magnification versus light gathering

[woofert]

While at the range today, a discussion about magnification versus light gathering came up.

My friend’s deer hunting set up is a  Bisley Blackhawk Hunter in 44 Mag with a 1” Millet red dot. His mind set is that the red dot is better in low light conditions during dawn or dusk and that any scope, regardless of the magnification, doesn’t have enough light gathering capabilities.

I have a 14” barreled Contender in 44 Mag with a Bushnell Trophy 2 x 6. My mind set is that I have the 2 power for low light conditions and close in shots, 4 power for just about everything else and 6 power for longer shots.

I don’t think it’s a matter of who’s wrong or who’s right but what works for you.

But I would like to hear from hunters who have used both a red dot and a scope, have any of you not been able to take a shot due to not being able to see through your scope in low light? Is a red dot really better in low light than a low power scope?

One question that came up is if a variable scope set at 2 power able to gather as much light as a fixed 2 power scope.

Another question is why do I always see a red "coma" instead of a red dot, dosn't matter what red dot I look throuth, I don't see a dot.

thanks,
Woofert

[Graybeard]

Scopes or for that matter any optical instrument DO NOT GATHER LIGHT.

Plain and simply they TRANSMIT LIGHT and none of them not even the best transmit 100% of it so clearly they cannot magnify it as some seem to think or gather it up and in any way cause more to come out than went in.

Some seem brighter to our eyes due to a larger exit pupil but in reality all that larger exit pupil does if over about 5mm is make it easier to see the image than if the exit pupil is smaller. Higher magnification seems to make it easier to see things in the dark but the ONLY thing that makes it brighter is a larger objective and larger internal lens and higher quality glass and coatings.

And illuminated red dot if not too bright can allow shooting in lower light than a scope but if not illuminated then most likely the scope would win out.

[spruce]

As GB said scopes merely transmit light - the best ones somewhere around 97% or maybe slightly more of the available light.  Large objective lenses are mostly a marketing ploy - they do more to sell scopes than they do to increase the brightness of the image.  A GOOD scope with a 32mm objective lens will be much brighter than a cheap scope with a 50mm obj. lens - it's all about the quality of the glass and quality multi-coatings.

One advantage of a scope over a red dot sight is that more magnification makes the target appear closer which allows you to see more detail.  Just as if you were out walking at night and saw an indistinct form - if you walk closer to it you can then see it clearly enough to identify what it is.

[charles p]

At the lowest time of light in the afternoon, I have often dialed my variable scopes to their highest magnifications then start lowering them until light-image quality appears to stabilize.  Normally this occurs around 6-7X for maximum magnification. 

About 25 years ago I shot a deer at about 200 yds, heard the bullet hit the deer, and walked across the field to recover it.  As I was going across the field my mind started playing tricks with me and I became fearful that what I shot might not have been a deer.  Off course it was a deer, but the terror that ran through my mind taught me a useful safety lesson.

[blind ear]

The dot appearing as a comma could be from your eye muscles. When you tilt your head to the side your muscles try to twist the eye to bring it back level. This can cause a warp in the lens. This could be the problem. An optomitrist once told me he thought many children develope astigmatism while young is school by resting thier heads on thier hands while in class. Doing this day after day, year after year developes a permanant wrinkle in the lens. I have a double astigmatism, In school I would rest my head flat on my palm or against my fist, two positions. I don't know, Just possibilities.
eddie

[ShadowMover]

I can't address the red dot versus 'coma', but I would suggest you have somebody else look through the scope to see if they see the same thing. Try looking through a similar scope and see if yours is out of adjustment.

As to 'light gathering' and magnification, there is a mathematical relation between them. It's true the scope just 'transmits' some of the light. It only takes light that comes in through the front lens and projects it into an image that floats in front of the eyepiece. This 'virtual image' is then seen through the final magnifying eyepiece and projected onto your retina.

The bigger the front lens (objective lens) the more light can come in to make the image. If you go from a 1" diameter objective lens to a 2" lens you will have 4 times the light gathering power (or transmitting). This isn't obvious until you figure the area of the lens goes up with the square of the change. So a 30 mm lens compared to a 25 mm lens would be 30/25= 1.2 and 1.2x1.2=1.44 times as much light.  This is why big front lens are good in low light.

Now for the other end. When you take the light transmitted or gathered by the objective lens and make an image, it can't be any brighter than when it came in the front. If your eyepiece didn't magnify it it we'll call that 1x power. If you magnify it 2x then the size of the image is twice as big in every direction, so the area of the image is 2x2 or 4 times as big. The brightness is now 1/4 of what it was. The image only gets dimmer and darker as the power goes up. 3 power is 1/9 as bright 4 power is 1/16 as bright.

This isn't always a problem in bright daylight, as the image is still bright. The problem is at dawn and dusk when the light is minimal.  It is possible to increase the front  objective lens by a certain amount to balance this dimming, which leads to bigger, bulkier and more expensive scopes.

As to coatings and other advances in optics, they only stop losses and don't really add anything to the amount of light coming in. They are good, but don't change the dimming involved in the magnification.

[SHOOTALL]

The quality of materials used do affect the out come no doubt . The largest the human iris can get is 7mm so a scope with a bigger exit pupil is of no use , To caculate the exit pupil divide the power into the objective lens size , 8X40 would give you an EP of 5 , an 8X56 would Give EP of 7 the limit of the iris

[blind ear]

Woofert, what do you mean by "coma" ? eddie

[woofert]

Woofert, what do you mean by "coma" ? eddie

thats what it looks like to me a thick, bright red "," or like a bright red "cheeto" (baked not fried), not a round dot, come to think of it, I've looked at a lot of red dots sights and have never seen a "dot".

My freind with the red dot on his Bisley Blackhawk says that it is a perfectly round dot, but I don't see it that way. Maybe 30+ years of welding has had a deprimental effect on my eye sight.

woofert

[blind ear]

I would tell my eye doctor about it. Might correct it with a lens and help all your shooting.

[SHOOTALL]

Woofert , been welding /fitting since 1972.
get checked for cataracts (sp) bright light can cause them . Easy fix now days most of the time .