i am considering to change my equipment now, any suggestion?

[rjlittlefield]

The good results with a 100mm converging lens VS the words on Nikons microscope site is what confuses me. Maybe the words do not fully represent how we use the equipment.

Tube lengths between 200 and 250 millimeters are considered optimal, because longer focal lengths will produce a smaller off-axis angle for diagonal light rays, reducing system artifacts. Longer tube lengths also increase the flexibility of the system with regard to the design of accessory components.

Nikon is describing their considerations in choosing a standard tube length to design a system around. To get a 10X objective, we have a lot of possibilities: 10 mm on a 100 mm tube lens, 15 mm on a 150 mm tube lens, 20 mm on a 200 mm tube lens, and so on. Which of those tube lengths will make it easiest to design and manufacture the objective? Well, an unstated assumption is that all of those objectives would be expected to cover the same size field and to have the same level of aberrations. What Nikon is saying is that it's easier to accomplish that goal with a longer objective than a shorter one, and that therefore the longer tube lens is a better choice to design around.

Now, once the objective is designed and manufactured, we can combine it with any length tube lens we want. When we use a shorter tube lens, nothing really changes except that the image gets smaller. If the sensor size is fixed, making the image size smaller means that the sensor sees more at the edge of the field.

I agree it is surprising that the Nikon 10X CFI60 and CFI BE hold up so well to this treatment. What this means is that the objective provides high quality coverage over a field that is much wider than is needed by the microscope. The situation is like pulling a normal 50 mm lens off a 35 mm camera, sticking it on a medium format camera, and discovering that the corners still held up well in this new usage as a wide angle lens.

So the NA is effectively doubled, a huge 0.5, and there's nothing near that at 5x.

No, the subject-side NA is left unchanged at 0.25, because for each point on the subject the cone of light accepted by the objective is unchanged. The camera-side effective f-number does change, from f/20 at 10X to f/10 at 5X, following the usual formula that effective_f_number=magnification/(2*NA).

--Rik

[conkar]

Nikon is describing their considerations in choosing a standard tube length to design a system around. To get a 10X objective, we have a lot of possibilities: 10 mm on a 100 mm tube lens, 15 mm on a 150 mm tube lens, 20 mm on a 200 mm tube lens, and so on. Which of those tube lengths will make it easiest to design and manufacture the objective? Well, an unstated assumption is that all of those objectives would be expected to cover the same size field and to have the same level of aberrations. What Nikon is saying is that it's easier to accomplish that goal with a longer objective than a shorter one, and that therefore the longer tube lens is a better choice to design around.

Now, once the objective is designed and manufactured, we can combine it with any length tube lens we want. When we use a shorter tube lens, nothing really changes except that the image gets smaller. If the sensor size is fixed, making the image size smaller means that the sensor sees more at the edge of the field.

I agree it is surprising that the Nikon 10X CFI60 and CFI BE hold up so well to this treatment. What this means is that the objective provides high quality coverage over a field that is much wider than is needed by the microscope. The situation is like pulling a normal 50 mm lens off a 35 mm camera, sticking it on a medium format camera, and discovering that the corners still held up well in this new usage as a wide angle lens.

--Rik

Thanks Rik!

I think one reason for Nikon and other manufacturers to use 200mm as their reference focal length are considering the Infinity space and placement of auxiliary components.

The Infinity space changes relative to the focal lenght of the tube lens, so 200mm will give the possibility of more room for accessories than 100mm. The distance to the image plane will also change.

http://www.microscopyu.com/tutorials/ja ... index.html

If you don't have the need for adding extra auxiliary components, you will be good with shorter focal lenght than 200mm.

I have not tested it, but I think even at 100mm it still will be room to add an iris diaphram in the Infinity space.

To have the opportunity to use an iris diaphram between the microscope objective and the tube lens is nice.

Regards,
Conny