Ons verander die velddiepte deur die lensopening te verstel.

Here, ons means we because it is the subject of the sentence: Ons verander ... = We change ...

Yes, ons can also mean us in other sentences. Afrikaans uses the same form for both meanings, and the grammar tells you which one it is.

• Ons verander die velddiepte. = We change the depth of field.
• Hulle help ons. = They help us.

Because Afrikaans verbs usually do not change according to the subject the way English verbs sometimes do.

So you get:

• ek verander = I change
• jy verander = you change
• ons verander = we change
• hulle verander = they change

This is one of the simpler parts of Afrikaans grammar: in the present tense, the verb usually stays the same.

Afrikaans very often makes compound nouns by joining words together.

So velddiepte is made from:

• veld = field
• diepte = depth

Together, they form one noun: velddiepte.

English often uses a structure like depth of field, but Afrikaans prefers a compound noun instead of using a separate word like of.

A useful pattern to remember is that the last part is the main noun. So velddiepte is a kind of diepte.

Because Afrikaans often expresses ideas like X of Y by making a single compound noun instead.

So where English says:

• depth of field

Afrikaans says:

• velddiepte

This is very common in Afrikaans, especially in technical or descriptive vocabulary. English often uses of, but Afrikaans often packs the same idea into one word.

For the same reason: it is another compound noun.

• lens = lens
• opening = opening

So lensopening literally means lens opening, and in this context it refers to the aperture.

Again, Afrikaans prefers one combined noun here rather than two separate words.

Because both velddiepte and lensopening are definite nouns here:

• die velddiepte = the depth of field
• die lensopening = the aperture

Afrikaans uses die as the definite article for:

• singular nouns
• plural nouns
• all grammatical genders

So unlike languages such as German or Dutch, you do not have to change the article for masculine, feminine, neuter, or plural. Die stays the same.

This is a very common Afrikaans way to express how something is done.

• deur = by / through
• te verstel = to adjust

Together, deur die lensopening te verstel means by adjusting the aperture.

So the phrase explains the method:

• Ons verander die velddiepte = We change the depth of field
• deur die lensopening te verstel = by adjusting the aperture

English often uses by + -ing, while Afrikaans often uses deur + ... + te + infinitive.

Te is the infinitive marker in Afrikaans, similar to English to.

So:

• verstel = adjust
• te verstel = to adjust

In this sentence, te verstel is part of the structure after deur, which gives the idea of by adjusting.

So even though te often looks like English to, the whole phrase should be understood as an idiomatic unit:

• deur die lensopening te verstel = by adjusting the aperture

Because this sentence uses the deur ... te construction, not the om ... te construction.

Learners often see om te and expect it everywhere, but Afrikaans has several infinitive patterns. After deur meaning by, the normal structure is:

• deur ... te + verb

So:

• deur die lensopening te verstel = by adjusting the aperture

not:

• deur om die lensopening te verstel

Because in Afrikaans, infinitive and subordinate-style structures often place the verb toward the end.

So the phrase is built like this:

• deur = by
• die lensopening = the aperture
• te verstel = to adjust

That gives:

• deur die lensopening te verstel

To an English speaker, this can feel a bit like by the aperture to adjust, but that is just the Afrikaans word order. The natural English translation is still by adjusting the aperture.

They are related in meaning, but they do different jobs in the sentence.

• verander = change
• verstel = adjust

So:

• Ons verander die velddiepte = We change the depth of field
• deur die lensopening te verstel = by adjusting the aperture

In other words:

• verander describes the result
• verstel describes the action used to get that result

Yes. Deur can mean through in some contexts and by / by means of in others.

For example:

• Ons stap deur die deur. = We walk through the door.
• Ons verander die velddiepte deur die lensopening te verstel. = We change the depth of field by adjusting the aperture.

So the exact meaning depends on the context. In your sentence, it clearly means by means of or by.