Càng lấy nét tốt, hình càng sắc nét.

It is a very common Vietnamese pattern meaning the more ..., the more ....

So:

• Càng lấy nét tốt, hình càng sắc nét.
• = The better the focus, the sharper the image.

This pattern shows a relationship between two things that increase together:

• first clause = the changing condition
• second clause = the matching result

You can think of it as the Vietnamese equivalent of English patterns like:

• The harder you study, the better you do.
• The more you practice, the easier it gets.

Because each càng has a job:

• the first càng introduces the first increasing idea
• the second càng introduces the second increasing idea

In other words:

• càng X
• càng Y

This is the normal structure in Vietnamese. Repeating càng is not redundant; it is how the pattern works.

So in this sentence:

• càng lấy nét tốt = the better the focusing is
• hình càng sắc nét = the sharper the image is

Lấy nét is a fixed expression in photography and videography meaning to focus or to set the focus.

It does not mean a literal word-for-word idea like take lines. You should learn it as one unit.

Common uses:

• máy ảnh lấy nét nhanh = the camera focuses quickly
• khó lấy nét = hard to focus
• lấy nét tự động = autofocus
• lấy nét bằng tay = manual focus

In this sentence, lấy nét tốt means to focus well or to achieve good focus.

In Vietnamese, words like tốt, rõ, nhanh, đẹp often come after a verb to describe how well the action is done.

So:

• làm tốt = do well
• nghe rõ = hear clearly
• chụp đẹp = photograph well / take nice photos
• lấy nét tốt = focus well

English often uses an adverb like well, but Vietnamese often uses an adjective-like word after the verb.

So lấy nét tốt is natural Vietnamese structure.

They are related to image clarity, but they are not the same thing.

• lấy nét = the action/process of focusing
• sắc nét = the quality of being sharp, crisp, well-defined

So:

• lấy nét is something you do
• sắc nét is how the image looks afterward

That is why the sentence makes sense:

• if you focus better,
• the image becomes sharper

Even though both expressions contain nét, they are different vocabulary items and are not interchangeable.

Here hình means image, picture, or photo depending on context.

It overlaps with ảnh, but they are not always identical:

• ảnh usually means photo
• hình is broader and can mean image/picture/visual

In a photography or camera context, hình is very natural. It can refer to the resulting image in a general way.

So in this sentence:

• hình càng sắc nét = the image becomes sharper

If you changed hình to ảnh, the meaning would still be very similar in many contexts.

Vietnamese often leaves out the subject when it is obvious, general, or not important.

This sentence is making a general statement, so it does not need to say exactly who or what is doing the focusing.

English often prefers a fuller structure, but Vietnamese is comfortable with this kind of omission.

Possible fuller versions would be:

• Máy ảnh càng lấy nét tốt, hình càng sắc nét.
• Càng lấy nét tốt thì hình chụp càng sắc nét.

But the shorter original sentence sounds natural as a general rule or technical observation.

Yes, thì can be used, and many learners will see this pattern with thì.

For example:

• Càng lấy nét tốt thì hình càng sắc nét.

That version is also natural.

About the comma:

• the comma separates the two linked halves
• it helps readability
• it marks a slight pause

So the sentence can be written with a comma, and that is perfectly fine.

Very roughly:

• càng ..., càng ... = compact style
• càng ... thì càng ... = slightly more explicit connection

Both are common.

Vietnamese allows some flexibility here.

The given sentence says:

• Càng lấy nét tốt, hình càng sắc nét.

But you may also hear or see:

• Lấy nét càng tốt thì hình càng sắc nét.

Both express basically the same idea.

The difference is mostly about where the speaker wants the emphasis or how the sentence flows.

• càng lấy nét tốt treats the whole action focus well as the thing increasing
• lấy nét càng tốt puts càng closer to tốt, so it feels a bit more directly like the better the focusing

For learners, the important point is that both are understandable and natural enough in the right context.

It is understandable and basically natural, especially in a technical or instructional context.

That said, some native speakers might slightly prefer one of these versions:

• Càng lấy nét tốt thì hình càng sắc nét.
• Lấy nét càng tốt thì hình càng sắc nét.
• Càng lấy nét chuẩn, hình càng sắc nét.

Why?

• adding thì can make the structure clearer
• moving càng can sound smoother to some speakers
• chuẩn can sound more specifically like accurate/precise focus

So the original sentence is fine, but it is not the only natural way to express the idea.

Yes, very often. It is one of the most useful Vietnamese sentence patterns.

Examples:

• Càng học nhiều, càng hiểu sâu.
  = The more you study, the more deeply you understand.

• Càng tập, càng giỏi.
  = The more you practice, the better you get.

• Càng gần, càng rõ.
  = The closer it is, the clearer it is.

• Càng chụp tối, ảnh càng nhiễu.
  = The darker the shooting conditions, the noisier the photo.

So the sentence you asked about is a very good example of a broader grammar pattern you will see again and again.