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#### IsaacT

##### New member
If that is the case then .098mRad stands as the measurement I received...

#### RA_pierce

##### Well-known member
If that is the case then .098mRad stands as the measurement I received...
That seems very low.
I measure divergence up to 30 feet. On my reds, the best I can get is about ~0.5mRad.

The goal is not to measure it focused. When you focus the laser, you are creating a focal point. The beam waist on the typical red laser could be around 20 feet from the aperture. If the beam is focused, it converges, so the beam is smaller at one point but then expands again.
If the beam is converging at some point, you will need to check at a much greater distance.
What you could be measuring is a beam with negative divergence, meaning your measurement could be skewed and artificially decreased because it is measured near the beam waist.

The goal is to minimize the diameter of the beam in the far field, away from the focus of the laser, and then take that measurement.
Typical divergence will be around 0.5mRad, which is good.

#### IsaacT

##### New member
hmm....so maybe focus it at 60 feet or something and then measure at 1 foot and 35 feet? Does that sound resonable?

#### RA_pierce

##### Well-known member
hmm....so maybe focus it at 60 feet or something and then measure at 1 foot and 35 feet? Does that sound resonable?
I think you are confused about the measurement process...

What you are trying to achieve is lowest divergence. That does not mean smallest dot, necessarily.
It is pretty self explanatory... you want the beam to not diverge (or converge). You want the beam to remain as parallel as possible so that the beam diameter is minimal at all distances.

If you have 60 feet available, use it. The more distance the better. I don't know why you would set it up at 60' though, and then only measure it at 35'?

I have no problem using ~30-40' for measurements, don't know why you are having problems.

I will reiterate: Do not measure the beam at or near the waist!

#### IsaacT

##### New member
Okay....I think I understand now....I could set it up for ~35 feet, but try to get both measurements the same....yes? so if I have 5mm at a set point close to the laser, I go for having 5mm on the wall?

#### RA_pierce

##### Well-known member
Okay....I think I understand now....I could set it up for ~35 feet, but try to get both measurements the same....yes? so if I have 5mm at a set point close to the laser, I go for having 5mm on the wall?
Yes.
But since a zero divergence beam is impossible, you should be getting a beam a little wider than 5mm.
And you want to make sure that the beam does not converge.

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