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Originally posted by Silver SlayerThe first number is the power, like in my 12X50 set, its
Thanks for the advice. I don't really the numbers 8x40 for example.
What does each num stand for?
a 12 power. The 50 is how wide the lens in front is, 50 MM or about
two inches. The number of regular binos are 7X50, 7 power and
50 MM lens. That number was chosen because it gives a very
wide field of view because the exit image, the one entering the
eyes, is the same size as mose people's pupils. This gives the
maximum field of view for that lens. If you had a 100 MM lens,
you could go to 14 power and have the same size exit image,
thus giving you the same field of view as the 7X50.
So if you had a 200 MM lenst, you could have a 28 power set
and the field of view would be the same as your 7X50.
So the smaller glasses, say a 7X35, 7 power but a 35 MM lens,
would have a smaller image in your eye and a narrower field of
view than a 7X50.
So ten times both numbers would give you a 70X500, or
what would be essentially two side by side telescopes of 70
power magnification and a lens diameter of 20 inches, a big
binocular indeed! Actually, you can buy dual telescopes with
lenses almost that big so you can have say, 50 power but
with the same field of view as ordinary binoculars. I would love
to have one of those you can be sure, but they are about
4000 bucks so its a bit out of reach.
I mentioned my 20X80 pair I recently acquired. I want to look at
the sun in the daylight, it has solar filters and see stars at night.
Well lo and behold, since christmas, here in Pennsylvania I have
had neither! That sucks. I used to live in Phoenix Arizona and
you go out of town a few miles to get out of the city lights and
you have instant organic planetarium! The skies there were fantastic.
Sigh. Thats why I never made a nice telescope. I even have a
REALLY REAALLY nice mirror, about 9 inches wide, saved from an
old Lithographic semiconductor pattern projector that was being
junked at General Instruments where I used to work in a cleanroom.
Never used it to make a telescope because I have hardly any nights
with good seeing here, mostly cloud cover.
BTW, the entrance image size goes through a 7 mm sized hole in the
eye which is the exit image size on the 7X50 binos.
So to get the maximum field of view, you have to have optics tuned to
have the same exit image size, 7 MM. So if you used a lens that
was 100 MM wide but still used 7 power, the exit image size would be
14 MM and you would have to scan across the image to see it all,
it would not all fit in your eye.
Originally posted by sonhouseWhat do you mean when you say "7 power"?
The first number is the power, like in my 12X50 set, its
a 12 power. The 50 is how wide the lens in front is, 50 MM or about
two inches. The number of regular binos are 7X50, 7 power and
50 MM lens. That number was chosen because it gives a very
wide field of view because the exit image, the one entering the
eyes, is the same size as mose people's pup ...[text shortened]... and you would have to scan across the image to see it all,
it would not all fit in your eye.
Originally posted by kw72ukThats the amount of times its bigger than what you see with your
What do you mean when you say "7 power"?
eyes. So something that would be one tenth of an inch wide to your
eyes would seem to be 7 tenths of an inch wide through the lenses.
There is another term, "area magnification' which is the power
squared. So in that format, a 7 power lens would give an area
magnification of 7 times 7 or 49.
Some cheapo bino manufacturers use area magnification and say,
12 POWER AREA MAGNIFICATION! with big letters. Actually the real
magnification is the square root of 12 which is a lens of 3.4 actual
power magnification!
Originally posted by sonhouseSo does 7 times bigger mean it's as if you were standing 7 times closer?
Thats the amount of times its bigger than what you see with your
eyes. So something that would be one tenth of an inch wide to your
eyes would seem to be 7 tenths of an inch wide through the lenses.
There is another term, "area magnification' which is the power
squared. So in that format, a 7 power lens would give an area
magnification of 7 times 7 or ...[text shortened]... l
magnification is the square root of 12 which is a lens of 3.4 actual
power magnification!
Say the moon was 700,000 miles away (I know it's 220,000-250,000 in reality) - would that mean it was as if you were only 100,000 miles away? Or doesn't it work like that?
Originally posted by Silver SlayerThe first number is the magnification, the second number is the field of view (and, ergo, the lght gathering properties). Don't be fooled by cheap brands boasting large magnification - you probably won't see anything clearly at the high magnification if the field of view is too small.
Thanks for the advice. I don't really the numbers 8x40 for example.
What does each num stand for?
Originally posted by kw72ukYes, exactly.
So does 7 times bigger mean it's as if you were standing 7 times closer?
Say the moon was 700,000 miles away (I know it's 220,000-250,000 in reality) - would that mean it was as if you were only 100,000 miles away? Or doesn't it work like that?
If you google a little, you will find many pages which explain what the numbers mean, give recommendations for different purposes etc. Here's one example: http://www.swift-optics.com/support/faq/binocular
Originally posted by znshoThats where you see those cheapo telescopes that claim
The first number is the magnification, the second number is the field of view (and, ergo, the lght gathering properties). Don't be fooled by cheap brands boasting large magnification - you probably won't see anything clearly at the high magnification if the field of view is too small.
455 POWER! Like totally unrealistic. You would just see a blur.
Just like those stupid camcorder specs that say 800 POWER
DIGITAL MAGNIFICATION! and 3 power optical! So that last pixel
gets the size of the whole screen🙂
So with telescopes, say you have a 4 incher, 100 MM, you get a
full field of view, that is, an exit pupil size of 7 MM with just 14 power.
a far cry from the 300 or 400 power they try to foist off an
unsuspecting public, like mom buying a kids first scope, the
actual scope isn't even the most important part. In a telescope,
the most important part is the MOUNT.
Try holding a 50 power scope in your hands and you will see
what I mean. You have to have a good steady tripod, not those
spindly pieces of crap you get at K mart or Walmart.
You can take most any of the cheapos and put it on a good steady
tripod and get decent images if you stick to 40 or 50 power.
So you have a 100 MM lens and you use 28 power, now the image
you see is half the size of your pupil so its starting to look like
a black wall with a circle in it.
Go to 56 power and the circle you actually see is only one fourth the
size of the black wall you are seeing in your eyes. So the more
magnification, the smaller the spot image looks, so you can
see if you have even perfect optics on a ten thousand dollar scope,
at 400 power, the size of the image will be around the size of
a fly at 3 feet!