Allrounder ?

[Ally8446]

Hi again folks. I know that as a rule aperture is king but as I'm drawing closer to upgrading my scope I was wondering if a 4-5 inch refractor would suit my needs more than the 5" reflector I have at present. My main interest is DSOs, however I do enjoy planetary work (probably 70%-30% ). I have read that a good 4" refractor will give you pin sharp planets and perfect points of light for stars but also reasonable images of DSOs. I'm trying to find the happy medium between visual gratification, portability (I'm very near a good dark sky site) and price (approx £400). What are your views on this? All input gratefully received thanks. Al

[Qualia]

I don't want this to go down a subjective refractor Vs reflector avenue, so I will try to be has 'cold' and critical as possible and just give a couple of thoughts.

Firstly, nice one on deciding to 'upgrade' or get a larger scope. It means to me the astro bug has bitten and that is always a nice thing to see...

...Next....

From my experience, my 10" reflector does not give me a larger image. What it does do is make the image a whole lot brighter ; it gathers a lot more light than my Tal 100rs 4" frac and this is really helpful for deep-sky observing. I mean, I barely saw much more than a hint of a galaxy, could never resolve a globular in the frac, so evidently the 10" Newt has a clear advantage here.

The actual image size of the object is determined by magnification and with my f/10 frac and f/5 newt both scopes come pretty close. A 10mm in the former will give a 100x, in the latter, 125x but in either case, there does seem to be an upper limit to what magnification I can actually play around with. Atmospheric conditions - even in dry desert lands - rarely allow me use of anything over 200x except, of course, with the Moon and on many objects, especially DSOs, this high mag is clearly overkill .

An f/10 focal length will be kinder on cheaper eyepieces; with cheap EPs, the f/10 ought to give a sharper, more pinpoint image than the same EPs used in an f/5. And I am sure this is true - especially when it comes to cheapy wide field view EPs. But all the EPs I use are under €100 brand new and I get wonderful views in both my scopes; contrasty and sharp.

I find the BGOs (5, 6, 7, 9mm) on planets and the moon really nice and don't find that with the dobsonian mounted scope the ortho's FoV is a challenge . In the range between 10mm to 25mm, I'm currently using X-Cel LXs and TV plossls and both types perform wonderfully in both telescopes. I guess, wanting to get widefield (68º & +), really sharp, contrasty image EPs in an f/5 will come at a price, but Rome wasn't built in a day and this type of EP upgrade would be a gradual project of development (unless you were loaded).

A frac will give you a left-right reversed image which some folk find confusing when coming to read star maps etc. The Newt image is south-north. I find both images easy to follow but I appreciate that folk may prefer just to turn the map upside down and use the Newt, rather than mentally juggle the frac's flipped images; especially at 3am in the morning.

On bright objects like Jupiter and the Moon, my frac shows a hint of chromatic aberration (which is no bad thing for me) whereas the Newtonian shows none. However, in the image of Jupiter, for example, the Newt shows diffraction spikes (which add an aesthetic feel just as CA for me) whereas the frac shows none. The Newt will need collimation, of at least the primary mirror, on a regular basis. The refractor, on the other hand, is always pretty much ready to go. Personally, of what I have seen, I find the images in both telescopes wonderful and spellbinding.

The 10" will see things the frac could never dream of doing. The Moon is just unbelieveable, as is the beauty of witnessing the spirals of a galaxy and resolving the majestic beauty of globulars, for example. However, the stars of an open cluster are just a tad tighter in my frac, there is this degree of contrast which makes star fields sparkle and in the daytime the 4" doubles as a lovely white-light solar scope. On planets, and to be honest, we are generally only ever referring to Saturn and Jupiter, I haven't had the 10" long enough to be able to make an educated opinion.

As to viewing comfort, I find the dob mount more comfortable to use than an EQ5, AZ 4 type system for the frac. I have got into quite strange positions with the frac whereas the dob eyepiece always remains at a reasonable height whether viewing at the zenith or horizon. On the question of portability, I'm fortunate enough to have a 10" portable dob which is a whole lot easy to get on a public bus to my dark site, than carrying a 4" frac, mount and tripod. It's also handy to have this extra 6" because I know that once I'm out in the field of darkness , I'm not limiting myself to just viewing planets, sparkly star fields and open clusters. Back at home, the dob uses up less of a 'foot-print' area than the tripods' extended legs. Weight wise, they're pretty similar, the 10" weighs in at about 20kg, the 4" + mount + tripod weighs in at about 15kg.

Finally, I really don't believe there is a 'best' all-rounder that will be 100% 'right' on all occasions which is why most folk have a number of telescopes. On a personal note, I feel a 10" Newt and 4" frac make a wonderful couple of love .

Good luck with what ever you decide to do and I hope this post helps a little

[Ally8446]

That's a fantastic reply Qualia, thank you. Food for thought indeed. As soon as the decision is made, SGL will be the first to know.

Clear skies

[breezy]

Just read q's advice and really can't add to it

[glowjet]

Qualia in his excellent reply, has mentioned the Baader BGO Orthoscopics, just for information these are now no longer made and are beginning to fetch ridiculous prices on Astro B/S. Although I believe not quite to the same manufacturing standards as the BGO, Baader have replaced these with a new Orthoscopic with a increased FOV, see FLO for details, in addition the famous Circle T has also finished production, the Master, (very senior in years) Japanese optical maker Mr Tani, closed his doors in December 2012

John.

[floppygoose]

Excellent response Qualia

Phil

[Qualia]

Thank you to all.

If you've got anymore enquiries, Ally please don't hesitate to post

[bendiddley]

i've got an 8" dobsonian (skywatcher 200p) and i have to say that i get great views of planets and dso's. i haven't looked through a refractor before so i only have this scope to go by, but for me i feel like i've got everything i need. jupiter is excellent at the moment, i saw 4 bands the other night and the grs, saturn looked amazing last year even through the stock 10mm ep which i now know is not a great ep, i now have celestron x-cel lx's so am looking forward to seeing it through those. i like looking at pretty much everything, especially dso's and my dob delivers it all very well. hope this helps. good luck with whatever you decide