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Choice of two scopes, but which?

Geo

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Geo

Geo

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So I'm finally getting back into astronomy after I had to sell my 10" dob due to some money/space issues...

I have the choice of two telescopes and was hoping for some good advice on which one to opt for. I'm mainly wanting it just for viewing pleasure, I'm not too bothered about astrophotography as I know it can be on the expensive side.

Anyway here are my choices...

- Orion Optics 200mm reflector telescope on a Dobsonian mount. It has a focal ratio of 4.5 which I believe is good for deep sky objects

- Celestron Nexstar 4se

I'm after a decent all rounder really, the 4se has a much higher focal ratio. They are both gonna cost me around the same price but the Orion comes with a few more EP's and a Telrad, dew shield etc. Nexstar is only supplied with one EP. I suppose I'm concerned that the Orion won't offer decent views of the planets and light pollution round here may affect the low focal ratio? I may be totally wrong as I'm still a bit of a newbie.

So, which one would you go for? Thanks for any help!

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jimmyjamjoejoe

jimmyjamjoejoe

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F4.5 is pretty fast, it'l be a nightmare on collimation and eyepieces. The skywatcher 200p is a more friendly F6, though tbh an 8" scope isn't really much of a spacesaver compared to a 10".

The 4SE will be great on planets etc, but you'l struggle to get satisfying widefield views.

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umadog

umadog

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Are you sure the OO 8" is f/4.5? The only one I can see on their website is f/6.

I'm not sure it's really right to think of f/4.5 as being "good for DSOs." Choice of focal ratio is influenced by a lot of things: the aperture of the scope and so the focal length, whether you trust the builder to make a rigid OTA, how important wide fields of view are to you (big DSOs), are you happy with tigh collimation tolerances, do you object to using a coma corrector, are you prepared to pay more for eyepieces which play well at sub f/5, etc.

Also, it's not really true to say that you need a slow scope for planetary viewing. For instance, my f/4.0 is stunning on planets. No complaints there.

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Geo

Geo

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Yeah the OO is from a private seller, definitely 4.5 ratio. Damn those are quite a few things to consider...

I'm pretty decent at keeping it collimated really. Since the OO scope is coming with Telrad red dot finder + dew shield + extension block, 25mm and 6.3mm sirius plossl, 20 orion(USA) expanse and 12.5mm plossl eyepiecess it's pretty much ready to go. I'm thinking I may just take the plunge with it as I'll be saving a bunch of money. It also seems to be in perfect condition. In fact I'll post a couple of pics...

If you say I'll be getting decent views with planets and it'll also be okay, or perhaps even better for DSO's then maybe I should go just for it, I'm also a sucker for that black finish...

2d91liv.jpg

14xe9fm.jpg

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umadog

umadog

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It looks nice. I obviously can't comment on the performance of that particular scope, but in my experience a fast scope can be great on planets. I think collimation, cooling, and quality optics are more important. An f/6 or f/7 will provide sharper views because there's less coma and because eyepieces are less likely to show astigmatism. A coma corrector will get rid of the coma (they're not cheap, though). A barlow doubles the focal ratio and so can make eyepiece astigmatism much less problematic. Nice eyepieces or eyepieces will narrower apparent fields will also show little or no astigmatism. A lot of fuss is made about smaller secondary sizes on slower scopes providing better contrast. You need to keep in mind that a secondary obstruction under about 20% by diameter is indistinguishable from unobstructed. An f/4.5 can potentially have a secondary that is under 20%. Also, keep in mind that the "better contrast" statement is vague. "Better" than what? A 12" with a 30% obstruction will provide better views than a 6" with a 15% obstruction. It will, however, be beaten by a 12" with a 20% obstruction. So it all depends what you're comparing to what.

The f/4.5 will provide nice wide views, which is very pleasant. Fast scopes can work very well and they aren't harder to collimate than slower scopes, they just have tighter tolerances. If you opt for it, you just need to keep in mind that there are some potential drawbacks. Nothing you can't work around, mind you...

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Geo

Geo

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From the Orion seller ..

"Its more of a deep sky objects scope - I never really used it for the moon and planets, except for brief looks. It's not bad, but not specifically what its designed for -*as I say I really*bought it for galaxies, nebulae etc."

Yet the Orion website states "If you are looking for a hand built British made telescope, designed for Galaxies, Nebulae clusters and even exceptional views of planets and the moon, we recommend the VX 8 our 200mm f4.5 model."

This is puting me off a bit, as I'm really after more of an "all rounder"

Should i just go for it or consider something else, I really want to get this right. I can't afford not to. Perhaps I should just take the plunge with this scope?

Thanks for your help guys.

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Geo

Geo

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No doubt I'll be in here annoying you all on which EP's to buy! For that I apologize in advance.

It comes with a 25mm and 6.3mm sirius plossl, 20 orion(USA) expanse and 12.5mm plossl

Decent starting point? First thing I'm going to grab is a barlow for it. Can i get a half decent one on a £60 budget?

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umadog

umadog

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Try them and see. The 25 mm probably won't look great but the 6.3 may be ok. The Explore Scientific eyepieces work well in fast scopes but I don't know if they're easy to get hold of in the UK. Here in the US they're permanently on sale and you get them shipped to the UK. Explore Scientific 82° Nitrogen Purged Products - OPT Telescopes

I'm sure people will chip in with stuff that you can source more locally. Look on the second hand market. You can always sell if you don't like it.

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