SPOTLIGHT: ALBERTO SCARANI, GG, FEATURED PRESENTATION: SYNTHETIC DIAMONDS DEMYSTIFIED: AGA LAS VEGAS, JUNE 1
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 Post subject: Re: dino-lite digital microscopes?
PostPosted: Sun Nov 11, 2012 1:32 am 
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G4Lab wrote:
After Brian proposed his experiement I couldn't stop myself from doing it. It took about 90 seconds to modify it for local conditions. In my desk is a Shutter mounted Rodenstock 105mm Ysaron. We discarded an old Polaroid MP3 bellows camera and I stuck this lens in my drawer. I opened the shutter and put a piece of white paper on my desk as a screen and formed a real image of the lit light fixture over my desk.

Doing all the things Brian mentioned did nothing except dim the image. Similarly closing the diaphragm down to f/32 only dimmed the image. In no case did it vignette nor change diameter. When ray bundles were stopped (with a sheet of opaque metal) the image dimmed and resolution was lost although just looking with my eyes you could not tell that much.
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G4Lab wrote:
I might be able to do your experiment using my office at work.


Not to put more fuel in the fire, this discussion about lenses brought me back to my film school days in the 90's. We used 16mm Arriflex cameras with Leica lenses. We were told that by opening up the aperture to the max would soften the focus around the edges. Some of used this fact for artistic purpose while filming. I found a some info on the Wiki about this phenomenon http://en.wikipedia.org/wiki/Aperture. Jump down to heading "Optimal Aperture".


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 Post subject: Re: dino-lite digital microscopes?
PostPosted: Sun Nov 11, 2012 2:58 pm 
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The statements on the Wiki you linked to do not put any fuel on the fire at all.
Nor do they contradict what Brian and I said in any serious way. The section on Optimal aperture has all sorts of disclaimers and conditions that apply for example "what the image is to be used for" "what kind of lens" etc.

But the thing that it does not cover is the fact that what resolution and sharpness are not the same thing. And humans will, like EVERY time,, fall for increased depth of field in an image versus higher resolution in the plane of critical focus every time.

Where this has been flogged to death is at my other favorite forum the http://www.Photomacrography.net/forum The experts there routinely squeeze every bit of possible sharpness AND resolution out of image forming optics with ZERO tolerance for chromatic aberrations and other optical defects. They use these optics for Z stacking which eliminates the need for flatness of field. The Z stacking software doesn't care whether the sharp area of an image is planar or not.

There are already several pictures made by these techniques on THIS forum. And a camera available that does it at the push of a "shutter" button.

But when humans evaluate images they just see what is on the paper or the screen and care about depth of field , flatness of field and they don't often look at the individual pixels with the 10x loupe which they might use on their diamonds.

We also covered the issue of stopping down being needed because there was extra glass and instead of stopping it out the manufacturer's leave it available at less optimum performance so that they can call the lens "faster".

Nothing new at all there. Sharpness and resolution are closely and interactively related,
but are not the same thing. To make an analogy with gemology Resolution is like the color or clarity rating of a stone. Pretty easy to get experts to agree on the numerical value. But sharpness is like the beauty of a stone. Needs the underlying fundamentals but like the cut value of a stone just is a relative an non numeric value. (Yes there are probably numeric methods for quantifying sharpness but they include more than resolution. Probably contrast levels and depth of field)


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 Post subject: Re: dino-lite digital microscopes?
PostPosted: Mon Nov 12, 2012 1:01 am 
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G4lab, I find your comments quite critical. I thought this forum was to assist others. We all have an opinion that was derived from either experience or education, or both.


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 Post subject: Re: dino-lite digital microscopes?
PostPosted: Mon Nov 12, 2012 1:44 am 
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Have you considered Beryllagem, that G4Lab's criticism is based on his experience and education. :D


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 Post subject: Re: dino-lite digital microscopes?
PostPosted: Mon Nov 12, 2012 2:38 am 
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My point is that everyone is entitled to an opinion. Shutting down others does not promote discussion.


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 Post subject: Re: dino-lite digital microscopes?
PostPosted: Mon Nov 12, 2012 7:23 pm 
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Beryllagem wrote:
My point is that everyone is entitled to an opinion. Shutting down others does not promote discussion.

Sure, everyone is entitled to their own opinion. But everyone is not entitled to their own facts.

Today I polled my students with the following question: "Is the image in a (plane) mirror reversed left-right?". And every student opined that the image is indeed reversed left-right. But those opinions don't change the fact that the image is not reversed left-right.


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 Post subject: Re: dino-lite digital microscopes?
PostPosted: Mon Nov 12, 2012 8:50 pm 
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G4lab, I find your comments quite critical. I thought this forum was to assist others. We all have an opinion that was derived from either experience or education, or both.


I did not intend for my comments to be critical. I went to the site you linked to and I don't think it supports the point you were trying to make.
In fact I was trying to help you to get your facts straightened out. And part of the reason I am trying to get you to be more rigorous, in your use of terminology and concepts, is that I was laboring under exactly the same misconception,which you are citing until I was about thirty, until after reading for the umpteenth time Lester Lefkowitz's great classic Manual of Close-up Photography and something about depth of field was bothering me, and finally the light went on in my head. In spite of what lots of people who don't have a solid understanding of optics think, resolution is at its max with the lens wide open. Resolution NOT apparent sharpness. And it does not matter if the manufacturer added a couple of stops.

Everyone is indeed entitled to their opinion, and their dignity as a person. I did not attack your dignity nor did I make fun of you. But the subject of resolution and numerical aperture (directly related to f/stop) is NOT a subject that has to do with opinion. The physics are a black and white formula that has been firmly established for about 150 years. Regardless of what some photographic "experts" on wikipedia (who you don't really know who they are ) say or print.

I have massive experience with film photography and microscopy and optics too. But I had these facts upside down and backwards and was very happy when the light went on inside of my little coconut and what I recognized as finally really understanding a subject. I was trying to share that. As in trying to assist people on this forum. That is exactly what I was attempting to do.


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 Post subject: Re: dino-lite digital microscopes?
PostPosted: Fri Nov 30, 2012 3:29 pm 
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http://www.photomacrography.net/forum/v ... .php?t=424

In case you don't want to believe me here is the definitive link on the subject, written by one of the moderators of that forum who is the author of Zerene stacker software. One of the people I consult if I happen to be confused. He reports experience similar to mine too. It is not an easy concept , since people are taught to stop down both for depth of field and because some lenses can open wider than their actual best aperture.


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