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May 28th, 2014
 While attending the CA Long Range Championship a while back, we had the opportunity to test the performance of a high-magnification (63X) spotting scope in near-ideal conditions (maybe the best I’ve ever witnessed). On the event’s last day we arrived at 5:45 am, literally as the sun was cresting the horizon. I quickly deployed our Pentax PF-100ED spotting scope, fitted with a Pentax SMC-XW 10mm fixed-power eyepiece. When used with the 100mm Pentax scope, this 10mm eyepiece yields 63X magnification. Befitting its $359.00 price, this eyepiece is extremely clear and sharp.
At the crack of dawn, viewing conditions were ideal. No mist, no mirage, no wind. The first thing this Editor noticed was that I could see metal nail heads on the target boards. That was astonishing. As soon as the first practice targets went up, to my surprise, I could see 6.5mm, 7mm, and 30-caliber bullet holes in the white at 1000 yards.
That’s right, I could see bullet holes at 1000. I know many of you folks may not believe that, but there was no mistaking when I saw a 7mm bullet cut the white line separating the Nine Ring and Eight Ring on the target in view. (I was watching that target as the shot was fired and saw the shot-hole form). And when I looked at the 30-cal targets, the bullet holes in the white were quite visible. In these perfect conditions I could also make out 3/8″ bolt heads on the target frames.
The Human Factor
When viewing the bullet holes, I was using my left naked eye (no safety glasses or magnification). I also had a contact lens in my right eye (needed for distance vision). To my surprise, while I could see the bullet holes without much difficulty with my left eye, things were fuzzier and slightly more blurry with the right eye, even when I re-focused the scope.
 Then I invited 3 or 4 shooters to look through the scope. One younger guy, with good eyes, said immediately: “Yeah, I can see the holes — right there at 4 o’clock and seven o’clock. Wow.” Some older guys, who were wearing glasses, could not see the holes at all, no matter what we did to the scope’s main focus and diopter adjustment.
The lesson here — if you have to wear glasses or corrective contact lenses, just that extra bit of optical interference may make a difference in what you can see through the scope. Basically anything that goes between the scope eyepiece and your eyeball can degrade the image somewhat. So… you may be better off removing your glasses if you can still obtain good focus sharpness using the diopter adjustment and focus ring. I did the left vs. right eye test a half dozen times, and I could definitely see small features at 1000 yards with my naked eye that I could not see with my right eye fitted with a contact lens. (I did have to re-focus the scope for each eye, since one had a corrective lens while the other did not.)
Mirage Degrades Image Sharpness and Resolution
The “magic light” prevailed for only an hour or so, and then we started to get some mirage. As soon as the mirage appeared I was no longer able to see raw bullet holes, though I could still easily see black pasters on the black bulls. When the mirage started, the sharpness of the visible image degraded a huge amount. Where I could see bullet holes at dawn, by mid-morning I could barely read the numbers on the scoring rings. Lesson: If you want to test the ulimate resolution of your optics, you need perfect conditions.
 Chromatic Aberration Revealed
As the light got brighter and the mirage increased I started to see blue and red fringing at the edges of the spotting disk and the large numerals. This was quite noticeable. On one side of the bright, white spotting disc you could see a dark red edge, while on the other side there was a blue edge (harder to see but still present).
The photo below was taken through the Pentax spotter lens using a point and shoot camera held up to the eyepiece. The sharpness of the Pentax was actually much better than this photo shows, but the through-the-lens image does clearly reveal the red and blue fringing. This fringing is caused by chromatic aberration — the failure of a lens to focus all colors to the same point. Chromatic aberration, most visible at high magnification, causes different wavelengths of light to have differing focal lengths (see diagram). Chromatic aberration manifests itself as “fringes” of color along boundaries that separate dark and bright parts of the image, because each color in the optical spectrum cannot be focused at a single common point on the optical axis. Keep in mind that the Pentax does have “ED” or low-dispersion glass, so the effect would be even more dramatic with a cheaper spotting scope.
If you wonder why top-of-the-line spotting scopes (such as the $3900 Leica APO-Televid 82) cost so much, the answer is that they will deliver even LESS chromatic aberration at long range and high magnification. With their exotic apochromatic (APO), ultra-low-dispersion glass, a few ultra-high-end spotting scopes can deliver an image without the color edging you see in the photo above.
The Pentax PF-100ED is a heck of a spotting scope. Any scope that can resolve bullet holes at 1000 yards is impressive. But if you want the ultimate in optical performance, with minimal chromatic aberration, you may need to step up to something like the 88mm Kowa Prominar TSN-883 with Flourite Crystal lenses ($2450.00 body only), or the 82mm Leica APO ($3899.00 with 25-50X eyepiece).
EDITOR’s NOTE: The purpose of this report is to show what is possible… in IDEAL conditions. With this Pentax 100mm, as well as a Swarovski 80mm, we have often been able to resolve 6mm bullet holes at 600 yards. But again, that performance requires really good viewing conditions. By 10:00 am at my range, even with the 100mm Pentax at 75 power, seeing 6mm bullet holes is “iffy” at best. So don’t go out and mortgage the house to buy a $4000 optic with the hope that you’ll be able to spot your shots at 1000 yards. If conditions are anything less than perfect, you’ll be lucky to see bullet holes at 500 yards. The real solution for very long-range spotting is to set up a remote target cam that broadcasts a video picture to a screen at your shooting station.
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July 22nd, 2013
 There is an excellent article about Mirage on the South Texas Marksmanship Training Center (STMTC) website. This article explains what causes mirage and how mirage can move the perceived aiming point on your target. Most importantly, the article explains, in considerable detail, how you can “read” mirage to discern wind speeds and wind directions. With simple but effective graphic illustrations, this is one of the best explanations of mirage (and mirage reading) we have found on the internet. This is a “must-read” for any serious competitive shooter. Here is a brief sample from the article, along with an illustration. NOTE: the full article is six times longer and has 8 diagrams.
The term “mirage” as used by the shooter does not refer to a true mirage, but to heat waves and the refraction of light as it is bent passing through air layers of different density. Light which passes obliquely from one wind medium to another it undergoes an abrupt change in direction, whenever its velocity in the second medium is different from the velocity in the first wind medium; the shooter will see a “mirage”.
The density of air, and therefore its refraction, varies with its temperature. A condition of cool air overlaying warm air next to the ground is the cause of heat waves or “mirage”. The warm air, having a lower index of refraction, is mixed with the cooler air above by convection, irregularly bending the light transmitting the target image to the shooter’s eye. Figure 1 shows (greatly exaggerated) the vertical displacement of the target image by heat waves.
Heat waves are easily seen with the unaided eye on a hot, bright day and can be seen with spotting scope on all but the coldest days. To observe heat waves, the scope should be focused on a point about midway to the target. This will cause the target to appear slightly out of focus, but since the high power rifle shooter generally does not try to spot bullet holes, the lack in target clarity is more than compensated by clarity of the heat waves.
CLICK HERE to Read Complete Mirage Article
Mirage Is Your Friend
While hot days with lots of mirage can be frustrating, mirage can reveal how the wind is flowing (and changing). If you learn how to recognize and read mirage patterns, you can use that information to shoot higher scores. That’s why many leading long-range shooters tell us: “Mirage is your friend.” As the STMTC article explains: “A mirage condition is not a handicap, since it offers a very accurate method of perceiving small wind changes[.]”
Story tip from Boyd Allen. We welcome reader submissions.
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March 21st, 2013
 Mirage shields really do help you hit your targets more reliably. Novice shooters may wonder “Why does that guy have a venetian blind attached to his barrel?” Here’s why. As the barrel gets hot, the heat from the barrel rises up, cooking and distorting the air directly in front of the scope’s front lens. In essense, the rifle creates its own nasty visual mirage, right in the worst possible place. You can have a $4000.00 custom rifle and a $2500.00 scope but if the air in front of your scope is distorted, it can literally move your apparent point of aim on the target relative to your cross-hairs, causing you to miss the shot.
As our friend Boyd Allen observed: “Varminters should use mirage shields. Think about it. You’ve invested thousands of dollars in a fancy varmint rifle and quality scope. You may have spent hundreds of dollars traveling to the varmint fields and spent dozens of hours loading up your ammo. Without a mirage shield on your barrel, once that barrel gets hot, you WILL get mirage effects that can make you miss a shot.”
So, we’ve established you need a mirage shield to shoot your best when the barrel gets hot. You can make your own shield from a scrap blind, or purchase a ready-made plastic or aluminum shield. Sinclair Int’l offers 2″-wide, white mirage shields in 18″ (#06-7200) or 24″ (#06-7300) lengths for $4.95. Shotmaster 10X offers a variety of Patterned Mirage Shields, starting at $6.00. These include a Patriotic theme and even Tiger Stripes:
Camo Mirage Shields for Tactical Shooters and Hunters
Though tactical shooters should use mirage shields for long-distance, slow-fire stages, for the most part, tactical shooters don’t bother. One reason is that mirage shields CAN detach if you’re crawling around in the bush. However, for many tactical shooting situations, a mirage shield IS both practical and recommended. And now, for the first time, tactical shooters can get mirage shields in camo patterns to match their rifles. These camo shields should also be popular with varminters and long-range hunters.
At the request of AccurateShooter.com, Shotmaster 10X created a line of camo-pattern mirage shields (see above). Made of 2″-wide aluminum strips, these are available in 18″, 20″, and 24″ lengths. The camo-pattern shields come complete with Velcro attachments, and start at $8.50 for the 18″ length. The 20″ models are $9.50, while 24″ shields are $11.00.
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December 8th, 2012
by Steven Blair, 2012 California State Long Range F-Open Champion
Assess the Terrain and How the Wind Will Interact with It
Before you begin a match, take a few minutes to look around the range at the terrain, any obstructions, range topography (berms and backstop), and trees, buildings or structures that could affect wind flow over the range. Imagine what might happen if the wind was from the left or right, headwind or tailwind. Depending upon the direction, significant effects may be seen on range. A head or tail wind may ripple across the berms, causing elevation changes, both high and low. A tall side berm, like the east side berm at Ben Avery, may cause turbulence when the wind comes from that direction. Blocking features might shield most of the wind but a break along the range can funnel strong gusts through the gap with no other indications. Take a few notes about the effects of different wind directions and refer to them if the prevailing direction changes. (Tip courtesy Tony Robertson.)
Use a Spotting Scope, Even When Shooting a Scoped Rifle
A good spotting scope can “see” mirage much more clearly than even an expensive rifle scope. Take your spotting scope to the line and position it as sling shooters do, close enough to use without much movement. Focus the scope approximately 1/3 of the way down range or where the most significant wind effects are likely to occur. Take a quick look while waiting for pit service, glance at the flags and compare to your scope sight picture. I often see ambiguous indications at the target through the rifle scope, but see a clear indication of wind direction and speed through the spotting scope at the shorter distance. When shooting the Arizona Palma Championship at Ben Avery last weekend, I was scoring while the wind was coming from the east. Shooters up and down the line were out to the left, losing points. Mirage at the target looked moderate and the flags weren’t indicating strong wind. As I focused the spotting scope back, the mirage suddenly looked like it was flowing twice as fast around 500 yards than it was closer or farther. It wasn’t until I realized that the access road cut through the berm there that I understood what was happening. (Tip courtesy Gary Eliseo.)
Don’t Over-React to Something That May Be an Anomaly
On ranges with sizable berms, a headwind or tailwind can cause significant elevation problems. It is generally not possible to see or predict when this will occur. When the conditions exist that cause elevation changes and other competitors are experiencing the same problem, the best strategy is to ignore it. Certainly, avoid shooting when the head or tail wind is gusting, the same as you would in a crosswind. But, if you react to random, range-induced elevation changes, the only likely result is to make it worse. Whether the problem is caused by range or ammunition, maintain your waterline hold until you have evidence that something has fundamentally changed.
My .284 Shehane will usually require a click or two down during a string as the barrel warms. That is normal and manageable. But, if your shots are just bouncing up and down in the 10 ring, leave it alone. The same is also true of an occasional gust pushing a shot into the 9 ring. If the conditions have not changed and one shot just went out, it may be the result of a random occurrence that was not predictable. (Tip courtesy “School of Hard Knocks”.)
Adjust Spotting Scope Focus and Magnification as Needed to View Mirage vs. Target Details
In F-Class we only need to see mirage, spotters, and scoring disks. That does not take a lot of magnification. My scope is a Nikon 25-75x82mm ED. It is a superb scope for the money and makes it trivial to see minor variations in mirage. It is good to have the high magnification available, and it can always be reduced if necessary. I use different power settings for different situations.
 Setting Magnification Levels
During a match, in very good viewing conditions, I set my spotting scope at 75X, full power. The mirage is more subtle in the morning and greater magnification is needed.
During a match with heavy mirage I set my spotting scope at about 40X. I have no problem seeing mirage, even at this magnification.
When practicing at 300 yards or closer I set my spotting scope at max power (75X) so I can see the little 6mm holes from my 6BR rifle. I usually need to focus back and forth between shots to see both bullet holes and mirage.
Steven Blair, 2012 California State Long Range F-Open Champion, has been shooting since childhood and competing for over 30 years. Before retiring, Steve spent 16 years in Engineering and IT with General Atomics. He has held Engineering and Marketing positions with several firearms companies and worked on projects from pistols to 155mm howitzers.
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August 30th, 2012
Even if you don’t shoot competitively, you can benefit from having a mirage shield on your barrel. The shield helps prevent barrel heat from “cooking” the air in front of your scope, which can distort the view you see through the optic. Barrel heat creates a mirage effect that can blur the target image and actually shift your apparent aiming point up and down. Competitors know that a mirage shield helps them shoot smaller groups and better scores. Mirage shields can likewise benefit Varmint shooters on those hot summer groundhog and prairie dog expeditions.
Make a Mirage Shield from Discarded X-Ray Film
Forum member Fabian from Germany, whose Sako 6BR was featured as a Gun of the Week, has devised a clever and inexpensive mirage band option. Fabian is a radiologist by trade. He notes that many X-ray machines require a daily test film for calibration. These are normally just discarded in the trash, so you can get them for free.
Fabian explains: “I’m a radiologist, so I handle medical x-ray films every day. Modern X-ray machines use laser-based printers and they need to print a test-film every day. One x-ray film is about 43×35 cm (16.9″ x 13.7″). Made from polyester, the films are very stable and only 0.007″ inches thick. They are light-weight, semi-transparent, and very stable. Using normal scissors, you can easily cut four mirage shields from a single sheet of film. Then glue on some velcro to attach to your barrel. Try it, you will not be disappointed.”
More Do-It-Yourself Ideas
Other forum members have made mirage shields out of common, inexpensive materials such as old venetian blinds, thin plastic edging strips, and even cardboard reinforced with strapping tape. There’s no “magic material”. However many shooters have found that wider shields (extending well past the barrel sides) work better than narrow shields, particularly in hot weather.
Mirage Shields with Printed Designs
If you prefer to purchase a mirage shield, Shotmaster 10X offers a wide variety of shields starting at just $5.00 for a plain white 18″ shield. Patterned shields (including camo designs) are priced by length: $8.50 (18″), $9.50 (20″), $11.00 (24″). All Shotmaster shields come with two (2) velcro patches with self-stick adhesive.
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May 18th, 2009
 Mark your calendars for Wednesday, May 20th, when a “must-watch” episode of ShootingUSA television is broadcast. On the 20th, Sergeant Grant Singley and other members of the USAMU Service Rifle Team explain wind-reading for long range competition. This should be a very informative segment, enhanced with on-screen graphics illustrating key points.
Sgt. Singley notes: “A 5-mph crosswind at 600 yards will move an 80gr .223 bullet about 15 inches. You can see that being able to accurately read the wind will greatly enhance your success on the rifle range.” The USAMU uses a clock method to estimate wind value based on the direction. Then you add in the measured (or estimated) velocity for the vector value (wind strength and angle).
Sgt. Singley recommends the use of a wind meter, such as a Kestrel, to gauge wind speed. But observed conditions will also indicate wind velocity. Sgt. Singley explains: “Zero-to-three mph, is hardly felt on the shooters face, but smoke will drift. Three-to-five mph is felt lightly on the shooter’s face. Five-to-eight mph keeps leaves in constant movement. Eight-to-12 mph will blow dust and loose paper, and 12-to-15 mph winds cause small trees to sway.”
Using Mirage to Estimate Wind Speed and Direction
Long-range shooters also need to learn how to read mirage. Mirage is the reflection of light through layers of air that have a different temperature than the ground. These layers are blown through by the wind, and can be monitored through a spotting scope, to detect direction and speed. You can see what appear to be waves running across the screen. This is the mirage. The waves appear to be running right to left, which indicates a wind coming out of the right. To clearly see the mirage through a spotting scope, you bring the target into focus, then adjust the focus about a quarter turn counter-clockwise.”
Graphics copyright 2009 ShootingUSA, used with permission.
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CLICK HERE to view LARGE PHOTO that shows aberration more clearly.
