This is probably a silly question

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woyjwjl
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This is probably a silly question

#1 Post by woyjwjl » Thu Aug 11, 2022 3:13 am

This is probably a silly question, which is a derivative of another post that
viewtopic.php?f=25&t=15888

Let's start with a comparison photo of the two objectives, both images are unretouched (except for the cut)
SPlan 40  .jpg
SPlan 40 .jpg (133.37 KiB) Viewed 1630 times
Neo40  .jpg
Neo40 .jpg (129.57 KiB) Viewed 1630 times
To be honest, the difference is very small and the SPlan lead is very slight (relative to the asking price)

My question is this.

Is the tube length 210mm for this NEO EPI light and dark field objective?

If so, how can the following conclusions be explained?

“Total magnification is also dependent upon the tube length of the microscope. Most standard fixed tube length microscopes have a tube length of 160, 170, 200, or 210 millimeters with 160 millimeters being the most common for transmitted light biomedical microscopes. Many industrial microscopes, designed for use in the semiconductor industry, have a tube length of 210 millimeters. The objectives and eyepieces of these microscopes have optical properties designed for a specific tube length, and using an objective or eyepiece in a microscope of different tube length will lead to changes in the magnification factor (and may also lead to an increase in optical aberration lens errors). Infinity-corrected microscopes also have eyepieces and objectives that are optically-tuned to the design of the microscope, and these should not be interchanged between microscopes with different infinity tube lengths.”

Translated with www.DeepL.com/Translator (free version)
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Finelld
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Re: This is probably a silly question

#2 Post by Finelld » Sun Aug 14, 2022 12:47 am

I will do my best to explain. It is easier to explain telescopes than microscopes because they use optical descriptions that more closely correspond to optical specifications in physics and most optical engineering. In telescopes resolving power is dependent on the diameter of the front element of the telescope. Magnification is the ratio of the focal length of the front element and the eyepiece. The formula is telescope focal length/eyepiece focal length. Microscopes are basically backwards telescopes. The large lens is the eyepiece. But the principles still apply just that instead of labeling the objectives with focal length they label them with an X value. The greater the X value the shorter the focal length. That is why all things being equal you need to get much closer to a slide with high magnification objectives than low magnification objectives. But also don’t forget that a microscope is a system of lenses each one working with the others for a final product. So the Focal length of the eyepieces play an integral role in total magnification. The total magnification is always going to be the ratio between the focal length of the eyepiece and the objective. Now when we incorporate the light path distance between the eyepiece and the objective things change slightly but not really that much. The focal length of a lens is determined by the distance from the lens where it places an object located at infinity in focus. You may think this is strange because your microscope slide is not anywhere near infinity. But microscopes are a bit backwards they are trying to project the image at the focal point to an object located at infinity. And the distance of 160, 200, etc is much closer to infinity than the focal length of the objective. But if you take an objective designed for a 160 mm system and place it in a 200mm system it will allow you to focus closer to the sample giving greater magnification. This is how extension rings on a camera will allow a photographer to get really close to a subject. But with microscopy you might not have enough room to play with in this regard. Going back to another thing I mentioned regards to resolving power. This is different than magnification. It is defined as the minimum distance between two points that can still be distinguished. The formula for this is theta min = 1.22 wavelength/Diameter. I really wish I had access to the Greek alphabet on my iPad 😁.

I hope that you understand all of my mumbo jumbo and it doesn’t confuse you too much. If you need any clarification on anything please let me know.

Best regards,

David Finell

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Re: This is probably a silly question

#3 Post by FatBassPlayer » Sun Aug 14, 2022 12:25 pm

I take a simpler, pragmatic view. It either works or it doesn't. It's either satisfying and rewarding to the viewer, or it's not.

And unless you have a PhD in optical physics, you and we won't understand why. Does that matter? Of course not, because it either works or it doesn't.

Just enjoy your microscope(s)!
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Re: This is probably a silly question

#4 Post by zzffnn » Sun Aug 14, 2022 2:59 pm

Lots of imaging parameters are not optimal in those two images. For example, stained thin sections are not the right material to evaluate objective to start with. In such suboptimal imaging conditions, image quality difference will be obscured.

If that is usually how you use microscope and the difference is not significant for you, then as FatBassPlayer said, just enjoy your microscope!

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Re: This is probably a silly question

#5 Post by woyjwjl » Tue Aug 16, 2022 2:25 am

Finelld wrote:
Sun Aug 14, 2022 12:47 am
I will do my best to explain.

Thank you for your easy to understand answers


According to my understanding, in an ideal state, the focal length is the distance of the focal point after the parallel light passes through the lens (sunlight (ideal parallel light) ignites a match through the lens).

The problem is that everything in the world is not in an ideal state. It can be considered that the focal length of the lens is not the only one.

The objective lens projects light (non ideal parallel light) from the specimen. The specimen can be magnified at a fixed distance (160mm, 210mm) in a fixed proportion. If the fixed distance is changed, the proportion will also change.

According to your explanation, if you shorten the distance, the "focal length" will become longer (the scale will become smaller), and if you increase the distance, the "focal length" will become shorter (the scale will become larger).

Unfortunately, I put this 210mm objective lens on the 160mm system (transmission illumination). The focal distance was significantly shortened, and the ratio was almost unchanged. It was really a strange objective lens.

Maybe it's the problem of transmission lighting? Should I try further in EPI lighting system?
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Finelld
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Re: This is probably a silly question

#6 Post by Finelld » Tue Aug 23, 2022 11:54 pm

Please correct me if I’m wrong. I think by ratio you are meaning magnification. If this is the case remember that magnification is a function of both the objective and the eyepiece. It is challenging for me to explain microscope optics because I’m most familiar with camera and telescope optics. Microscopes do things backwards or differently and use different terms for similar concepts. If you have an objective with a given magnification factor than it makes sense that the focal distance would change in a shortened system to achieve that magnification factor.

The points you made at the start of your last post are perfectly valid and true. This is why lenses are made up of several elements and don’t have just a single concave lens. Each element in an objective or lens system is there to help correct for the non ideal characteristics of real life. You have elements that correct for chromatic aberration, spherical aberration, planar aberration, geometric distortion, and even non parallel light. The optical engineers will use several types of glass and optical elements to get the best compromise for the money and current technology. Each element adds manufacturing cost. Some elements are extremely fragile, some can dissolve with common solutions and must be well sealed. Some elements can even be radioactive. Thorium doped glass was widely used to combat chromatic aberration. Generally speaking the more corrections and more elements the less contrast a lens will have. Every lens, objective, eyepiece, etc is a compromise. Not every lens will incorporate all possible corrections because of cost.

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