Mirage... Strategies for dealing with a murky sight picture

[DaveMc]

I will add one more comment for our original poster. Winding down the power does help the sight "picture" for sure. Our brain seems to cope better with reduced magnification. BUT be aware the overall refraction is exactly the same viewed at 20 power as it is at 40 power - we just have it less magnified.

Scintillation however may just be a different story (to be quite honest I am not sure on this one) as it is possible we are magnifying a smaller depth of field to high power and hence maybe magnifying the smaller, more isolated affects where as at lower power you have an increased depth of field and maybe (just maybe?) a better "average" condition.

As I said I am not sure on this - the way to test would be to set up two similar rifle scopes with video cameras behind. One set at low power (say 10x) and one set at high (say 40 x) then digitally zoom the low power one to same power as high and compare.
Anyone want to have a go???

[williada]

Dave I am glad you contributed to the discussion. No wonder you guys were so successful as you have examined every nuance. Its just so hard to put in words sometimes, all the information for our fellow shooters to gain a practical insight from. Well done.

Indeed mastering mirage is as easy as riding a bucking horse, and you are never really sure when you are going to bight the dust, and you bight the dust but hopefully less often.

In the 1970’s at Williamstown, a bloke by the name of Harry Ryan who worked at Monash Uni and was Captain of the strong club Dandenong, who also made the long bore micrometers did similar experiments with a telescope he fashioned with a crosshair performing countless hours of observations. Much of my understanding comes from Harry whose scope was passed to me and his mate Jack Harby who taught me to read mirage. I can say I wept at his funeral with the passing of such a great man who also made sure this knowledge was not lost. Harry was a quiet achiever. David.

[yelnats]

Hi. I am an avid photographer and ALL of my camera lenses, and they are Canon DSLR lenses costing $1000 to $3500 each are fitted with LENS FILTERS.
reason one. I can clean them as much as is needed and it does not damage the original camera lens.
reason two. It protects the original camera lenses from damage. I recently dropped a $1500 lens as I was fitting it to the camera and as bad luck would have it it dropped onto the steel corner of my desk and shattered the lens filter. NO damage to my camera lens just the $100 lens filter
reason 3 I can change the lens filter to reduce glare, reduce ultra violet light or haze and to improve the contrast of the camer lens.

I have fitted quality camera filter lenses to all of my rifle scopes. Schmidt and bender, zeiss, nightforce, steiner military, leupold, and others I have are showing improvements in image in haze reduction and in contrast by the use various camera lens filters. Particularly noticeable in hot bright conditions.
And also I dont feel guilty in cleaning my scope objective lens more often.

The filters I use are B&W, Schnieder, and Hoya. Lots of new and used for sale on Ebay.

Does the extra piece of glass reduce image quality.?? I can still see bullet holes at 600 yards on white background with many of my scopes. I dont know but the advantages to me of fitting lens filters are worth the $100 cost of them.

[plumbs7]

Another good thread ! At 1000 yds I've found 5/8 Moa in cloud and light in a rare time of perfect conditions! I'll try and find that vid of Dave Mc .

Edit ! This happened to me even at 500 yds at Belmont today . 2 nd detail 1st sighter went 1/2 Moa high! Ok adjust down and was trucking just fine then the Sun came out and down out the bottom . Ok bad shot , pulled another one and that shot joined it's mate. Then made sure the target was bright and aimed opposite to jag the centre again for 3 shots !

Just another thing to remember ! But is this limited just to Belmont or is accros the board ?
My Gut feeling is it varies from range to range and condition to condition, but certainly not sure!

" light up sight up, light down sight down!"


Courtesy of Dave Mc.

[plumbs7]

Look I really didn't want to post and put this back up the top of the threads! But just in the interest of the sport I thought I would post my hex data of the infringement of light and dark target . Lucky it wasn't in a Queens as I would have been way down the list just because of refraction.

Shot A was the first shot in the second detail and went high as the target was dark at 5.0 Moa . 284 win 168 vld load was looking promising till shot 7 when the Sun came out ( ended up on about 4.5 flat)! Thought was a bad shot and fired again , same result! Then the penny dropped with the Target now in full sun! Aimed opposite for the last 3 shots with the target in full sun !

What's interesting and this why I posted the above is shot A is equidistant from the centre to shot 7&8!

Which tells me it was the sight picture that screwed me !
It also tells me and one should always take the positives out of a situation . That the 168 Gr load is working quite well !
The lousy spread accross the 6 ring just shows I wasn't wind reading all that well ! Lol!
Refraction is just something to watch and it's not at every rifle range as severe ! So how do u account for it ? Don't know , but if there is a flyer check light and and dark before throwing another point down the drain ! Tough sport it is !

[williada]

Graham there are four things to distinguish with this group in terms of importance. Firstly, the apparent aiming mark shift due to mirage, secondly the changing light conditions, thirdly the interaction of gyroscopic spin drift and finally, the air density.

By what you describe, refraction caused by mirage was not significant. However, the old rule of light up sight up, light down sight down was significant. I assume the wind was a left wind when those shots 7 and 8 appeared? Did the air density change?

When light is bright the target appears clearer and so there is a tendency to aim lower. Conversely, when light is dull there is a tendency to aim higher. The other thing is that the position of the sun in the sky can draw you to the side the sun is shining from and its angle in the sky determines how much you maybe drawn to one side of the target; and there is also the interaction with spin drift.

Even tight groups can display those corner shots when spin drift interacts with that left wind. You can see that on Bartman’s 60.10 group at 600 yards when a couple of shots caught the x line when he won the Gippsland Champ of Champs this year. The day also had up and down light with the element of left wind kicking in at times. On some days the air density coupled with the spin drift is a bigger factor in dispersion. Of course a tight tune will reduce the dispersion but it is always present in the best of kits. At some point horsepower is not enough and reading conditions will increase score. But I will say, new shooters with a poorly tuned rifle will not find it easy to distinguish what is going on. Give them the best gear to learn with.

The sun going in and out can add to the dispersion in two ways. Firstly, causing you to aim in the wrong place in the vertical with just a little horizontally too. These effects tend to be noticed on switching light conditions. It can in constant condition appear that your zero has altered if you zeroed in different light conditions however. With further regard to variable light, it has an almost instant effect on cooler days of warming the atmosphere and changing the density which interacts with the spin drift too. We notice this in Gippsland when it is cool and you can instantly feel the heat come on your hands from the sun when it comes out of cloud cover. When the atmosphere is already warm this is not so much a factor.

The important thing to do is centre your group with a bias - a little up and to the left and concentrate on wind direction and speed. With that left wind at times, it can come at such an angle with a pulse to tip you out further. This is about shooting for score rather than group and being aware of light up and down. Combine that with mirage and it is trickier again.

[plumbs7]

Hi David , I really appreciate your thoughts . The wind was from the left 7-9 o'clock . Im having lunch atm. As per usual I have to digest fully what u have said and I'll maybe able to come back with a half intelligent response . Sort of the fish and the eagle again lol!

[williada]

Michael's group was shot on the same wind vector in the main but with an occasional puff from behind and to the right. He handled it very well.

[plumbs7]

Hi David , yes the sight picture was good and one of the locals at Belmont commented that the effect was accross the board from 300 -1000 . And I've as mentioned before found that to be true at 1000yds.
At Gundy a month before the light and dark was there but it held in the 6 ring . Wind vectoring vertical or I call it gyroscopic torque precession vertical at Gundy was no where as severe as Belmont with wind coming from the right with a Rh twist barrel as you have mentioned before that both forces are crashing into eachother . I've seen this cause ( thanks to studying ETs) a 2-8 o'clock vertical. It's not so much the vectoring but the but changes BC on a right wind and this vertical .its linear but varies from range to range for several other factors can be at play eg gullies and mounds , tree etc !
I'll explain later the effect later as I know lots people would be saying that I'm quite full of it and I can keep my orings too! Lol!
But the lighting effect was definitely a player on the day a couple of weekends ago.