Obiectivul este pe aparatul foto.

In this sentence, obiectivul means the lens.

The base word is obiectiv, which can mean different things depending on context:

• lens in photography
• objective/goal in other contexts
• objective as an adjective in some cases

Because the sentence also has aparatul foto (the camera), the meaning lens is the natural one here.

Because Romanian usually puts the definite article at the end of the noun, not before it.

So:

• obiectiv = lens
• obiectivul = the lens
• aparat = device / camera
• aparatul = the device / the camera

So English the often becomes a suffix in Romanian.

A useful extra point: both obiectiv and aparat are neuter nouns. In the singular, neuter nouns often look like masculine nouns, which is why they take -ul here.

Because aparat foto is a fixed expression meaning camera (literally something like photo device).

In this phrase:

• aparat is the main noun
• foto acts like an invariable modifier

So only the main noun gets the article:

• aparat foto = camera
• aparatul foto = the camera

This is very common in Romanian with compound expressions.

Here, pe means on.

So:

• pe aparatul foto = on the camera

In context, it can suggest attached to or mounted on the camera, not just loosely sitting on top of it.

Also, pe is a very common Romanian preposition, and it has other uses too. For example, it can mark certain direct objects:

• Îl văd pe Andrei = I see Andrei

But in your sentence, it simply means on.

In normal Romanian, este is needed here.

So:

• Obiectivul este pe aparatul foto = correct
• Obiectivul pe aparatul foto = not correct as a normal full sentence

In everyday speech, people very often use the shorter form e instead of este:

• Obiectivul e pe aparatul foto.

That sounds natural and common.

The given order is the most neutral and natural one:

• Obiectivul este pe aparatul foto.

Romanian does allow other word orders, for example:

• Pe aparatul foto este obiectivul.

But that version sounds more marked and is usually used for emphasis or contrast, not as the plain default sentence.

So for a learner, the original order is the best one to use first.

Yes, aparat foto is a very common and natural way to say camera.

You may also see:

• cameră foto
• aparat de fotografiat

But aparat foto is extremely common in everyday Romanian.

It is also helpful because cameră by itself often means room, so aparat foto is very clear.

You would use the indefinite article un:

• Un obiectiv este pe un aparat foto.

That means A lens is on a camera.

So compare:

• obiectivul = the lens
• un obiectiv = a lens
• aparatul foto = the camera
• un aparat foto = a camera

This is a good sentence for seeing the difference between Romanian definite and indefinite forms.