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Accurate or BS? |
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pass-thru
Optics Apprentice Joined: February/20/2009 Location: Hubert NC Status: Offline Points: 109 |
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Posted: April/14/2009 at 12:14 |
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"If you are talking a scope with a 1" tube (the part of the scope in the middle) you max out the light transmission of that 1" tube with a 44mm objective. The 50mm objective will give you no better light gathering than a 44mm, but it will be better than a 40mm. With the 50mm you do gain field of view. Think of it as a funnel attached to a 1" tube, no matter how big your funnel is, the water still has to go through the 1" tube. So increasing the size of the funnel to some monsterous size does you no good. For a 1" tube, 44mm is the max funnel size. Anything above that is just added field of view. "
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Shenko
Optics Apprentice Joined: April/20/2008 Location: WA Status: Offline Points: 249 |
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BS. You don't get a wider field of view, either.
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jetwrnch
Optics Apprentice Joined: July/03/2006 Location: Knoxville, TN Status: Offline Points: 294 |
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The 30mm scopes I've looked at have an advertised wider field of view than comparable 1" scopes. Not saying the tube is the reason. What you will gain is more erector adjustment. You should probably use a different mount if you have to move it that far though. Seems like scopes perform best near the center of the adjustment range. The 30mm Elite 4200 1.25-4x24 has a lot wider field of view than the 1" Trijicon 1.25-4x24.
Edited by jetwrnch - April/14/2009 at 13:13 |
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Roy Finn
MODERATOR Steiner Junkie Joined: April/05/2004 Location: United States Status: Offline Points: 4856 |
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Maxing light transmission will depend on what the upper end of a scopes magnification is. For instance, if the scope in question max's out at say 10x, the 44mm will have a 4.4 exit pupil. A 50mm will have a 5mm exit pupil. I don't believe that the size of the objective has much bearing on field of view. If you looked at the specs on Leupold's 3.5-10 models with 40 and 50mm objectives, you will see that the FOV specs are roughly the same. Exit pupil sizes will have much more influence on how bright a scope appears so long as everything else is fairly equal (meaning the glass, coatings and internal light management quality). Lastly, the person behind the scope must have healthy enough eyes to be able to benefit from a scope that can provide upper magnification values along with exit pupil sizes up to 6-7mm in diameter.
Edited by Roy Finn - April/14/2009 at 13:30 |
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Chris Farris II
TEAM SWFA - Admin MODERATOR Joined: August/13/2007 Location: United States Status: Offline Points: 3196 |
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On a 10x42 42/10=4.2 So the exit pupil is 4.2mm.
The most light the human eye can take in is 7mm. Once above that point your eye will no longer be able to distigiush the difference.
So an 8x56 and a 6x56 will both appear equally bright to you even though one is transmitting more light your eye can not take in that light because your pupil does not dialate beyond 7mm.
Also a 6x42 and an 8x56 both have 7mm of light being transferred through them the 8 will not be any more or any less bright than the 6, however with the added magnification it will show more detail.
The TUBE size is of no revelance to how much light you can take in. Light is not like water. While water travels through the most possible area, light only travels through the middle of the tube and if it is over 7mm it travels through you can not see anymore than that 7mm because that is all your eye can take in. The rest does not make it any brighter.
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One day your life will flash before your eyes; Make sure it's worth watching.
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Rancid Coolaid
MODERATOR Joined: January/19/2005 Location: United States Status: Offline Points: 9318 |
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BS.
All that, and scopes don't "gather" light. |
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Respect is something you earn. Equality is something you whine about not being given. |
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Chris Farris II
TEAM SWFA - Admin MODERATOR Joined: August/13/2007 Location: United States Status: Offline Points: 3196 |
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They Transmit light.
Edited by Chris Farris II - April/14/2009 at 13:44 |
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One day your life will flash before your eyes; Make sure it's worth watching.
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silver
Optics Master Joined: November/04/2005 Location: United States Status: Offline Points: 2291 |
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How much light that gets through (transmited) has to do with how good a job everything is ground and coated. Only when that is equal, then can you truely compare. Otherwise it is just a paper exercise.
Compare it to a camera's sensor. You have two lenses one is a cheap knock off the other is the factory best. They both have the same size objective lense. You set them in a room with the same light. All the settings are the same, but the cheap knock off shows a bit underexposed. That means not as much light is getting through it.
The same thing is true with scopes. You have two 6x42 scopes. One lets 94% of the light through. The other one lets 88% of the light through. At first glance paper they are both the same 7mm on paper... A quality 40mm can out perform a lessor 50 mm scope for the reasons I have stated. It's all 'bout the quality.
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"If we weren't all crazy we, We would go insane." Jimmie Buffet
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Dale Clifford
Optics Jedi Knight Joined: July/04/2004 Location: United States Status: Offline Points: 5087 |
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not sure I interpret your post but-- the inside tube which contains the lens elements can be any size, up to the size of the tube, in the last case the adjustments are on the outside as in the case of some of USOs target scopes. most of the hunting scopes have an inside tube dia. about 1/2 to 5/8 in which allows the movement of the element inside the outer tube which acts as a mounting bracket for the delicate innards. A scope with a 35 or larger tube can accomodate both. The light rays are inverted (image is upside down) as it passes thru this system and flipped again in the last lens. A larger inside tube increases the surface area in proportion to its dimension and can improve the image sweet spot needing less curvature in the lens element formula. while the term light gathering infers an active principle on the part of the scope, it can gather light in the sense a tub gathers water in a rainfall. (seen and measurable as an increase in temp.) |
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John Barsness
Optics Optimist Joined: January/27/2009 Status: Offline Points: 785 |
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I'm curious about where the quote that started this thread came from. It sounds as though the person who made it is quite sure of themselves, but knows nothing about optics. Or let's say they know just enough about optics to thoroughly confuse themselves.
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Rancid Coolaid
MODERATOR Joined: January/19/2005 Location: United States Status: Offline Points: 9318 |
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...and those who listen to them. |
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Freedom is something you take.
Respect is something you earn. Equality is something you whine about not being given. |
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Urimaginaryfrnd
MODERATOR Resident Redneck Joined: June/20/2005 Location: Iowa Status: Offline Points: 14964 |
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silver
Optics Master Joined: November/04/2005 Location: United States Status: Offline Points: 2291 |
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There are a lot of "old wives tales" out there. A lot of it comes from old claims made by the industry its self. They dumb down the ad copy and this is what you get.
Then you have the bigger must be better crowd. Funny most of them don't use that same logic when it comes to swim suit models (Steal my line for an article JB and you owe me a ball cap). Then again there is 8 Shots...
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"If we weren't all crazy we, We would go insane." Jimmie Buffet
WWW.formitch.com |
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pass-thru
Optics Apprentice Joined: February/20/2009 Location: Hubert NC Status: Offline Points: 109 |
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The quote comes from an individual who is always quite certain in his opinions, who apparently worked at a gun shop and picked up this knowledge from training done by swarovski.
I don't crap about the physics involved in scopes. But it just didn't make sense to me, the funnel analogy. There are several reasons that it seemed fishy. For instance, his claim that only a fixed amount of light could pass through a 1" tube, and that such capacity was reached with a 44mm objective lens did not take into account the fact that light availability is variable. Therefore, in low light, when scope quality is most important, it seems highly unlikely that an objective lens larger than 44mm would provide so much light as to overwelm the capacity of a 1" tube.......
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Dale Clifford
Optics Jedi Knight Joined: July/04/2004 Location: United States Status: Offline Points: 5087 |
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at the time the amount of the amount of light overwelming the capacity of the 1" tube the phosphorous in your body will be convert to cesium. |
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John Barsness
Optics Optimist Joined: January/27/2009 Status: Offline Points: 785 |
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Silver, it's a deal. Pass-through, Some of the folks at Swarovski have been a little, uh, misleading in the past, in order to promote their products. In fact a Swarovski ad campaign was responsible for the widely-held notion that somehow 30mm scopes transmit more light than 1" scopes, which isn't true. That's partly why I asked. It sounded vaguely like some of the BS I'd heard from a Swarovski ad guy from time to time. By the way, he no longer works for them, and they are much more straightforward now. |
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8shots
Optics Jedi Knight Lord Of The Flies Joined: March/14/2007 Location: South Africa Status: Offline Points: 6253 |
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Then you have the bigger must be better crowd. Funny most of them don't use that same logic when it comes to swim suit models (Steal my line for an article JB and you owe me a ball cap). Then again there is 8 Shots... [/QUOTE]
Is this what you are talking about?
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mastsif man
Optics Apprentice D. Overton Joined: March/25/2009 Location: North Carolina Status: Offline Points: 62 |
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mr. finn has hit the nail on the head. there are multiple variables having to do with light transmission through a rifle scope and with respect to fov he has proven his point quite well. look through the specs of scopes of the same specs, fovs are all over the place. when a company quotes their percentage of light transmission, i sort of take it with a grain of salt. what wave length was it measured at if any, or was it from a flashlight. ad campaigns can twist anything to what they want people to hear. that is where the scope ratings scale comes in handy as a guide where to start looking. you would not buy a 5000 dollar custom rifle a put an atn on it, even if they said they had 99 percent light transmission.
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medic52
Optics Professional Joined: October/05/2006 Location: Missouri Status: Offline Points: 893 |
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CF II......
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"The true soldier fights not because he hates what is in front of him, but because he loves what is behind him." G.K. Chesterton
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8shots
Optics Jedi Knight Lord Of The Flies Joined: March/14/2007 Location: South Africa Status: Offline Points: 6253 |
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Field of ViewIn addition to magnification the field of view of an eyepiece is important. The field of view is a function of the optics of the eyepiece itself and its magnification which is a function of the telescope focal length. Typical eyepieces have field of view ranging from 40° to 65° or more. The intrinsic eyepiece FOV must then be divided by the magnification to get the effective field of view at the telescope. A 25 mm eyepiece on a 1 meter focal length telescope has a magnification of x40. This will yield a 1° field of view if the eyepiece has a 40° intrinsic field of view Telescope Field of ViewHow is the telescope field of view calculated? Some more information is required. Eyepieces are not created equal. They are given names such as Kellner, Nagler, Plossl, Erfle or more generic names such as Super Wide Angle. There are three basic facts to know about any eyepiece, the eyepiece focal length (e), the diameter of the barrel (so it fits the diameter of your focusser), and the eyepiece field of view sometimes known as the effective field of view. The eyepiece field of view is the theoretical field of view in degrees the eyepiece would provide at a magnification of one. Of course such a low magnification can neither be achieved or used in practice. Alternatively, the eyepiece field of view can be thought of as the magnification required to give a telescope field of view of one degree (about twice the angular diameter of the full Moon). The eyepiece field of view varies with the type of eyepiece. The actual telescope field of view is calculated by dividing the eyepiece field of view by the magnification. So Kellners have an eyepiece field of view of about 40 degrees. This means that at 40 magnifications a Kellner eyepiece will give a 1 degree telescope field of view no matter what the aperture of the mirror or the focal length or focal ratio of the telescope. Alternatively most Plossl eyepieces will have an eyepiece field of view of about 52 degrees. So at 52 magnifications, this eyepiece would also give a 1 degree telescope field of view and at 40 magnifications would give a telescope field of view of 52/40 = 1.3 degrees. Consider our example telescope with a 200 mm f/6 mirror with a focal length of 1,200 mm. Consider using various eyepieces of 25 mm focal length. Whatever the eyepiece type, you now know the magnification will always be 1,200 / 25 or x48. For a Kellner eyepiece Eyepiece field of view = 40° Telescope field of view = Eyepiece field of view / Magnification = 40/48 = 0.83 degrees = 50.0 minutes of arc For a Plossl eyepiece Eyepiece field of view = 52° Telescope field of view = Eyepiece field of view / Magnification = 52/48 = 1.08 degrees = 65.0 minutes of arc So for our 200 mm f/6 telescope, a 25 mm Kellner eyepiece would show a patch of sky about 1.66 times the diameter of the full Moon at a magnification of x48. The 25 mm Plossl eyepiece would show a patch of sky about 2.17 times the diameter of the full Moon at the same magnification!
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