Re: Darkfield microscopy
>>One thing that is possable is checking the sizes of particals with the >>darkfield. If we want a uniform size partical and if it is viewed to be >>many different sizes under the darkfield then we know that something >>has to be changed. If we know that we need .001 and we know that it's >>not possable to see .001 under the m-scope but we see particals then >>we know that they aren't .001. So we take a picture filter and look again. >Good point. If you have a filter that that cuts off at say 0.05 microns, >then you should filter out all particles that are resolvable in the >microscope. However, you have to make sure you are not also filtering out >smaller particles as well. Since the CS particles are charged, you must >insure that they are not retained on the filter due to the charge, only due >to their size. >I think someone already talked about this. The CS particles carry a positive >charge, correct? Then you must insure that the filter does not carry a negative >charge since opposite charges attract. CS, Paper and wood are also a positive charge so they wouldn't nutralize the CS if it was ran through them. So that should be a good start. >> Now here's something else to consider. What would happen if a person >>used inferred light? What would happen to the ability to view partical size >>then? >I think you are referring to infrared light, correct (I always have to look >this word up myself because I have a hard time remembering how to spell it)? Yep, I suck at spelling. Thanks for that info. Take Care Reid -- The silver-list is a moderated forum for discussion of colloidal silver. To join or quit silver-list or silver-digest send an e-mail message to: silver-list-requ...@eskimo.com -or- silver-digest-requ...@eskimo.com with the word subscribe or unsubscribe in the subject: line. To post, address your message to: silver-list@eskimo.com List maintainer: Mike Devour
Re: Darkfield microscopy
>Darkfield microscopy is accomplished by using a special condenser. The >condenser delivers a hollow cone of light with the tip of the cone focused >on the specimen. The angle of the light rays is such that all of the light >misses the microscope objective, thus causing a dark field of view. >However, a specimen can refract or reflect some of the impinging light and >divert it into the microscope objective. Therefore, objects in the specimen >appear to be bright against a dark background. >With this type of specimen illumination it is possible to detect objects >even when they are smaller than the resolution limit of the microscope. >However, this does not mean that you can measure their size, at least not >directly. One thing that is possable is checking the sizes of particals with the darkfield. If we want a uniform size partical and if it is viewed to be many different sizes under the darkfield then we know that something has to be changed. If we know that we need .001 and we know that it's not possable to see .001 under the m-scope but we see particals then we know that they aren't .001. So we take a picture filter and look again. Now here's something else to consider. What would happen if a person used inferred light? What would happen to the ability to view partical size then? Take Care Reid -- The silver-list is a moderated forum for discussion of colloidal silver. To join or quit silver-list or silver-digest send an e-mail message to: silver-list-requ...@eskimo.com -or- silver-digest-requ...@eskimo.com with the word subscribe or unsubscribe in the subject: line. To post, address your message to: silver-list@eskimo.com List maintainer: Mike Devour
Re: Darkfield microscopy
>One thing that is possable is checking the sizes of particals with the >darkfield. If we want a uniform size partical and if it is viewed to be >many different sizes under the darkfield then we know that something >has to be changed. If we know that we need .001 and we know that it's >not possable to see .001 under the m-scope but we see particals then >we know that they aren't .001. So we take a picture filter and look again. Good point. If you have a filter that that cuts off at say 0.05 microns, then you should filter out all particles that are resolvable in the microscope. However, you have to make sure you are not also filtering out smaller particles as well. Since the CS particles are charged, you must insure that they are not retained on the filter due to the charge, only due to their size. I think someone already talked about this. The CS particles carry a positive charge, correct? Then you must insure that the filter does not carry a negative charge since opposite charges attract. > Now here's something else to consider. What would happen if a person >used inferred light? What would happen to the ability to view partical size >then? I think you are referring to infrared light, correct (I always have to look this word up myself because I have a hard time remembering how to spell it)? This is light that can't be seen by the human eye. Furthermore, infrared light has longer wavelengths that visible light. Therefore, if you built a special microscope to view with infrared, assuming you had something like a night vision scope to visualize the infrared light, the microscope would not resolve particles as small as those which can be resolved in a standard light microscope. The shorter the wavelength of light, the better the resolution. It is unfortunate that our eyes can't see in the ultraviolet region of the spectrum. Then we could build light microscopes with higher resolution capabilities. In fact, ultraviolet light is used for fluorescence microscopy. In this case you use a special stain on the specimen that will fluoresce with visible light when illuminated with UV. In order to make this work, your condenser must be made from quartz (expensive) because glass absorbs UV (that is why you don't get sunburned when driving in a car all day even if the sun shines on your skin through the windows). Jeff La Favre -- The silver-list is a moderated forum for discussion of colloidal silver. To join or quit silver-list or silver-digest send an e-mail message to: silver-list-requ...@eskimo.com -or- silver-digest-requ...@eskimo.com with the word subscribe or unsubscribe in the subject: line. To post, address your message to: silver-list@eskimo.com List maintainer: Mike Devour
Darkfield microscopy
Here is a response to questions by Johan and Jim. Darkfield microscopy is accomplished by using a special condenser. The condenser delivers a hollow cone of light with the tip of the cone focused on the specimen. The angle of the light rays is such that all of the light misses the microscope objective, thus causing a dark field of view. However, a specimen can refract or reflect some of the impinging light and divert it into the microscope objective. Therefore, objects in the specimen appear to be bright against a dark background. With this type of specimen illumination it is possible to detect objects even when they are smaller than the resolution limit of the microscope. However, this does not mean that you can measure their size, at least not directly. A similar situation is known in astronomy. When you look at the stars at night with the naked eye, they appear as pin points of light. Because of their vast distance, the diameters of stars can't be resolved by the naked eye. In fact, even when one observes the stars with the most powerful telescopes on Earth, they still look like pin points of light because their diameters are too small to be resolved!!! Nevertheless, the stars are seen easily, we just can't see their shape or measure their diameters (although astronomers have special techniques to measure the diameter of stars). Here is an example that most of us have seen. Early during the day, or late in the day, when the sun shines through a window, it is easy to see dust floating in the air. These particles are much too small to be resolved by the naked eye, yet we can see them. The operating principle in this case is similar to the darkfield microscope. So the question is, can you measure a smaller particle size with darkfield illumination than brightfield? Perhaps you could push the theoretical resolution limit slightly with darkfield. Suppose you could measure a particle with a 0.1 micron diameter using darkfield compared to 0.2 micron with brightfield. Will this help our research significantly? I don't think so but correct me if I am wrong. But there is one thought I had. Perhaps one could estimate the relative size of CS particles in a darkfield according to how bright they appear. If the amount of light diverted by a CS particle is proportional to its size, then larger particles should appear brighter in the field than smaller particles. To do darkfield work you need to pay attention to the numerical apertures of the condenser and objective. The numerical aperture should be stamped on the body of the condenser and the barrel of the objective. For example, an Abbe condenser (for brightfield work) typically has a numerical aperture of 1.25. This is a measure of the cone of light it will deliver to the specimen. The numerical aperture of the objective is a measure of the cone of light that it will accept from the specimen. A typical achromat objective of 100 power (oil immersion) will have a numerical aperture of 1.25, a high dry objective of 40 power will have a numerical aperture of about 0.65. You also need to have some understanding about the refractive indices of different materials. Air has a refractive index of 1.0, water 1.33, glass 1.5. If you want to use the full numerical aperture of an Abbe condenser, it is necessary to apply immersion oil between the condenser and the bottom of the specimen slide. Without the oil, you limit the numerical aperture to just below 1.0 because the refractive index of air is 1.0 (i.e., light rays of a greater angle will be reflected at the glass to air interface and not proceed into the specimen). My darkfield condenser has a numerical aperture of 1.33. The cutoff for the inner surface of the hollow cone of light it delivers is 1.2 (condenser is stamped with 1.33 - 1.2). Therefore, this condenser would be totally useless if it is not oiled to the slide (or one could use water since it has a refractive index the same as the NA of this condenser). If you don't oil this condenser to the bottom of the slide, all of the light from the condenser will be reflected off the glass-air interface and none will reach the specimen. Now if I want to use my high power objective with this condenser, I have a problem. Some of the light from my condenser will enter the objective because it has a higher NA (1.25) than the inner cutoff of the condenser (1.2). In order to overcome this problem, my objective is fitted with an adjustable iris (like in a 35 mm camera) which can be used to stop down the objective (i.e., reduce the NA). Then the iris is stopped down just until the field becomes dark. At this point I have maximum resolution with a dark background. What if you don't have an iris in your high power immersion objective? If it has a higher NA than the cutoff of your condenser you have a problem. You could try to fashion a stop to insert inside your objective but I would not recommend doing this. In th
