J
jesilva
Guest
Does the position of the sun affect POI when using a scoped rifle as it does with iron sights.
Jim
Jim
David Valdina
Member
Probably not
When the sun is hitting a front bead, it can act like a full moon, half moon or a new moon. Some of the articles from black powder days and early smokeless days speak of this. Different mechanics if you will with a scope.
When the sun is hitting a front bead, it can act like a full moon, half moon or a new moon. Some of the articles from black powder days and early smokeless days speak of this. Different mechanics if you will with a scope.
O
OldPPC
Guest
When you're dealing with open sights (iron sites) you're forced to work in a three dimensional environment over a series of distances. Focusing on the front bead/ramp/blade while aligning it with the rear "V" or notch and at the same time aligning it with the bulls eye involves a lot of hand/body/eye coordination and sunlight on one side or the other of the front bead/ramp/blade can cause you to misalign the sights in favor of the sunny side. Your scope reduces the image to two dimensions at one focused distance so the impact of the sunlight on the target (even with shadows on the target area) or the barrel shouldn't be a factor. However, obviously, if the sun is striking the scopes objective lens can be a factor, especially in scopes with lower quality lens coatings. POI is relative to POA so, if bad lighting causes you to aim incorrectly, the impact will vary accordingly.
The sun and it's reflected heat waves are probably a more critical factor than any of its other influences. Mirage can be devastating ...
The sun and it's reflected heat waves are probably a more critical factor than any of its other influences. Mirage can be devastating ...
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SGJennings
New member
I think that's all a way of saying NO. It doesn't effect the scope in that way.
Now, let some Texas sun shine on that dark scope for a good while and it might walk, but that's a discussion for another thread.
Now, let some Texas sun shine on that dark scope for a good while and it might walk, but that's a discussion for another thread.
SGJennings
New member
Mirage? <that's a real question, not a rhetorical one>
Thought about mirage, but thought it was a different question.
Thought about mirage, but thought it was a different question.
JerrySharrett
Senile Member
One thing the hot sun will do. If you leave your rifle sitting in the sun while cleaning, etc., then go to the line, in the shade, as the scope tube cools the POI will change. Been there, done that!!
Also, on bright sunny days where occasionally a cloud come across just as a single shot is fired, it will go out of the group. Been there , done that too!!
(It will go out high or low, can't remember which-high I think for the cloudy shot)
Also, on bright sunny days where occasionally a cloud come across just as a single shot is fired, it will go out of the group. Been there , done that too!!
(It will go out high or low, can't remember which-high I think for the cloudy shot)
E
eww1350
Guest
a bright sunny day..with shade clouds floating in/out let one float in and shade the area...
your bullet will drop out the bottom...
I speak from experience...
your bullet will drop out the bottom...I speak from experience...
JerrySharrett
Senile Member
You may be correct on the cloudy/low shot. At the 2009 Shamrock, I shot a 340 under a cloud and it probably cost me first place in lv100.a bright sunny day..with shade clouds floating in/out let one float in and shade the area...
I speak from experience...
Why do I not know which? I had one out the top and one out the bottom, omitting either one I had about a 190 on that target. But with that shot I had a 23 final agg and it took a 20 to win.
SGJennings
New member
The scope heating and cooling is exactly what I was talking about when I said it would "walk". Not too much in any short timeframe, but it adds up. I've always thrown a white towel over mine when I'm out in the sun.
Never heard of cloud causing one to drop out of the bottom of the group. But, do you think that's an optical effect like sun on open sights? Is it a downrange optical effect like mirage? Or, is it a ballistic effect?
I'm sure going to keep my eyes open and if a cloud comes in, I'm going to the sighter!
Greg J.
SGJennings
New member
While I'm thinking about it, I got something interesting from a long-time shooter while at the Wilmore fun match.
On the Weaver t-36, with the sun shade on, look through the scope and get someone to gently push on the side of the sun shade to simulate a stiff breeze. Watch the POA deflect.
Don't know how much wind it would take to do it, but it sure is interesting.
On the Weaver t-36, with the sun shade on, look through the scope and get someone to gently push on the side of the sun shade to simulate a stiff breeze. Watch the POA deflect.
Don't know how much wind it would take to do it, but it sure is interesting.
J
jesilva
Guest
Thanks for all the replies. My situation is such; the range is oriented east/west at 300 yds. During an mid-range F-class match beginning at 0900, the three stages might be fired at 0915, then 0945, then 1030. The sun moves on the shooters right side in a low arc at this time of year. Using the scope setting from the early relay, it appears that the group center moves as the day gets on. It could be from fatigue or other concerns. However, I jsut wanted to hear from the experienced shooters what they thought. Oh, by the way, the shooting area is covered to the extent that the shooters scopes may or may not have the same light throughout the shoot.
Jim
Jim
J
JonE
Guest
When I shot IHMSA we were always told that the shot went high when the sun shined because it caused an updraft, went down when a cloud went by because the air cooled and cused a down draft. If this is true or not, I have no way of knowing, but it sounded as good as any other explaination
Hey...... it's a good way to remember the direction anyway
As long as it's right.
The phrase I've often heard is "light's up, sights up"....................... whatever THAT means!
al
SGJennings
New member
Hi Francis,
My Weaver is on the shelf as a backup and has never had the sunshade on it. My Leupold has never had it on either.
A couple of guys that I was shooting with at the Bluegrass Sportsmans Club (aka "Wilmore") had them on. One of the experienced shooters showed the effect of the crowbar. I thought it was really interesting and worth spreading the news.
Now, my son has a NightForce. He thinks it looks "wicked" with the sunshade on it. I'm going to have to fight him over this. Practicality is not the forte of a 17 year old with lacrosse, girls and cars on his mind...not necessarily in that order.
Greg J.
I think, it is similar to mirage. Sun or snow. Over the Target.
When a cloud moves over the target. Optically/what we see. The POA/target moves. And the POI is moved. If you are in tune.......and the flags are read correctly.
And maybe, the cooling of the shade on the target has some effect also....
When a cloud moves over the target. Optically/what we see. The POA/target moves. And the POI is moved. If you are in tune.......and the flags are read correctly.
And maybe, the cooling of the shade on the target has some effect also....
D
dpapadimitrio@g
Guest
Lights up sights up?????
As a metallic silhouette shooter this is a mantra I've heard repeated over the years, seeing it here was cause to finally see if there is anything behind this. I come to this site to learn
Did a search for index of refraction changes in air with changes in ambient temperature.
Did find a website that covered this, and it appears with an increase in ambient temperature, the index of refraction is reduces, and thus the appearance of the target shifts. Did this for a change in temperature of 70 to 90 degrees. temperature shifts of 15 degrees are common in the west, between shaded and sunny areas. Based on this, figured the 20 degree F shift would illustrate.
On that basis the index of refraction changed from 1.000266682 to 1.000256460. The impact needs to be considered at distances of 100 to 500 meters, and on that basis, it appears the old adage has some substantiation.
Take it for what it is worth
As a metallic silhouette shooter this is a mantra I've heard repeated over the years, seeing it here was cause to finally see if there is anything behind this. I come to this site to learn
Did a search for index of refraction changes in air with changes in ambient temperature.
Did find a website that covered this, and it appears with an increase in ambient temperature, the index of refraction is reduces, and thus the appearance of the target shifts. Did this for a change in temperature of 70 to 90 degrees. temperature shifts of 15 degrees are common in the west, between shaded and sunny areas. Based on this, figured the 20 degree F shift would illustrate.
On that basis the index of refraction changed from 1.000266682 to 1.000256460. The impact needs to be considered at distances of 100 to 500 meters, and on that basis, it appears the old adage has some substantiation.
Take it for what it is worth