Eyepieces and barlow lense

[AstroB]

I'm considering purchasing some quality optical equipment for better views. I still use the optics that came with my scope:p The Baader Planetarium Hyperions caught my eye - they look fairly decent and have as far as I know gotten good reviews. I want to look at galaxies and nebulae, but would also like to view some of the planets. This is why I'm wondering whether I should get a proper barlow lense as well, in order to get a good big view of saturn:) If I purchase a quality barlow lense, such as a televue, should I go for a 2x or 3x? Will the image be a lot more fussy at 3x, or will good optics make the view good? Also, if I go for the Hyperions, which are SWA eyepieces, what properties do I miss out on which a non-SWA eyepiece would have?

Thanks for all replies:)

[david o]

If you could tell us what 'scope(s) you've got and what kind of observing you'd like to do, then we'll be better able to advise you.

For the ins 'n' outs of choosing EPs, you might find these posts : "Eyepieces - the very least you need" and "Understanding and choosing eyepieces" a help in guiding you through the basics.

I'd be tempted not to buy anything for now, just use what came with the 'scope. With eyepiece time under your belt you'll know what needs replacing or if there's a gap that needs filling.

HTH

[AstroB]

Thanks for the links David, useful reading:)

As for my scope, it's an f/5 reflector (1000mm focal length and 200 mm aperture). I'd like to view some Messier objects; galaxies, nebulae and clusters but also some of the planets.

I'm not planning to buy anything just yet, was planning to wait another month until I can decide which power eyepieces I want. What I'm most curious about is the Barlow lense - 2x vs 3x given that the optics are good. Will 3x be a lot more fussy? I'm thinking a 5mm eyepiece and 3x barlow will give quite a big view of saturn, question is if the barlow lense will cause much fussiness, or if the quality of the optics will keep the image clear.

[John]

Your scope has a focal length of 1000mm so a 5mm eyepiece on it's own gives 200x which is a useful maximum for Saturn and Jupiter on most nights. A 2x barlow would give 400x and a 3x, 600x both of which are far too much magnification either for the scope or, and this is the real limiting factor, for our seeing conditions. This applies regardless of the quality of the eyepieces.

You might be able to use 250x on good nights - that would need a 4mm eyepiece or an 8mm with a 2x barlow lens.

[stick]

i recently got some BST Explorer ED eps, and have been well impressed with those

they aren't as good as the beaders (obviously) but well priced and great views

stick

[Moonshane]

John's right of course. With more magnification than about 200x (except on the moon and maybe double stars which can usually stand more than other targets) the image just gets less detailed due to seeing conditions. there's the occasional (rare) night when you can push to 250x with no loss of detail. on Jupiter late last year, I was lucky to get more than 140x due to seeing and that's even with a 12" scope.

personally I am not really a fan of barlows but if you want one there's not many if any better than the TV one (or the Powermate). I'd prefer a couple of decent orthos instead of a barlow but I don't wear spectacles to observe.

[AstroB]

Okay, it's starting to get a bit clearer now:) I was wrongfully somehow under the impression that it was only the magnification caused by the eyepiece that was limited, and that the barlow lense simply magnified the image the eyepiece produced. I guess it's better to go with a 2x then if any, because I was planning to get at least one high-powered eyepiece.

[Moonshane]

I'd agree that generally for visual astronomy a 2x barlow will be more than enough. I have never used one but have heard the you can get vignetting with some 3x barlows.

For astro photography (which I don't do) I hear people often used stacked barlows so maybe a 2x in a 3x to get a 5x but this is a completely different thing to visual.

[legoalan]

Does anyone know what a decent spec is to observe DSOs (galaxies, nebulae etc). I've got a 1400mm focal length 150mm aperture scope right now (f/9) but I am thinking whether I should upgrade to a skyliner 200p dob to see DSOs. (I am having no luck locating them right now). Should I keep the scope I've got right now or upgrade if I want to be able to see DSOs?

Also can anyone recommend which DSO is the easiest to located or see?

Thanks =]

[twotter]

Depends where you are and what is around you to block the view. If you've got Stellarium (free download planetarium software) you could time advance to when you usually go out observing and see what's around you.

[legoalan]

Thanks twotter, I use a neat little app called starwalk which tells me what i'll be able to see at a given time. Do you know if my telescope would be able to see DSOs or should I upgrade to a 200P dob? I should add that with my current scope I have 25mm, 6.5mm EPs and 2x barlow and 1.5x erecting EP.

[iamjulian]

The f/9 bit of your scope means that it isn't as "fast" as the 200P dob you are referring to, which is about f/5? If you think about it in camera terms, everything else being equal, a photograph taken at f/9 will need a longer shutter speed than a photograph taken at f/5 to produce the same exposure. That's why a faster telescope, will be better at seeing faint DSOs.

In other words, yes, an f/5 scope will be better for DSOs than than an f/9 scope. There are trade offs though. Eyepieces will generally perform better in your current scope. And your current scope will be better for planets. If you want more detail, you'd be better posing the question again in your own thread, as a lot of people won't see it hidden at the bottom of AstroB's thread.

[legoalan]

Thanks for the help Julian, appriciate it =]

[Moonshane]

really focal length does nothing to hinder or benefit seeing DSOs. what is does (for the same aperture) is reduce (or increase) the field of view so with a slower scope (eg f9) you'd see half the sky that you would in the same aperture but f4.5. This might make them harder to find but the image (ignoring field of view) should be about the same assuming similar optical quality. Double stars are of course DSOs and a longer focal length / slower focal ratio will be good for them as well as planets and moon, as often the contrast is better in such scopes.

Two things affect the fainter DSOs like galaxies and nebulae etc. These are aperture - generally the more the better and dark skies - the darker the better. In order the best to worst conditions are as follows I feel:

1) dark site large aperture

2) dark site moderate aperture

3) light polluted site large aperture

4) light polluted site small aperture

It's amazing what can be seen at a dark site compared with a light polluted garden even with your naked eyes let alone a scope even if a small aperture.

Hope this helps a bit.