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Markos Symeonides

Jupiter seen as rainbow coloured ball

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23 minutes ago, John said:

I think Dave's F/16.5 is a refractor.

Sometimes you can see spikes through bright object if there is something like a powerline or telephone cable crossing near the line of sight. It does not actually need to be right through it, just near to it and you get a diffraction spike from it. I've discovered this the hard way by having a few such lines crossing my garden !

Also a 45 degree / 90 degree erecting prism type diagonal can cause a spike through bright objects. I think the Celestron 70 comes with such a diagonal as standard, which might not be helping things, astronomically speaking.

Yes, a refractor.

According to much published wisdom aperture in inches x 50 is the max magnification you should use. My scope ought to be good at 150x by the reckoning but I prefer it at 100x, just looks better, if smaller.  I suppose these formulae don't really take into account seeing, transparency, light pollution, thickness of the atmosphere. Perhaps if I were pointing the scope at the zenith from the Atacama desert 150x would be a piece of cake. Perhaps not so easy in south London, especially to the north where on a good night the sky is a yellow/orange glow...

 

Edited by digital_davem

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In theory the 50x aperture in inches (2x aperture in mm, 0.5mm exit pupil) applies to the splitting of double stars. The optimum magnification for planetary detail is lower at 25-30x aperture in inches (0.85-1mm exit pupil) while unfiltered DSOs (galaxies!) are best viewed with an exit pupil of 2-3mm which is the same range as your daytime pupil and the best corrected part of your eye lens. However, this is all based on the average telescope and the average eye and so it should all be taken as a rough guide with a pinch of salt and the actual optimum/maximum values are going to vary from person to person. 

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2 minutes ago, Ricochet said:

In theory the 50x aperture in inches (2x aperture in mm, 0.5mm exit pupil) applies to the splitting of double stars. The optimum magnification for planetary detail is lower at 25-30x aperture in inches (0.85-1mm exit pupil) while unfiltered DSOs (galaxies!) are best viewed with an exit pupil of 2-3mm which is the same range as your daytime pupil and the best corrected part of your eye lens. However, this is all based on the average telescope and the average eye and so it should all be taken as a rough guide with a pinch of salt and the actual optimum/maximum values are going to vary from person to person. 

Thanks.

That makes sense in that it explains why I prefer the crispness and "look" of views at 100x compared to 150x with scope. I'll try some double stars to see if the higher mag works better.

 

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On ‎05‎/‎03‎/‎2017 at 09:43, Markos Symeonides said:

Next time i get a telescope what would you recommend for a budget of about 300-400 euros?

Bump - No-one has answered this.   

I am a real beginner too so won't do any recommending, but from what I read on SGL that seems a fair budget esp. on the second-hand market to buy manual something better than you have, though factor in 50 Euros of that budget to buy a useable plossl eyepiece in case what you buy doesn't have a brilliant EP to use.  Not a recommendation (I AM NOT QUALIFIED TO OFFER A RECOMMENDATION), but as a 'for example' I know you are Cyprus, but look here https://www.firstlightoptics.com/dobsonians.html and read about theSkywatcher 150P, even new, this is within that budget (they also seem quite popular on SGL), and I am sure they come up second-hand.   However, the advice to read the thread on what to expect even in a better telescope is an essential one before you go shopping - I did this, was surprised by what I read, but then proceeded with a purchase, but replete with the knowledge of what I could achieve rather than unrealistic expectations.

Edited by JOC

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Paul73, well of course it is (it seems the most recommended 'scope on SGL LOL), but I could hardly recommend more or less what I own could I?  I'm not qualified to do so LOL

Edited by JOC

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5 minutes ago, JOC said:

Paul73, well of course it is (it seems the most recommended 'scope on SGL LOL), but I could hardly recommend more or less what I own could I?  I'm not qualified to do so LOL

Haha. I see. ??  Didn't read your equipment list! Nice settup.

Good point re unqualified reccomenders. You can state what you can see with your settup and perceived ease of use / quality etc.   Which, properly qualified, is all useful info for the potential buyer

Having owned or looked through most of the SW, I'm pretty happy to recommend even though I'm no expert. And, enough people who I would regard as "experts" have recommended this scope.

Paul

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Your 70mm will show a good number of things, the reral trick is to pick the right objects :icon_biggrin: Try aiming it at Auriga and the 3 Messiers in there, keep the magnification lowish at say 25x to 30x, well within the scopes ability.

As has been said the scope is an an inexpensive achro and chromatic aberration will be a factor. A big bright thing like Jupiter will show a fair amount. However it sounds like you had a bad time with it.

As to magnification do not plan on greater the 70x - the scope diameter. Most scope seem able to deliver that and I then consider any more a bit of a bonus or luck. Equally 70x is fine for Jupiter. 60x is likely better.

A "next" scope will depoend on what you want, cost and type. If you want to stick to refractors then maybe try the Bresser refractors. They do something like a 102mm @1000mm focal length - not the 102mm at 600mm focal length as this will again display CA to a fair extent. Something like the 102/1000 should be good for Saturn if you drop an 8mm eyepiece in. Don't go thinking that dropping in a 4mm will be better, it won't. All scopes have their limits, and the limit tends to be a lot less then the box says.

Bresser do a 127mm option if I recall and if that fall into budget may be worth contemplating, but it will be bigger and heavier. So therefore will the corresponding mount required.

You might want to try a plossl eyepiece on the 70mm, say 8mm (not a 4mm). Just thinking that the eyepieces supplied will be basic and they may be adding to the CA that you are experiencing.

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I have the same scope. While I do see a fair amount of colour fringing, I've only had a chance to observe Jupiter when it's been quite low on the horizon, so I'm hoping that most of this is due to the atmosphere and not the scope.

I found that the prism diagonal that came with my scope was terrible. You could try viewing without the diagonal to see whether that makes an improvement. You might not be able to focus without the diagonal - if so try holding the eyepiece out of the end of the tube. Or if the scope came with a barlow (mine did) you could try that, although the barlow is likely to be pretty bad too.

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