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Accurate or BS?

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post 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. "
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/14/2009 at 12:50
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BS.  You don't get a wider field of view, either.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/14/2009 at 13:12
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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
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/14/2009 at 13:22
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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
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/14/2009 at 13:26
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Originally posted by pass-thru pass-thru wrote:

"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. "
BS. If you put a 40, 44, and a 50mm Scope all side by side all on 10 power the 44 will be brighter than the 40 and the 50 will be brighter than both. This is due to exit pupil, (the size of the  Objective in MM divided by the power).
 
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.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/14/2009 at 13:34
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BS.

All that, and scopes don't "gather" light.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/14/2009 at 13:42
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They Transmit light.

Edited by Chris Farris II - April/14/2009 at 13:44
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/14/2009 at 17:11
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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.   
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/15/2009 at 08:26
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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.)

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/15/2009 at 09:14
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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.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/15/2009 at 09:23
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Originally posted by John Barsness John Barsness wrote:

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.

...and those who listen to them.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/15/2009 at 09:49
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/15/2009 at 09:57
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Originally posted by John Barsness John Barsness wrote:

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.
 
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... 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/15/2009 at 10:30
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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.......
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/15/2009 at 10:59
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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.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/15/2009 at 11:53
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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.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/16/2009 at 06:40
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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?
 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/16/2009 at 12:23
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Originally posted by Roy Finn Roy Finn wrote:

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.
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.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/16/2009 at 22:27
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/17/2009 at 03:06
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Field of View

In 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 View

How 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!

Binoculars 101
Field of View

Avid binocular users pay attention to this critical performance factor, because field-of-view is the actual width of the sight picture provided by your binoculars at a specific distance. Field-of-view is determined by magnification and the focal lengths of the objective and eyepiece lenses. But one thing is always true: More magnification means less field-of-view.

Field-of-view may also be expressed in degrees, which is called the angular field. To convert angular field to the more practical linear field, multiply the angular field by 52.5.

 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/17/2009 at 03:14
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So after copying and pasting all the above info, field of view is determined by the type of lens and magnification. (It has nothing to do with the objective size of the lens). The other variable is focal length. The shorter the focal length the larger the field of view. So generally speaking a short telescope would, due to its shorter focal length, have a wider field of view. However a manufacturer could built a long telescope and arrange the lenses in such a way that they have a short focal point and vice versa.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/17/2009 at 10:32
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I was at a shop that had a vendor rep (will remain unnamed).  I was looking at their mid line scope ballistic type reticle and it was a 1" tube.  Just for s&*ts and grins, since I have more Euro 30 mm tubes, I asked him what the difference was between their top of the line 30 mms and the 1 in tubes.
 
His reply, "they transmit more light".  I put his scope down, thanked him for his time and walked away.  If the rep is that ignorant, I don;t need to buy their line of scope (although I had purchased 2 in years previous).
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/17/2009 at 10:34
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Oh John, that guy you're talking about must have switched companies...
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/17/2009 at 12:19
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He has worked for a couple of other European optics companies since leaving Swarovski. I would hate to tell you who he's working for now, because they make really good stuff!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/17/2009 at 13:50
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I am always impressed with how little various sales reps typically know about the products they sell.  To this day, I have NEVER seen a gun shop employee who knew anything about optics.  A few people I have seen mounting optics in gun stores, had not clue what they were doing.  Even roaming around SHOT show and asking question, you get a feeling that most reps have a hard time telling the difference between a scope and a baseball bat. 

ILya
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