أما العاكس الضوئي فهو نظيف.

In this pattern, أما usually means something like as for..., regarding..., or when it comes to....

So:

• أما العاكس الضوئي فهو نظيف
• literally: As for the optical reflector, then it is clean

In natural English, you often would not translate every part literally. The point of أما is to introduce a topic and contrast it with something else, stated or implied.

A very common structure in MSA is:

• أما ... فـ...
• As for ..., ...

So this sentence is a textbook example of that pattern.

Because أما is very often followed by the particle فَـ in the answer or comment that comes after it.

This is a standard construction:

• أما زيدٌ فهو مجتهدٌ
• As for Zayd, he is hardworking

So in your sentence:

• أما العاكس الضوئي فهو نظيف

the فَ links the topic introduced by أما to the statement about it.

You can think of it as part of the fixed pattern أما ... فـ....

The pronoun هو is commonly used here to resume the topic after أما. It refers back to العاكس الضوئي.

So:

• أما العاكس الضوئي فهو نظيف
• literally: As for the optical reflector, it is clean

This resumptive pronoun is very normal in Arabic. It helps make the structure clear and smooth.

In some contexts, Arabic can omit such pronouns, but in this kind of أما ... فـ... pattern, using هو is very common and natural.

It is basically a nominal sentence.

The core statement is:

• هو نظيف
• It is clean

That is a nominal sentence: subject + predicate, with no written present-tense to be.

The whole sentence begins with أما, which introduces the topic, but the main clause after that is still nominal.

In Arabic, present-tense to be is usually not expressed in simple sentences.

So:

• هو نظيف means
• It is clean

There is no separate word for is here.

This is very normal in Arabic. Compare:

• الرجل طويل
• The man is tall

But in past or future expressions, Arabic does use verbs such as كان:

• كان نظيفًا = it was clean
• سيكون نظيفًا = it will be clean

Yes, الضوئي is an adjective describing العاكس.

So this is not an iḍāfa construction. It is:

• العاكس = the reflector
• الضوئي = light-related / optical

Together:

• العاكس الضوئي = the optical reflector

One important clue is that both words have الـ:

• العاكس
• الضوئي

In an adjective phrase, the adjective usually matches the noun in:

• definiteness
• gender
• number
• case

Since العاكس is definite, the adjective الضوئي is also definite.

Because it is an adjective agreeing with a definite noun.

In Arabic, adjectives follow the noun and match it in definiteness. So:

• عاكس ضوئي = an optical reflector
• العاكس الضوئي = the optical reflector

If the noun is definite, the adjective is definite too.

This is different from English, where adjectives do not change form for definiteness.

Usually, in normal Arabic writing, short case endings are not written. So نظيف may stand for:

• نظيفٌ in full vowelled form

Here it is the predicate of a nominal sentence, so in fully vocalized classical/MSA style it would normally be:

• أما العاكسُ الضوئيُّ فهو نظيفٌ

not نظيفًا.

نظيفًا would usually appear in different grammatical environments, such as after certain particles or verbs that make the word accusative.

So the short answer is:

• unvowelled writing: نظيف
• full grammatical form here: نظيفٌ

In fully vocalized MSA, it is typically nominative:

• أما العاكسُ الضوئيُّ فهو نظيفٌ

The topic introduced by أما is normally in the nominative.

A learner does not always need to master all the case theory immediately, but if you are looking at fully vowelled text, that is the form you would expect.

No. That is a common source of confusion.

Depending on context, أما can feel like:

• as for
• regarding
• for its part
• sometimes a contrastive but as for...

In your sentence, as for the optical reflector, it is clean is usually the best way to understand it.

So أما is not simply the ordinary word for but in every situation. Often it is better understood as a topic-setting or contrast-marking word.

Yes. Very often أما ... فـ... suggests contrast, even if the other side is not stated in the same sentence.

For example, the broader context might be something like:

• أما العاكس الضوئي فهو نظيف، لكن العدسة متسخة
• As for the optical reflector, it is clean, but the lens is dirty

Even if the contrasting item is omitted, أما can still give that as for X... feeling.

A careful fully vocalized reading would be approximately:

• أَمَّا الْعَاكِسُ الضَّوْئِيُّ فَهُوَ نَظِيفٌ

A rough guide to the parts:

• أمّا
• al-ʿākisu
• aḍ-ḍawʾiyyu
• fa-huwa
• naẓīfun

A few pronunciation notes:

• الضوئي begins with ض, a heavy emphatic consonant.
• The ال before ض is assimilated in pronunciation, so it sounds like aḍ-ḍawʾiyyu, not al-ḍawʾiyyu.
• هو is pronounced huwa in careful reading.