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Posted: 1/16/2004 9:07:17 PM EDT
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I saw a used ITT tactical scope today for sale. It was 3-10X with a objective lense around 50-54mm and had target style turrets with 1/4MOA adjustments. It really gathered a lot of light and seemed like a pretty good quality optic. Is anyone familiar with these? Are they good scopes? What do they usually cost? |
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It doesn't matter how much light a scope can gather as your eye can absorb just so much light after a certain point. An objective lense that big, gives no benifit over a 40mm in ability to gather/see in dim light. Large objectives only cause trouble mounting as low as you might want to, but some can give a bit wider field of view. You won't normaly see real military snipers with huge objective lenses for these reasons. Companies the say gathers more light are not telling you the full story, but a sales pitch it is. Good Shootin, Jack |
| Actaully at the 10X power the 40mm objective would appear dimmer than the 50mm scope. Our eyes can dialate up to 5-8mm depending on age. The 10X gives a 4mm exit pupil for the scope with a 40mm objective and the 50mm objective gives 5mm. Therefore the larger objective is brighter to everyone regardless of age when at full power and in low light. |
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Picatinny did an extensive reasearch on that issue since they were in charge of the optic program for sniper scopes. All the experts on light gathering from all the militaries have concluded that over 40 mm is not needed for light gathering, hence that is the common one thru out the worlds militaries. The report actually said that a 32MM was all that was needed for the amount of optimum light needed, but to compensate for dirty lenses in field use and practical field of view, 40 MM became the standard. Good shootin, Jack |
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Jack, Were these findings for a scope of fixed 10 power? I think lens quality and coatings have a lot more to do with light transmission than exit pupil size. I do know that a large exit pupil does seem to reduce my felt eye strain. I'm comparing time spent behind my Mark 4 to time spent behind my 3.5-10 on a lower power setting. |
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Since this thread is fully hijacked.... The 40mm objective only allows a maximum magnification of 5X untill it begins creating a darker image if its only dusk or your old with a dialated human pupil. If your young and its evening then you can use up to 8X before the exit pupil of the scope becomes smaller than the pupil of your eye. A fully night adapted eye can be as large as 10mm but noone uses a scope with a fully night adapted eye because once you look at anything bright enough to see your pupil contracts slightly. Duffy, The Elcan and ACOG have 8mm exit pupils. Thats why they are so bright. Once the exit pupil is smaller than YOUR pupil the image you see dims. Go zoom a VERY high magnification spotting scope in at dusk to see the effects in an exagerated way. At first you can zoom in with no effect on brightness. After you get the exit pupil smaller than your pupil in your eye the image will dim darker and darker as you continue to zoom in. Exit pupil in mm = Objective size in mm / Magnification of scope. If its less than 3mm then you will see a darkened picture even during the day. If your eye sees a light so bright it must try to contract below 2mm you instictively blink. (like looking at a Surefire light) I hope this explains things adequately. While the military does not see MUCH use in an objective larger than 40mm for a 10X scope at least you know why they exist. Its has to do with magnification in very low light levels. I have never tried the scope mentioned in this thread. Your best bet is to ask at one of the bolt gun forums. |
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"Relative Brightness (RB) assigns numerical ratings to binoculars and scopes e.g. 25RB for a 7x35, 50RB for a 7x50 - telling the user that a 7x50 is twice as effective as a 7x35 at night when his eye pupil is 7mm in diameter. The RB numerical ratings are the squares of the exit pupils of the two instruments concerned, i.e. 5x5 for the 7x35 and 7.1x7.1 for the 7x50. The weakness of the RB system is that it does not take into account the instrument's magnification - and magnification has a big influence on target visibility at night. For example a 6x42 and an 8x56 riflescope both have exit pupils of 7mm (RB rating 49) but the 8x56 is almost 50% more effective at night when the user's eye pupil is 7mm. The Twilight Factor is the square root of the product of magnification and front lens diameter, i.e. for an 8x56 scope the Twilight Factor is (square root 8x56)=21.17. For a 6x42 it is 15.87. The "weakness" of the system, if indeed it can be called a weakness, is that it gives misleading results for high power, small diameter instruments - a 20 power scope with a 20mm front lens diameter has a Twilight Factor of 20 but in practice the user would see almost nothing through it at night. A user of this system must stay aware of the major importance of 5mm, 6mm and 7mm exit pupils for conditions ranging from dawn/dusk to starry darkness." [url]http://www.lynxoptics.com.au/FAQ/question_7.html[/url] |
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