One of my hunting buddies and I have had an ongoing argument/discussion. With a variable scope in last light does your eye get more light at more magnification or less. Some people say one some the other. Some say the less magnification the more light is available. Some say of what light that is available it is concentrated on a more concentrated part of the eye. Which is it? Is it a double edged sword? No question that you can see more detail with more magnification, but do you get more light? Anybody got the Facts. Thanks D

the average pupil is ~6-7mm.

if you have a 1" scope that's ~25.4 mm so the light from the bell can make it in

a 42mm front lens in the objective, at 6 power, is
42/6=7
that 7 is in the MM size of the image..

If you go with a larger power, you are putting a SMALLER image into the eye, resulting in a poorer image.


this is simple math,
to have the same size image on the eye, you would have to have a 49mm front for 7x, and 56 for 8.

after that max X, you are reducing light


jeffe

I Think the Europeans are ahead of everyone else on low light/night hunting.
From everything I have read the best scope is one of 8 power with a 56 mm objective lens.
My own testing with fixed 8x56 and a 2.5-10x56 agree. Second best is a 6x42 scope.
Thick reticles work best. I like a "picket post"
Even better is an illuminated reticle.

More magnification does NOT mean more light, quite the opposite in fact. This is one of the old wive's tales of shootingdom, and even Jack O'Connor had it all wrong on this subject.

When you increase the magnification of the scope, you increase what is known as the "twilight factor" of the scope. In other words, as you increase the magnification, the brighter the image will be.

Leupold had Jim Carmichel write an extensive, scientific explaination of this phenomenon about twilight factor, which was printed in Leupold's catalog one year.

In Tanzania, I had the chance to shoot a huge leopard that came to a lion bait early in the morning. It was so early that I could barely see the leopard, and I didn't have time to wait for the morning to get any brighter -- I had to shoot him right now. My rifle wore a Leupold 2.5-8x, and it was set, as usual, at 4x. I had trouble finding an exact spot to aim at, so I cranked up the scope to 8x, increasing the twilight factor, and the entire sight picture changed instantaneously, and I was able to execute the shot perfectly, which was impossible when the scope was at 4x.

You can test this for yourself and see the difference.......

AD

I am quite a sick night pig hunter
I use a Scmidt and Bender 4-12x42 n°1 reticle

I find more comfortable at 5/6 x than at the higher magnifications. Also too much maginfication difficults me to find the animal in low light conditions, so I prefer less mag. and more field of view.

I think that 6x42 scopes are a very good choice for plains game hunting in most of the cases.

I don't understand why americans don't use more european reticles, I find the plex ones too thin for poor light condition and for running shots also. A very good american scope for me is the leupold 6x42 mc4 with reticle n°4, this reticle can be instaled by leupold at 50 or 60 bucks I think.

But I'm in love with german scopes... for me the scope is for the hunting gear what the rod is for the freshwater flyfisherman, you need to buy the best one you can afford and with any spare money buy the rifle/reel/etc

L

Less magnification means more light gathering abiliy as a rule...

quote:

When you increase the magnification of the scope, you increase what is known as the "twilight factor" of the scope. In other words, as you increase the magnification, the brighter the image will be.

This has been my experience as well.
I will also add that I don't think illuminated reticules are as good as most people would like you to believe. They help in dim light to a degree but are not very effective in the dark if using a light and in my experience work against you even at low intensity. I haven't used the dot but some of the fellows who have actually used them say they work if the dot is small.

Boy this sure looks like consensus.NOT, So nobody knows for sure? Looks like this should be a measureable thing. D

quote:

Originally posted by D Hunter:
Boy this sure looks like consensus.NOT, So nobody knows for sure? Looks like this should be a measureable thing. D

I think as long as you do not increase the magnification to the point that the exit pupil diameter is smaller than the pupil of your eye you should not notice a decrease in brightness. This is a function of the objective lens diameter. (This is essentially what Jeffe said above with a bit more detail.)

Borrowed from BoatUS:

Relative Brightness

Relative brightness indicates how well binoculars will perform in dim light, and is the square of the exit pupil diameter. Exit pupil diameter. is the objective lens divided by the magnification. For 7 x 50s, that's 7.14. If the exit pupil diameter is as large or larger than your pupil (about 7mm in darkness), you'll see an image that's almost as bright as the image viewed with the unaided eye. That's why 50mm objective lenses are so popular with boaters. The larger the objective lens diameter the larger the exit pupil diameter and thus the greater the relative brightness. Compare the exit pupil diameters of 8 x 50s (6.25) and 7 x 35s (5).

There is a formula to determine relative brightness:

( Diameter of Objective Lens ) 2
Power

For example, a 7 x 35 binocular would have a relative brightness of: (35/7)2 =25. If the optics are fully coated, the relative brightness is increased by 50% (so in the above example, the relative brightness becomes 37.5.

Edited to add the discussion of "twilight factor" mentioned above copied here from Eagle Optics, which seems to have more to do with resolution than brightness (resolution being your ability to distinguish objects and so obviously as important as brightness, although the question posed here was brightness):

Twilight Factor:
During daylight hours magnification will be the principal factor in image resolution. At night when the eye pupil is dilated, aperture size is the controlling factor. In twilight conditions both of these factors control resolution effectiveness.

Twilight factor compares binocular performance under these conditions. Binoculars with a higher twilight factor will do a better job of resolving images under dim light conditions. To calculate the twilight factor of a binocular:
1) multiply the magnification by the aperture
2) find the square root of this product.

Jeffeoso said it best. Ray et al are also correct. What he's talking about is the "exit pupil." A great reference to that can be found at:

http://www.daviddarling.info/encyclopedia/E/exit_pupil.html

It points out that the exit pupil represents the amount of light that can come through they system, that it is equal to the image of the primary objective (could/should be *aperture*) divided by the magnification. This implies that larger magnifications reduces the image of the lense you're actually seeing. A great thing about the above article is that it describes other related ideas, such as field of view.

HOWEVER, Jeffeoso didn't say one thing right: yup the math is easy (divide aperture by magnification) -- but you really have to draw pictures to figure out WHY that's true. That part is NOT as easy. But you can see a PICTURE of what it looks like and another description at:

http://www.moosegear.com/Includes/info_exit_pupil.html

Charles Helm is accounting for the fact that our eyes don't see as much detail in dark conditions (rod vs. cone densities), so we need larger magnification just to make out what we're seeing, but the sharpness goes down with light -- sort of a tradeoff situation. The geometric avrage (square root of product) tries to account for that tradeoff.

Dan

We were heading back to camp at what can only be called last light when my PH spotted a nice duiker ambling along the edge of a wooded area. I grabbed my .30-06 which has a 4.5 x 14 Leupold. It was set at 14 power and I couldn't see the trees let alone that duiker. I started moving the power down and when I reached 8 power or a little less it was as if someone had suddenly turn the lights on. That duiker must have seen the same damn light because he bolted at that very same instant.

LOW LIGHT, LOW POWER.

Twilight factor is a load of crap. It is a mathmatical formula that doesn't take into account such things as quality of glass and more importantly, lens coatings. If you go only by mathmatics, a $25.00 Bushnell has the same twilight factor as a $1500.00 Zeiss.

When you lower the power, you increase the angle of view. When you raise the power you decrease it. The larger the angle, the greater the light transmission and as a result, a brighter view.

Once the exit pupil is larger than your eye's pupil, decreasing magnification won't help. Same way, larger objectives won't help if the size of the exit pupil is larger than your eye's pupil. The light has to make it into your eye for it to help.

That's one place where lens coatings come in in a big way towards helping improve transmission. Another place that helps is reducing the number of optical elements/surfaces. Each one of those is expensive in loosing transmitted light.

But the idea *behind* "twilight factor" isn't complete garbage. It should be taken with a grain of salt when comparing optical systems, but when it comes to your eye, opening up to lowest magnification may not be your best choice (young-un's eyes will open up to 7mm; older guys only open up to 5mm or so -- some of that extra light transmission won't even get through, while the density of light receptors that work in dim light is lower than full-light color receptors, so you won't see images as sharply -- so magnification *can* help). That's an advantage of a variable -- somewhere in-between might help more than max or min.

Dan

Interesting subject. I'm just not so sure you can get a 'book' answer. Everybody's eyes are different, throw in about 2 dozen types of scopes on top of who knows how many types reticles, powers, etc. What you get is a bunch of different answers, so I'll answer with what I see, and I hunt a lot at night, with quality European glass (Swarovski, 3-12 x 52, Nr 4 w/illuminated dot, which brightness can be turned up or down to nothing):

With ample light: Either moon or snow, any power is like daylight.

Dusk/Dawn: between 6-8 x

Low light/Night: 8 to 12x depending on distance and background.

So there's just too many variables to get a book answer. Maybe it is low power = more light, but I don't find that holds true for all occasions or for my eyes, Waidmannsheil, Dom.