James Park
02-01-2003, 04:41 PM
As you go to shorter distances your sight pin needs to go higher up the sight bar. As noted in other posts, sooner or later you get close enough that your sight pin needs to start going down again. This is due to your eye not being behind the nock but above it, which results in a parallax. The distance at which you sight starts to go down again is the "turnover distance", and is calculated accurately in "Accurate Sights" (as you would expect).
If you would like to calculate it, you can use a simple formula as follows:
V= arrow velocity in ft/sec
P= peep-arrow distance (or eye-arrow distance for recurve) in Metres
D= sight turnover distance in Metres
Then:
D=0.1377*V*sqrt(P)
For example:
V= 290 ft/sec
P= 0.11 M
gives: D= 0.1377*290*sqrt(0.11) = 13.2 Metres.
This formula is not exact (because it ignores drag and assumes Sin(x)=x and Tan(x)=x (all of which are good assumptions for short distances), but it will give answers very close to the real value.
Note that the turnover distance depends only on the arrow velocity and on the peep-sight distance. It does not depend on the peep-sight distance.
The turnover distance gets greater as the arrow velocity increases and as the peep-arrow distance increases.
By selecting your peep-arrow distance correctly you can arrange to have your 10M and 15M sights on an identical setting (for a compound bow). I generally do this for field, as it gives me better accuracy for the very short targets. (If you have Accurate Sights, the easiest way to do this is to change the peep-arrow distance 1mm at a time and watch the calculated sight markings as shown by Accurate Sights - when the 10M and 15M markings coincide you will have the optimum peep-arrow distance. If the 15M mark is lower than the 10M mark, increase the peep-arrow distance, if it is higher then reduce it.)
If you would like to calculate it, you can use a simple formula as follows:
V= arrow velocity in ft/sec
P= peep-arrow distance (or eye-arrow distance for recurve) in Metres
D= sight turnover distance in Metres
Then:
D=0.1377*V*sqrt(P)
For example:
V= 290 ft/sec
P= 0.11 M
gives: D= 0.1377*290*sqrt(0.11) = 13.2 Metres.
This formula is not exact (because it ignores drag and assumes Sin(x)=x and Tan(x)=x (all of which are good assumptions for short distances), but it will give answers very close to the real value.
Note that the turnover distance depends only on the arrow velocity and on the peep-sight distance. It does not depend on the peep-sight distance.
The turnover distance gets greater as the arrow velocity increases and as the peep-arrow distance increases.
By selecting your peep-arrow distance correctly you can arrange to have your 10M and 15M sights on an identical setting (for a compound bow). I generally do this for field, as it gives me better accuracy for the very short targets. (If you have Accurate Sights, the easiest way to do this is to change the peep-arrow distance 1mm at a time and watch the calculated sight markings as shown by Accurate Sights - when the 10M and 15M markings coincide you will have the optimum peep-arrow distance. If the 15M mark is lower than the 10M mark, increase the peep-arrow distance, if it is higher then reduce it.)