Objective?

In terms of lenses a camera lens and a camera objective are the same thing and they don't change whether they are on or off a camera.

"I used a 100mm objective" as the same as "I used a 100mm lens" or "I used a 100mm job" - it depends upon the individual writer's preferences.

English is a very rich and varied language that has more words than any other, so one idea or item can often be described in many different ways.

That's where I was coming from.
I had a rummage round on the internet and couldn't find reference to a subjective lens ( I definitely remember hearing the phrase in school ), but the rear "glass" in a camera type lens was referred to as the "projection" lens, presumably as this is the lens which projects the focused image onto the film/sensor.

In Norwegian the lens is called an "objektiv" or "linse", the first being considered to be the professional expression, while the other is more a laymans term.

I would continue to use the word lens in English, because it apppears to be the most common term, it is not misunderstood and certainly is easier to read.

That's what I've always understood too.

And in Dutch I hear a lot of people use the English lens rather than objectief.

A magnifying lens doesn't make a real image (i.e. one that could be seen if you put a piece of paper in the optical path), so in this sense it couldn't be an objective lens. The number of physical lenses in an objective also isn't relevant - we've some microscope objectives that are single element designs.

As for the reference to rifle sights, the rear assembly being known as an ocular assembly isn't just to do with the presence of the eye - it also tells you that the outgoing beam (the one travelling towards your eye) will be about 5mm in diameter (since that's about the size of a dilated pupil).

Yes you hear the word lens more but when you look at an internet shop they almost all call it objectieven and not lenzen but I've never found an English shop that calls them objectives and i know from myself that I use the word quite often as well depending on how scientific I want to sound.

I think you've nailed it