Michael et al
When I first began benchrest competition, I noticed this morning-to-afternoon, sunny/cloudy POI vs. POA shift. Several experienced BR competitors cited this as a 'refractive' effect, caused by changes in the angle of light entry into the scope. I decided to track this down to get a solid scientific explanation (with a diagram showing light lines rather than vague references!). I called and spoke with the technical gurus at all of the major scope manufacturers. Response was unanimous. There is no 'refractive' or 'reflective' optical effect related to the change of angle of the sun etc. It seems that this effect is due to mirage, humidity and other factors, and is not an 'angle of entry' issue. I personally have struggled with vertical at one range that is built in a pit. Incredible POI vs. POA shift as the morning sun rises and the air in this pit warms.
Stysh
When I first began benchrest competition, I noticed this morning-to-afternoon, sunny/cloudy POI vs. POA shift. Several experienced BR competitors cited this as a 'refractive' effect, caused by changes in the angle of light entry into the scope. I decided to track this down to get a solid scientific explanation (with a diagram showing light lines rather than vague references!). I called and spoke with the technical gurus at all of the major scope manufacturers. Response was unanimous. There is no 'refractive' or 'reflective' optical effect related to the change of angle of the sun etc. It seems that this effect is due to mirage, humidity and other factors, and is not an 'angle of entry' issue. I personally have struggled with vertical at one range that is built in a pit. Incredible POI vs. POA shift as the morning sun rises and the air in this pit warms.
Stysh