Air lens from objective to target...

[BoydAllen]

"As you well know, when the wind is still, and there are no significant thermals, the scintillation is negligible."
That is exactly the opposite of what I have seen through high magnification rifle scopes many times. When the sun is shining, and the wind dies completely, the target image will look very distorted, like boiling water with the bubbles going straight up, and if you shoot during that condition your shots will be significantly high. If the wind blows above a certain level, all of that will disappear and the target image will appear clear and sharp.

In his book The Accurate Rifle Warren Page has a chapter titled Shooting Through the Swimming Pool. I recommend it, not that you seem to lack understanding of how the bubbles and refractive index thing works, but for the practical and clear explanations.

 

[Fred Bohl]

In order to keep this thread active, I will contribute this field observation:

Thermal induced "mirage" will always move the apparent target position and distort the target shape. When the image of the target is not distorted in shape then the position is also true.

 

[Depart123]

When the image of the target is not distorted in shape then the position is also true.

I don't believe this is a given. The only time you can count on the image position being true is during heavy overcast, or maybe very early in the morning before the sun comes all the way up.

Not to say that it is never true in any other condition, just that in my experience there is almost always some offset.

The target image may align with your current zero, but let a cloud throw the span between you and the target in shadow and the offset will be readily apparent.

 

[Fred Bohl]

I don't believe so. The only time you can count on the image position being true is during heavy overcast, or maybe very early in the morning before the sun comes all the way up.

Not to say that it is never true in any other condition, just that in my experience there is almost always some offset.

The target image may align with your current zero, but let a cloud throw the span between you and the target in shadow and the offset will be readily apparent.

Ok, I should have noted that most of my shooting and testing is done at short range 100 and 200 yards. I've done some testing and shooting at 600 yards and one match at 1000 yards. Particularly in a timed score relay it can be very difficult to find that distortion free target image then aim/fire at the sighter and next X five times (especially in an afternoon relay in bright sun with variable winds).