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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/13/2009 at 14:54
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I have been looking around and testing various different scopes from several brands and in a variety of magnifications. To my eyes, the biggest factor for low light performance (at least inside of a hundred yards) is simply the magnification of the scope. Just through some amateur side by side tests I found that the determining factor for my scopes tends to be what magnification they are set on.

For example, my Kahles CL 4x12x52 is better optically than my Nikon Prostaff 3x9x40. However, the Prostaff has better low light visibility on 6x or 7x compared to the Kahles at 4x. I found the same thing to be true with a variety of cheaper scopes as well. It seems that on equal power optical clarity comes out ahead. However, by amping up the magnification on some of the cheaper scopes, the low light performance is actually better than the high dollar scopes on low powers.

I am interested in the 4x Conquest because it seems to be such a deal. But, if my experience with these other scopes holds true for the Conquest as well, perhaps I would be better off purchasing a cheaper scope in a slightly higher variable, maybe something like a 2.5x8 or even a 1.5x6?

I should clarify that when I say better low light performance, I am referring specifically to my ability to see the target through the scope. My Kahles has a sharper sight-picture in very low light at 4x than the Nikon on 7x. But, the additional magnification allows me to see the target, albeit fuzzy, whereas with the Kahles I simply can't see the target even though the foreground or background may be sharper and more in focus.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/13/2009 at 16:13
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That is a pretty shocking thing you say Shocked , especially in regards to the price difference.  Similar situations have been reported by folks who did all kinds of comparisons.
One of the toughest one I heard, was the one of a quite experienced hunter who perceived his Barska scope to be better in low light than his Z6. I still have a hard time swallowing that but ...who knows.
Another guy compared a Burris fulfilled II with a Zeiss Victory and he felt like he didn't notice any difference.
What can one say to this? Hard to say. I love German and Austrian optics and I find it to be exceptional but I do leave the door open for such possibilities.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/13/2009 at 17:31
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At higher magnification, your ability to resolve detail increases, but light transmission to your eye decreases because if the decrease in exit pupil size.  So, at some point, low light performance actually decreases as you continue turning up the power.  If you have a really large diameter objective and good optics to begin with, you can take advantage of higher magnification while still maintaining a large exit pupil and good light transmission.  This all assumes you are comparing optics of similar quality.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/13/2009 at 19:46
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I have limited experience with optics.  But, I have found the opposite with original poster.  Now, I do not own high end optics, but some mid-range models, such as a few vx-IIIs, a couple Mueller sport dots, some BSAs and a Tasco or two.  But, now matter what mag. I have the Leupolds on, compared to an equal mag. on the other scopes, the images are more detailed and much brighter.  The objective sizes are similar, but there is a clear difference.  I just received a Zeiss 2.5x8 32mm scope and looking through the window, it is fantastic, equally as good as the Leupold scopes, but have not had a chance to compare directly.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/13/2009 at 20:12
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I am in full concurrence with everyone's shock and/or disbelief as I didn't want to believe it myself. Now I suppose I could have just gotten a bad Kahles CL, but since the scope functions fine and is clear as a bell etc I doubt that it the issue. Its not that there is anything wrong with the scope...I just can't seem to see that there is anything significantly "more right" so to speak than the Nikon. 

As I said before, on the same power, the Kahles has a bit of an edge for sure. But the Nikon provides a more visible image under very dark conditions on 7x than the Kahles does on 4x despite the price difference and the much larger objective on the Kahles (52mm Vs. 40mm on the Nikon).

I wish there was a much more significant increase in the Kahles performance, considering what I payed for it. But, I have repeated these same findings over and over in difference optical tests (amateur at best but still appropiate for situational hunting comparisons.)
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/13/2009 at 22:31
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I think that you have to look at the exit pupil size, as Chris mentioned.  Exit pupils below 6mm are going to geometrically decrease the light transmission ability of scopes which in turn darkens the field of view.  You may be comparing apples to bananas. 
 
Cheap scopes do not have the precision lens alignment, interior lens coatings and glass quality to beat the expensive scopes vis-a-vis.  Even my Nikon Monarch can not beat the Kahles, Swarovski and Zeiss scopes that I own, head to head.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/13/2009 at 22:41
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I have to ask the question as to why you are comparing one scope set at 4x and another set at 7x.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2009 at 03:10
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I wasn't intending on comparing them at different magnifications...its just how it turned out. I started by comparing them both at 4x. But then I just started messing with the adjustments to see what kind of performance I could get out of them both. This was the result. 

I have no agenda in furthering cheaper scopes and I have no reason to favor the Nikon, specifically since I payed the rather high price to get a scope (he Kahles) that is commonly referred  to as top of the line or at least very near it. I am just describing the results of what I have seen with my scopes.

The fact is that, set on 7x, the Nikon Prostaff provided a better visible picture than the Kahles on 4x. Whether this means anything in the real world, I'll leave it to more experienced and knowledgeable people to decide. I was just a little confused by the results as well and was hoping someone could help me by providing an explanation. The truth is, I was not expecting the Nikon to perform as well as it did. However, the tests I did which consisted of discerning objects in basic low light (night time) hunting scenarios, showed that magnification rather than optical quality (price) was the determining factor in the ultimate visibility of the target in low light. 

Again, perhaps my results are limited to these two scopes, or maybe even it is simply my eyes and someone else would have drastically different results. But, I wont lie and say one scope vastly out-performed the other just to justify the amount of money I spent on it. I believe in honesty and integrity, if that means saying something that is not popular and goes against common wisdom so be it; that is the result I got and until I get a different result, I can't in good conscience change the opinion I have forwarded.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2009 at 05:18
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You are comparing apples to bananas.
Whilst it may be true that a bigger magnification on a cheap scope is clearer then a lower magnification on an expensive scope, you now may own a scope with a magnification that does not suit your needs.
As stated above the overall quality is what matters, not the percieved quality tested at different levels.
It is like racing a Formula1 car stuck in first gear, against a normal car using all its gears. Guess which one will win.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2009 at 07:29
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Kinda understand what you're saying but what happened when you compared both images at 7X?  Would have thought that the Kahles would provide the better image.  Image quality differences should become more apparent as the mag is dialled up.
 
The increased mag had the affect of moving you closer to the target so you could perhaps see more detail albeit fuzzy, this is where the superior optics at the same mag of the Kahles should provide the benefit.
 
Assuming we would want to maintain a minimum exit pupil of 6 your Kahles could be dialled up to almost 9X versus almost 7x for the Nikon and give you still more detail and  a sharper image.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2009 at 07:38
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Yes, side by side at the same magnification the Kahles did outperform the Nikon as it should. But I guess I was just shocked by the discrepancy between the two when on different powers. It almost makes me wonder whether I should save several hundred dollars on each scope purchase by buying a mid to lower end scope with a nice variable magnification range. 

I was considering buying a 4x Conquest, but now I am thinking that perhaps I should buy something in a variable. I guess I just always though optical quality was going to be the primary indicator of how much you can "see" through a scope at any given time. Consequently, I was none to happy to find out that a  fairly cheap 140 dollar scope like the Prostaff could outperform a thousand dollar scope like the Kahles simply by dialing up the magnification. Haha, the high-end scope manufacturers sure don't put anything like that in their literature. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2009 at 08:03
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I guess it all depends on how good the cheaper scope is to begin with.  While the fuzzier image was acceptable through the Nikon (which is not a terrible scope anyway), it may have been completely unacceptable through a Barska or a BSA for example.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2009 at 10:43
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"For example, my Kahles CL 4x12x52 is better optically than my Nikon Prostaff 3x9x40. However, the Prostaff has better low light visibility on 6x or 7x compared to the Kahles at 4x. I found the same thing to be true with a variety of cheaper scopes as well. It seems that on equal power optical clarity comes out ahead. However, by amping up the magnification on some of the cheaper scopes, the low light performance is actually better than the high dollar scopes on low powers."

Isn't that what is called twilight factor?

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2009 at 11:11
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Yes that is twilight factor and you can't compare scopes fairly without setting both scopes at the same power, if the exit pupil is over 6mm.  Then you have apples to apples.  The rest is not a fair comparison.  It is only an anomaly especially if clarity is different.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2009 at 14:53
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Stated another way...
 
Even in low light conditions, as you increase power -- to a point -- you gain better visibility of your target because you can resolve finer details.  However, this works until the power is high enough that the exit pupil size decreases to the point that you have a noticeably dimmer image.  In other words, best low light visibility involves a "happy medium" compromise of both high enough magnification and large enough exit pupil size.  Once the exit pupil decreases below 4 - 5mm, increasing magnification further will only reduce light transmission to your eye.  Turning magnification really low makes the image through the scope "brighter," but reduces the amount of detail you can resolve.  Turning the scope's power up to the highest magnification that still provides at least 6 - 7mm exit pupil gives the best low light performance that particular scope is capable of delivering.
 
Regardless, unless the two scopes being compared are set at the same magnification, you are seeing the results of the differences in magnification and not making a comparison of optical quality.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2009 at 15:09
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So would everyone agree that if you want low light performance, it would be better to have a mid-range scope in a 3x9x40 or something similar, instead of a top of the line swaro/zeiss/kahles etc in say a fixed power of 4x or even a variable power of 1-4x20?

I certainly appreciate the advantages in clarity and resolution provided by some of the ultra-high dollar scopes. But, the truth is if I can get better performance during hunting situations (such as low light in the woods) from a cheaper scope with a little more magnification, I see no reason other than status to buy the more expensive scope. 

I know this only works up to a certain point, because eventually as magnification increases your field of view basically disappears and in order to maintain a good exit pupil the objective becomes enormous. However, it looks to me like a medium powered variable in a decent quality scope is more fitting for low light hunting than even the most expensive low powered scopes if visibly identifying your target in low light is your primary concern.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2009 at 15:29
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My personal favorite low light hunting scope configuration is a high end 2.5-10X50.  The 50mm objective allows you to use the scope's full range of magnification to good use in low light, though it's at its best up to about 8X.  50mm is about my personal maximum objective size.  Larger than that, and the scope gets a little too unwieldy for my taste.
 
To answer your question, a decent 3-9X40 will usually outperform even a high end 1-4X24 or fixed 4X in low light.  I emphasize "decent," though.  You still need good resolution, contrast, and coatings optimized for good light transmission in the blue spectrum.  A high end 1-4X24 will still outperform a low end, $50 3-9X40.  All else being equal, better optics still perform better in low light, so a good 3-9X40 still won't quite perform as well as a great 2.5-10X42, for instance.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/15/2009 at 00:14
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Keep in mind the ratio between twilight factor and exit pupil.  Below 5mm exit pupil size the amount of light entering a lens is decreased geometrically (!!!).  Twilight factor is nothing more than (the square root) of exit pupil times magnification.  So, as long as the exit pupil is above 5mm, twilight factor is relevant and means better brightness relative to the quality of the scope!  This is "twilight factor"and is why some think that a cheaper scope at 9x is better than an expensive scope at 4x (it is not, only twilight factor is higher, get it!).
 
Also consider that a cheaper scope will not outperform a more expensive scope that is in alignment with all lens surfaces coated properly.  The single exception is the Bushnell 4200, 3-9x40 at $299.  Almost always, you spend more money for more precision, better glass and better coatings.  A cheaper scope will NOT outperform a more expensive, better built and coated one, power vis-a-vis power, at the same exit pupil!  It just won't happen.  You generally get what you pay for. 
 
Corrected twilight factor equation.


Edited by Oldtrader3 - August/15/2009 at 08:32
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/15/2009 at 00:32
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As I recall:
Exit pupil is objective diameter divided by magnification power.
Twilight factor is the square root of the ojective diameter multiplied by the magnification power.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/15/2009 at 00:33
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So is it likely there is something wrong with my Kahles??? Because it does not show that significant an advantage over my Nikon Prostaff, and as mentioned above, the magnification was the determining factor of which scope had better visibility not simply the fact that the Kahles is supposed to be a "better" scope.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/15/2009 at 00:34
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Keep in mind I am talking strictly above low light performance (actually tested at night under a full moon)
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/15/2009 at 05:37
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Michael,
Test the two scopes at the same magnification so that you are removing magnification as a variable and are then comparing optics.  You cannot make a fair comparison of low light performance with two scopes at different magnifications, especially when you're talking about nearly double the magnification difference.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/15/2009 at 08:28
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Whew!  Thank you RifleDude.  I guess that I made my explanation too involved or something.   
 
Shenko, you are correct about twilight factor.  It is the sq. root of exit pupil x magnification.  It was late and I was tired.  That is why brightness (twilight factor) decreases geometrically as the exit pupil changes.  Just a slip of the old brain, a senior moment.  There is probably nothing wrong with your Kahles, and your Nikon is not a better scope.  The problem is just with your testing protocol.


Edited by Oldtrader3 - August/15/2009 at 08:35
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/15/2009 at 13:31
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I realize the descrepancies inherent in testing two scopes at two different magnifications. I thought I mentioned that I also tested them at the same magnification and that the Kahles did have better optics. 

I guess my point was that if my findings about magnification being the primary factor instead of "optical quality," why would anyone spend thousands of dollars on a top end scope when they could simply buy a good scope with slightly higher magnification and outperform the high dollar model. Again, this is speaking specifically in reference to low light performance. I know there are other variables that play into scope quality and ultimately into their price. But if a 130 dollar scope can outperform a thousand dollar scope by simply amping up the magnification a little....I guess I just feel foolish for believing I needed the expensive scope to begin with.Whatever
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/15/2009 at 13:41
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Gotta be careful about "magnification being the primary factor instead of "optical quality,"
 
It will not be the primary factor in a cheap poorly made scope.  No good having a bright image that doesn't define anything.
 
To requote Rifledude: a decent 3-9X40 will usually outperform even a high end 1-4X24 or fixed 4X in low light
 
Big emphasis again on decent.
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