New Mineral Named After GIA’s John Koivula
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 Post subject: Re: NA - R - DOF
PostPosted: Tue Nov 02, 2010 12:39 pm 
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I received my M42 adapter ring so the canon can now be used to shoot scope piccies... yay! :P

Here's the combo,

Image

And here's a print screen of what that Canon software makes possible... you are looking at a live preview of what the scope is focused on at that moment: one of those micrometer slides. Taking a pic, and changing settings is as easy as mousing around a bit and clicking a few icons... I love it! The image that is being displayed in this image is a blown up version of what the cam is seeing. The software allows you to digitally magnify the image 5 and 10 times. The 10 times gets a bit noisy but the 5 times is just perfect to get your focus just right.

This really is the main advantage over my previous cam: being able to super-fine focus on a big screen. Of course, when one has a parfocal system (the cam and the eyepieces are in focus at any given time) one can just assume that the cam will pick up exactly what you are seeing but this big screen is just a tidbit cooler. Scores way high on the 'I got one, you don't' scale. It's pretty cool when you work with customers too: you can show 'm around in their own gemstone like a real estate agent!

Image


And to get back on topic: below you will find two uncropped images of the same micrometer slide (I cut off the uninteresting bits but that's it), left on full res and right on the lowest res (if you have a wide screen monitor... the low res pic lives below the high res one on all other monitors) This to check what would be more desirable, lower res in order to minimize the negative effects of overpixellation: diffraction artifacts or more detail by using the camera's full potential. Mind you, you are looking at 1 mm total length!

ImageImage

I guess that this 2D object isn't really a good test to induce diffraction artifacts, but looking at this my money is on full res... I'll see if I can get some artifacts going somehow. Gemstones should be the ultimate test case with all that refraction and reflection.


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 Post subject: Re: NA - R - DOF
PostPosted: Tue Nov 02, 2010 1:32 pm 
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That looks pretty good to me. Stage micrometers are often used on the PM forums
to see if there is any chromatic aberration and I don't see any on your pix.

I guess I wasn't clear on my previous post. You find some piece of electronic gear that is dead but has an Electrically Programmable Read Only Memory. These have a window at the top which allows you to erase the programming and also to actually see the memory cells in the chip. They are very precisely lithographed either using uv light or even electron beams so the structures are quite small. They were instantly adopted by microscopists as imaging targets. You can find them in old computers where they are the bios chip. Peel the label off and there is a window. The kind in the third image has a better lens to shoot through. They are a little harder to find. The second image is what you will see when you peel the label. That kind of chip is as common as dirt. Sometimes the lenses aren't real flat because they are only there to transmit UV light.

Images from Google images.



http://img21.imageshack.us/img21/6953/eeprom.jpg
http://img508.imageshack.us/img508/4872/erasable.jpg
http://img26.imageshack.us/img26/7162/gooderasable.jpg


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 Post subject: Re: NA - R - DOF
PostPosted: Tue Nov 02, 2010 2:39 pm 
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This post has been edited to use the corrected information Tim provided in his third post down on this page of this thread.

Tim wrote:
I guess that this 2D object isn't really a good test to induce diffraction artifacts, but looking at this my money is on full res... I'll see if I can get some artifacts going somehow. Gemstones should be the ultimate test case with all that refraction and reflection.


Your two photographs of the 2D object does a good job of showing diffraction effects. Straight lines produce one of the simpler diffraction patterns to analyze.

In your high-res photo, how many pixels high is one of those grey lines? I zoomed in 1200% in my "paint" program to see the individual pixels that make up the line. The darkest grey portion of a bar might be one pixel high, or two pixels high, or it might be three pixels high, depending on which bar you choose. This sort of uncertainty in what are supposed to be equal thickness lines is a diffraction effect.

Also in your high-res photo, above and below the darkest grey part of each bar, you see fading off from grey to lighter grey to green. The bands of "fading" are referred to as "fringes" and this also is a diffraction effect. These fringes make up an additional three or more lines above the middle dark grey and an additional three or more lines below.

Now lets look at your low-res photo. Again, how many pixels high is one of those grey lines? Again, I zoomed in 1200% to see the individual pixels that make up the line. For the low-res photo, the darkest grey portion of a bar might be one pixel high or two pixels high, depending on which bar you choose. Still some variation. But the fringing is, proportionally speaking, smaller in the low-res photo, only an additional bar above and below in the low-res photo.

So, because of the diffraction, the high resolution photograph does not allow you to determine the size of an object any more exactly than the low resolution photograph. And in fact, the high resolution photograph shows proportionally more diffraction fringes.

oops, needed to edit 1200x to 1200%... 12x magnification


Last edited by Brian on Thu Apr 28, 2011 2:11 pm, edited 3 times in total.

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 Post subject: Re: NA - R - DOF
PostPosted: Tue Nov 02, 2010 3:00 pm 
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crystal clear explanation! Thanks... :D

one or two pixel wacko stuff I can live with though, nobody is gonna notice :wink:


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 Post subject: Re: NA - R - DOF
PostPosted: Tue Nov 02, 2010 3:46 pm 
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This post has been edited to use the corrected information Tim provided in his third post down on this page of this thread.

Just as you say, most people won't notice. Where it becomes a problem though, is when you start zooming in on a picture (as I did and, after re-reading, as you did) looking for more detail. Once fringes begin to overlap, you get into a real mess.

I was going to ask about the size of the high- and low-res photos to compare with my original prediction, but again... its amazing what you find when re-reading what's been written. Your low-res reduces pixels 2x2 from your high-res... exactly what I suggest is needed. :)


Last edited by Brian on Thu Apr 28, 2011 2:11 pm, edited 2 times in total.

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 Post subject: Re: NA - R - DOF
PostPosted: Mon Feb 21, 2011 8:42 am 
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I may have had a bright moment just now... :mrgreen:

Brian, going back to page one of this conversation you use the magnification factor of 32 (without aux lens) and 64 (with aux lens) to calculate the minimum spacing of two objects to be resolved but it only just appeared to me that this isn't the objective magnification. It is the total magnification after a 10x ocular has done its job. So... it is safe to conclude that the objective only puts out 3.2x and 6.4x, no?

In my current setup there is no glass between the objective and the ccd except for a prism so there is no extra magnification...

In that case the minimum spacing in the real image would become 0.75 x 6.4 = 4.8um

Now that would change things a bit...

Bright moment? or not? :P


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 Post subject: Re: NA - R - DOF
PostPosted: Mon Feb 21, 2011 11:15 am 
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yes, Tim, you are correct. If the objective magnification is ten times smaller, then the spacing that can be resolved is ten times smaller. Makes quite a difference.

Bright moment. :D


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 Post subject: Re: NA - R - DOF
PostPosted: Sun Apr 10, 2011 3:23 pm 
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Fascinating stuff, even if nearly every bit of it was over my head.

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 Post subject: Re: NA - R - DOF
PostPosted: Thu Apr 28, 2011 2:10 pm 
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In Tim's last post above, he mentioned a major correction to our original assumptions... the objective (+ aux lens) magnifies a factor 6.4x instead of 64 times. So I went back and edited all my old posts in this thread, correcting for this new magnification factor.

This correction makes quite a difference. For example, when Tim uses the low-res photo setting on his camera, it is matched well to the image being produced by his objective... no overpixellation. Also, Conny is using a camera producing a hi-res photo that is well matched to the image produced by his objective.


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 Post subject: Re: NA - R - DOF
PostPosted: Thu Apr 28, 2011 2:19 pm 
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I'm currently working on a Wild microscope website and will incorporate the info mentioned here into it in an easily readable format. Without your explanations all this would still be way abstract stuff to me Brian, your input is invaluable!


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 Post subject: Re: NA - R - DOF
PostPosted: Fri Apr 29, 2011 6:27 pm 
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Brian, I don't get this:

I wrote:

Quote:
The M400 has a NA of 0.055 - 0.230 with the 2x aux lens in place (the lower value being at the lowest magnification, the highest one at the highest magnification, right?).


but after reading this:

Quote:
An important fact to note is that magnification does not appear as a factor in any of these equations, because only numerical aperture and wavelength of the illuminating light determine specimen resolution.


on this page discussing NA and the Rayleigh equation... I am tempted to think that the 'NA = 0.055 - 0.230' which is stated on the Wild spec sheet has nothing to do with the magnification but with the diaphragm that's built into the scope. Would that make sense? Is the NA indeed constant in a zoom objective?


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 Post subject: Re: NA - R - DOF
PostPosted: Fri Apr 29, 2011 11:48 pm 
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hi Tim

I don't use zoom lenses, but I'm pretty sure that NA changes with magnification of the zoom lens. You can verify this by answering either of two questions. First is an effect... "If you increase magnification, does depth of field decrease?" Second is a cause... "If you increase magnification, does the working distance (between objective and object) decrease?" If the answer to either question is "yes", then definitely the NA is increasing with magnification.

Note that there isn't a direct relation between NA and mag, but they both vary with working distance. Typically, increased magnification requires a smaller working distance. And smaller working distance increases NA. Magnification varies according to lots of physical parameters, but curiously it doesn't depend on lens diameter. In contrast, NA (in air) depends on only two parameters, working distance and lens diameter. So one could imagine a situation where the diameter of a lens is increased (i.e., opening up your diaphragm), which would increase NA without increasing mag. So as I said, the two are not directly related.

So, lastly, the values for NA that you read from the spec sheet are with the diaphragm (or iris, a much more pleasant term) completely open.


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 Post subject: Re: NA - R - DOF
PostPosted: Sat Apr 30, 2011 10:55 am 
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Roger that :D As usual, you state the right questions to make me realize I already knew (or should have known) the answer...

The working distance doesn't change when one zooms but the DOF seems to increase when you zoom out...

Sanks!


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 Post subject: Re: NA - R - DOF
PostPosted: Sat Apr 30, 2011 3:49 pm 
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I was looking at new Leica scopes... (just for giggles) the spec sheet of the new Z16 lists N.A. values that are comparable with my old timing M400 but... the zoom range is 16:1 instead of my measly 5:1... the max magnification of that objective is 11.5x (115x with 10x oculars).

So one would need even bigger pixels in ones chip to catch that light correctly? As microscopes advance we have to revert back to older chips?

Que? I must be missing something here... :smt017


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 Post subject: Re: NA - R - DOF
PostPosted: Sun May 01, 2011 12:13 am 
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Yes, well, microscopes are still made primarily for ocular use, not camera use. A camera can resolve image features about 5um, but even with 10x ocular lens the eye isn't going to see a 50um feature. Bump the magnification of a feature up to 50um and no camera operates at that large size pixel, but the eye (with ocular lens) can distinguish a 0.5mm feature. So what is "empty magnification" to the camera brings into view something normally not seen by eye.

So the upshot is the new microscope provides no useful improvement for camera vision (which in my line of work is called "machine vision") but it does help human vision.


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