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Adjustable Objective VS light transmissio

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/16/2007 at 19:09
stubewan View Drop Down
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What effect does an adjustable objective have on light transmission?

 

Will it lessen the amount that is transmitted?

 

Will it degrade the clarity?

 

Stubewan

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/17/2007 at 08:11
Dale Clifford View Drop Down
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all things being equal no--the screw only moves the front lens in relation to the rest of the scope, clarity in a way is increased because it allows close focus, which would otherwise be unclear.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/17/2007 at 10:31
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Any scope that has a parallax adjustment will have an additional lens.  Every time light passes through a lens it loses a small percentage of its original value.......so technically a scope with any type of parallax adjustment will transmit less light.  Question is, can the human eye perceive the loss??
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/17/2007 at 23:00
stubewan View Drop Down
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Thanks Chris,

That is how I have always understood the AO. If the scope is a Nikon Mon. 3.3x10x44, how much light is really being transmitted to the eye. The 95%, that is advertised? I know that the 95% is per lens, but what is reaching the eye?

 

Stubewan

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/18/2007 at 10:31
Dale Clifford View Drop Down
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the additional lens chris mentions is side parallex focus, I don't think the front focus have the additional lense as you can watch the lenses move when turning the Ao. its put there because of the distance back to the front lens and the gearing that would be requireed. the method of calculations is say 99% each lenses would then be .99 x 99 or .9801 for the 2nd and .98.01 x .99 or 97.06 for the 3rd and 97.06 x x.99 and so on.  why some cheap scopes appear to be "brighter" than some with many more lenses elements  say a tasco vs. uso, and why the use of the term brighter is misleading. so--- in your last question affecting clarity not necessarily.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/18/2007 at 17:29
stubewan View Drop Down
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Thanks Dale,

 

So Am I to undertand that a scope like the  Nikon Monarch 3.3x10x44 AO, which has the AO mounted in the very front, does not have any more lens for light to be transmitted through? And that, a side focus scope like the Nikon Monarch 2.5 x 10.x 42 30mm SF uses extra lens, because of the positioning of the focusing knob?  I am so very sorry if this sounds stupid, but I am trying to become a bit more knowledgable about scopes.

 

Stubewan

 

 

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/19/2007 at 10:18
Dale Clifford View Drop Down
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yes thats as I understand it. the side focus usually puts a lens in front of the erector set (sounds like a toy). but again a high quality side focus may still be better than a front AO. another note front and side AO aren't really focus however the use of the term focus to describe them is rampant.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/20/2007 at 15:50
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Every AO scope I'm aware of contains an extra lens........front adjustable or side should have another lens for light to pass thru.

    focus


Edited by Focus
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/06/2007 at 16:26
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.0004387 loss. Achromats

more loss on inside of tube walls than the lenses.

Obj lenses are larger which compensates for loss.

you can probably getter a better "light" using a filter to aid in value transmissions.



Edited by Boneyfreak
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/06/2007 at 17:11
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There is a light loss due to reflection and absorption at each glass-to-air transition. This also reduces contrast, which is more significant, since it reduces acuity. For our eyes things look "sharper" due to better contrast. The lower the contrast, the "unsharper" is what we see. Additional parasitic reflections inside the tube further reduce the contrast, which is why correct coating of inside of the tubes with material that absorbs practically 100% of the light is very important and what separates really good scopes from the also-rans and cheap junk made in 3rd World countries. Loss due to absorption is usually more significant in blue/violet spectrum if I recall correctly.

With light transmission calculation is therefore simple. Say it's 99% per surface. If there are 5 lens elements in the scope, it means 10 surfaces. So, ideally the scope would transmit a total of (.99)^10 = 90.4% of light.

Which is why most high-end European scopes usually specifically mention that light transmission of the scope is over 90%. Most other manufacturers, especially American companies, play the marketing horn and constantly advertise "99% light tranmission rate!", with small print somewhere indicating they meant "per surface".

Hope it helps.

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