Possibly naive question about magnification

[marcdearn]

If I put a 20mm eyepiece into my scope (650mm f/l) I get a magnification of 32.5X

Just say, for instance, Jupiter looks 2 mm across

If I then put a 5mm ep in I get 130X four times the 20mm ep but Jupiter doesn't look 8mm across

Am I missing something???????

[perrin6]

It will be 4 times bigger in the high power - perhaps the 'apparent' field of view of the 5mm eyepiece is wider than the 20mm, making jupiter look smaller than your eye expects it to. An old fashioned term for magnification is 'diameters' ie the 130X will make Jupiter look 130 diameters bigger than it does with the naked eye.

[perrin6]

It amazes me that jupiter appears about one 40th the size of the full moon and so to see the planet as big as the full moon looks to the naked eye requires 40 X magnification. So at 130X Jupiter looks about 3 times the size of the full moon ! Seems unbelievable but it's true !

(the moon is about 30 arc minutes (1800 secs) , Jupiter a bit less than 1 arc minute (between 40-50 arcseconds mostly).

[moonraker1234]

Hi

Depends on the atmospheric conditions prevailing that night too. Greater magnification means less clarity generally, unless you have a powerful telescope to use it in!

[marcdearn]

I must be doing something wrong or have a funny brain or something then

With a 20mm (32.5x)eyepiece Joop looks like a "o"

with a 6.3( over 100x) mm Ep it looks like O

4 times the size of a full moon!!!!

No chance

[perrin6]

re: 40X magnifies Jupe to full moon size:-

I know it's hard to believe - the moon looks different sizes according to what objects or lack of objects are near it. The classic case is when the moon is low down it looks huge because we are seeing ground objects near it and the way the eye judges size is by comparisons - Above a nearby house the moon looks smaller than when it is above a distant house because the eye judges the moon's size by comparing it with a familiar object of known size (the house). When high up the moon tends to appear smaller as there are no objects to compare it to. Jupiter's size in the eyepiece is hard to judge as there is no familiar object to compare it to.

Just a link to a site to show at least one person agrees with me ! :-

http://www.oneminuteastronomer.com/page/5/