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djwarner
Optics GrassHopper Joined: August/23/2010 Status: Offline Points: 16 |
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I had Lasik done on my eyes in 2001. I told the opthamalogist that I was a pilot and I would favor distant vision over reading distance. He adjusted his calculations to achieve this.
Lasik is not a panacea. A common problem centers around the fact the your eyelids may no longer close perfectly when sleeping leading to dry eyes. Lasik will also not compensate for aging eyes needing reading glasses. The bias in my perscription only made this worse. All in all, considering my 20/240 vision, I would do it again.
As far as considering your scopes, there are three areas to consider, exit pupil diameter, contrast and resolution.
For any given magnification, the 50mm objective will have a larger exit pupil. However this will only be apparent when your pupil is dialated due to low light. In normal daylight, your pupil diameter is smaller than that of either scope and thus you will not detect a difference. In low light, the 50mm objective lens will be superior.
Contrast is a function of the glass, construction, and coatings. For scopes of similar construction, coatings usually make the difference.
Resolution is a function of the optical quality of the lenses.
One thing you may want to consider is the field of view. One scope may afford a greater view at the same magnification.
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Non nobis tantum nati
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TexasPhotog
Optics Apprentice Joined: July/22/2009 Location: Texas Status: Offline Points: 133 |
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Have a hard time believing that 20% figure. If it was true, things would get a noticeably brighter at dusk when I raised my glasses up. It doesen't.
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djwarner
Optics GrassHopper Joined: August/23/2010 Status: Offline Points: 16 |
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TexasPhotog
Your eye sensitivity is measured on a logrithmic scale, not linear. This is similar to fstops on a camera. 1 fstop doubles the light striking the sensor. A 20% increase would be about 1/4 of an fstop.
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Non nobis tantum nati
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saitotiktmdog
Optics Apprentice Joined: June/08/2010 Location: IN Status: Offline Points: 256 |
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My contacts affect me when I look through a scope. Of course the affect me when I am not looking through a scope. They are old and I need a new perscription. Maybe your having the same issue. When did you last get your eyes checked. Its been a few years for me.
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kelly1278
Optics Apprentice Joined: May/04/2009 Status: Offline Points: 53 |
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i had them checked a little over a year ago
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Magnumdood
Optics Apprentice Joined: January/17/2009 Location: Illinois Status: Offline Points: 226 |
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Anecdotal evidence doesn't weaken or strenghten a measurable fact.
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TexasPhotog
Optics Apprentice Joined: July/22/2009 Location: Texas Status: Offline Points: 133 |
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That's my point exactly. A 1/4 stop is discernible (you know this especially if you've ever shot much transparency film). If there was a 20% difference, then, in low light, I should be able to raise my glasses and the world should look noticeably brighter. That doesn't happen. |
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Magnumdood
Optics Apprentice Joined: January/17/2009 Location: Illinois Status: Offline Points: 226 |
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As I said, anecdotal evidence is just that, anecdotal. You're ONE case, and you're also biased; you don't want the facts to be true, so you see what you want to see.
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TexasPhotog
Optics Apprentice Joined: July/22/2009 Location: Texas Status: Offline Points: 133 |
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So you've measured this? How did you do it?
Or you repeating what someone who wanted to sell you a procedure said? Obviously, all lenses reflect some light. But this figure of 20% for eyeglasses doesn't square with my experience, and it would seem to me that the reflectance would vary greatly with what the lens is made of (glass, polycarbonate) and with the shape of the lens. Perhaps an optics scientist, like Koshkin, could weigh in here. Edited by TexasPhotog - September/02/2010 at 14:57 |
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djwarner
Optics GrassHopper Joined: August/23/2010 Status: Offline Points: 16 |
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Just remember, your eyes are constantly adjusting to varying light conditions. A quarter stop would be almost instanteous. If you can see a quarter stop shift, great for you, I can't.
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Non nobis tantum nati
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Magnumdood
Optics Apprentice Joined: January/17/2009 Location: Illinois Status: Offline Points: 226 |
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Nope; I had the procedure done, and then found out that my opthalmologist was a shooter on one of my subsequent visits. I don't feel the need to measure it for two reasons: 1. A professional in the field of GLASSES gave me the information, and, 2. it is no longer a problem for me. Rather than waiting until dusk and raising and lowering your glasses, try looking through a scope with your glasses on then looking through the scope with your glasses off. That sounds like a much better "test" of an already proven fact. Edited by Magnumdood - September/02/2010 at 18:24 |
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koshkin
MODERATOR Dark Lord of Optics Joined: June/15/2004 Location: United States Status: Offline Points: 13182 |
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Interesting thread.
A few comments: -I wear contacts -I refused to do laser surgery specifically because it would prevent me from seeing some optical effects that I can see with contacts. However, procedures get better all the time, so perhaps some day they will get good enough for my purposes -For your glasses to reflect 20% of the light, they would have to be made of material with very high index of refraction (n=2) and be completely devoid of AR-coatings. That is unlikely. Even without AR coatings on your glasses, the highest index of refraction I have heard of used for eyeglass lenses is ~1.74, which gives you ~14% light loss due to reflections -Either way, trying to look through your glasses or under your glass to gauge the loss of light is silly (but funny, so if you decide to do it, record a video and post it). Apparent brightness of an image depends on a number of factors and you can not determine light loss with your eye. It is not difficult to measure with the right equipment and very easy to calculate using basic arithmetics. -If you can not see the difference between Zeiss Victory and Elite 4200 under any lighting conditions, consider yourself lucky and sell the Zeiss. If it makes no difference for your eyes, use a cheaper scope and spend money on practice ammo. -Everyone's eyes are different. -If your eyes are capable of seeing the difference, it will be most apparent under challenging lighting conditions, no in broad daylight. -The fact that you do not see the difference between is unlikely to have ANYTHING to do with you contacts. Did I miss anything? ILya
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Magnumdood
Optics Apprentice Joined: January/17/2009 Location: Illinois Status: Offline Points: 226 |
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You forgot to mention you put me and my opthalmologist in our respective places...
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koshkin
MODERATOR Dark Lord of Optics Joined: June/15/2004 Location: United States Status: Offline Points: 13182 |
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I have nothing against your ophtalmologist. I suspect he simply threw the 20% number as a conversational estimate and never meant for it to be a hard reference. ILya
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Oldtrader3
Optics Journeyman Joined: May/16/2009 Location: WA (state) Status: Offline Points: 445 |
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Light passing through lenses is multiplicative, meaning that each lens will let through some lesser amount than 100% of the atactic photons being transmitted and the next lens will pass that subtractive resultant from the first lens to the second lens, et cetera. This is true of scopes as well as corrective lenses. Every lens (or lens grouping) substracts light from the total. From what I remember (and it has been a long time). Cast or molded Polyterphalate or CR39 plastic opthalmic lenses pass about 98% of the atatic light that strikes its surface. Without coatings, it is less.
This will get you started but Koskin is much better qualified than I am to answer questions about eyeglass and contact lens coatings that are available and their resulting transmission, refraction losses and reflection rates with atactic light.
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CDR3
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TexasPhotog
Optics Apprentice Joined: July/22/2009 Location: Texas Status: Offline Points: 133 |
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That's interesting stuff. Thanks for your replies, Koshkin and Oldtrader3.
For what it's worth, I think shooting with some sort of glasses is a good idea for safety reasons. I've seen two bad Kabooms. Metal, super hot gas and powder are tough on people and could be real hard on an eye. |
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Sparky
Optics Master Extraordinaire Joined: July/15/2007 Location: SD Status: Offline Points: 4569 |
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Since you look through a scope with one eye it should be 10%. But that figure is high as has been previously discussed. Also since one should always use eye protection, that is your base line so to speak and you will still see a difference if you know what to look for. |
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Oldtrader3
Optics Journeyman Joined: May/16/2009 Location: WA (state) Status: Offline Points: 445 |
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If you buy the good cast CR39, Opthalmic, coated, shooting glasses (i.e. B&L), you will get about 93% light transmission (or 7% loss if you prefer). Refraction loss depnds on coatings and color. I am talking about clear lenses. I was an engineer for a company that makes CR39, cast, opthamic, lenses years ago, but don't take my word for it.
Edited by Oldtrader3 - September/03/2010 at 13:04 |
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CDR3
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Magnumdood
Optics Apprentice Joined: January/17/2009 Location: Illinois Status: Offline Points: 226 |
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I use eye protection at the range where resolution and low-light capabilities aren't all that important. When I hunt, I use just my eyeball and the scope; no sense in paying through the nose for that level optic and not use it to it's utmost.
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America - Home of the Free
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Oldtrader3
Optics Journeyman Joined: May/16/2009 Location: WA (state) Status: Offline Points: 445 |
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That statement is not accurate. The difference between optical clarity, contrast and light transmission between cheap and good scopes is marked. If you have looked through good scopes with high performance matched refraction lenses, under low light conditions, you would know that. Don't make absolute judgements based of lack of experience and generalities based on that lack. You will get yourself into missing the best of optical performance if you generalize that you can not see it without knowing that for sure. Try it for yourself before you decide that it is of no benefit.
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CDR3
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