I shoot F-class exclusively. At 70 years old, that discipline suits me just fine. I shoot a 308 caliber F-TR rifle of my own design. I did make NRA High Master at 1000 yards with it, not with an F-Open gun. Dealing with mirage in high powered optics is a way of life in F-Class, especially in South Texas, where I shoot matches year-round. I have tried many different optics over the decades of competition. As the magnification increased, mirage intensified; that's axiomatic you might say, but there are mitigating factors.
Around 2012, I was using an NF NSX 12-42X56, which was pretty much the standard for F-Class in those days. I would start the day at 42X and as the day wore on and the mirage would come out and play, I would dial back the magnification, all the way to about 25X or so by 11:00AM. The F-class target is a big aiming black with a diameter of 44 inches with concentric rings down to a 5-inch diameter X-ring. In mirage conditions at greater than 30X, the round aiming black would start pulsating like an amoeba on crack and the rings would be invisible, lost in the quagmire of the blob. That was just a fact of life.
Around that time, I got a March-X 5-50X56. I noticed that it was brighter in the early late fall mornings and that helped me. I had set the riflescope at 40X, which was the same as the NSX, and left it there. After a while, it dawned on me that I never changed the magnification, it was always at 40X, every match, all the time, regardless of where I was shooting. Several years later, I sent it back to Japan to get the reticle swapped to the MTR-5, because I was growing older and my eyesight was diminishing. I got it back within a month and at the subsequent match, I was very pleased with the new reticle.
A little while later, I got a March-X 10-60X56 High Master. Where the 5-50X56 had an ED element in the optical formula, the 10-60X56 has 2 big pieces of Super ED glass in the objective bell. As a life-long, avid photographer, I knew about ED and Super ED, and fluorite crystal glass. I realized that DEON was the first riflescope manufacturer to use ED glass in riflescopes and is currently the only one using Super ED glass. This type of glass is used to control dispersion of the wavelengths in optical devices. This is what people refer to as CA (Chromatic Aberration) or color fringing. This allowed DEON to produce high magnification riflescopes with minimum or no detectable CA, without the weight inherent in other designs.
I noticed that I was at 50X all the time with my 10-60X56 HM. I remember vividly several events where the mirage was very intense and everyone else had to dial down to the 20s and I stayed at 50X. Atterbury was one of those places. That really underlined to me that something was helping me with mirage. I formulated a hypothesis and submitted it to DEON. The basis if my hypothesis is the use of ED, and especially Super ED glass in the riflescopes. I discussed this at length on AccurateShooter about 5 years ago. DEON did not believe me at first. But I was insistent, and others started to report the same thing. So, DEON went out and tested this and to their great surprise, discovered than I was not completely out to lunch. They refer to it as shimmer resistance. They even wrote a news article about it and posted it at their site.
I am not going to delve into the details of the hypothesis here, but suffice it to say that the Super ED lenses in the March-X 10-60X56 HM , and the March-FX 5-42X56 HM (the one being discussed on this thread) have greater shimmer resistance than optics with ED or non-ED glass. In F-class, the 10-60X56 HM has long been regarded as the gold standard for high magnification, mirage cutting view. It therefore is no surprise that the 5-42X56 HM would behave the same way as it has the same Super ED glass as the 10-60X56 HM.
Now, before you jump to the conclusion that mirage disappears in such an optic, that is not the way reality operates. Mirage is a disturbance in the air between your riflescope and the target. The IQ (image quality) will decrease because of that. However, the IQ diminishes less rapidly with these two optics. The image will not win any photographic awards, but for an F-class shooter, the rings remain distinct, and we use the rings to hold on target. If we dial down too much, we can't see the rings, and if the mirage (shimmer) hides the rings, we can't use them.
Another effect of the Super ED glass (and pure fluorite crystal spotters, such as Kowa) is that it will detect mirage sooner compared to other glass. I can detect twinges of mirage when other shooters can't see it. It doesn't mess up the target and I can still see the rings, but I also see the ripples of the mirage.
I do not shoot PRS, I tried it once and realized that I was way too old and arthritic to shoot it. I could not even finish the competition that one time. I understand people shoot it at about 20-25X or so, for various reasons. I would think the IQ of the March-FX 5-42X56 HM Gen 2, with its Super ED glass and 26° AOV must be glorious and present a superb, shimmer free image and yet still be able to detect whatever mirage is out there.
Sorry for the long rambling post.
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