OpticsTalk by SWFA, Inc. Homepage SWFA     SampleList.com
Forum Home Forum Home > Scopes > Rifle Scopes
  New Posts New Posts RSS Feed - contact lenses and optics
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Visit the SWFA.com site to check out our current specials.

contact lenses and optics

 Post Reply Post Reply Page  <123>
Author
Message
djwarner View Drop Down
Optics GrassHopper
Optics GrassHopper
Avatar

Joined: August/23/2010
Status: Offline
Points: 16
Post Options Post Options   Thanks (0) Thanks(0)   Quote djwarner Quote  Post ReplyReply Direct Link To This Post Posted: August/29/2010 at 17:57
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.
 
Non nobis tantum nati
Back to Top
TexasPhotog View Drop Down
Optics Apprentice
Optics Apprentice
Avatar

Joined: July/22/2009
Location: Texas
Status: Offline
Points: 133
Post Options Post Options   Thanks (0) Thanks(0)   Quote TexasPhotog Quote  Post ReplyReply Direct Link To This Post Posted: August/31/2010 at 11:34
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.
Back to Top
djwarner View Drop Down
Optics GrassHopper
Optics GrassHopper
Avatar

Joined: August/23/2010
Status: Offline
Points: 16
Post Options Post Options   Thanks (0) Thanks(0)   Quote djwarner Quote  Post ReplyReply Direct Link To This Post Posted: August/31/2010 at 12:15
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.
Non nobis tantum nati
Back to Top
saitotiktmdog View Drop Down
Optics Apprentice
Optics Apprentice
Avatar

Joined: June/08/2010
Location: IN
Status: Offline
Points: 256
Post Options Post Options   Thanks (0) Thanks(0)   Quote saitotiktmdog Quote  Post ReplyReply Direct Link To This Post Posted: August/31/2010 at 12:23
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.
Back to Top
kelly1278 View Drop Down
Optics Apprentice
Optics Apprentice


Joined: May/04/2009
Status: Offline
Points: 53
Post Options Post Options   Thanks (0) Thanks(0)   Quote kelly1278 Quote  Post ReplyReply Direct Link To This Post Posted: August/31/2010 at 19:49
i had them checked a little over a year ago
Back to Top
Magnumdood View Drop Down
Optics Apprentice
Optics Apprentice
Avatar

Joined: January/17/2009
Location: Illinois
Status: Offline
Points: 226
Post Options Post Options   Thanks (0) Thanks(0)   Quote Magnumdood Quote  Post ReplyReply Direct Link To This Post Posted: August/31/2010 at 22:04
Originally posted by TexasPhotog TexasPhotog wrote:

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.
 
Anecdotal evidence doesn't weaken or strenghten a measurable fact.
America - Home of the Free

               Because of the Brave
Back to Top
TexasPhotog View Drop Down
Optics Apprentice
Optics Apprentice
Avatar

Joined: July/22/2009
Location: Texas
Status: Offline
Points: 133
Post Options Post Options   Thanks (0) Thanks(0)   Quote TexasPhotog Quote  Post ReplyReply Direct Link To This Post Posted: September/02/2010 at 13:29
Originally posted by djwarner djwarner wrote:

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.


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. 
Back to Top
Magnumdood View Drop Down
Optics Apprentice
Optics Apprentice
Avatar

Joined: January/17/2009
Location: Illinois
Status: Offline
Points: 226
Post Options Post Options   Thanks (0) Thanks(0)   Quote Magnumdood Quote  Post ReplyReply Direct Link To This Post Posted: September/02/2010 at 13:39
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.
America - Home of the Free

               Because of the Brave
Back to Top
TexasPhotog View Drop Down
Optics Apprentice
Optics Apprentice
Avatar

Joined: July/22/2009
Location: Texas
Status: Offline
Points: 133
Post Options Post Options   Thanks (0) Thanks(0)   Quote TexasPhotog Quote  Post ReplyReply Direct Link To This Post Posted: September/02/2010 at 14:21
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
Back to Top
djwarner View Drop Down
Optics GrassHopper
Optics GrassHopper
Avatar

Joined: August/23/2010
Status: Offline
Points: 16
Post Options Post Options   Thanks (0) Thanks(0)   Quote djwarner Quote  Post ReplyReply Direct Link To This Post Posted: September/02/2010 at 15:21
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.
Non nobis tantum nati
Back to Top
Magnumdood View Drop Down
Optics Apprentice
Optics Apprentice
Avatar

Joined: January/17/2009
Location: Illinois
Status: Offline
Points: 226
Post Options Post Options   Thanks (0) Thanks(0)   Quote Magnumdood Quote  Post ReplyReply Direct Link To This Post Posted: September/02/2010 at 15:55
Originally posted by TexasPhotog TexasPhotog wrote:

So you've measured this?  How did you do it?

Or you repeating what someone who wanted to sell you a procedure said?
 
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
America - Home of the Free

               Because of the Brave
Back to Top
koshkin View Drop Down
MODERATOR
MODERATOR
Avatar
Dark Lord of Optics

Joined: June/15/2004
Location: United States
Status: Offline
Points: 13182
Post Options Post Options   Thanks (0) Thanks(0)   Quote koshkin Quote  Post ReplyReply Direct Link To This Post Posted: September/02/2010 at 16:37
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
Back to Top
Magnumdood View Drop Down
Optics Apprentice
Optics Apprentice
Avatar

Joined: January/17/2009
Location: Illinois
Status: Offline
Points: 226
Post Options Post Options   Thanks (0) Thanks(0)   Quote Magnumdood Quote  Post ReplyReply Direct Link To This Post Posted: September/02/2010 at 18:31
You forgot to mention you put me and my opthalmologist in our respective places...Kneel Suckers
America - Home of the Free

               Because of the Brave
Back to Top
koshkin View Drop Down
MODERATOR
MODERATOR
Avatar
Dark Lord of Optics

Joined: June/15/2004
Location: United States
Status: Offline
Points: 13182
Post Options Post Options   Thanks (0) Thanks(0)   Quote koshkin Quote  Post ReplyReply Direct Link To This Post Posted: September/02/2010 at 18:37
Originally posted by Magnumdood Magnumdood wrote:

You forgot to mention you put me and my opthalmologist in our respective places...Kneel Suckers

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
Back to Top
Oldtrader3 View Drop Down
Optics Journeyman
Optics Journeyman
Avatar

Joined: May/16/2009
Location: WA (state)
Status: Offline
Points: 445
Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldtrader3 Quote  Post ReplyReply Direct Link To This Post Posted: September/02/2010 at 20:28
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.
CDR3
Back to Top
TexasPhotog View Drop Down
Optics Apprentice
Optics Apprentice
Avatar

Joined: July/22/2009
Location: Texas
Status: Offline
Points: 133
Post Options Post Options   Thanks (0) Thanks(0)   Quote TexasPhotog Quote  Post ReplyReply Direct Link To This Post Posted: September/03/2010 at 09:50
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.
Back to Top
Sparky View Drop Down
Optics Master Extraordinaire
Optics Master Extraordinaire


Joined: July/15/2007
Location: SD
Status: Offline
Points: 4569
Post Options Post Options   Thanks (0) Thanks(0)   Quote Sparky Quote  Post ReplyReply Direct Link To This Post Posted: September/03/2010 at 10:36
Originally posted by Magnumdood Magnumdood wrote:

I had laser surgery 4 years ago, and corrected my eyes to 20-15.  My surgeon and I were talking, as he’s a shooter too, and he told me glasses reflect 10% of the usable light from each side.  So, wearing glasses all those years was costing me 20% of the usable light coming from my scopes.  Not a good thing, especially when you spend top $$ for an Alpha-Optic and expect to get 95+% light transmission. 

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.

Back to Top
Oldtrader3 View Drop Down
Optics Journeyman
Optics Journeyman
Avatar

Joined: May/16/2009
Location: WA (state)
Status: Offline
Points: 445
Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldtrader3 Quote  Post ReplyReply Direct Link To This Post Posted: September/03/2010 at 13:00
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
CDR3
Back to Top
Magnumdood View Drop Down
Optics Apprentice
Optics Apprentice
Avatar

Joined: January/17/2009
Location: Illinois
Status: Offline
Points: 226
Post Options Post Options   Thanks (0) Thanks(0)   Quote Magnumdood Quote  Post ReplyReply Direct Link To This Post Posted: September/03/2010 at 23:09
Originally posted by Sparky Sparky wrote:

  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.
 
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.
America - Home of the Free

               Because of the Brave
Back to Top
Oldtrader3 View Drop Down
Optics Journeyman
Optics Journeyman
Avatar

Joined: May/16/2009
Location: WA (state)
Status: Offline
Points: 445
Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldtrader3 Quote  Post ReplyReply Direct Link To This Post Posted: September/04/2010 at 07:10
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.
CDR3
Back to Top
 Post Reply Post Reply Page  <123>
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.01
Copyright ©2001-2018 Web Wiz Ltd.

This page was generated in 8.180 seconds.