Refractor vs reflector?

[fondofchips]

I have 8x42 Opticron Binoculars & a Lyra 120mm refractor.  I also have a SW 200P, fully flocked with motorised focuser, I get much more pleasure from the first two.

The Newt is a pain to get on target, I could look as much stuff with the Lyra before I got cold.  Even upgrading the finder to a SW ST80 has improved the situation but not the improvement I had hoped for.

I have 2 choices now, use the GOTO to get the Newt on target or sell it & buy a bigger frac.  For out & out capability the Newt is better, but for me not twice as good.  I'm still enjoying finding my own way around the night sky, it's part of the fun of it.

I would say the original 3" frac vs 6" Newt rule mentioned at the beginning of this topic, though not particularly accurate, is not far out.

Best feature, you can sit down to look through a frac!  Just my sixpenneth.

Clear Skies,

Fondofchips.

[The Flinty Fox]

Hi.

Have read this thread with interest and i am quite aware that the OPs question doesn't have a real answer to it, so I'm going take a more simplistic approach. Now this could end up being nonsense but i just want to talk about what a reflector will have to undergo to come down in performance to that of a smaller aperture refracting scope. I know the OP question is comparing 3 inch refractor to a 6 inch reflector but i will compare a 4 inch refractor to a 6 inch reflector which seems a more common comparison these days.

As i understand it resolving power is based on aperture, i.e surface area of objective mirror/lens. The suface area of a 102mm lens is 8167mm square, the surface area of a 150mm mirror is 17663mm square. That means the total surface area of the 102mm lens is only 46% of the total surface area of the 150mm mirror. This means that the larger reflector has over twice the light gathering and resolving power of the smaller refractor. So if you are comparing a 150mm reflector and a 102mm refractor of similar quality and the views through both show a similar level of detail then that suggest that the reflector is operating at only 46% efficiency of its full capacity. So it is losing 54% of its resolving power.

I am sure that you are all aware of this and i am not trying to tell you something you don't already know, but this is a huge performance deficiency for the reflector. To think that my 150p at running at 102mm capacity is too much to bear, and apo maybe, but not a refractor of equal quality. This is just something i was thinking about after reading many threads on this subject (must stop reading those). I do have a smaller 80mm refractor, ok it's an F5 so maybe not a fair comparison, but it does not compare well to my 150p on anything.

But anyways thats my 2 pennies.

Now where was that website i was looking at with that nice refractor...

Paul

[Moonshane]

as far as I can tell resolution is a function of aperture not optical area so not quite the same as light gathering.

in arc seconds it is approx. 11.6/D (D=aperture in cm)

so 11.6 / 10 = 1.16 for a 100mm scope and 11.6/15 = 0.77 for a 150mm scope. therefore the 150mm scope provides a 33% increase in resolution. the 150mm scope does though gather twice as much light and produces a brighter image at the same magnification.

[The Flinty Fox]

as far as I can tell resolution is a function of aperture not optical area so not quite the same as light gathering.

in arc seconds it is approx. 11.6/D (D=aperture in cm)

so 11.6 / 10 = 1.16 for a 100mm scope and 11.6/15 = 0.77 for a 150mm scope. therefore the 150mm scope provides a 33% increase in resolution. the 150mm scope does though gather twice as much light and produces a brighter image at the same magnification.

That's good, so not as much of a difference as i though. Your right sorry about that i thought it might end up being nonsense.

Cheers Paul.

[mikeDnight]

Some might imagine that buying that amazing top end apochromat costing a thousand pounds per inch or more, would end the desire to compare the scope with others, but it doesn't! A quick brows through CloudyNights will reveal that refractor lovers can't resist the temptation to critically assess, or in layman's terms rip to shreds, every other design and make on the market. They will spend thousands on their telescopes, then spend much of their time looking for the minutest fault in their own instruments or those of others. I can't ever remember seeing reflector users getting so passionate about which reflector is best.

You have to laugh!

The truth is that some reflectors are noticeably better than others. A 6" F10 Newtonian will wow even the most passionate refractor fan, but then a 10" F 10 becomes not so much fun to use.

I have to confess that I've never, ever seen a sub F10 reflector deliver a view of the planets that in anyway approach the views delivered by my Takahashi FS128, and I have used a great many Newts up to 30" aperture. A few years ago at my local astronomy centre where a large number of these reflectors are set up, one newcomer asked me Why the Vixen Fluorite gave better views of Saturn than anything else? Out of the mouths of babes!

When I took my FS 128 along during the 2003 close approach of Mars, I set the scope up in an out of the way place in the hope of not being pestered by the visitors to the centre. All was going well as my friends and I observed Mars from a distant corner of the field, when an Asian gentleman stumbled upon us. He asked if he could take a look and I reluctantly acquiesced to his request. It was a mistake! At the top of his voice he revealed our cover by shouting "Abdul, this is the best one here!"A squabble of would be astronomers descended on the telescope ending our peaceful viewing session.

The point here is that time after time people with no axe to grind, and after looking through the larger reflectors before hand, considered the Stunningly sharp and contrasty Apo's to deliver the finest planetary views.

A good apo is expensive but in my view well worth the cost. When a 5" fluorite doublet such as the FS 128 reveals the rings of Saturn as a mass of concentric fine lines and Enkes division is an obvious feature nearly every time, then there has to be something in this refractor mania that's worth paying attention to.

I've decide that this is my last comment on this topic as I can yap forever about it and I have to draw the line somewhere. :-)

Mike

[Qualia]

At the end of the day, it matters not what telescope type is used. Each in their own manner will present and frame the universe in a slightly different way which suggests that each type is essential to own and enjoy and learn from .

I truely feel that each telescope we use inevitably brings us back to ourselves; that we have been a nebula and an open cluster, a red giant and a supernova and one day, we will be again. There is no correct telescope separating us from the stars and the DSOs, there is only time....

[paulastro]

I agree with Nick regarding seeing, it's certainly a leveller, and really no conversation of the merits of various scopes is really very meaningful unless we consider the observing conditions under which they are mostly used - and of course what  the favourite objects of the observer are.

I live in the maelstrom of weather patterns in West Yorkshire.  The seeing from early Autumn and through Winter is usually very poor whatever way you wish to measure it.  If you have a scope of six inches or larger, you will be lucky to get a single night where it can perform to it's theoretical limit.  You may get the odd moment, but you have to be a dedicated planetary observer if you have a six inch or larger to catch them.  I have an 80mm ED which is the only one of my current scopes which routinely will perform as it can and show consistently sharp images - it can give a wow planetary image in very poor conditions.  If I only have a brief window of opportunity this is always the telescope I will choose for Lunar and planetary work.

If I have more time I will use my six inch refractor and hope I can catch some of the fleeting moments of good seeing which occasionally  crop up despite the prevailing poor seeing.  Of couse the six inch is far better on deep sky.

Peter Drew (who runs The Astronomy Centre and a highly experienced observer of course) has frequently related to me the wonderful Lunar and planetary views he commonly achieves using his 8inch SC in Tenerife where the seeing is usually a zillion ( a slight exaggeration  ) times better than I  ever have at home.  It's not unusual for Peter to be able to usefully use x400 and above magnification during his observations.  How many of us can truly say this is the same when using the same scope in good old blighty?

I suspect if we lived in New Mexico or California many of our choices of telescope would be quite different. 

[Azelfafage]

After a couple of years being scope-less, I'm considering putting my toes back into the water. I think space and portability also need to be considered in the equation when debating what's "better" - apart from the optics -  because you have to be able to store and move about your nice shiny new toy once you've decided what to get in the first place.

I take people's point (on numerous other threads) about Dob scopes like the Skywatcher 200 being the best value for money on the market, being an "all rounder" and reasonably inexpensive, but I share the concerns of some who comment on their "footprint" and having one is out of the question for me for reasons of space (small shed) or being threatened with divorce if I tried to keep one in the house  however a smallish (up to 4") refractor or Mak could be a possibility, with the mount folded up in the shed.

I did once own, as a first scope a battered 4.5" second-hand Tasco reflector (once upon a time, many years ago, Tasco really DID actually make half-decent scopes ) - this provided nice enough views of the Moon and Jupiter's belts and for example could just begin to resolve the outer parts of the Hercules clusters, and the whole thing was quite compact when put away even with an EQ mount. I think f ratio was about f8 IIRC, so a manageable tube length. At about the same time, I knew someone with a 3" refractor and looking through this I couldn't see any noticeable performance difference compared to mine. I remember reading somewhere that the modern comparison should be 3" frac vs 4.5" (not 6") Newt, and in my experience there was nothing much between them.

I recently phoned a dealer (who shall be nameless and it wasn't FLO anyway )  and enquired about 2 (manual) scopes I was interested in, one of which was a refractor. He was rather snooty about the refractor, saying he "didn't sell many" and in his opinion, it was a dying market, which surprised me rather. "It's all SCT's and GOTO's these days" he went on to say.

So, to conclude, two thoughts:

Is the traditional refractor market really diminishing?

Is it anyone's experience out there that dealers are "pushing" SCT's/GOTO's as "trendy" instruments over and above traditional refractors and reflectors?

If both the above are true, then this renders the current debate less relevant over time anyway.

Regards,

A.

[Qualia]

Skywatcher 200...I share the concerns of some who comment on their "footprint" and having one is out of the question for me for reasons of space

I don't want to derail the thread but my 10" truss dob principally made of decent, solid wood, weighs about 18kg. An AZ 4 and Tal 100rs weighs around 13kg. In terms of weight, they're pretty much on a equal footing. When it comes to occupying space, the frac and AZ 4 take up more. Not only when packed and stored in two long canvas bags, but also when fully assembled. The AZ 4's foot print is greater than the 10" dob's. I really don't know anything about SW's 8" but my gut feeling is that a mounted 4" f10 frac won't be smaller, lighter or occupy less space than a 8" dob.

I honestly don't know which telescope is the most popular but I feel all the three principle types still have a very active market. Furthermore, I imagine most astro-dealers of some respect - and it was the case when I started out - would advise their clients on a one to one basis, pointing them to a range of possible telescopes rather than plugging just one type.

But I feel this is beside the point. Even if it were the case that SCTs, or fracs or newts were the most popular scopes purchased, it wouldn't render the debate of the merits of each telescope type irrelevant.

[iapa]

On 26/02/2015 at 18:28, damnut said:

Great thread, pandora's box opened. Currently have five scopes, SWMBO asked why five and only two eyes, asked her to get her jewellery box, I said so you only have five fingers on each hand....

 

That 1 I must remember.

Not sure I have the guts to use it tho'