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Thread: New Scope

  1. #1
    MGO Member DEVIL DOG's Avatar
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    New Scope

    Going to need a scope for my NEF single shot rifle in .223. My range setup UP NORTH will allow me to shoot about 85 yards. Not wanting to put an expensive scope on a hundred dollar gun. Eyes are getting pretty old. Think a 3-9x40 would work out? Any suggestions ?
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    My eyes are starting to go too but I would think a 3-9x40 would be ok at 85yards.

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    As my eyes age, I find that I need additional brightness more than additional magnification to identify targets and shoot well. Fixed power scopes usually have larger internal lenses (no cam tube to occupy space around the erector tube) and can offer 25% or more extra light transmission.

    I look for 4x fixed power scopes with limited bullet impact adjustment - no better than variables' at the same power. This means the erector tube used is much larger than that used in variable power scopes and thus light transmission is much better. Some of the Chinese fixed power scopes use the same erector tubes as their variable power counterparts and provide no additional brightness - but a lot of extra bullet impact adjustment.

  4. #4
    MGO Member Ol` Joe's Avatar
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    Are you planning on shooting at 6” gongs or grapes on the fence post?
    The target size will make a difference in the amount of magnification you will want. A 3x9 should be fine for bouncing tennis balls in the lawn, but may not work well if you are plinking acorns off the wood pile. That 3x9 should be fine for general use as may a 2x7 but the target size may end up being larger then you planned on.
    10x25 is correct the older we get the more light becomes an important consideration. There is a limit though that we can generally use and exceeding it gains us nothing more then a larger “window” in the eye piece that makes head placement less critical. The human pupil normally only opens to a max of ~7mm and a exit pupil on a scope that is larger then that simply goes to waste. Yes your eye is getting all the light it needs but it is not capable of using all the scope supplies. You can figure the exit pupil size of a scope by dividing the objective lens diameter (the front one) by the magnification. Hence a 4x scope with a 40mm objective will have a exit pupil diameter of 10mm. The variables work the same, the exit pupil size however varies with the power setting. A 3x9x40mm would have a max pupil diameter of ~13mm- 4.5mm. Enlarge that objective to 50mm and your exit pupil will grow to 5.5mm at the 9x peak power. Still under the max mount your eye can use. A 50mm objective on a 7x scope would give a 7mm exit pupil and could be considered about perfect as far as providing the brightness one might be looking for. A over large exit pupil may make extended viewing more comfortable too with a bit less eye strain, but for the average shooter they likely will not notice any difference in the sight picture other then the mentioned less critical cheek weld need. Keep in mind too the quality of the glass and its coatings will make a big a difference in brightness. The amount of light lost between the objective and eye piece due to poor glass, distortion, and reflection can be pretty surprising and is where the big advancements have been made in recent years in scope clarity and brightness.
    https://www.celestron.com/blogs/know...r-sport-optics

    Considering the gun it will be mounted on distance used and that you will likely be shooting at 1.5” or bigger bullseyes or simply bouncing tin cans I would stay with a 3x9. If you want to pop grapes off the fence post... maybe going to a scope with a top end of 14x or 16x would make sense. Nikon, Bushnell, Vortex, in other words most better name brand scopes all make a affordable line of good quality scopes that should fit your purpose and not break the bank.
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  5. #5
    MGO Member DEVIL DOG's Avatar
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    The gongs are 8". From 85 yds through a scope they are actually quite large. I think from the info here & other sources, a 3-9 should be fine. Any real advantage of an increased front lens size?
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    Quote Originally Posted by DEVIL DOG View Post
    The gongs are 8". From 85 yds through a scope they are actually quite large. I think from the info here & other sources, a 3-9 should be fine. Any real advantage of an increased front lens size?
    Front lens size increases the exit pupil, one geometric component of light transmission. The formula is:

    Exit Pupil (mm) = Objective lens diameter (mm) ÷ Magnification (powers)

    The other geometric component of light transmission is a cumulative function of the diameter of the internal lenses. This is roughly a function of tube diameter (e.g. one inch vs. 30mm)

    The material component of light transmission is actually more important. Light is reflected and absorbed at every air/glass interface. This loss is ¼% to 2%, depending upon the sophistication of the glass coatings. Each lens has two air/glass interfaces, so the loss per lens is ½% to 4%. Total light loss is each of these losses in train, i.e. 1.0025 times 1.04 times 1.02.....for each air/glass interface.

    Variable power scopes have the two external lenses, plus seven to ten internal lenses. Fixed power scopes have the two external lenses, plus two internal lenses. Really good, high dollar variables transmit about 60% of incident light. Poor quality variables may transmit less than 40% of incident light. Really good fixed power scopes transmit about 80% of incident light. Poor quality fixed power scopes rarely transmit less than 65% of incident light.
    Last edited by 10x25mm; 05-08-2019 at 09:51 AM.

  7. #7
    MGO Member DEVIL DOG's Avatar
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    My senile brain does well with simple answers. But if I understand what you're saying, I would be best served with a 1" tube, with a fixed power, & a large front lens ?
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    Quote Originally Posted by DEVIL DOG View Post
    My senile brain does well with simple answers. But if I understand what you're saying, I would be best served with a 1" tube, with a fixed power, & a large front lens ?
    Yes, unless you want to spend a lot of money. A decent 4x or 6x fixed power scope with a large objective will outperform a much better variable scope at the same power settings, all else being equal. Don't sweat unusable exit pupil. That is theoretical. A fixed power scope will also demonstrate better durability due to its much simpler internal construction. Less to screw up.

    Get a variable if you are going to be shooting at a variety of targets, at various ranges, under different conditions. Then you accept the loss of brightness and durability, or spend a lot more money.

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    MGO Member DEVIL DOG's Avatar
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    You should be able to get a decent fixed power scope for around $ 25.00. Don't overlook air rifle scopes. They actually tend to be better built than firearms scopes and have their parallax set to 50 yards, which works well for your shooting. Look at used scopes on GunBroker. There are some real deals there, even after paying $ 10.00 for shipping.

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