What Will I See?

[Greenswale (Wren)]

Ah, the drama of it all!

I have my Celestron Nexstar 6 - and am quite delighted with it. No dramas with an outback trip, apart from issues with SA local time, full moon, cloud and rain............!

With developing enthusiasm (read, like, that I am seriously hooked!), I need to learn stuff about eyepieces. I have the standard 25mm (50° fov) and a Hyperion 8mm (68° widefiled), and I am thinking of adding to these.

Questions:

What can I expect to see comparatively at, say, 10mm with the various types that I see discussed - planetary, Plossl, widefield, etc, using Jupiter and its moons as a sample target? Currently my 25mm shows Jupiter and four moons within about 2/3 fov diameter; the 8mm just fits all in; scope focal length is 1500mm.

Do widefields loose detail of planets when viewing same? (ie would a tighter fov provide better detail?)

What specific uses would be best assigned to what ep types?

Does a dissertation exist that may provide me with the 'stuff' that I need to know on this topic?

[Blue Skies (Jacquie)]

Well, I'll get the ball rolling by saying in my experience the 'right' eyepiece will vary from person to person, it's a personal preference thing.

But since you've helpfully given the aperture and focal length I'll add this advice:

The max magnification your 6" can theorectially provide is 300x (ie 2 x 150mm) So to work out what range of eyepieces you might usefully use I do up a list like this -
25mm = 60x
15mm = 100x
12mm = 125x
9mm = 166x
6mm = 250x
Also remembering that on an average night the atmosphere doesn't support magnifications above 200x (which would be usinga 7.5mm ep in your case.) I recommend three eps, one in a the low range, your 25mm, one in the middle around 100x and one at the higher end for the planets around 200x.

To answer your questions:

wide field or narrow field ep? - depends on who you talk to! Personally I prefer a wide field for planets, but others may tell you to get rid of all that surrounding distraction and go for narrow field. And they may eve start jabbering on about exit pupil...

There are different types for different scopes but you'll find that the modern day eyepieces will all work well in different scopes as they are designed for the relatively short focal lengths of today. If I had a really old scope with a long long focal length that going back to a Huygens or Ortho may be worth it.

To sum up - you really just have to try different eps in your scope to find the one you like. If you join a local club or attend a star party this is not so hard to do - just put the word out you'd like to try some different eps in your scope and several people should pop along to show you their favourite ones. Otherwise you just have to buy one and hope it works. And as the americans say, "Your milage may vary."

[csb (Craig)]

I found a link for you.

At bottom it has descriptions of 6 types of ep's, pros & cons, what they are best for (planetary, deepspace) - plus internal pics.

http://www.astronomical.org/astbook/eyepiece.htm

[Greenswale (Wren)]

Thanks Craig - I begin to learn. Astonomy is somewhat engaging, huh?!

[csb (Craig)]

Yes, Mr Green it is.

The hardest thing to learn is what do I want. I've decided to move my resources towards solar observing.

That site was a great read. I never understood what physical difference there was between the diff types of EP's. And also why they are different.

The best thing I learned is that it doesn't really matter so much on the type of EP - they can all be used as I see fit.

That page is saved on pc for reference and reread.

PS I've been curious since I first saw your avatar: Is that a frog on your face. Nice snap though, shows your character I think

[Greenswale (Wren)]

Yep, 'tis a green tree frog. They love to talk to certain people, but they tend to get in one's face a bit!

[BigJ]

I was wondering about the frog too, but I didn't want to ask. Some people have very embarrassing facial growths, and you never know... It's like asking a "large" woman if they are pregnant, and when they are due - only to be told "I'm not."

Reminds me of a joke my grandmother used to tell, about a woman who catches a bus and sits down next to a woman carrying a disturbingly ugly baby. Before she can stop herself, she jumps up in fright, saying "EUUGHG!!! What an ugly baby!". The mother is affronted and says "hey, that's my baby you're talking about!", to which the first woman replies sheepishly "... but it suits him..."

Sorry, I know if't off the topic but I couldn't resist...

[cahullian]

Greenswale

I would recommened a good x2 barlow, that will turn your 25mm ep into a 12.5 mm and a 15 mm wide view ep into a nice size 7.5mm.

Gazz

[ving (David)]

www.scopesim.com

[ballaratdragons (Ken)]

Hey Vingo, you beat me to it. I was about to post that link too

[duncan]

Hi all,
What a shame they didn't include a globular and a galaxy or two in that simulator. Excellent what they have got though.

[ving (David)]

yeah it shows brightness and fov given diferent telescope and ep combos... clever really.

they tried to sell it but obviously no one would buy it

[Greenswale (Wren)]

Thanks for the site Ving.

Had a play with it, and consider that it has some value. EP comparison is quite valuable.

Notably, I consider that my scope is returning larger and brighter images than demonstrated by the simulator. Even with Jupiter boiling and bumping around over Melbourne city (I live to the west ad am surrounded by street lights!) over the last few nights, I have had really good viewing sessions, observing pretty good detail, even with old eyes. But I do need to stay up later, or maybe arise earlier........

[Uchtungbaby]

I have a 4 inch Hugo. It came with a 25mm and a 10mm eyepiece. I use the 25mm to locate the planet after identifying it in the finderscope. Then I go down to the 10mm when I want to get up close and personal with it.

I use this method particularly when viewing Venus since it is the Goddess of Love. I've been this way ever since I found out that Professor Issaac Newton had an affair with a castrarsi.

When viewing Jupiter you should try averting your gaze slightly every now and again as you look through the 10mm eyepiece. After a time it will start to resolve with the bars clearly visible.

The reason I start off with the 25mm eyepiece is because I need to centre the planet in the eyepiece first; before I resolve it further with a 10mm eyepiece or smaller (.i.e., if you're lucky enough to have a decent mirror).If I don't start off with a large eyepiece first, I find that it is difficult to locate objects easily.

[Greenswale (Wren)]

Last night the clouds parted, and there was Jupiter begging observation!

Great session, got to see the shadow of the closest moon tracking across the face of the planet - truly excellent. Lots of detail on the planet too. Grouse fun until all was obscured behind a building. Might move.......

EP was 8mm Baader Hyperion 68° Widefield. I gotta try a 10mm - is EP fever something like aperture fever?

[Uchtungbaby]

Gee that's amazing. I never thought it was possible to make a visual of a shadow on the planet face without some fancy technology to help...

You have a 6inch mirror (?) I only have a 4 inch mirror. That extra 2inches of aperture must really increase the magnification(?)

I might have a look tonight myself and see if I can see anything. I remember a number of months ago how I was able to get a distorted image of what I thought was one of the closer moons to Jupiters surface. But as far as I know that is about as good as it gets when it comes to glimpsing near objects on the planets surface with a 4 inch telescope.

So yeah, I'm gonna have a look out for that now. I'd just be happy to capture it on a time exposure. I think it would be amazing to look at.

[matt]

Originally Posted by Uchtungbaby

You have a 6inch mirror (?) I only have a 4 inch mirror. That extra 2inches of aperture must really increase the magnification(?)

Don't confuse aperture with magnification, which is a function of your scope's focal length divided by the focal length of whatever eyepiece you are using.

Aperture relates entirely to light gathering ability, which will determine resolution and limiting magnitude.

[Uchtungbaby]

Yes, I suppose you're right. Of course, you know we could all play shell games with each other on the issue. I might say that aperture increases light. More light equals more detail. More detail takes place because there is more aperture. Saying that little tidbit, I might also mention that you are in fact correct also. Magnification is a function of focal length. Theoretically, mirror size is irrelevent. If one could collimate a mirror the size of a 20 cent piece to the secondary mirror and eyepiece, then it is possible to create magnification as large as one chooses within practical limits.

The reason telescope makers use such large mirrors is because they cannot as yet collimate very small mirrors to the level of precision that would be required. What I am saying is that it is possible to make lens as small as microscope lens for celestial viewing but they are impractical because of vibration considerations and heat shrinkage for example.

So putting that all to one side for the moment, I must say that it is very impressive to think that an extra 2 inches of aperture can create such an incredible difference in detail ; not magnification.
Thank you for correcting my word choice.

Yeah anyway, so I did have a look last night up in the sky. I just moved to a country town in Tasmania, so the sky is really black and it is difficult to get ones bearings. The stars are so bright I mistake many of them for planets, and I find myself attempting to rediscover the known planets. While looking for the known planets I spy a bright star I confuse with a planet. Closer examination in a telescope reveals that it is not a planet. It is a double star.
The brightness of the double star is intense when viewed with the naked eye. Closer examination however reveals that it is in fact two stars closely bound together in orbit.

I think I will look for it again tonight and see if there is any change in position between the two double stars. I hear that sometimes they can change orbital position a little bit over time if the orbit is erratic (?)