7x magnification, because more makes 'em jittery and hard to aim. You pretty much need a tripod past 10x, and 7-10 is a good compromise with enough field of view to quickly find an object against an empty sky.
Less than 7 doesn't really show you much more than you can see with the naked eye.
50mm objective lens gives you good light-gathering power. Which you don't need for a day launch or birdwatching, but it's important for night stuff. You could get 7x20's (opera glasses) and be just fine, but the 50's aren't that much more expensive and they'll apply to a lot more situations.
I think the main useful thing about 7x50 is that 50mm (diameter of the input lens) divided by 7 (magnification) is just over 7mm, which would be the diameter of the image in the output lens and is also approximately the maximum diameter of your pupil, meaning that the field of view is never smaller than your pupil and you can always see properly. If the exit diameter is smaller than your pupil then it is like you are peering through a small hole.
If you know you are going to be viewing in bright daylight then your pupils will be smaller and you can use smaller lenses like 7x35 or so or for extra magnification you could use 10x40 but with higher magnification you get more jitter anyway.
In low light conditions, if you compare the field of view through some 7x50's vs straight gazing, you will notice that the scene seems brighter as well as closer. That is because you are receiving light from 50mm dia onto your retina vs light from 7mm diameter.
and thats enough about optics, back to the space rockets.
7x50s are traditional marine/astronomical binoculars. They are about as big as you can get, without getting too heavy to comfortably hold. I use mine to stargaze/satellite gaze fairly regularly.
Although, for daytime observation, 7x35s should be just fine.
Comments
Don't forget a good pair of 7x50 binoculars.
I know nothing about binoculars. Why 7x50 specifically?
7x magnification, because more makes 'em jittery and hard to aim. You pretty much need a tripod past 10x, and 7-10 is a good compromise with enough field of view to quickly find an object against an empty sky.
Less than 7 doesn't really show you much more than you can see with the naked eye.
50mm objective lens gives you good light-gathering power. Which you don't need for a day launch or birdwatching, but it's important for night stuff. You could get 7x20's (opera glasses) and be just fine, but the 50's aren't that much more expensive and they'll apply to a lot more situations.
I think the main useful thing about 7x50 is that 50mm (diameter of the input lens) divided by 7 (magnification) is just over 7mm, which would be the diameter of the image in the output lens and is also approximately the maximum diameter of your pupil, meaning that the field of view is never smaller than your pupil and you can always see properly. If the exit diameter is smaller than your pupil then it is like you are peering through a small hole.
If you know you are going to be viewing in bright daylight then your pupils will be smaller and you can use smaller lenses like 7x35 or so or for extra magnification you could use 10x40 but with higher magnification you get more jitter anyway.
In low light conditions, if you compare the field of view through some 7x50's vs straight gazing, you will notice that the scene seems brighter as well as closer. That is because you are receiving light from 50mm dia onto your retina vs light from 7mm diameter.
and thats enough about optics, back to the space rockets.
7x50s are traditional marine/astronomical binoculars. They are about as big as you can get, without getting too heavy to comfortably hold. I use mine to stargaze/satellite gaze fairly regularly.
Although, for daytime observation, 7x35s should be just fine.
Binoculars with image stabilization can render a still field at 15x magnification without being much heavier than those without IS. I bought these ten years ago: worth the $$$ https://www.usa.canon.com/internet/portal/us/home/products/d...