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Saphire
2007-Nov-26, 05:51 PM
Umm hello fellow astronomers this my first post and was just wondering what the minimum lense size would be for viewing nebulas. The one I would like to see most is the helix nebula. Or if I can see it even with a telescope. Thanks

RickJ
2007-Nov-26, 06:09 PM
Minimum would be a pair of binoculars. I've seen it from a dark site easily in 7x35 binoculars. Just as easily as in a large scope! When I was in New Zealand with it high overhead and no atmospheric extinction I saw it as a tiny (half the size of a full moon) fuzz patch with the naked eye. So I guess that's the minimum. I can't do that from here in northern Minnesota though.

If your main interest is seeing this nebula attend a local star party but go early, this new moon it will be low in the SW at 7 p.m. local time but will return next summer.

At the star party you can see it through scopes of all sizes though big ones will have problems showing it all to you at once, it is big. Actually it is as bright in a pair of 7x35 binoculars as it is at 70x in a 14" scope. Just smaller. If you lower the power of that 14" scope the nebula won't get any brighter as some of the light will not fit in your eye. It will just get smaller and be as difficult to see as in binoculars.

This guy is faint in ANY telescope of ANY size. OIII, UHC or similar filter (not light pollution however) helps a lot.

Rick

Saphire
2007-Nov-26, 10:00 PM
Minimum would be a pair of binoculars. I've seen it from a dark site easily in 7x35 binoculars. Just as easily as in a large scope! When I was in New Zealand with it high overhead and no atmospheric extinction I saw it as a tiny (half the size of a full moon) fuzz patch with the naked eye. So I guess that's the minimum. I can't do that from here in northern Minnesota though.

If your main interest is seeing this nebula attend a local star party but go early, this new moon it will be low in the SW at 7 p.m. local time but will return next summer.

At the star party you can see it through scopes of all sizes though big ones will have problems showing it all to you at once, it is big. Actually it is as bright in a pair of 7x35 binoculars as it is at 70x in a 14" scope. Just smaller. If you lower the power of that 14" scope the nebula won't get any brighter as some of the light will not fit in your eye. It will just get smaller and be as difficult to see as in binoculars.

This guy is faint in ANY telescope of ANY size. OIII, UHC or similar filter (not light pollution however) helps a lot.

Rick

Thanks alot for quickly answerng but I was also wondering what magnification I would need to see Jupiter or Saturn well. (about a centimeter minimum I would like) Thanks

aurora
2007-Nov-26, 10:06 PM
Thanks alot for quickly answerng but I was also wondering what magnification I would need to see Jupiter or Saturn well. (about a centimeter minimum I would like) Thanks


If the reason you are asking that question is because you want to use the answer to select a telescope, then don't do it.

I say this because shoddy telescopes use wild claims of magnification as an advertising gimmik to lure the unwary. Magnification can be adjusted in a telescope by using eyepieces of different focal length. A more important question is how much aperture do you need to see dim objects.

You will need something with more magnification than normal binoculars to see Saturn's rings, but you can see Jupiter's moons with binos.

Saphire
2007-Nov-26, 11:06 PM
If the reason you are asking that question is because you want to use the answer to select a telescope, then don't do it.

I say this because shoddy telescopes use wild claims of magnification as an advertising gimmik to lure the unwary. Magnification can be adjusted in a telescope by using eyepieces of different focal length. A more important question is how much aperture do you need to see dim objects.

You will need something with more magnification than normal binoculars to see Saturn's rings, but you can see Jupiter's moons with binos.

Thanks alot for the warning. I also would like to know if I need a laser pointer scope or some other type of apature (now that you bring it up) to see nebulas and planets or other dim objects.

RickJ
2007-Nov-26, 11:43 PM
Resolution not power is what is important to see detail on planets. That and good contrast. In approximate terms a 4" scope will be able to resolve 1" of arc detail. But this is very misleading in some ways. A linear feature of high contrast that is much smaller than 1" of arc can be seen in such a scope, such as Cassini's division in the rings. That is about a half second of arc at its widest point but a 4" scope will show it quite clearly not only where it is widest but even a lot narrower than that. But detail in Jupiter's cloud belts requires a telescope that gives high contrast as well as good resolution. A photo is misleading because the imager can boost the contrast far beyond what the human eye sees. While a Newtonian and a refractor of the same size will have the same resolution you will see more in the refractor because it's contrast in higher. This is due to it not having a central obstruction. So to see the same low contrast detail you need a reflector about 50% larger than a refractor that just shows this detail. This is a very general statement. A long focal length newtonian with a very small secondary obstruction can come close to refractor performance. My home built (mirror included) 6" f/12 with half inch secondary equals any 5" apo refractor I've looked through. Of course Newtonians (especially Dobsonian mounted ones) are far cheaper than an equivalent refractor. Right now my planetarium program tells me Jupiter is 32" of arc across while Saturn is 17" though the rings are 41" across. A 60mm refractor or 3" reflector will show Jupiter and Saturn with its rings very nicely but to see detail on Saturn's disk or in Jupiter's bands you will need a 4" refractor or 6" to 8" Newtonian.

Back to that 4" objective giving 1" resolution, if you double that to 8" then you have 0.5" resolution IF the atmosphere allows it. By 8" you are starting to put some pressure on the atmosphere to deliver a steady image. Much above this aperture you'll gain little resolution but contrast at should continue to increase meaning even though you don't see finer detail of high contrast you do see a lot more finer detail of low contrast. The appearance is you are seeing a lot more detail over all. A imager however will likely see little difference after he's pushed the contrast to optimum levels. Now if you are on Kitt Peak or other location with better than average seeing then larger aperture will greatly improve the view. Where I live that's sadly not the case.

In other words you soon get aperture fever until the scope is so big it literally breaks your back to carry it.

You need to get to that star party I mentioned and actually look through a bunch of scopes to get an idea of what all this means. I can type on and on but as they say one star party is worth 10,000 posts here for what you will learn and really start to understand.

The link below will locate a club near you. Don't even think of buying a first scope without going to one and learning what you really see through the various types and sizes of scopes. Actually your first scope should be a pair of binoculars. They are half way in light gathering ability and resolution of your eye and a 13.5" telescope! No amateur astronomer would ever leave his house for star gazing without them. See Dave's post on binoculars. This is a lot more important than you can imagine.

http://www.skyandtelescope.com/community/organizations

Aurora has already told you why I never mentioned power in this post. Power tells you little to nothing about what you'll see in the scope. That's determined by its quality and aperture and our atmosphere. I could take any telescope to any power you mention, even one million. It won't help you to see anything, except a virtual black hole, but it can be done.

In fact power can be your enemy. For instance a galaxy will be 25 times brighter at 20x in a 4" scope than at 100x. Since they are faint to start with you will likely see far more at 20x than at 100x and certainly far more than at 200x which is where the image starts to break down from being enlarged too much, same as a photo or your TV screen. But since everything is really dim anyway it hardly matters it is fuzzy too.

Rick

cjl
2007-Nov-26, 11:53 PM
Quick note: a pair of binoculars is nowhere near halfway between your eyes and a 13" scope in light gathering capability. However, the difference between your eyes and the binoculars is roughly the same proportion as the difference between the binoculars and the 13.5" scope. For halfway between (linear), you would need a 9.5" scope.

RickJ
2007-Nov-27, 06:45 AM
But the eye sees proportionally on log scale not linearly. Still even a 9.5" scope by your way of looking at it is far larger than most beginners would expect. They don't consider binoculars a true scope at all. $50 to $100 to go half way to a several thousand dollar 9.25" SCT is quite a deal I'd say! Or even a $500 basic 10" Dob.

I see 4.5 magnitudes deeper with my 10x50 binoculars than I can naked eye and I see 4.6 magnitudes deeper than binoculars in my 14" scope. I'd say that's about half way and is what I was referring to. Of course as stars get dimmer there are far more of them so you'll see far more than twice as many stars in the 13.5" scope. Deep sky objects also increase rapidly with faintness so again you'll see far more than twice as many.

Still I've logged over 200 deep sky objects in 10x50 binoculars. Enough to keep a beginner busy for some time. They are darned good for a starter "telescope" and a great way to learn your way around the sky so can actually locate something to look at when you get a scope besides the moon and bright planets.

Seems I see far too many posts here that ask; "I've looked at Mars and can't see anything but a disk. What else is there to look at?" all too often here. If they'd have just spent time at a few star parties and with binoculars and a star atlas we'd not see such posts and have a lot happier beginners in our hobby.

Rick

aurora
2007-Nov-27, 04:29 PM
I also would like to know if I need a laser pointer scope .

No, you don't need a laser pointer. I find a 1x finder scope (like a Telrad or a red dot finder) to be helpful for star hopping, and I think beginners have better luck with that than with the typical small finderscopes that come on many scopes.

If you look through back threads in this group ( Astronomical Observing, Equipment and Accessories) you will find messages with lots and lots of links to articles written specifically for beginners who are thinking about getting a telescope. I would strongly recommend you do some reading here and by following those links.

Many times people run out and buy a telescope that looks slick in the advertisement, but then later they discover to their disappointment that they did not select a telescope that meets their needs. Or they had unrealistic expecations from the start.

This could be avoided simply by doing some research, doing a little reading, and going to a astronomy club star party.

cjl
2007-Nov-28, 05:50 PM
But the eye sees proportionally on log scale not linearly. Still even a 9.5" scope by your way of looking at it is far larger than most beginners would expect. They don't consider binoculars a true scope at all. $50 to $100 to go half way to a several thousand dollar 9.25" SCT is quite a deal I'd say! Or even a $500 basic 10" Dob.

I see 4.5 magnitudes deeper with my 10x50 binoculars than I can naked eye and I see 4.6 magnitudes deeper than binoculars in my 14" scope. I'd say that's about half way and is what I was referring to. Of course as stars get dimmer there are far more of them so you'll see far more than twice as many stars in the 13.5" scope. Deep sky objects also increase rapidly with faintness so again you'll see far more than twice as many.

Still I've logged over 200 deep sky objects in 10x50 binoculars. Enough to keep a beginner busy for some time. They are darned good for a starter "telescope" and a great way to learn your way around the sky so can actually locate something to look at when you get a scope besides the moon and bright planets.

Seems I see far too many posts here that ask; "I've looked at Mars and can't see anything but a disk. What else is there to look at?" all too often here. If they'd have just spent time at a few star parties and with binoculars and a star atlas we'd not see such posts and have a lot happier beginners in our hobby.

Rick

They aren't halfway to a 9" either :)

A set of binoculars with 50mm apertures is halfway to a single, 100mm scope. No more. As you said though, they are enough of an improvement over the naked eye to be well worth it, and there is much to be found with a decent pair of binoculars that can keep one occupied for a long time. Definitely a worthwile investment.

RickJ
2007-Nov-28, 08:13 PM
We're playing semantics here. I gave my definition of half and stand by it.

All this misses the point. Binoculars are the most cost effective way to start in the hobby. That and attending club star parties until you know the sky well enough and know enough what you want out of the hobby to know which larger instrument to buy.

Rick