*"Oculars or eyepieces are needed to magnify and view the image produced by the objective.*

To make optimal use of the resolution afforded by the objective, an overall magnification equal to 500–1000 times the NA of the objective lens is required.

More magnification than this gives “empty” magnification, and the image appears highly magnified but blurry.

For most applications, 10x eyepieces work well. When higher magnifications are required for a specific objective, a magnifying booster lens (in Zeiss microscopes, an Optovar lens magnification system) can be rotated into the optical path. Alternatively, a different set of higher-magnification eyepieces can be employed."

To make optimal use of the resolution afforded by the objective, an overall magnification equal to 500–1000 times the NA of the objective lens is required.

More magnification than this gives “empty” magnification, and the image appears highly magnified but blurry.

For most applications, 10x eyepieces work well. When higher magnifications are required for a specific objective, a magnifying booster lens (in Zeiss microscopes, an Optovar lens magnification system) can be rotated into the optical path. Alternatively, a different set of higher-magnification eyepieces can be employed."

The reason I looked this up was that I thought that in making this video: viewtopic.php?f=6&t=1171 I might have overdone the magnification and entered into the realm of

*Empty Magnification*.

The objective used was a Zeiss Neofluar 25x/0,60

Upper range = NA 0.60 x 1000 = 600x

Lower range = NA 0.60 x 500 = 300x

I used the objective in conjunction with the 2x of my Optovar (available magnifications are: 1x, 1.25x, 1.6x and 2x) and a 10x eyepiece.

So, 25 x 2 x 10 = 500x

It would seem therefor that I was within the optimum magnification range.

However, the use of Phase Contrast reduces the effective NA (see: http://www.microscopy-uk.org.uk/mag/ind ... -test.html), if the drop were to be to NA 0,50 for example, that would give an upper

*optimum magnification range*of 500x, putting the video on the limit of Empty Magnification.

Similarly in Brighfield one also has to subtract NA due to the action of the Condenser Diaphragm, the use of which entails an inevitable compromise between NA and contrast.

One can see how reaching Empty Magnification under all types of illumination is not hard to do.

We are assuming of course that we are starting out with the full NA of the objective, this assumption rests on the condition of the microscope, the care taken in setting it up, the precision which which we have achieved Köhler and last but not least the condition of the objective.

What I did not know until I read up on this is that if one is below the

*optimum magnification range*of the objective's NA, even though the full resolution and therefor the detail provided by the specific NA of the objective is there, it will not be apparent.

To return to the original example, using just a 10x eyepiece with the Zeiss Neofluar 25x/0,60 gives a total magnification of 250x, that is below the

*optimum magnification range*of 300x - 600x for the objective's NA.