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Eyepieces


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Is there anything I should look for when buying eyepieces?

I don't quite get what the numbers means, seems like smaller the number the bigger the magnification..but I could be wrong...

Sorry for bombarding you all with questions..

Kain

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Hi kain,

Yep, the smaller the number the bigger the image. You divide the focal length of the scope in mm by the eyepiece focal length in mm and that gives you the magnification.

So your scope has a focal length of 500mm.

A 4mm eyepices gives 500/4 = 125

a 10 eyepiece gives 500/10 = 20

But you can only generally magifiy usefully 50 times for every inch of aperture of you scope. Yours is a 4 inch (ish) scope so your top is x200 (more realistically 150)

Gaz

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The seben eyepieces arnt fantastic but will be a lot better than the Kelners that you currently have. The 6.5mm focal length will give you a 77x magnification. I'de also advise that you throw away your plastic 3x barlow (or, as Warthog recommended, make a flute from it!) and see if you can find a half decent 2x barlow. The televue ones are the best, but are probably beyond your price range. The celestron Omni is a half decent cheap barlow.

Take a look at the Celestron eyepieces on ebay, they are higher quality than the seben ones and not much more money.

here and here.

Let us know how you get on with the seben!

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The eyepieces provide different levels of magnification. I typical assumption about how much magnification your scope can provide is to multiple it's aperture in inches by 50. So a 4" scope can provide 200x magnification easily. A 114mm scope (4.5") can provide about 225x magnification. If you scope has a 500mm focal length then to provide this maximum magnification you would need a 2.5mm eyepiece. However i wouldn't advise that you go and buy one as a 2.5mm eyepiece will have short focal length and a small exit pupil. I would say you would be better off with a 10mm eyepiece (or 9 if you already have one on order) that will provide 50x magnification and give good wide field views. Look at things like clusters and the larger galaxies. To be fair with only a 500mm focal length, you are not going to get much magnification out of your scope, so you wont get good images of the planets or smaller objects.

However if you invest in a 2x barlow then your 500mm focal length becomes 1000mm which is much more friendly towards the planets. You can then double the magnification of any eyepeices you already have. So your 10mm eyepiece giving 50x magnification becomes 100x magnification etc. To get to your maximum 225x magnification would require a 5mm eyepiece and a barlow (ish).

It's all swings and roundabouts, and depends on what you want to look at. I would advise that you dont buy anything (other than the books and planispheres i've already recommended) and then have a think about what you want to look at. You might find you would be better off with a different scope, but then you are looking at spending more money than you possible want to.

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That Barlow appears to be in about the same quality as the two I have. One is an Omni, the other came with the Celestron kit, and they both work OK. I have a couple eyepieces for sale, BTW, for about £10 - 12 each, in the Members Buy Sell section, if you are interested.

Try and select your eyepieces so you dont' get overlaps - if you have a 20mm ep, and a 2x Barlow, do you really need a 10mm ep?

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Well I got my Seban eyepiece today, and I must say, although I wouldn't have a clue if I get a better view with it (peeing down here) It does seem a million times better with the stock EPs that came with the scope..

I guess only time will tell now if it's actually any good!

Oh, I also got my Planisphere too...looks complicated!

Kain

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Hi Kain,

Be careful on what / how much you buying off ebay, its very easy to spend £10 here and there then relise you have spent a fortune on loads eyepieces.

I have made some very selective purchases and produced a nice kit bag worth of fair EP's!. Keep an eye out for Mead 4000 series from a supplier called kpphototeddy. Hes based in the states and lists the ep's as £'s.. Ive bought a few from him now, all new @ around £20 del each. Just had del a 32mm series 4000 for £25 del :shock:. They retail around £45.

Keep an eye out and dont worry that he's in the states. no additional duty is charged.

Reagrds

Rob

Admin

P.s Welcome to the forum

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Not an easy one to answer that.

I like to think there are 3 alrounder EP's that have always been in my kit bag, and would never let go. Now I have 3 scopes - 80mm Refractor / 150mm Newt / 127mm Mak. 3 different types of scope.

My top tip 3 EP's are one of the following sizes 17 or 18 or 19 mm does not really matter here? (I have a 17mm Celestron Nexstar plossl & 19mm Anares wide plossl) / 26mm Mead Series 4000 plossl / 32mm Mead Series 4000 plossl - I know I've only just got the 32mm Mead, however I sold a 32mm Antares plossl and wished I had not!!.

All 3 are work horse EP's for all 3 scopes!!.

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Well from my understanding, the hight the number the less powerful the magnification, so what would be the function of a 32mm eyepiece? Or does it vary between scopes?

Man I sound a right idiot lol..

Kain

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Ahhh!

The reason for the 'scope is not for magnification of size, it's to collect enough light so that you can see the stuff. Did you know that the Andromeda galaxy is several (2 or 3 but don't want to start a war) times bigger than the moon in apparent size? But most people in the UK can't see it because it isn't brighter than the rest of the sky because of street lighting etc.

The bigger number EPs let you see bigger lumps of sky to home in on stuff as well as being able to see fainter objects.

Firstly the more sky that you can see means that more light is getting to your eye so the image is brighter. This is good for large scale dim things. It also lets you find dim things to "zoom in on" by changing EPs to increase the magnification. Centre the (bright) blurred star, change EP, look at (dimmer) fuzzy object a zillion miles away, job done.

HTH

Captain Chaos

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Well from my understanding, the hight the number the less powerful the magnification, so what would be the function of a 32mm eyepiece? Or does it vary between scopes?

Man I sound a right idiot lol..

Kain

As the magnication increases the field of view decreases, so some objects need low power eyepieces in order to fit them into the observers field of few. The other main reason is that everytime you double the magnification of an object you make it 4 times fainter. So if you have a faint object amgnifying it will make it larger but it may also make it too faint for you to see. It doesn't matter too much on the Moon and planets but the faint galaxies often need to be viewed at low mags.

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A lot of it is counterintuitive, I mispent my youth trying to see stars by making overly high magnification stuff and got put off when I couldn't see anything at all through the " 'scopes" that I made. Recently I have learnt that all you need is to collect lots of light as many things are big enough already but just too dim to see.

Its quite a steep learning curve so you will learn enough to see stuff without a lot of hard study. The stuff you need to try really hard at is generally esoteric enough that you can wait until you feel the urge. Stick to the brighter stuff if you lack aperture and you'll be fine.

Captain Chaos

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