distance between the LED diodes you can construct a scale bar for your microscope images. 

Jan

[grepper]

Yeah, that's the advantage of a USB or dissecting scope over a biological scope.  But then USB scopes are generally rather cheap and have other issues, and dissecting scopes are generally low power.  It would be nice to have a mash of the best of all three!

I had an 800 X USB scope once that I returned because it came with some crud on the inside of the lens.  (It was specially manufactured in, and imported from the Orient). It did seem to work OK, but had an extremely small FOV and focusing was a hair pulling freak show because it must be held perfectly steady on a rock solid stand and it came with no stand.  Just a tube with a wire sticking out of it.  Add that to a depth of field about as deep as a hair and you kind of get the frustration when using one.  You can pick one up to play with for on $29.00 or so.  Very inexpensive.  Might be worth it just to play around with again.  Strapping one to the quill of a milling machine or drill press would probably make a nice stand.

[grepper]

From the true distance between the LED diodes you can construct a scale bar for your microscope images. 

Here you go Jan.   Full FOV image.

Download full size JPG of original BMP.  https://www.dropbox.com/s/tvm4y9grflz5llj/ff.jpg?dl=0 Press the DOWNLOAD button upper right corner of the screen.  At the bottom of the annoying JOIN UP dialog click No Thanks Continue with Download.

FWIW; 600 grit grind, lightly stropped with Tormek Honing Compound.  It looks kind of scratchy but easily shaves arm hair, push cuts paper, glides through onion skin at very thin angle, etc.  A nice, sharp blade that will work well for general food cleaving tasks.

[Jan]

Congrats Mark, you have not only a scale bar but you can also add dimensions to selected features of the captured image. I think that is all what we need for our edge inspection activities. 

Your FOV is significantly larger than mine at 50X magnification. My FOV is circa 1.4 mm wide for 50X and decreases to some 0.56 mm for 125X magnification. 

What concerns your edge's, I think your grinding and stropping is uniform, the burr is flawlessly removed and no deeper scratches are reaching to the cutting edge. Nice edge, no wonder that it has performed well in all your tests. 

Jan

[grepper]

Moved to General Questions.