total beginner needs some help on eyepieces

[tonysheedy (Australia)]

hi, i bought a meade 102mm audiostar goto telescope, it has 800 mm focal lenght, the eyepieces i got with it are 25mm and 9 mm, i went outside tonight to give it a go, pointed at some stars and all i see are bright dots, pretty much what i see by eye, how can i zoom in on a planet ? i guess i need stronger eyepieces? if this is the issue could someone advise what size eyepiece is best to look at planets? i need to try again possibly the stars are just bright dots and maybe i need to be looking at a planet more visible to the scope, i remember years ago i had a cheap telescope and i could see the craters on the moon easy, no moon tonight but from what stars i pointed it at it was just bright dots in the eyepiece, and yes as u see i'm dumb as can be on the telescope....thanks

[pw (Peter)]

The stars are always points, no matter what scope/eyepiece combo.
Planets are different and you can get a better view with a shorter focal length eyepiece (as long as the seeing is good enough). A 6mm or 5mm might be a sensible next step for you.

[Renato1 (Renato)]

Well, stars are dots - and we don't spend much time looking at them unless they are double stars or open clusters of stars. Much more interesting are emission and reflection nebula, globular clusters, galaxies and planetary nebulas. Your 25mm eyepiece will be fine for them.

Your 9mm eyepiece gives you 89X power, which will show you the bands on Jupiter, the moons around Jupiter, the crescent phases of Venus, and the rings of Saturn.

Though, as already suggested, you'd want a higher power eyepiece to get better views of those planets.
Regards,
Renato

[tonysheedy (Australia)]

ok so i guess my first attempt was wrong, i was probably just looking at stars which will just be bright dots if i got it right, so i need to find a planet, this telescope has the automatic function to go to planets, though i have not worked out how to use it , but will, i will try again and look into buying a 5 mm eyepiece, thanks

[Camelopardalis (Dunk)]

Not only are stars dots, but quite often they are coloured dots the colour is usually subtle, but not always. If you look at Betelgeuse or Arcturus for example they are distinctly orange, Rigel and Spica have quite a blue hue to them. The colour indicates their temperature. There are some weird stars called carbon stars that can be quite red...R Leporis (Hind's Crimson Star) is a good example of these.

Then there are double and multiple stars as the guys above mentioned...and just sometimes, the individual stars of these have different, contrasting colours....for example, Albireo where one is pale blue the other yellow...quite beautiful!

Then within open clusters you often get stars of different colours, visible in the same field of view...take a look at the Jewel Box for example.

All I'm trying to get across is...these dots can be quite interesting themselves as well as in the ways they manifest

[barx1963 (Malcolm)]

Tony
Welcome to IIS and well done on buying a scope.
You have encountered the first thing that new observers find out, that a telescope is not a guarantee of seeing views like the wonderful images we see in the media.
As mentioned stars are points. They are so far away that even the most powerful telescopes in the world cannot resolved a disc on more than a handful of them. But if you think about it, that is something marvelous in itself. If you find Betelguese in the night sky and you check it out all you see is a point of light. But this is an object so vast that if it was to replace the sun, it would extend to way past the orbit of Mars!
With planets you are lucky ATM. There are 3 planets easily observed right now. Jupiter is lowish in the North West sky. It is the brightest object in that part of the sky. Mars is near Spica in Virgo and is a fairly bright red object in the eastern sky. Saturn rises fairly late in the evening so you will need to be patient for it to rise high enough to observe and is a moderately bright, faintly yellowish point sitting north of Scorpio's claws.
With higher power eyepieces, be careful. More power also magnifies any atmospheric distortions which are even more apparent when the planets are low. This can make them harder to observe successfully. Patience and good conditions are needed for planets!

Cheers

Malcolm

[OzStarGazer]

Originally Posted by Camelopardalis

The colour indicates their temperature.

The funny thing though is that blue is hotter than orange or red (red being colder than orange) in the stars, so blue stars are hotter than orange or red stars. Funny because our mind usually thinks of red as hotter than blue...

[Camelopardalis (Dunk)]

Originally Posted by OzStarGazer

The funny thing though is that blue is hotter than orange or red (red being colder than orange) in the stars, so blue stars are hotter than orange or red stars. Funny because our mind usually thinks of red as hotter than blue...

Yeah cos we think of red hot and icy cold, it's just our association

The hotter stars emit more energetic (shorter wavelength) blueish light, the cooler ones emitting cooler, less energetic longer wavelengths that we see as red.

[Quoll (Bill)]

Download Stellarium, it’s free, and it will help you find the planets and much more

http://www.stellarium.org/

[noeyedeer (Matt)]

no one cuts through metal with a yellow flame .. only blue will do it because it's hottest that's like grade 8 science playing with the bunson burner.. and white like magnesium burning .. love the engine block experiment where magnesium burns through it

matt

[OzStarGazer]

Originally Posted by Camelopardalis

Yeah cos we think of red hot and icy cold, it's just our association

Yes, I know it is just our association. We are just surrounded with this association - including programs like Photoshop when you process an image...
I managed to capture some of these colours in my photos, but they are mainly in the halo. (I don't know if this is normal? The colours are OK though, looking at a chart, I mean - what they should be... Spica for example has a blue halo. There is some colour also in the stars themselves, but it is "mainly" in the halo.)

[tonysheedy (Australia)]

Originally Posted by Quoll

Download Stellarium, it’s free, and it will help you find the planets and much more

http://www.stellarium.org/

great i just downloaded and will get into it, this looks good.....thanks

[Ryz (Ryan)]

Wondering what the best equipment to purchase after using kit 10mm and 20mm eyepieces is?

[astro744]

Originally Posted by tonysheedy

great i just downloaded and will get into it, this looks good.....thanks

Make sure you set your location as the default in Stellarium otherwise you'll get the wrong sky each time you start the program. You can download extra star sets to better match your purposes. If your telescope limiting magnitude is say 13 then no need to get stars that are fainter unless you are imaging. Note the extra stars show when you zoom in on an area.

[ManUtdFans (Alan)]

Originally Posted by astro744

...If your telescope limiting magnitude is say 13 then no need to get stars that are fainter unless you are imaging. Note the extra stars show when you zoom in on an area.

How to find out if a telescope has this limiting magnitude?

[OzStarGazer]

Originally Posted by ManUtdFans

How to find out if a telescope has this limiting magnitude?

You can find out here: http://www.stargazing.net/naa/scopemath.htm

[astrospotter (Mark)]

The ideal eyepieces for a given person vary depending on your focal ratio of your scope(s) and not so much your focal length of your scope(s) as has been mentioned (I think). I think it is sometimes best to think about your eyepiece collection in terms of exit pupil and that is a sole function of your scope(s) f ratio(s) and the eyepiece focal length.

Exit pupil is the eyepiece focal length divided by your telescope's f ration. So if you have a f/7 scope then a 15mm eyepiece has a 15/7 or about a 2.1 mm exit pupil. For an f/3.6 fast scope the same 15mm eyepiece has a 4mm exit pupil. This makes a big difference in terms of your eye's ability to use that light energy.

Try to be sure to have something in the exit pupil ranges of 4, 6, 8mm exit pupil range and if you do really deep stuff with larger scopes even have a favorite eyepiece in 2mm exit pupil range for deep sky if you are good at averted vision like most deep sky observers tend to be.


A dark adapted eye of a an observer of 40 years or younger will be around 6mm and as you get older it gets usually smaller like 5mm by age 50 (these are all just averages, your mileage may vary).

When you get to an exit pupil of less than half the diameter than your own dark adapted eye the view becomes darker and darker as you are able to utilize so much less than your full eye's dark adapted pupil.

When the exit pupil is greater than your eye's opening this is where you search around in the field by moving your head and don't see the whole field. This can be it's own fun but I'm just explaining the mechanics of it here.

So the above reason is why it is thought that much less than 2mm exit pupil looses too much light to be of value BUT if you have massive aperture that of course compensates.

mark

[Wavytone]

Close but no cigar.

Longest eyepiece focal length for your scope = telescope focal ratio x 6mm

Mid-power eyepiece focal length = telescope focal ratio x 2mm

Shortest useful focal ratio for your scope on most "good nights" = telescope focal ratio x 1 mm assuming the optics are good.

Absolute shortest you could ever use = telescope focal ratio x 0.7 mm, but only if the telescope is a really excellent optically (many aren't).

The latter might be useful about 1 night per year.

IMHO you could get by with just three eyepieces - low, medium and high power where medium is the geometric mean (not arithmetic mean) of low and high.

Alternatively 4 eyepieces, the focal lengths increasing at roughly at 1.5x from one to the next.

[Renato1 (Renato)]

Originally Posted by Wavytone

Absolute shortest you could ever use = telescope focal ratio x 0.7 mm, but only if the telescope is a really excellent optically (many aren't).

The latter might be useful about 1 night per year.

I don't agree with that entirely. It may well be true for your telescope and for where you live, but I don't think it generally correct.

In my C8 (Focal length 2032mm) from a suburban backyard a 0.5mm exit pupil (406X) delivered a decent image several times a year (usually in Spring or Autumn when neighbours didn't have air conditioners or heaters on). A 0.64mm exit pupil (317X) was useful around a third of the time. An 0.8mm exit pupil was good 67% of the time, and a 1mm exit pupil was good on all but a couple of times a year.

In my 5" MAK (Focal length 1500mm) it can easily deliver a steady image at 300X (0.42mm exit pupil) though there is empty magnification where one can't really see more at the higher magnification than one sees at say 250X - other than for floating things in one's eye.

I recollect at the Nagler site, their recommendation for high power was 0.5mm to 1mm exit pupil, recommending 0.7mm as probably the most useful.
Regards,
Renato

[Steffen]

If you're into splitting doubles 0.5mm is where is starts getting interesting. I routinely go that low with my Mak, and in recent months had terrific views of the planets at 360x (0.5mm exit pupil), during those special nights of great seeing.

Cheers
Steffen.