Стоит только убрать штатив, как кадр начинает дрожать.

Here стоит is not about price. In this pattern, стоит только + infinitive means:

• one only has to...
• it only takes...
• as soon as...

So:

• Стоит только убрать штатив, как кадр начинает дрожать. = One only has to remove the tripod, and the frame starts shaking.

This is a very common Russian structure for saying that one action immediately leads to another.

A few similar examples:

• Стоит только выйти на улицу, как начинается дождь.
  As soon as I go outside, it starts raining.

• Стоит только отвлечься, как он уже что-то натворил.
  The moment you get distracted, he has already done something.

So yes, the verb is historically the same стоить, but in this expression it functions more like it is enough to / one only has to.

Because this is an impersonal fixed construction.

In стоит только убрать..., there is no real subject like I, you, or it doing the action of стоить. Russian simply uses the 3rd person singular form стоит in this expression.

You can think of it as similar to English it only takes..., where it does not refer to anything concrete.

Common forms are:

• стоит только сделать...
• стоило только сделать... = it only took / as soon as ... did
• стоило мне сделать... = as soon as I did...

Examples:

• Стоит только спросить, как он начинает спорить.
• Стоило только спросить, как он начал спорить.

So in your sentence, стоит is just the normal present-tense form used in this idiomatic pattern.

Because the sentence refers to a single completed action: removing the tripod.

• убрать = perfective, to remove / put away completely
• убирать = imperfective, to be removing / to remove repeatedly / in general

In this sentence, the meaning is:

• once the tripod is removed,
• or the moment you remove the tripod,

the frame starts shaking.

That is why perfective убрать fits well.

Compare:

• Стоит только убрать штатив, как кадр начинает дрожать.
  As soon as you remove the tripod, the frame starts shaking.

If you used убирать, it would sound less natural here because the focus is not on the process of removing, but on the completed trigger event.

No. Here как does not mean how.

In the pattern стоит только..., как..., the word как introduces the result that follows immediately. The whole structure means something like:

• as soon as...
• no sooner ... than ...
• the moment ...

So:

• Стоит только убрать штатив, как кадр начинает дрожать.

literally feels like:

• One has only to remove the tripod, and immediately the frame begins to shake.

This is a set pattern:

• Стоит только X, как Y
• Стоило только X, как Y

Examples:

• Стоит только лечь спать, как кто-то звонит.
  As soon as I go to bed, someone calls.

• Стоило только открыть окно, как стало холодно.
  As soon as we opened the window, it got cold.

So как here is part of the construction, not the ordinary question word how.

Because the sentence has two clauses:

1. Стоит только убрать штатив
2. как кадр начинает дрожать

Russian normally separates such clauses with a comma. In this particular construction, the comma before как is standard.

So the punctuation reflects the structure:

• trigger/action first
• immediate consequence second

That is why the comma is required here.

Кадр can mean several related things, depending on context:

• a frame in a video
• a shot in filming
• the image you see in the camera
• sometimes a still frame or photographic composition

Here, because of штатив (tripod), the idea is probably:

• the image in the shot
• the camera frame
• the filmed picture

So кадр начинает дрожать means that the image becomes shaky once the tripod is removed.

English might translate it as:

• the frame starts shaking
• the shot starts shaking
• the image starts to wobble

Because кадр is the subject of the second clause:

• кадр начинает дрожать

Here:

• кадр = subject
• начинает = verb
• дрожать = infinitive complement

So кадр must be in the nominative.

It is the thing that starts shaking.

Because начинает дрожать emphasizes the onset of the shaking.

Compare:

• кадр дрожит = the frame is shaking
• кадр начинает дрожать = the frame starts shaking / begins to shake

In this sentence, the point is the immediate change after removing the tripod. So начинает дрожать is more expressive and more precise.

It shows a sequence:

1. remove tripod
2. shaking begins

That is exactly why начинает дрожать is a good choice here.

Because after начинать, Russian normally uses an infinitive that names the action as a process:

• начинать делать
• начинать работать
• начинать говорить
• начинать дрожать

So начинает дрожать means begins to shake.

Using a perfective infinitive after начинать is usually impossible or unnatural in ordinary usage, because you do not normally begin to complete something; you begin doing it.

That is why:

• начинает дрожать is correct
• a perfective counterpart would not work here in the same way

It is in the present tense, but it most naturally expresses a general repeated situation or general truth.

So it means something like:

• whenever the tripod is removed, the frame starts shaking
• this always happens

Russian often uses the present tense this way, just like English:

• You remove the tripod, and the image starts shaking.

So the sentence is not necessarily describing one specific moment happening right now. It more likely describes a regular cause-and-effect relationship.

Yes. A few natural alternatives are:

• Как только убираешь штатив, кадр начинает дрожать.
  As soon as you remove the tripod, the frame starts shaking.

• Если убрать штатив, кадр начинает дрожать.
  If you remove the tripod, the frame starts shaking.

• Стоит убрать штатив, и кадр начинает дрожать.
  Also possible, with a similar meaning.

• Стоит лишь убрать штатив, как кадр начинает дрожать.
  лишь can replace только.

The original version with стоит только..., как... is especially good for expressing a quick, almost automatic consequence.