Nikon Objective ID

augusthouse · Post by **augusthouse** » Wed May 07, 2008 1:06 am

Could someone educate me in regard to the Nikon CF Plan 20x/.40 objective in the attached pictures.

It is the (infinity) ∞/0 EP that I am unsure about, and I think it reads WD 3.1 ( I am assuming this refers to working distance - which is okay for what I have in mind).

At the price I paid I could afford to be curious. My intended use is with a bellows.

Am I correct in assuming that the Infinity-Corrected aspect is not a good thing with regard to its use in photomacrography? Also, it seems to prefer Brightfield; but also likes EPI?

So we have Transillumination (transmitting light through sample/subject), EPI Illumination (reflecting light off sample/subject)?? Brightfield which seems to my limited understanding to be similar to transillumination. Then, just so it doesn't feel left out, we have Darkfield. All of which can be applied for photomacrography - in principle, individually or in combination? (now I'm thinking out loud).

*These are additional details that I have just discovered in a Google search:
CF Plan EPI 20x Achromat Objective - Infinity-Corrected Brightfield. Numerical Aperature 0.46, Working Distance 3.1mm. For Nikon Optiphot.

However, the objective in the attached images only appears to indicate EP (not EPI)? Not sure if this has any significance.

The images are from the eBay listing. The item is somewhere between the US and my place.

Craig

Charles Krebs · Post by **Charles Krebs** » Wed May 07, 2008 3:20 pm

Craig,

The main thing here is the "infinity" symbol. These objectives (as are virtually all the current offerings from the "Big 4" microscope manufacturers) are designed to be used with an additional lens... a "tube lens"... that is normally built into the microscope. You should be able to get an image with it on a bellows, but I would not even try to guess what it's quality would be. I've only tried it once with an American Optical "infinity" style objective and the image was very poor. But I don't know if it was simply that objective.

The objectives that can more readily be used on bellows are a type known as "finite" objectives. They have a specific "tube length" that is usually denoted on the lens... typically 160mm or 210mm. They were designed to form a "real" image without use of a tube lens. As we have discussed before, the Nikon CF ones do not require additional chromatic correction by an eyepiece, so they would be my first choice.