All you F-Class HM, Light shift vs POI, Tell me what you know.

[Dave M.]

LIGHTs UP, Sights UP. LIGHTs DOWN, sights DOWN!

Can you explain what you mean by this?

 

[kyreloader]

I thank everyone for the input, I am surprised more of the National HM are not chirping in?? Does in not bother them, do they know the secret handshake?

Please explain the time frame to shoot the target, was it one large cloud movement between the shot groups? Thx Ted

Typical timeframe to shoot a 20 shot string, approximately 15 minutes.
It was a partly cloudy day where the target was going in and out of the bright sunlight. The shots were alternating groups based on the lighting condition.

 

[JFrank]

Gotta pay your dues, bud. get out there and figure it out.

Tough love but reality, and when you get it figured out it’s yours to share or not .

 

[Medic505]

Don’t shoot in boils

I think this was the first advice I received when I started shooting F Class. The thing I noticed was the advice givers were the ones that were hammering away and shooting 10's and X's while I was laying there waiting for the wind to blow.

 

[Laurie]

I think it's a mirage effect, not a light effect. I've never noticed any impact change when mirage is not present.

I'm not sure about that. I more than once sat behind 1,000 yard F-Open details on Bisley's Stickledown Range panning across the targets on a spotting scope during European F-Class Championship matches. With typical autumn British weather, the sun would be continually on/off on the targets as clouds moved over and mirage was usually nil, or so light it wasn't visible in the cool temperatures. When the targets lit up after a duller patch, I'd always see a trend of lower POIs panning across as many as 20 targets with over half showing low 5s and a few even dropping into the 4-ring just 'out'. Prior to the light change, Vs would make up the majority of hits with light steady winds, then become exceptions for the first shot after the sun reappeared.

 

[Jdne5b]

I think this was the first advice I received when I started shooting F Class. The thing I noticed was the advice givers were the ones that were hammering away and shooting 10's and X's while I was laying there waiting for the wind to blow.

Shade low and send it. If I don’t have a sighter in the boil… well now I do.

 

[Laurie]

Can you explain what you mean by this?

This advice goes back to iron sights and blade foresights as in Service Rifle shooting where the shooter would place the top of the sight underneath the 'black' with a gap of white background between the two. The aim was to keep that gap the same for every shot, and in settled light conditions, accomplished shooters were really remarkably consistent across many shots.

However when the light changed, the shooter's perception of the gap also changed affecting the aim. Lights up; sights up countered that. However, mirage aside, scope sights shouldn't be affected by light changes on the target. As my previous post says that IMO, they are, I can't account as to why that should be so - and I've yet to see an explanation. This isn't the first time this has been raised - I remember a long discussion on the US Palma Teams' Long Range Forum many years ago.

 

[XTR]

I concur with Laurie's statements re: a "6 o'clock hold" with open sights. The lighting can change the perception of the bottom of the black will make a difference, esp for those who shoot with a "line of white" under the black.

Shooting F class at Connaught in '17 the difference in POI in and out of the mirage was very evident. At 900m that range has condition variations that go from dirty aquarium soup to spotting flies walking on the target in the same relay. The theory I am working with is that the mirage makes the image appear higher than it's actual location, so if you are zeroed up center in the clear when the mirage comes in the image at 900m goes up, you hold center (which is now up), and your POI goes up. Same in reverse if you're centered up w/o mirage. What ever the case, there was a solid ½MOA change between the clear and the soup.

Pay attention to it on your range when you shoot. Speaking for myself one of the things that can sometimes be hard to do is to stop competing and start learning when you shoot in a match. Funny thing is that when I do my scores tend to go up.

 

[LVLAaron]

Light matters.

We tested this at 500 on a clear sunny afternoon with large clouds, so we'd have many distinct light changes that lasted a few minutes.

We had 3 scopes on the line..
- Vortex Golden Eagle
- Nightforce Comp
- March High Master

I've got notes somewhere, but it went something like this: In order to keep elevation between the changes, there was as much as 1 MOA of adjustment needed. We were really testing the optics... The golden eagle needed a minute... the march only needed 1/4 minute in the same changes... the NF was somewhere in the middle of the other two.

Long story short... good scopes are worth the money for more than the usual reasons people consider.


edit; The above was on a fairly low mirage day. very dry

 

[dcali]

I concur with Laurie's statements re: a "6 o'clock hold" with open sights. The lighting can change the perception of the bottom of the black will make a difference, esp for those who shoot with a "line of white" under the black.

Shooting F class at Connaught in '17 the difference in POI in and out of the mirage was very evident. At 900m that range has condition variations that go from dirty aquarium soup to spotting flies walking on the target in the same relay. The theory I am working with is that the mirage makes the image appear higher than it's actual location, so if you are zeroed up center in the clear when the mirage comes in the image at 900m goes up, you hold center (which is now up), and your POI goes up. Same in reverse if you're centered up w/o mirage. What ever the case, there was a solid ½MOA change between the clear and the soup.

Pay attention to it on your range when you shoot. Speaking for myself one of the things that can sometimes be hard to do is to stop competing and start learning when you shoot in a match. Funny thing is that when I do my scores tend to go up.

That's been my experience. With irons, it definitely changes because of shooter perception with or without mirage. With scopes? I haven't seen that happen unless mirage is present (and it usually is if you see a light change). When it's there, the target seems to dance upwards to my eyes, but "snap" back to its original position. If I hold at the low end of that dance, I find that it's where the target was without mirage. If I try it hold in the average position of the target, I hit high.

 

[FrankG]

Here is a excellent video. This was done by Vortex a few years back at Lodi, WI (Winnequah Gun Club). Spotting scope was set up on the 1k yard line. Tried to make the mount as solid/as permanent as possible so the wind etc... wouldn't bounce it around. They also covered/shaded the scope so the sun would never directly hit it and heat the scope up.

They started recording with a camera at about 8am and till like 5pm (going off of memory). So the scope doesn't move and the target doesn't move. The sight picture is being altered by the light conditions, the terrain and moisture. So the conditions are basically bending the light waves and affects what you see.

That's a big shift in how much the sight picture wanders. Now imagine that happening in the middle of your string of fire... or come off the line... and go back to the line an hour or two later and you didn't touch your sights and you blow a 8 on the target and cannot figure out why.

The video is sped up. Click on the settings button and slow the video back to it's slowest play speed.

 

[Rset]

Here is a excellent video. This was done by Vortex a few years back at Lodi, WI (Winnequah Gun Club). Spotting scope was set up on the 1k yard line. Tried to make the mount as solid/as permanent as possible so the wind etc... wouldn't bounce it around. They also covered/shaded the scope so the sun would never directly hit it and heat the scope up.

They started recording with a camera at about 8am and till like 5pm (going off of memory). So the scope doesn't move and the target doesn't move. The sight picture is being altered by the light conditions, the terrain and moisture. So the conditions are basically bending the light waves and affects what you see.

That's a big shift in how much the sight picture wanders. Now imagine that happening in the middle of your string of fire... or come off the line... and go back to the line an hour or two later and you didn't touch your sights and you blow a 8 on the target and cannot figure out why.

The video is sped up. Click on the settings button and slow the video back to it's slowest play speed.

Great video. Now the question is what do you need to do to compensate. There will be answers on both sides of the solution.

 

[Ned Ludd]

For clarification, what Ted is asking about is apparent movement of the POI in relation to the reticle POA during a change in light intensity such as when a cloud passes overhead. This is not at all the same thing as is shown in the video in post #31. What is illustrated in the video is simply a time lapse of the reticle crosshair moving across the target face up/right as the day progresses. It does not appear to show any sudden and reversible jump in the POA as clouds pass over. Further, what Ted is asking about is not a change in the POA in response to something like a cloud passing over, it is a change in POI when something happens to the light intensity, such as a cloud passing overhead, where the POA/hold remained exactly the same. In other words, someone doesn't change their hold on the target, but the shot impacts at a different spot from the previous POI when the light intensity changes, possibly causing loss of points. The issue being described is that because the shooter didn't know the POI had shifted with respect to the POA, they didn't change the POA to compensate for it. In other words, Ted is not asking about a situation where one could easily observe the crosshairs moving as the light intensity chages. He's asking about a phenomenon where the shot placement changes in relation to the POA as the light intensity changes. If this was as simple as the crosshair visibly moving under changing light intensity, the shooter could simply move the crosshair back to where it had been previously before taking another shot.

FWIW - I have never personally observed this phenomenon to happen in many years of shooting, so I am a skeptic. Further, I am not aware of any explanation as to why a change in light intensity would affect a modern rifle scope in that manner. Nonetheless, I have heard the same observation coming from other shooters whose expertise I trust. I fully believe that those who claim to have experienced this phenomenon themselves actually believe what they saw, so I cannot completely discount that it could be happening by some mechanism that is not fully understood. I think the main problem with explaining such a phenomenon is that it would be extremely difficult to isolate only the ambient light level in most of the experiments we might attempt as shooters. Thus, there might be several variables changing that could account for the observed phenomenon, the most likely being some combination of wind and mirage, IMO.

 

[diego-ted]

For clarification, what Ted is asking about is apparent movement of the POI in relation to the reticle POA during a change in light intensity such as when a cloud passes overhead. This is not at all the same thing as is shown in the video in post #31. What is illustrated in the video is simply a time lapse of the reticle crosshair moving across the target face up/right as the day progresses. It does not appear to show any sudden and reversible jump in the POA as clouds pass over. Further, what Ted is asking about is not a change in the POA in response to something like a cloud passing over, it is a change in POI when something happens to the light intensity, such as a cloud passing overhead, where the POA/hold remained exactly the same. In other words, someone doesn't change their hold on the target, but the shot impacts at a different spot from the previous POI when the light intensity changes, possibly causing loss of points. The issue being described is that because the shooter didn't know the POI had shifted with respect to the POA, they didn't change the POA to compensate for it. In other words, Ted is not asking about a situation where one could easily observe the crosshairs moving as the light intensity chages. He's asking about a phenomenon where the shot placement changes in relation to the POA as the light intensity changes. If this was as simple as the crosshair visibly moving under changing light intensity, the shooter could simply move the crosshair back to where it had been previously before taking another shot.

FWIW - I have never personally observed this phenomenon to happen in many years of shooting, so I am a skeptic. Further, I am not aware of any explanation as to why a change in light intensity would affect a modern rifle scope in that manner. Nonetheless, I have heard the same observation coming from other shooters whose expertise I trust. I fully believe that those who claim to have experienced this phenomenon themselves actually believe what they saw, so I cannot completely discount that it could be happening by some mechanism that is not fully understood. I think the main problem with explaining such a phenomenon is that it would be extremely difficult to isolate only the ambient light level in most of the experiments we might attempt as shooters. Thus, there might be several variables changing that could account for the observed phenomenon, the most likely being some combination of wind and mirage, IMO.

Yep, thx for clearing that up!! Clear as mud. LOL

 

[diego-ted]

I think it's a mirage effect, not a light effect. I've never noticed any impact change when mirage is not present.

I cannot discount this theory, not at all?? And just blamed it on light change? Hmmmm?

 

[buckhunter62]

I saw Mid Thompkins test this many years ago at Ben Avery range in Phoenix Az. many years ago. He mounted a rifle scope on a tri pod & pointed It at a target on the 1000 yd line in the morning. Every once in awhile we would look to see if it was still pointed in the middle.. As far as we could tell it never changed thru out the day.

 

[Immike]

Open blade sights tend to shoot away from the sun, I have watched this for years competing with them but I believe it was the light on the sights not anything else.

 

[memilanuk]

what Ted is asking about is not a change in the POA in response to something like a cloud passing over, it is a change in POI when something happens to the light intensity, such as a cloud passing overhead,

A few years back (2016 or 2017) @ Connaught, we were in a team match getting ready to shoot, and... our coach was staring up into the sky. Not downrange, at the flags or the mirage, but up at the sky. We waited... and waited... until someone finally asked him (nicely) what he was looking at. Turned out he'd noted a correlation between the big cloud banks rolling through, and shot fall on the target. The effect wasn't immediate - maybe 5-10 minutes? The best explanation that we had was that as the clouds came over, the ground cooled, ever so slightly, resulting in a little less mirage. When the clouds moved on, the sunlight on the grassy range heated things back up, intensifying the mirage and 'pushing' the target image up. Again, the effect wasn't immediate, but it was there. As best I can recollect, it was worth about 3/8 moa on target at distance - more than enough to leak a few points here and there if not accounted for. As a result of the guy staring up at the sky, one of the other coaches jokingly referred to the effect as 'space mirage'

This was on a range that is, IIRC, pretty close to a river and is covered all the way from the parking lot to the targets in grass. So the mirage was fairly pronounced. Maybe not Houston TX level mirage, but pretty heavy by most other standards. Whether one would notice the same effect / level thereof on other ranges that are say, mostly sand/gravel with minimal vegetation (i.e. Ben Avery or Raton, for example) I couldn't say.

 

[dcali]

I cannot discount this theory, not at all?? And just blamed it on light change? Hmmmm?

Like a lot of things in shooting, I attribute this to older truths that have lost their context and are no longer valid. With iron sights - a front post and rear aperture - light intensity matters - it's not just mirage. The perception of the size of the bullseye changes a little, and since most shooters seem to hold a sight picture where the bullseye "rests" on top of the sight post, if it appears smaller or larger, that will change your vertical impact point. Throw in that small amounts of mirage are very hard to see without a scope, and you get the idea that light is all that matters if you're shooting irons. In reality, it's a little of both.

With a scope, you don't have that sight picture, and all you see is mirage. With high power F Class scopes, you can see it very well and with a little practice, you know how much the image is lying to you.

That's my experience at least (and a little speculation).

 

[dcali]

Here is a excellent video. This was done by Vortex a few years back at Lodi, WI (Winnequah Gun Club). Spotting scope was set up on the 1k yard line. Tried to make the mount as solid/as permanent as possible so the wind etc... wouldn't bounce it around. They also covered/shaded the scope so the sun would never directly hit it and heat the scope up.

They started recording with a camera at about 8am and till like 5pm (going off of memory). So the scope doesn't move and the target doesn't move. The sight picture is being altered by the light conditions, the terrain and moisture. So the conditions are basically bending the light waves and affects what you see.

That's a big shift in how much the sight picture wanders. Now imagine that happening in the middle of your string of fire... or come off the line... and go back to the line an hour or two later and you didn't touch your sights and you blow a 8 on the target and cannot figure out why.

The video is sped up. Click on the settings button and slow the video back to it's slowest play speed.

That's really interesting, but I can't help but think that the scope is moving as the day progresses. I've never experienced anywhere near that much movement, even in heavy mirage. The fact that it's a slow and constant movement makes me think it's more related to temperature changes and thermal expansion, and not an optical effect. It doesn't take much of a temperature change to move metal enough to shift the crosshairs. Heating the tripod could conceivably do that - the relatively long legs will expand a fair amount even with small temperature changes.