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twilight factor

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/02/2010 at 23:50
jgm1981 View Drop Down
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can anyone explain the twilight numbers given to scopes. for example on the Zeiss website a diavari victory 1.5x6x42 has a twilight factor of 4.2-15.9 where the 2.5x10x50 has a twilight factor of 7.1-22.4. is this just calculations to confirm that the 50mm scope will draw more light at dusk than the 42mm?? someone lease explain. i apologize if this had been covered before
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2010 at 07:45
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The Germans use these numbers as a scale for low-light performance. The higher the #, the better. Generally, 50-72 mm german optics will have a twilight factor of 19 - 28 with 21.5 ( on a 56mm) seeming to be the average.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2010 at 12:59
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Twilight factor is a number derived from a formula.

Square root of (objective lens diameter in mm X magnification.)

So a $20 3-9X40 and a $2000 3-9X40 have equal twilight factor numbers.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2010 at 14:11
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We do have one new member here that is re-writing previously accepted scientific fact that is shedding new light on worn out theories such as Twilight Factor. For example it is now possible to boost low light performance to unprecedented levels by restricting exit pupil values and high levels of magnification.
This new information has many a scientist at Zeiss, Leica and Swarovski burning the midnight oil and new products are feverishly being developed to keep them on the cutting edge.
 
 
 
 
 
 
 
 
 
 
 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2010 at 14:12
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2010 at 18:47
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Originally posted by Roy Finn Roy Finn wrote:

We do have one new member here that is re-writing previously accepted scientific fact that is shedding new light on worn out theories such as Twilight Factor. For example it is now possible to boost low light performance to unprecedented levels by restricting exit pupil values and high levels of magnification.
This new information has many a scientist at Zeiss, Leica and Swarovski burning the midnight oil and new products are feverishly being developed to keep them on the cutting edge. 
 
Have you ever tried what the new poster tried?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2010 at 19:10
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Yes, but my vision is healthy and functional so it didn't work out so good.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2010 at 20:04
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Here's a real life experience from a hunter.  Fortunately his professional hunter knew something I learned only from experimenting.
 
"Relevant number or not, the concept of twilight factor was vividly illustrated to me in Africa. We were hunting wildebeest just after dusk, in fact it was getting into full dark.

We spotted some but looking through my  1.75-6x32 scope set at 1.75 I couldn’t see the beests well enough to aim, they were just too dim and blended into the surrounding brush. The PH (JJHack) told me to crank up the power, so I dialed it up to 6X. Suddenly I could see the animals quite clearly.

Same objective size, same coatings, only difference was power. The exit pupil went from 18mm down to 5mm (still sufficient) but the twilight factor went from 7.4 up to 13.8 and that was what made the difference."
 
Here's a real life experience from a hunter.  Fortunately his professional hunter knew something I learned from experimenting.


Edited by Roy Finn - December/03/2010 at 20:35
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2010 at 20:32
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I just told you I've tried different ways over the years. Are you calling me a liar ? Do you believe everything you read at the 24HourCampfire ? Do you know the poster ? Does he have good vision ?
Do you know the significance of Twilight Factor as it relates to one's vision ?
The hunter you refer to, "Jim in Idaho" understands TF and apparently you do not.


Edited by Roy Finn - December/03/2010 at 20:49
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2010 at 20:54
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i think somebody is going to get Butt Kick real soon
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2010 at 21:04
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Roy Finn,
 
I sorry you misunderstand my post.  It is ment for the original poster. 
 
Why do you say I don't understand T.F. because I tried to help the original poster see something from real life?  Never the less, you know two of the same size optics of differnt quality will both have the same T.W. but the one with the better glass and coatings will get more light to the viewer's eye.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2010 at 21:22
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Originally posted by Rich Coyle Rich Coyle wrote:

Here's a real life experience from a hunter.  Fortunately his professional hunter knew something I learned only from experimenting.
 
"Relevant number or not, the concept of twilight factor was vividly illustrated to me in Africa. We were hunting wildebeest just after dusk, in fact it was getting into full dark.

We spotted some but looking through my  1.75-6x32 scope set at 1.75 I couldn’t see the beests well enough to aim, they were just too dim and blended into the surrounding brush. The PH (JJHack) told me to crank up the power, so I dialed it up to 6X. Suddenly I could see the animals quite clearly.

Same objective size, same coatings, only difference was power. The exit pupil went from 18mm down to 5mm (still sufficient) but the twilight factor went from 7.4 up to 13.8 and that was what made the difference."
 
Here's a real life experience from a hunter.  Fortunately his professional hunter knew something I learned from experimenting.
Would have been a big difference I'll bet if the exit pupil went from 7mm down to 2.5MM When it was at 13.8 mm, the eye wasn't using it all anyway. Cranking up the magnification is a great idea if you have the exit pupil to do so. If you suffer from night blindness, the exit pupil probably doesn't make much difference, as your eyes can't use it. Since the exit pupil only went down to 5 mm, it may have been all the light his eye could use. We'll never know since we don't know who this person is, and how far their eyes dialate. But to assume you can see in the dark as well with an exit pupil of 2.5MM at 20x as you can with a 5MM exit pupil at 10x is rediculous..........Unless you are night blind.........Then you can't see S#!t either way.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2010 at 21:26
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Thank you. You saved me from typing exactly what I was thinking.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2010 at 21:39
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Originally posted by Rich Coyle Rich Coyle wrote:

Roy Finn,
 I sorry you misunderstand my post.  It is ment for the original poster. 
 
 
Then why did you quote me and ask me a question ?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2010 at 22:35
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i sure opened up a can of worms here...Ouch thanks for the good information. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/04/2010 at 03:49
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Yep yep this forum is just like all the others   lol
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/04/2010 at 05:16
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I am pretty sure I have covered this before, but twilight factor (along with quite a few other made-up useless terms) is primary utilized by unscrupulous marketing people in order to sell scopes.

It is pure rubbish.  10x40 and 40x10 designs have the same twilight factor.  Their performance in twilight or in low light is far from being the same.

ILya
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/04/2010 at 05:24
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Originally posted by Cooper25 Cooper25 wrote:

Yep yep this forum is just like all the others   lol
No, Cooper, it is usually not. But Rich has a way of getting our dander up, usually buy posting pure rubbish. Such as quoting an unknown "hunter" on a unknown trip  to Africa.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/04/2010 at 08:09
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Twilight Zone Factor?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/04/2010 at 09:10
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That explains a lot Palehorse.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/04/2010 at 12:28
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Ahhh ok Billy will have to watch and see.  From what I have so far,  some people think their word is all that is needed. 
Anyway that African hunters' expeience is just the opposite of mine.  Darker it gets the better I can see at lower power.......I don'tknow  anything about twilight factor and that, just what myeye tells my brain it is seeing.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/04/2010 at 16:55
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Originally posted by Cooper25 Cooper25 wrote:

Ahhh ok Billy will have to watch and see.  From what I have so far,  some people think their word is all that is needed. 
Anyway that African hunters' expeience is just the opposite of mine.  Darker it gets the better I can see at lower power.......I don'tknow  anything about twilight factor and that, just what myeye tells my brain it is seeing.

stick around friend you will like us.Big Grin
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