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Advice required

Sparky and Gaz

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Sparky and Gaz

Sparky and Gaz

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Hi Folks,

Just got my first telescope for my birthday a few weeks ago from my girlfriend :0) A Sky Watcher D=114 F=500

I got a 25mm, 10mm eyepiece and a barlow x 2.

I have been looking at jupiter through the 10mm and can see its 4 moons but not much detail on the planet, using it with the x2 barlow i thought i would see more detail but can't.

My question is if i bought a 5mm eyepiece would i see more detail?, i realise both give me 100 x mag but was thinking it would maybe be better??

As i said im just a few weeks into this so any help would be appreciated before i go buying additional bits n bobs lol..

ooo of to view the moon :0)

Thanks again..

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Capricorn

Capricorn

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The answer is: It might do.

Usually the eyepieces supplied are not great and the barlow supplied is equally not great. Combined they work really poor.

So a reasonable 5mm could show an improvement. Would go as far as to say I would expect it to.

The problem is the scope is basic, it isn't going to show the furthest reaches of the universe.

The comes the fact that what defines a reasonable eyepiece, more importantly what budget are you considering.

I would avoid the 5mm plossl's. Have one and not great also they have a small amount of eye relief. You have to get very, very close to look through them.

The almost standard suggestions presently are the BST Explorer and the TMB II planetary. Both of which do a 5mm eyepiece. BST is £41, TMB is £39, both from Sky's the Limit.

Prefer the BST myself, they both fit the requirements and aren't too expensive.

P.S. It could be that the scope needs collimating. I assume that it is a reflector.

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malc-c

malc-c

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Part of the problem is you are restricted by aperture, which is what gives you the resolution or brightness. If you have say a 6" telescope with a focal length of 750mm the focal ratio is 750/150 = 5. Now next to this you have an 8" telescope with a focal length of 1000mm - this also has a focal ratio of 5 (called f5). However if you use the same eyepiece in each telescope and looked at Jupiter, you will see a brighter image and thus more detail in the 8" than in the 6".

Now when you increase the magnification, the image becomes dimmer in appearance, no matter what scope you have, and there is a limit as to what becomes the highest practical magnification that still resolves plenty of detail. With larger apertures and scopes with longer focal lengths it's possible to get high magnification but still have a bright image and with lots of detail.

To be honest, with a 4.5" aperture f4.3 scope you won't get a lot of magnification, and a 4mm eyepiece will result in a max 125x, and you might get disappointing results. A decent 8mm like one of the Celestron's (£50 - £70) would probably be a better bet. An alternative would be to get a webcam, capture the footage and then stack the results in registax, but then it's not like seeing Jupiter visually.

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Capricorn

Capricorn

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However if you use the same eyepiece in each telescope and looked at Jupiter, you will see a brighter image and thus more detail in the 8" than in the 6".

No you don't. The image in the 8" is magnified and bigger then that in the 6"

The magnification ratio is equal to the aperture ratio, so the images are the same brightness.

You get a brighter image if the magnification of both scopes were the same as then you are pushing 8" aperture collection into the same image as the 6" collects so the 8" image is 1.778 times as bright.

Start safe, buy the 8mm instead, unless it is too late to change the order. In which case don't worry, not a lot you can do now.

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