FOV size and dimension of objects question

[N3ptune]

Hello I am trying to evaluate the rough size of things under the microscope at a power of 1000x but my understanding must be incorrect, I seeking for some help today.

To roughly evaluate the size of objects in the field of view, this is what I did:

Leitz Diaplan: Unknown for the moment (See picture bellow)
Eyepiece: 10x/20
Objective: 100/1.32 oil
Tube factor: ??

EP magnification number 10 x objective magnification 100 = 1000x of power, then field number of the EP 20 / magnification number 1000x = 0.02mm = 20μm.

Next I made this paper ruler to visually and roughly evaluate by simply dividing 20μm in 1/2, 1/4, 1/8.. up to 1/256 so I can compare what I see at the eyepiece and say something like "by looking at the sheet, it look like 5μm in size" etc, you know, rough, fast evaluation.



My problem is the following: A light microscope can't produce the image of an object that is smaller then the length of the light wave and according to my ruler, I can see many objects fitting in the 1/256 range (without sharp resolution), which is 78 nm (Seems impossible?)

Mostly pale small white dots, however the disk is visible, it's not a dot like a star in the telescope, these things would be around 100 nm and even less.

My conclusion is, my numbers are wrong... I suspect that the problem could be the tube factor, I don't know if there is one present. If i have a tube of 0.8, the situation is not improving, if the tube is 1.25 then things could improve a bit.

confusing.

My microscope

[FredH]

Hello,

The eyepiece field of view is 20 mm, which means you can see 20 mm of the intermediate image produced by the objective. With a 100x objective, this 20 mm field of the intermediate image corresponds to (20mm/100) field of the object, i.e. 200 micrometer, not 20 micrometer. So your scale is off by a factor of 10.

FredH

[apochronaut]

Regarding your question about the tube factor. That is calculated into the nominal magnification of objectives designed for any specific microscope. Therefore the actual magnification of a 10X objective made for 170mm tube length microscope is only 94% that of one designed for a 160mm tube length microscope, so as long as you are using objectives designed for your microscope or other objectives designed with the same tube length or in the case of infinity corrected microscopes, the same reference length, field diameter calculations as illustrated in the post above will hold.

[N3ptune]

Hello,

The eyepiece field of view is 20 mm, which means you can see 20 mm of the intermediate image produced by the objective. With a 100x objective, this 20 mm field of the intermediate image corresponds to (20mm/100) field of the object, i.e. 200 micrometer, not 20 micrometer. So your scale is off by a factor of 10.

FredH

Ahh oki, I misunderstood the procedure, it makes more sense now with 200 μm total FOV, the smallest things would be in the range of 781 nm and smaller, I guess down to something around 500 nm, maybe a bit less even.

Thanks for the help clarifying this.

Regarding your question about the tube factor. That is calculated into the nominal magnification of objectives designed for any specific microscope. Therefore the actual magnification of a 10X objective made for 170mm tube length microscope is only 94% that of one designed for a 160mm tube length microscope, so as long as you are using objectives designed for your microscope or other objectives designed with the same tube length or in the case of infinity corrected microscopes, the same reference length, field diameter calculations as illustrated in the post above will hold.

I guess the objectives must be designed for the microscope because they are all extremely sharp!

Thanks for the info, looks like I am all set to evaluate the size of objects with all of my 5 objectives now!