Milton Wilcox R.I.P
Quote:P.S does anyone know if the Rothenberger 2 pound claw -hammer is nitrogen purged ?
Quote: The smaller and lighter a binocular is the less magnification it should have in my oppinion- because it's harder to hold a light pair still. But as the objective lens keeps getting heavier and heavier it becomes easier and easier to hold it steady.
Quote:Hey Daniel,First, I didn't say that exit pupil and magnification don't relate. They very much do. For a GIVEN objective diameter, the same magnification will always give the same exit pupil. Change one, and you change the other. I'm just saying that strictly speaking, exit pupil and magnification aren't the same thing. They have their own definitions. Magnification refers to ratio of light path angles coming from the objective vs. the eyepiece, while exit pupil refers to the diameter of the image when all the parallel rays of light coming from the EP converge. So, they're directly related, but they describe different things.Just to clarify...I'm not saying that a higher power EP gathers light from a narrow portion of the sky than a lower power EP. I mean, yes, this IS true, but what I was talking about specifically is that a higher power EP will collect fewer rays of light...even from a given object.Consider this figure I put together. At top, 5 on-axis rays of light coming from a single object, e.g., the center of Saturn. All 5 rays pass through the EP lens. At bottom, the lens is high-power (shorter focal length, smaller lens diameter). Not all of the rays pass through. So, with the higher magnification lens, the object is dimmer. So, I'm talking about less light passing through...not just in terms of less-sky, but in terms of fewer light rays from the same piece of sky.Is this right? Ed?
Quote:The ray diagrams are wrong. The exit pupil is an image of the entire aperture. If you will, it is the effective aperture of the system. The image gets dimmer with magnification because the effective focal length of the system is increasing, but the aperture is not, hence, larger effective focal ratio and dark image.
Quote:What is "image brightness"? Can anyone give a clear definition?
Quote:jmoore, I suppose it's not surprising that this works differently for different people. For myself, my hands are extreamly shaky; people comment on this all the time. I'm always asked if I'm nervus or if somethings wrong because I *CANNOT* hold my hands still out in front of me. But when I add several pounds it's completely eleminated.
Quote:That's a good explanation for it edcannon. But that would mean that people should be able to hold binoculars with twice the magnification just as steady as others as long as the weight is twice as much! So a 2 lb 10x50 should be just as hard to hold steady as a 4lb 20x100! This is of course not including the larger motions, but there's a reason I'm not including it.
Quote:Have you ever noticed that most people who don't like high magnifications also have steady hands? No really, have you- because I have no idea, but just assume this is true. That would mean that they've become used to steadier images and so they notice the increase in the big movements. But someone who has shaky hands is used to the amount of shake, and so trading one type for another doesn't really bother them. I think this makes sense.
Quote:Given equal exit pupils it is impossible to determine which binocular will gather and use more light withour more info.
Quote:... in order for them to be equal there would need to be exactly 4x as many stars with exactly the same brightness in order for them to be equal- and we all know this isn't going to happen. So it depends on what part of the sky you are looking at with each bino. Also I suppose the sky has different levels of brightness as well- and galaxys might be in the field of view of one and not in the other.
Quote:In order to determine the brightness of a view through a binocular you not only need to know the exit pupil size, but also the AFoV. A binocular with a larger exit pupil doesn't *always* give more light to the observer. Although the sky and anything else simliar will be brighter.
Quote:if you took a photometer and mesueared the amount of light coming out of the optical tube you would measure more light(doesn't matter what kind- could be useless like sky glow) than any other size optical tube as long as the exit pupil was the same size and the AFoV was larger in size.