1) Crown glass or plastic or polycarbonate?
Neal Stepp recommend just glass. He said they are optically best. Agree?
10pt9 uses plastic. Another vender use polycarbonate.
I assume glass will stay clear for a long time, where as plastic/ polycarbonate will discolor into yellowish hue?
2) AR coating or no. AR coating on those lens will add up cost, usually the cost of the original lens. Is reflection really an issue on small lens 25mm or 33mm ?
Pistol shooting glasses lens recommendation please
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ShootingSight
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Polycarbonate and AR coating.
PC is impact resistant. You can also get safety glass that is tempered and impact resistant, but standard crown glass is not. CR-39, the other 'plastic' used for lenses is not impact resistant. Also, I think custom glass lenses are more expensive, because almost no one works in glass any longer. I make and sell PC lenses with AR, delivered, for $40. I don't think you'ff find a price even close to that for glass.
PC fundamentally blocks 99+% of UV light, Glass and CR-39 do not. You can add UV blocking coatings, but as you pointed out, they cost money so why pay for something you can get for free?
You can tint PC if you want, I think it is about $5 extra. PC will not yellow in the sun (after all, they are used in eyeglasses, have you ever seen a yellowed eyeglass lens?). A pale yellow tint can reduce that last 1% of UV, though I'd say less than 1% of the lenses I sell come with a request for tint. Tinting blocks that last 1% of UV, but it also blocks a few percent of visible light, so its a two edged sword. I believe that if you have extra light to give away, the best thing to do is reduce your rear aperture size. That way you at least get a depth of field benefit.
As for AR, in glass you absolutely want it. The issue is not that reflections bother you, the issue is that all reflected light is NOT passing through the lens, so the transmitted image is dimmer. Glass reflects about 5% of light per surface. So passing through both surfaces of a lens, you lose about 10% of image brightness, which reduces contrast. Adding AR can reduce that 10% loss to about 2% loss. Plastics, PC or CR-39 do not reflect as much in the first place, so even without coating they only lose 2-3%, but with coating they lose less, so I still think it is worth it. You spend $1,000 on all your shooting setup, why would you skimp $10 on a lens and lose 1-2% of the image?
Is glass better optically than polycarbonate? Yes, and no. If you just superficially look at the data tables, you can see that the abbe value of glass is better than PC. But if you dig in and understand the context in which it is being applied, you will understand that there is no difference to the human eye. Abbe value is a measure of how much the refractive index varies by frequency. In other words, blue light will bend slightly more than red light. In glass, it blue bends a little more than red, and in PC blue bends a lot more. When light bends differently it creates a rainbow, and you can get a colored fringe, known as chromatic aberration, think of it as rainbow blur.
However when you really dig into the optical math, the actual width of the blur that you get is a cosine function of the angle at which the light strikes the lens. In other words, dead center, where the light hits the lens perpendicular, the error is zero, regardless of the abbe value. It is only when you start looking at the extreme edges of the lens where the error gets big enough that it is even detectable by the human eye. This can be an issue for eyeglasses, where the lens is close to your face, and if you look at something in the extreme periphery of your vision, and you might be looking through the lens at a 45 degree angle. But for shooters, looking more or less centered through a lens, and especially a lens with a low power, any chromatic aberration is much less than the human eye can detect, so PC performs as well as glass.
Regards,
Art Neergaard
ShootingSight LLC
www.shootingsight.com
shootingsight@nuvox.net
PC is impact resistant. You can also get safety glass that is tempered and impact resistant, but standard crown glass is not. CR-39, the other 'plastic' used for lenses is not impact resistant. Also, I think custom glass lenses are more expensive, because almost no one works in glass any longer. I make and sell PC lenses with AR, delivered, for $40. I don't think you'ff find a price even close to that for glass.
PC fundamentally blocks 99+% of UV light, Glass and CR-39 do not. You can add UV blocking coatings, but as you pointed out, they cost money so why pay for something you can get for free?
You can tint PC if you want, I think it is about $5 extra. PC will not yellow in the sun (after all, they are used in eyeglasses, have you ever seen a yellowed eyeglass lens?). A pale yellow tint can reduce that last 1% of UV, though I'd say less than 1% of the lenses I sell come with a request for tint. Tinting blocks that last 1% of UV, but it also blocks a few percent of visible light, so its a two edged sword. I believe that if you have extra light to give away, the best thing to do is reduce your rear aperture size. That way you at least get a depth of field benefit.
As for AR, in glass you absolutely want it. The issue is not that reflections bother you, the issue is that all reflected light is NOT passing through the lens, so the transmitted image is dimmer. Glass reflects about 5% of light per surface. So passing through both surfaces of a lens, you lose about 10% of image brightness, which reduces contrast. Adding AR can reduce that 10% loss to about 2% loss. Plastics, PC or CR-39 do not reflect as much in the first place, so even without coating they only lose 2-3%, but with coating they lose less, so I still think it is worth it. You spend $1,000 on all your shooting setup, why would you skimp $10 on a lens and lose 1-2% of the image?
Is glass better optically than polycarbonate? Yes, and no. If you just superficially look at the data tables, you can see that the abbe value of glass is better than PC. But if you dig in and understand the context in which it is being applied, you will understand that there is no difference to the human eye. Abbe value is a measure of how much the refractive index varies by frequency. In other words, blue light will bend slightly more than red light. In glass, it blue bends a little more than red, and in PC blue bends a lot more. When light bends differently it creates a rainbow, and you can get a colored fringe, known as chromatic aberration, think of it as rainbow blur.
However when you really dig into the optical math, the actual width of the blur that you get is a cosine function of the angle at which the light strikes the lens. In other words, dead center, where the light hits the lens perpendicular, the error is zero, regardless of the abbe value. It is only when you start looking at the extreme edges of the lens where the error gets big enough that it is even detectable by the human eye. This can be an issue for eyeglasses, where the lens is close to your face, and if you look at something in the extreme periphery of your vision, and you might be looking through the lens at a 45 degree angle. But for shooters, looking more or less centered through a lens, and especially a lens with a low power, any chromatic aberration is much less than the human eye can detect, so PC performs as well as glass.
Regards,
Art Neergaard
ShootingSight LLC
www.shootingsight.com
shootingsight@nuvox.net
I had 2 glass lenses made last year at Pacific Eye Doctors in Richmond, BC. They're used to dealing with competitive shooters there. Chemically hardened glass, with as flat a cross section as they could manage, $38 each plus tax. Didn't want coatings as I'd like the lenses to be scratch-free for a long time. My experience with coatings onto either glass or plastic has been that sooner or later I'll clean a lens and a piece of grit all sneak onto the cloth and in an instant the lens will be ruined. From a photographic enlarger lens to binoculars to reading glasses, all the same no matter how careful I am. So far my un-coated plastic 'progressive' reading glasses are clear after 10 months of use in my workshop, and I'm being very careful. Wanted glass, by they talked me out of it for the everyday glasses based on weight. And yeah, the light weight is nice. But with a shooting lens that's not really an issue.