Мы закажем фотохромные линзы, если только оптик не посоветует прогрессивные линзы.

In this sentence, если только means unless or except if.

So:

• Мы закажем фотохромные линзы, если только оптик не посоветует прогрессивные линзы.
• = We’ll order photochromic lenses, unless the optician recommends progressive lenses.

This is not the emotional if only... meaning.

Because Russian often expresses the idea of unless as if ... not.

Literally, the clause is:

• если только оптик не посоветует...
• if the optician does not recommend...

That is logically equivalent to:

• unless the optician recommends...

So the не is normal and important here. Russian is structuring the condition negatively, while English often prefers unless + a positive verb.

This is a very important distinction:

• если только = often unless / except if
• только если = only if

So:

• Мы закажем линзы, если только оптик не посоветует другие.
  = We’ll order the lenses, unless the optician recommends others.

But:

• Мы закажем линзы только если оптик их посоветует.
  = We’ll order the lenses only if the optician recommends them.

Same words, different order, different meaning.

Both are future tense perfective verbs.

• закажем = we will order
• посоветует = he/she will recommend

Russian uses the perfective future here because both actions are seen as single, completed events:

• one act of ordering
• one act of recommending

This is very natural in a sentence about a future decision.

Because закажем fits better when you mean a single completed action: we’ll place an order.

• закажем = we will order (as one completed act)
• будем заказывать = we will be ordering / will order in an ongoing or repeated sense

Here the speaker means a specific decision about what lenses to order, so закажем is the natural choice.

They are in the accusative plural because they are direct objects:

• order what? → фотохромные линзы
• recommend what? → прогрессивные линзы

Since линзы is an inanimate plural noun, its accusative plural looks the same as the nominative plural.

So:

• nominative plural: линзы
• accusative plural: линзы

The adjectives match that plural form:

• фотохромные
• прогрессивные

Because after these verbs, the noun is a direct object, so it takes the accusative, not the genitive.

• заказать линзы = to order lenses
• посоветовать линзы = to recommend lenses

Линз is the genitive plural form, and it would be used in other contexts, for example after certain numbers or in negative/quantity expressions:

• пара линз
• нет линз

But not here.

Yes, it could be omitted.

Russian often leaves out subject pronouns when the verb ending already makes the subject clear:

• Закажем фотохромные линзы...
  = We’ll order photochromic lenses...

Including мы gives a bit more explicitness or emphasis. It can sound like as for us, we’ll order... or simply make the sentence a little clearer.

It is simply omitted because it is understood from context.

Russian could say:

• если только оптик не посоветует нам прогрессивные линзы

Here нам = to us

But Russian often leaves out such words when they are obvious. Since the people ordering the lenses are also the ones receiving the advice, нам is not necessary.

Here оптик means optician: the eye-care professional helping choose lenses.

Depending on context, English sometimes uses optician, optometrist, or another profession word, but in a sentence like this optician is the most straightforward translation.

It refers to the person, not the shop.

Yes. Russian word order is flexible.

For example, you can also say:

• Если только оптик не посоветует прогрессивные линзы, мы закажем фотохромные линзы.

This has the same basic meaning: Unless the optician recommends progressive lenses, we’ll order photochromic lenses.

The original version puts the main decision first and the condition second. The reordered version foregrounds the condition.

Yes, you could:

• Мы закажем фотохромные линзы, если оптик не посоветует прогрессивные линзы.

That means We’ll order photochromic lenses if the optician doesn’t recommend progressive lenses.

Adding только gives the sentence a stronger exception flavor, which makes it feel closer to unless. So если только is a bit more idiomatic here if the speaker means except in that one case.

Yes, in other contexts it can.

For example:

• Если только он придёт!
• If only he would come!

But that is a different use. In your sentence, если только is part of a conditional structure with не посоветует, so it means unless, not a wish.

Context tells you which meaning is intended.