Magnification & what you see

[Cornflake]

Excuse the ignorance of the question but is there a magnification that you need to see various things ie for a good view of Jupiter you need 200x or for nebula you need 70x.

I've just come back to the hobby after many years and am having to relearn alot of this stuff.

Thanks.

Chris

[nephilim]

I'm fairly new to this but as far as I know and from experience with observing jupiter a lower magnification can sometimes be better than a higher.

[knobby]

No real rule for me, I just go as high as I can until detail starts to diminish. Some nights seeing is better than others so you can use more mag. Also scope cooling helps.

[TonyD]

Hi Chris,

Magnification is not really the key here - it is all to do with the telecsope's focal length and aperture (the diameter of the lens at the front of the telescope - it's light-gathering potential).

In order to see images of optimum quality you need to ensure that the eyepiece (EP) is right for the rest of your setup. A smaller crisp image can contain more detail (and satisfaction) than a blurry diffuse image which will not provide any more information to your eyes. Imagine a small thumbnail of a computer picture. If you enlarge the thumbnail itself (rather than using it as a link to display a much higher resolution version) the result is very difficult to make out - even if the thumbnail itself looked sharp and detailed!

What are the details of the telescope you are planning on using?

Tony

[Cornflake]

Tony - The reason for the question is that I've had 1 night with my new scope and caught Jupiter and 4 moons but they were dots of various sizes with no detail in Jupiter. I've got a Meade LT8 but only the 26mm EP that came with it which if my maths is right gives a mag of 77x. I asked the question so that I could work out what EP would give my the mag to see some detail in Jupiter and hopefully Saturn later in the year.

Chris

[Moonshane]

before you start you need to cool down the scope for a period of time - I think your scope is a closed tube design so perhaps as much as two hours if going from warm house to cold garden.

at 77x you should be able to see good detail on Jupiter but I tend to use 120-200x depending on conditions.

I'm with others - use the magnification that gives the most pleasing view; this is often a little lower than you'd think, especially for things like galaxies and clusters as you see them in their context against a background.

[Qualia]

Taking the caveats raised raised by Moonshane into account, good seeing conditions override problems with LP, and assuming collimation is spot on, you'll also find that on average, Jupiter doesn't really need much more - or can take much more - than about 140x to 160x.

A 4" frac from a light polluted city, for example, can make out the north and south equatorial and temperate belts, great red spot, and the north and south polar regions. If you stick with Jupiter, gradually, after 15 minutes or so, it starts to reveal more and more subtle markings in the north and south temperate zones and larger markings in the north and south tropical zones. The entire image in the eyepiece is really no bigger than a large pea.

Another thing of great help is to observe Jupiter as much as possible on your different sessions and train your eye by sketching it whenever possible. The more time you spend with Jupiter in your eyepiece, the more skilled you get at tweaking out subtler, fainter features. There are folk who argue that filters don't help and others who suggest they do. General advice suggests that Wratten numbers 8#, 11#, 82a#, 80a# will do the business. I use a #80 and it is extremely helpful on occasions.

By way of example, here's a sketch I made the other night in the city. It's not a show-piece, but I hope it gives you some idea of what is being observed at about 140x with a little 4" in the city. I spent about thirty minutes with Jupiter before picking up the pencil and the entire thing took no longer than 15 minutes:

Hope this helps

[acey]

Things need to be big enough for the eye to resolve them. Jupiter with the naked-eye looks like a star because we can't resolve its tiny disc. Magnify it in binoculars and the image is large enough that the disc-shape should be apparent. But the cloud belts will still be too small to make out: a magnification of about 30 should be enough to show at least one of them, assuming that the instrument is of good quality and isn't scattering too much light (in which case you just see a white blob).

How high you can go depends on the stability of the atmosphere, the quality of the instrument, and the state of your own eye. Assuming steady atmosphere and perfect optics, the limiting factor is the size of the disc of light coming out of the eyepiece (exit pupil = aperture/magnification). If this is less than a millimetre or so then diffraction in the eye tends to dominate, making higher magnification redundant. The common rule of thumb for minimum exit pupil is 1/50th inch (0.5mm), equivalent to saying that the highest useable magnification is 50 times aperture in inches. But everyone's eye is different, the atmosphere is never perfectly stable, and optics are never perfect. You just start low, work up, and stop when there is no more to be gained.

How big does Jupiter look through a telescope? To say it looks like a pea is a bit meaningless if we don't know how far away the pea is. Jupiter can be magnified to the same apparent size as the full moon seen with the naked eye. A full moon near the horizon looks big, one overhead looks small, though both are the same angular size. Looking through a telescope, our eye is apt to focus for near vision, as if we were looking at something small and close. Also we don't have distance indicators such as horizon objects (which contribute to making a low full moon seem large). So we are apt to see Jupiter as tiny. Concentrating on detail rather than size is one way of counteracting this effect, another is to try and let the eye relax and focus at infinity - though with some eyes this may give a poorer view. Experience is usually enough to make the viewer realise that even in a "pea sized" planet you can see a great deal.

With deep-sky objects (nebulae, galaxies etc) there is the complication that increasing magnification will lower the surface brightness of the image, and also of the sky (i.e. the background gets darker). Hence a certain amount of magnification makes the object easier to see, but too much can make it disappear completely. There has been much discussion of "optimum magnification" for DSOs but a lot of it comes down to personal preference. For large, bright DSOs it may be that the best view is with lowest useable power (i.e. exit pupil equal to your own eye pupil), but again the general rule is that you start low and work up. Most of my viewing is of small, faint galaxies, seen from a dark site, and I do most of it with high power, which shows most detail. Really the important thing is not magnification but exit pupil, and you'll find from experience what works best for you.

[Capricorn]

Many variables come into it.

What scope is being used, parabolic or spherical mirror, achro, ED or apo lens, Then comes the eyepiece, supplied with scope, BST, X-Cel, TV Nagler, ES, Pentax.

I have seen Saturn through a TAL at around 120x, very good.

I suspect that it might have taken a bit more magnification but not much.

Would 300x through an APM 150 with a Delos in be possible, well yes I would expect it to be, but you are looking at several thousands of pounds of equipment, not a few hundred.

You should/can take the magnification up until the image becomes unacceptable. What is unacceptable is different person to person, and varies between the equipment.

For Jupiter you should get a good image at 50x or 60x (had less).

Saturn from experience I would aim at 120x(ish)

Nebula come into the catagory of being dim so you need to collect light, if a big nebula then low magnification will help but if a small nebula, M1, then you will have to magnify in order to see anything useful.

Start out with low magnification simply to locate that faint dot, blur or shadow. The increase magnification to the best compromise for you, with the equipment you have. Welcome to the world of eyepiece purchasing.

There is no rule, more suggestions based on experience, and personal preference.

Someone saying they can see Jupiter with 200x has no real interest to me, magnification isn't a race yet is so often treated as one. It is most often the first thing mentioned. Scopes are sold on the idea of 625x from a 60mm.

[Ajohn]

I posted something on this subject in another thread. It's worked for me on several sizes and types of scope over a number of years but bear in mind that much depends on seeing conditions. Light pollution, high mist etc reduce contrast so lower magnifications have to be used. General optical quality and holding collimation also come into it. At low powers in the wide field areas these don't matter so much but become a severe problem when trying to see detail in planets. The post is part way down this thread.

http://stargazerslou...ow/page__st__20

I posted it because some one looked at a planet using a magnification that may give diffraction images of stars if conditions and optics are good - rings round them. He saw a large bright disk - all he could expect to see really. As I pointed out in the post many people are likely to find magnification levels of a little under the diameter of the scope too much due to conditions.

John

[spurius]

Many variables come into it.

What scope is being used, parabolic or spherical mirror, achro, ED or apo lens, Then comes the eyepiece, supplied with scope, BST, X-Cel, TV Nagler, ES, Pentax.

I have seen Saturn through a TAL at around 120x, very good.

I suspect that it might have taken a bit more magnification but not much.

Would 300x through an APM 150 with a Delos in be possible, well yes I would expect it to be, but you are looking at several thousands of pounds of equipment, not a few hundred.

You should/can take the magnification up until the image becomes unacceptable. What is unacceptable is different person to person, and varies between the equipment.

For Jupiter you should get a good image at 50x or 60x (had less).

Saturn from experience I would aim at 120x(ish)

Nebula come into the catagory of being dim so you need to collect light, if a big nebula then low magnification will help but if a small nebula, M1, then you will have to magnify in order to see anything useful.

Start out with low magnification simply to locate that faint dot, blur or shadow. The increase magnification to the best compromise for you, with the equipment you have. Welcome to the world of eyepiece purchasing.

There is no rule, more suggestions based on experience, and personal preference.

Someone saying they can see Jupiter with 200x has no real interest to me, magnification isn't a race yet is so often treated as one. It is most often the first thing mentioned. Scopes are sold on the idea of 625x from a 60mm.

Would such magnifications in a telescope that small be any good for looking at distance objects on earth in daylight? or the moon?

I pointed my telescope at a mountain once, I didnt realise just how much it magnified things until I pointed it at something the size im familiar with.

[acey]

Would such magnifications in a telescope that small be any good for looking at distance objects on earth in daylight? or the moon?

Yes - that's why telescopes were invented. Looking at things in space came as an interesting bonus.

A magnification of x100 makes things look a hundred times bigger, i.e. a hundred times nearer. Look at an object ten miles away at x100 and it will look a tenth of a mile away (176 yards). The Moon is about a quarter of a million miles away, so at a magnification of x250 it looks a thousand miles away.

[Mr Spock]

Here's something I posted a while back. It shows Jupiter at various magnification to show what might be expected from a C9.25. The impression you will get will depend on what size screen resolution you are using, but it should be close enough for most.

[Moonshane]

I thinks that's spot on Michael.

[Naemeth]

Here's something I posted a while back. It shows Jupiter at various magnification to show what might be expected from a C9.25. The impression you will get will depend on what size screen resolution you are using, but it should be close enough for most.

Funnily enough, 260x on my 130P looks more like 150x on there... hmm

[Moonshane]

I took it that it's the jupiter detail not the size of the disc in the black that's important?

[spaceboy]

As others have commented on planetary magnifications which are really more in the hands of Zeus than anything else I thought it pointless repeating what has already been said. Saying that there was a really good thread some time ago that may have made interesting reading for you. It basically went to say that it is not so much magnification that has to be taken in to consideration but more so the exit pupil. We are at the end of the day looking at the light being reflected from these distant objects and although we are all differing in what maximum exit pupil we can utilise most of us are able to take advantage of the light that hit the retina between the exit pupil of (if my memory is any good ??) 2-3mm. This obviously relates more so to faint and fuzzies etc than planetary observing. You will find some nebula filters recommend an optimum magnification for use. Obviously this relates to a similar 2-3mm exit pupil in any given scope.

[Cornflake]

Thanks for all replies and useful info. If we ever get a clear night I can try some of this out.

Chris