Magnification or Enlarged Image

[lorez]

I'm posting this query here because it has a little bit to do with imaging although not too much. It may be so inane that is does not merit discussion.

Mr. gekko mentioned in another thread a 2800X image (or thereabouts) and since I recently had an opportunity so show an image taken with 4X objective on a 60" HDMI monitor it made me begin to wonder how a screen image should be described.

I generally think only in terms of the objective magnification because that's where the resolution is going to originate, so an image taken with any camera is a 100X image (when the 100X objective is used) regardless of any other aspects of the system.

What thinkest all of you ?

lorez

[mrsonchus]

Hi Lorez, a good question I'd say.

I agree with you - the only constant across all platforms, screen sizes and/or resolutions etc is the objective's value which obviously stays the same and retains it's original meaning of course. I think personally that rather than refer to an object as 'seen at xxx magnification' for example, that it may be more meaningful to say either that the object 'is xx-measurement units in size', or to include a scale bar which of course implicitly does the same job.

Many folk will have a preference for this question I'm certain, we all encounter this decision at some time!

[gekko]

Mr. lorez, this is a very interesting subject-- thank you for starting it. I don't know if what I say below addresses directly the subject you raised, but I think it is related to it, even if tangentially, so I take the liberty to try to reply. I agree with you that the objective used is the most important factor, since, as you say, its NA (along with the working NA of the condenser) determines the resolution. The other side of the coin (if that is the right expression) is that magnification of the visual image (through the eyepiece) as well as when an image is projected onto a computer screen or printed on paper is also important in that too much of it and you've got empty magnification, as you well know. Now we all know that the rule of thumb for visual magnification (through the eyepiece, where the image is theoretically at 25 cm from the eye) is that it should not exceed 1000 X NA. However, when viewed on a computer monitor, several factors complicate the picture, and it would be very useful for someone knowledgeable in that area to explain where empty magnification starts. Factors that may enter into this, assuming that the camera sensor has more than enough resolution, are the size of the image on the screen, the resolution of the screen, and the viewing distance from the screen. I don't know enough to say much about those other than to say that we normally view our screens at distances greater than 25 cm which means the image can be larger than the rule of thumb for through-the-eyepiece work, and that in my subjective experience and with my poor eyesight and my old computer screen, a total magnification (i.e. image size on screen divided by actual size) of 2000 X NA to 2500 X NA seems to give very good results. People with better vision or a different screen resolution would probably have a different practical limit to total magnification.
I would be very interested in your comments, including whether what I said makes any sense, as well as in other members' comments.
Not exactly relevant, but it's a pet peeve of mine: illustrated books or websites showing images of microorganisms frequently give magnifications of images as objective magnification x eyepiece magnification, totally oblivious of the fact that these necessarily have no relation to the size of the printed or projected image.

Edit: John B posted his reply while I was writing this. I totally agree with John, which is why I normally add a scale bar (the only reason my latest few images don't have one is that I replaced my camera, and I haven't yet "calibrated" the new one).

[75RR]

I do not think total magnification (which can vary in any case) is that important. It brings to mind sales hype of 2000x
What is important to me is the Objective, including type and NA i.e. Zeiss Plan 40x/0.65 for example
Any additional magnification given by an Optovar or equivalent which would have a bearing on the Objective magnification
Object size and Illumination Technique.
and if Single image or whether Stacking/Stitching was used + software and Camera.

I find this information quite helpful in understanding how a specific image was made.

[lorez]

Gentlemen,

Thanks for your comments. I think we are in the same corner on this issue.

I agree that the scale bar would be the best solution to establishing some understanding of size, but sometimes the scale bar is not available. In some cases the audience has little concept of size when measured in microns and when nothing is available it is very hard to relate. The scale bar gives some relativity to the image.

Regarding the very large images on the display, it really depends upon the quality of the display. I was really impressed with the 60" HDMI monitor I had available as it showed no sign of image deterioration at all. In fact, the resolution was so good I was able to show the group of numismatists I was addressing that I had the only penny in existence where George Washington was sitting in the Lincoln Memorial (funny that Mr gekko would mention the 'other side of the coin'.

lorez

[75RR]

In some cases the audience has little concept of size when measured in microns and when nothing is available it is very hard to relate.

That is a good point. I find members of my family relate better to millimeters when I show them some of the images I have taken.
"... and this Diatom is about one twentieth of a millimeter"
For example:
500µm = 1/2 mm
250µm = 1/4 mm
100µm = 1/10 mm
50µm = 1/20 mm

[wmodavis]

Lorenz - I have a question that more likely belongs in the beginner section but here goes.
And the background as a retarded engineer is that I prefer the scale bar on the picture.
But my question is...
"How do you add a scale bar and how is it calibrated?"

And a secondary comment re 75RR's statement, I prefer a measurement unit of furlongs over mm.

[lorez]

"How do you add a scale bar and how I us it calibrated?"

I have a stage micrometer that I use to make a reference line for each objective I use. Then I can use the programs available to add the line to the photo. Some of my cameras have the capability of doing it all on the original photo. For a good detailed explanation I recommend Mr gekko as he is the master of scale bars.

And a secondary comment re 75RR's statement, I prefer a measurement unit of furlongs over mm.

For drama and emphasis I use 1/1,000,000 of a meter for younger kids, but for pure confusion it's 1/1XXXXXX of a cubit.

lorez

[billbillt]

Here in the USA, if you speak of millimeters to your wife, all you get is a blank stare.. The inch system is still prevalent here when trying to express the size of something.. Myself, I can use either one..

BillT

[KurtM]

I submit the human hair as a standard everyone can relate to. Now what's the average thickness (diameter) of a human hair (assuming hair from the scalp)?

[75RR]

For drama and emphasis I use 1/1,000,000 of a meter for younger kids ...

Then you are right back to microns again!

Now what's the average thickness (diameter) of a human hair (assuming hair from the scalp)?

Wiki says 100µm or 1/10th of a mm as I like to say :)

I can't visualize the width of a hair - perhaps it is too small. I can however visualize a millimeter.

[wmodavis]

Just measured the diameter of a strand of my hair with my new stage micrometer. It was approx. 1.988384e-7 furlongs.