B How Does Telescope Magnification Differ from Resolving Power?

[roineust]

In order to get a very general sense of the scale of order of magnification power of telescopes:
If a hobby telescope i have, has a magnification power of X100, what would be the magnification power in terms of X, of the following:
1. Hubble
2. James Webb
3. Gravitational lensing

 

[phinds]

In order to get a very general sense of the scale of order of magnification power of telescopes:
If a hobby telescope i have, has a magnification power of X100, what would be the magnification power in X of the following:
1. Hubble
2. James Webb
3. Gravitational lensing

Have you done any research on this? What have you found? Seems like it should be readily available information, at least for the first two. I think the last one is variable.

 

[roineust]

I had problems to find the answer via Google in terms of zoom X. Could not understand well enough the math and physics of 'magnification' in wiki in order to conclude that way, so tried to estimate according to random data and got the impression, that James Webb would be in the order of 10^6 in terms of X. But i am not sure this estimation is correct and anyway, most interesting to me is to find out if gravitational lensing in general, is stronger than James Webb, in terms of X and if it is, are we talking a magnitude of order and if so, how many magnitudes of order? Say we relate separately to micro, medium and strong gravitational lensing? I am looking only for the general orders of magnitude.

 

[phinds]

As I understand it the magnification of gravitational lensing is approximately zero. It's just a matter of light from a very distant object bending around a less distant object. Since the light is repeated, I would think there is SOME magnification but very little and I suspect the distortion more than obliterates any magnification advantage.

 

[russ_watters]

I had problems to find the answer via Google in terms of zoom X. Could not understand well enough the math and physics of 'magnification' in wiki in order to conclude that way, so tried to estimate according to random data and got the impression, that James Webb would be in the order of 10^6 in terms of X. But i am not sure this estimation is correct...

The theory here is really easy; it's just angles. Draw a triangle with you at one end and Jupiter at the other and use its distance and diameter to find the angle it subtends. Then apply that to a magnified image.

The practical difficulty is that for cameras, how you view the image is what ultimately determines the magnification. So find a Hubble picture of Jupiter, get a tape measure (seriously) and measure its diameter on your computer screen and distance from which you are viewing it, and calculate the angle again. Then divide the second by the first to find the magnification.

The basic answer to your question though is that for small objects like Jupiter you'll find the useful magnification of a telescope like Hubble to be maybe 10x that of a typical hobby telescope. Some really good amateurs can reduce that to maybe 4:1.

For larger objects like nearby nebulae or galaxies (or the moon/sun), the typical display magnification is the same because it is restricted by viewing considerations -- the size of the screen.

 

[roineust]

The theory here is really easy; it's just angles. Draw a triangle with you at one end and Jupiter at the other and use its distance and diameter to find the angle it subtends. Then apply that to a magnified image.

The practical difficulty is that for cameras, how you view the image is what ultimately determines the magnification. So find a Hubble picture of Jupiter, get a tape measure (seriously) and measure its diameter on your computer screen and distance from which you are viewing it, and calculate the angle again. Then divide the second by the first to find the magnification.

The basic answer to your question though is that for small objects like Jupiter you'll find the useful magnification of a telescope like Hubble to be maybe 10x that of a typical hobby telescope. Some really good amateurs can reduce that to maybe 4:1.

For larger objects like nearby nebulae or galaxies (or the moon/sun), the typical display magnification is the same because it is restricted by viewing considerations -- the size of the screen.

What about gravitational lensing? Do you agree that it is ~X0 and if it is, why is it so?

 

[russ_watters]

What about gravitational lensing? Do you agree that it is ~X0 and if it is, why is it so?

I don't think it's a lot, but I'm not sure. A quick look at the wiki page tells me it's probably buried in there somewhere, but I don't have time to dig right now.

 

[roineust]

The following article, which i found just now, if i understand correctly, would suggest that in some cases, gravitational lensing could multiply the zoom by X10. Here is a quote: "The discovery was made using the lensing power of the mammoth galaxy cluster Abell 2744, nicknamed Pandora’s Cluster, which produced three magnified images of the same, faint galaxy. Each magnified image makes the galaxy appear 10 times larger and brighter than it would look without the zooming qualities of the cluster. "

Would the following statement not be considered absolutely incorrect, accounting all the above:

A hobby telescope zooms in the order of 100X, Hubble zooms in the order of 10 times stronger, so it would zoom in the order of 1,000X, James Webb zooms in the order of 10 times stronger, so it would zoom in the order of 10,000X, James Webb, coupled by gravitational lensing, of type such as Abell 2744, zooms in the order of 10 times stronger, so they would zoom 100,000X ??

 

[davenn]

...snip......
A hobby telescope zooms in the order of 100X, Hubble zooms in the order of 10 times stronger, so it would zoom in the order of 1,000X, James Webb zooms in the order of 10 times stronger, so it would zoom in the order of 10,000X, James Webb, coupled by gravitational lensing, of type such as Abell 2744, zooms in the order of 10 times stronger, so they would zoom 100,000X ??

You are missing some important factors in your thoughts.

Magnification isn't the be all and end all of a good telescope, be it your home one or one on a mountain or in orbit.
1) Lens or mirror diameter is the most important as it determines how much light is collected ... bigger is better ! therefore the collection of more light = the ability to see fainter and more distant objects
2) Resolution
3) and least important is magnification

Now talking of magnification ...
You cannot compare magnification of the Hubble or most other science observatory telescopes to your telescope because those telescopes don't use eyepieces, that is, they are for photographic imaging, instead of an eyepiece there is a camera. In fact, the magnification factor of these big telescopes like Keck, Hubble etc
is not even mentioned in most science articles.

We will consider that you haven't told us anything about this scope of yours that supposedly has a mag capability of 100x ... ( this statement is meaningless without more information about your scope.
Now magnification of a telescope is worked out very easily, it is the Focal Length of the objective lens divided by the focal length of the eyepiece. eg.

So, let's say your scope has a focal length of 300mm ( it will be written on the label on your scope) and you use a 40mm eyepiece ( will be written on the eyepiece)
therefore the magnification = 300 / 40 = 7.5x.
you might also have a 15mm eyepiece so again the magnification now is

300 / 15 = 20x

From that you can see that different eyepieces will provide different magnifications for a given telescope.

Also note, there is a HUGE difference between maximum magnification of your scope ( any scope) and the
maximum USEABLE magnification ( which will be significantly less). Maximum useable magnification is where
you can still get a sharp and clear view. Atmospheric conditions also have a huge bearing on this which is one big reason why Hubble was placed in orbit at that time.
That feature of Hubble is now pretty much overcome these days with ground based scopes that use adaptive optics that can produce results comparable to those from the Hubble and the ground based scopes are now 3 to 10 times the diameter of the Hubble's 2.4 metre diameter mirror.


I have 3 scopes for night-time use ... pictures of them can be seen in other threads in this astro forum section.

A Celestron CPC925
Focal length of 2350mm, 2350 / 25mm eyepiece = 94 x magnification ( have various eyepieces)
I could stick a 6mm eyepiece into this scope and get 392 x magnification but I truly doubt that the seeing would be any good.

A Skywatcher EVO120
Focal length of 1000mm, 1000 / 25mm eyepiece = 40 x magnification

and my latest scope
A Skywatcher ESPRIT 100 ED
Focal length of 550mm, 550 / 25mm eyepiece = 22 x magnificationI really hope you are now starting to see that magnification is the least important of the features of a telescope. Light gathering ability and optical performance are so much more important.Here's a couple of good pages with all the info on working out telescope magnification etc ...

http://rocketmime.com/astronomy/Telescope/Magnification.html
https://cosmicpursuits.com/943/telescopes-explained/
https://user.xmission.com/~alanne/AstronomyFormulas.html
http://www.pgccphy.net/ref/hst-optics.pdfregards
Dave

 

[sophiecentaur]

In order to get a very general sense of the scale of order of magnification power of telescopes:
If a hobby telescope i have, has a magnification power of X100, what would be the magnification power in terms of X, of the following:
1. Hubble
2. James Webb
3. Gravitational lensing

This question cannot be answered usefully, in those terms. We should look at what really counts in telescope performance.
Despite what the adverts for cheap (toy) telescopes tell you, the Magnifying Power of a telescope is of little interest in most cases. Also, Magnifying Power (Angular Magnification) is only of interest for visual use. Many celestial objects are too large (in angular size) to fit into the visual field for a high magnification. None of the large telescopes are used for 'stargazing' and they do not use Eyepieces at all so the angular magnification formula just doesn't apply . Resolving power is what counts.
In practical terms, there is little point in producing magnifications of Hundreds of Times if the aperture and quality of the main optical element (mirror or objective lens) cannot produce a recognisable image. When used for serious amateur astrophotography ( which is the only way to obtain the images of coloured nebulae and sharp images of Saturn's Rings that we drool over) there is no eyepiece at all and the image is projected directly onto a sensor array. Many images are taken and stacked together for the impressive results.

1. 2. and 3. are useful because of their size and light gathering power and also the resolving power of a wide aperture, not because of any 'angular magnification'

Don't get me wrong about the visual, personal astronomy experience. Some fantastic views can be had from many back gardens and with low magnifications but you have to be selective. A large blurry image of Saturn, viewed at maximum obtainable magnification will probably be nothing like as impressive as with a more modest eyepiece that makes the planet look smaller and sharper. Under moderate magnification you can also see some stunning objects like the Pleiades cluster of stars and the Andromeda Galaxy ( which is three degrees in angular width)
See this link about angular resolution of telescopes.