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mati1979
Guest
Hi, this is my ask.
What benefits have a tube 30mm ?
tx
What benefits have a tube 30mm ?
tx
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Louis Boyd
Guest
The is no reason in optical theory that a 30mm tube should give a brighter image than a 1" tube. Apparent image brightness is limited by the size of a scopes exit pupil relative to the size of the eye's entrance pupil and the losses from reflections and absorption by the various optical elements. The ratio of light in the image to scattered light in the image (usually called contrast) is more important to a "clear" image than it's actual brightness.
Few scopes actually have specifications for contrast.
The two main reasons for a larger tube are that a tubes rigidity (not necessarily strength) increases with the cube of it's diameter and it gives more room for a larger adjustment range of the erector tube usually resulting in a larger range of adjustment in elevation and windage.
Few scopes actually have specifications for contrast.
The two main reasons for a larger tube are that a tubes rigidity (not necessarily strength) increases with the cube of it's diameter and it gives more room for a larger adjustment range of the erector tube usually resulting in a larger range of adjustment in elevation and windage.
tx
Brightness of an object, like a target paper, depends on the magnification you are using in your scope. As the magnification of a scope increases, the light that was collected is spread over a larger area and the surface brightness of the object you see (as it gets bigger) drops. Since the area of the objective lens is determined by the radius of the object squared, the brightness drops as the magnification squared. Conversely as you reduce the magnification the image gets brighter. This effect is easy to see in a telescope with a zoom eyepiece.
The key to understanding telescope image brightness is to recognize that the brightest image of a object happens at the minimum magnification, the one at which the size of the exit pupil is equal to the size of the eye pupil of the observer, as already mentioned. During daytime the eye pupil is relative small compared with the diameter in a dark room for instance. Eye pupil diameter is not fixed.
The exit pupil is the point of light coming out of the eyepiece, and its size is equal to the diameter of the objective divided by the magnification of the scope. Make yourself a scale in mm on paper and if you can increase the maginfication of say a spotting scope move the paper back and forth till the exit pupil is focused sharply on the paper then measure it and you'll see what I mean. Image brightness is rooted in basic optics.
Brightness of an object, like a target paper, depends on the magnification you are using in your scope. As the magnification of a scope increases, the light that was collected is spread over a larger area and the surface brightness of the object you see (as it gets bigger) drops. Since the area of the objective lens is determined by the radius of the object squared, the brightness drops as the magnification squared. Conversely as you reduce the magnification the image gets brighter. This effect is easy to see in a telescope with a zoom eyepiece.
The key to understanding telescope image brightness is to recognize that the brightest image of a object happens at the minimum magnification, the one at which the size of the exit pupil is equal to the size of the eye pupil of the observer, as already mentioned. During daytime the eye pupil is relative small compared with the diameter in a dark room for instance. Eye pupil diameter is not fixed.
The exit pupil is the point of light coming out of the eyepiece, and its size is equal to the diameter of the objective divided by the magnification of the scope. Make yourself a scale in mm on paper and if you can increase the maginfication of say a spotting scope move the paper back and forth till the exit pupil is focused sharply on the paper then measure it and you'll see what I mean. Image brightness is rooted in basic optics.
jackie schmidt
New member
Tube
I have looked through a 35x Competition Series Leupold, (30mm tube), and the originol 36x BR Series, (1 inch tube), and it would take a pretty astute eye to ascertain any appreciable difference in the "brightness", or anything else, forthat matter.
Of course, those 36x Leupolds are known for their top quality glass.......jackie
I have looked through a 35x Competition Series Leupold, (30mm tube), and the originol 36x BR Series, (1 inch tube), and it would take a pretty astute eye to ascertain any appreciable difference in the "brightness", or anything else, forthat matter.
Of course, those 36x Leupolds are known for their top quality glass.......jackie
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Bill Ohio
Guest
All other things equal, the answer is "no".
Generally the bigger tube will enable a more robust erector assembly, or greater internal adjustment range. Tube diameter does not affect "brightness".
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buffalobob
Guest
Are the exit stop and the exit pupil one and the same for a rifle scope?
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Bill Ohio
Guest
Do you mean aperture stop? I don't know what an exit stop is...
Exit pupil, i.e. the image transmitted to the ocular lens, is derived by dividing objective lens diameter by magnification. It's generally thought that an exit pupil larger than 7mm diameter is unnecessary and not advantageous, because the human eye in a healthy young person can dilate to about 7mm maximum.
A smaller exit pupil means a dimmer image. A 36x40 scope, i.e. 36 power by 40mm objective lens diameter, will have an exit pupil of just about 1.1mm. That's almost as dim as the schmuck currently residing at 1600 Pennsylvania Ave.
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buffalobob
Guest
Correct !
Is the APERTURE stop the exit pupil on a rifle scope?
Do you know the answer ?
Is the APERTURE stop the exit pupil on a rifle scope?
Do you know the answer ?
Not the same.
An aperture stop is the opening which limits the amount of light which passes through an optical system, as in an adjustable camera lens. Reducing the size of the aperture reduces light thruput and increases depth of field. Aperture stops are used on cheap optics to counter the poor quality of the objective lens. The exit pupil is the diameter of the light cone exiting the eyepiece and is a functionof lens diameter in mm divided by the magnification of the system. Typically the daytime diameter of your eye pupil is 2-3mm so an exit pupil of the scope greater than that is not fully captured by the eye.
An aperture stop is the opening which limits the amount of light which passes through an optical system, as in an adjustable camera lens. Reducing the size of the aperture reduces light thruput and increases depth of field. Aperture stops are used on cheap optics to counter the poor quality of the objective lens. The exit pupil is the diameter of the light cone exiting the eyepiece and is a functionof lens diameter in mm divided by the magnification of the system. Typically the daytime diameter of your eye pupil is 2-3mm so an exit pupil of the scope greater than that is not fully captured by the eye.
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buffalobob
Guest
All of that is fine but it does not answer the question.
Where and what is the aperture stop on a variable power rifle scope?
Unless
you are dealing with a cheap ChiCom piece of junk there should be no aperture stop in a quality spotting scope. Take the eyepiece out and look up toward the objective end. If there is one, you will see it not too far behind the front lens(objective). Don't confuse light baffles along the length of the tube with an aperture stop. These are put in to control reflected light. In quality scopes you'll see the inside painted flat black and possibly rippled, again to capture and diffuse reflected light to help image quality. An aperture stop and the exit pupil are different things. If you have a 2" front lens and a 1.5 inch aperstop behind it you have effectively a 1.5 inch lens. Lens diameter/magnification = exit pupil diameter in the same units as you input the lens diameter.
you are dealing with a cheap ChiCom piece of junk there should be no aperture stop in a quality spotting scope. Take the eyepiece out and look up toward the objective end. If there is one, you will see it not too far behind the front lens(objective). Don't confuse light baffles along the length of the tube with an aperture stop. These are put in to control reflected light. In quality scopes you'll see the inside painted flat black and possibly rippled, again to capture and diffuse reflected light to help image quality. An aperture stop and the exit pupil are different things. If you have a 2" front lens and a 1.5 inch aperstop behind it you have effectively a 1.5 inch lens. Lens diameter/magnification = exit pupil diameter in the same units as you input the lens diameter.
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