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Leupold Golden Ring Spotter Question

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/11/2010 at 23:36
Goatnuts View Drop Down
Optics GrassHopper
Optics GrassHopper


Joined: April/11/2010
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I've got a question about the golden ring compact,

The 10-20x40 says it has a twilight factor:20.0-28.3 and the 15-30x50 has a twilight factor: 27.6-39.0

They also list "twilight" factors for the mark 4 tactical, sequia and the regular golden ring.

Optics experts what is the "twilight factor," and how is it measured?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/12/2010 at 08:03
silver View Drop Down
Optics Master
Optics Master


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"Twilight Factor"  does not take into account the quality of the internal or external lenses or thier coating. Cheap crap and deluxe scopes can have the same factors.  It tells you nothing about the resolution of the optic.  So even after you figure it out, you end up asking yourself is it relavant?   Looking for a spotter with ED glass will be more productive.  If you look for resolution, then this other "stuff" sorts it's self out.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/30/2010 at 13:07
lucznik View Drop Down
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Originally posted by silver silver wrote:

"Twilight Factor"  does not take into account the quality of the internal or external lenses or thier coating. Cheap crap and deluxe scopes can have the same factors.  It tells you nothing about the resolution of the optic.  So even after you figure it out, you end up asking yourself is it relavant?   Looking for a spotter with ED glass will be more productive.  If you look for resolution, then this other "stuff" sorts it's self out.


This answer is essentially truthful but, it misses a major point - which is that almost all comparative measurements for optics can be dismissed with the same argument.  For example:
  1. Exit Pupil - probably the most commonly used ways to compare the relative brightness of an optic.  But the thing is, an 8x42 Leica and an 8x42 Barska both have the same exit pupil and if a guy thinks he's getting the same amount of light out of that Barska that the Leica provides, he's crazy. 
  2. "Multi-coatings" -  All a manufacturer has to do to be able to claim they offer a "fully multi-coated" binocular is to have at least two coatings on all glass-to-air surfaces.  The firm that uses 30 or more coatings can still only call it "fully mutli-coated" but you can bet there is a BIG difference between the two. 
  3. ED glass - Yes, even good old Barska offers options that claim to use ED glass. They are not the same.  Even among quality optics manufacturers, there are differences in the type and quality of the ED glass used.  The ED glass that Bushnell uses on its $300 Excursion, while good in its own right,  is nowhere near the same quality as the ED glass that Kowa uses in the TSN883 - but they both can still be called ED spotters.
All means and methods of comparing one optic against another are subject to the caveat that quality trumps all and in all cases the prudent shopper will heed the old adage of "buyer beware."  Such comparisons are not meant to be in-and-of-themselves definitive.

To answer the OP's original question:  Twilight Factor is a mathematical calculation that attempts to measure an optic's ability to be useful under low-light conditions.  For example, an 8x42 binocular has an exit pupil of 5.25mm and a 10x42 binocular has an exit pupil of 4.2mm. Thus a person might naturally assume that the 8x binocular will be better than the 10x in low light because it lets more light through to the eye, but what the exit pupil doesn't account for is the fact that the 10x binocular brings you in closer to the item of viewing interest - which may be more critical to seeing it than is the level of light.

To illustrate, let's conduct a little experiment. Tonight go into a room in your house and turn off almost all of the lights.  Make sure there is just enough light that you can barely see around the room.  Place an object on a table and then stand 10 feet away from that object.  Look at it closely.  Now cut the distance in half and stand 5 feet away.  Even though the amount of light in the room will not have changed, you should be able to see the object better. Why?  Well, of course it's because you're closer.  Take this a little further if you can and dim the lights a little bit more.  You will see that, even in the dimmer light, being closer allows you to see the object just as well when you are closer as you could with greater light yet standing farther away.  Twilight Factor is an attempt to mathematically quantify this reality that getting closer can mean seeing better, even if the amount of available light is a bit less.

Of course, the basic premise of what silver posted remains absolutely true.  Quality absolutely trumps all.


Edited by lucznik - April/30/2010 at 13:19
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