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"Aperture is king" - Why refractors?

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#1 Hanns

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Posted 16 July 2012 - 10:18 PM

Inspired by many discussions I've seen over time about how aperture is king and how the impact of the central obstruction on other designs is overstated, I am curious why people spend the extra money on refractors.

Consider that you can get an 8" f/4.9 newt from Orion for $300. You get the relatively wide field of view, no CA, and a lot more aperture for way, way less than even a no-frills 5" ED doublet would run. Heck, throw in the coma corrector too, and you still don't even come close.

I can only speak for myself, but having owned a Newt, and SCT, and now refractors, I find that there is a certain visual aesthetic that decent refractors provide. Very sharp images, high contrast, no diffraction spikes. Bonus: no messing with collimation (not hard, but convenience is worth a lot to me since my observing time is limited... and I might just have two left hands [I'm right handed :lol:]).

I'd love to hear your reasons.

#2 jmiele

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Posted 16 July 2012 - 10:38 PM

:gotpopcorn:

#3 David Pavlich

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Posted 16 July 2012 - 10:49 PM

Depends on what you're looking at. The vast majority of these conversations usually revolve around looking at Saturn or Jupiter because of the clarity of view. However, for me being someone that likes to see M74 from my typical suburban backyard, a 6" scope won't see M74 regardless of its optical quality. 6" of aperture can't overcome the light pollution. Trust me, I've tried.

So...it comes down to what you want to see and what your viewing conditions will allow.

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#4 mark8888

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Posted 16 July 2012 - 10:57 PM

I hope this is seen as fitting neatly within the original question rather than any sort of hijack: why big expensive refractors? Like the AP 175, the TEC 180? These get into the 20K+ range. To hear many posters, theres no advantage at all of a refractor over a reflector if the reflector just has slightly more aperture to compensate for the central obstruction, especially if you are visual only. So, is there some real advantage to using a 7 inch APO refractor rather than a reflector with a bit more aperture? :gotpopcorn:

#5 jrbarnett

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Posted 16 July 2012 - 11:36 PM

Very simple. Because the "aperture is king" folks are dead wrong. :winky:

Regards,

Jim

#6 BWAZ

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Posted 17 July 2012 - 12:11 AM

I would say "quality aperture is king".

#7 GOLGO13

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Posted 17 July 2012 - 12:23 AM

There are advantages and disadvantages to all of the different types of scopes. For certain objects, aperture is most certainly king. Have you ever been in a dark sky with a 10 inch telescope? A 16 inch telescope? A 30 inch telescope? I have...and they were not refractors. Did they have disadvantages? sure. But when you can count a ton of Saturn's moons, see crazy views of galaxies, nebulas taking on a whole new meaning, color in planetary nebulas, Globular clusters shimmering like star dust...it's something special. Did I have to climb a ladder, you bet.

On the other hand, refractors do have some great features and visuals. For their aperture, APO refractors out-perform similar designs in my opinion. But, they cannot make up for aperture in many cases. Maybe if we compared a 4 inch apo to a 5 inch SCT, I could buy that. But a 6 inch F8 newt would probably out perform the 4 inch apo on many objects. Even an inexpensive one. Now, consider that if you bought a premium newt (which you could for the price of a small quality apo), it's a different story. I think people forget that there are higher quality newts out there...which would then be on par for comparison with high end refractors as far as quality goes.

As far as I'm concerned...it's great to have both. A big newtonian and a small to medium apo refractor. Then you cover all your bases.

#8 beatlejuice

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Posted 17 July 2012 - 12:33 AM

For me, if I just want to spend an extended period of time on something (yes Jupiter,Saturn or the moon) and more recently the Venus transit,or, certain star clusters that have a habit of mesmorizing me, I find it much more relaxing to let my inexpensive drive do the work while I concentrate on observing with my refractor.

On the other hand when I really want to explore faint objects or really bring out the fainter stars in those star clusters and resolve globulars while still having the option of observing solar system objects, my dob is the instrument of choice.
I truly enjoy both options.

#9 mark8888

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Posted 17 July 2012 - 12:41 AM

As far as I'm concerned...it's great to have both. A big newtonian and a small to medium apo refractor. Then you cover all your bases.


I see this comment very often... which is why I wonder in particular, within the context of the OP's "why refractors" question, about the place/value of large apo refractors, like the AP 175 or TEC 180.

#10 SeattleScott

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Posted 17 July 2012 - 01:21 AM

Those big refractors are going to have a limited market because they just about require an observatory, and a trust fund. If my backyard was dark and I had an observatory and $25k I didn't know what to do with, I would likely go with a big refractor (although if I had an observatory I would have a hard time passing up a 25" dob if I could get past the ladder thing). But for most people the large apos aren't a viable option, due to portability and price.

It really is a personal thing about those clean pinpoint stars. I remember looking at M13 through a 4.3" premium refractor and a 10" Chinese dob. The dob obviously resolved M13 better and even the refractor owner felt the dob gave the better view. But I felt myself drawn to the clarity and pinpoint stars in the refractor. Can't say I necessarily liked the view in the refractor better but it was different, and nice in its own way.

#11 Lane

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Posted 17 July 2012 - 01:23 AM

I recently acquired a couple of small APOs (92mm and a 106mm) and I regularly use an 11" SCT. There is no doubt that the 11" sees more detail on planets and can find many more DSO's. But on 4 of the last 6 trips I have made to a dark site, all I took with me were binoculars and one of those refractors. I have picked off several hundred DSOs and double stars with those little scopes so far and enjoy using them every bit as much as the 11". The secret is "DARK LOCATION". Being in a place that is free or almost-free of light pollution makes a huge difference in what you see with a smaller scope. I am not saying that M13 is going to reveal as much detail as you would see in the big scope, but what you do see can be more pleasing to the eye mainly because of the crisp star images produced by a refractor. M22 a fairly plain looking globular in the 11" is a sparkling jewel in the 4" refractor. Then of course there is the wide field of view you get with most of the popular short APO refractors being sold right now. Seeing several magnificent DSO's in a single view is hard to top. Large star clusters always look better in a wider field. My favorite all time view of the veil nebula is with an NPB narrowband nebula filter in my 92mm scope. And of course I am seeing the entire complex in one view, with the 11" I am scanning around for 3 minutes just to see the whole thing. The other advantages are obvious like fast setup, fast temperature acclimation, smaller mount required, easier to transport.

So the bottom line is that you can definitely see more with a big reflector or sct, but what things you can see with the small refractor can often be more pleasing. To me the best approach is use both types of scopes in the same session if you have enough space to pack them for the trip to a dark site.

#12 Astrojensen

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Posted 17 July 2012 - 02:41 AM

While aperture really is fun to have, it sometimes create more trouble than it solves. Aperture has drawbacks:

- it can be expensive

- it can be too large to store in a small house or apartment. Not everyone has a backyard shed or garage.

- it can be too large to transport

- it takes a while to thermally stabilize

So, if, for example, you live in a small house or apartment and can only observe for about an hour or so each evening, a big reflector makes very little sense. It takes up too much room and will not (in my climate, at least) acclimate before needing to go back in and thus never deliver steady images. Storing it outside may not be an option for many people. In such a situation, which I believe is quite common, a refractor makes a lot more sense. It can be broken down in small parts and stored in a closet or under the bed, perhaps, and has fast cooldown and deliver sharp images quickly. My own 6" f/8 takes about 20 minutes to cool down from a warm room, before it is limited by the seeing. Couple this with the versatility of the refractor, I can also use it for solar observing, for example, and it's obvious to me that there's always going to be a refractor in my telescope arsenal.

There's good reason refractors remain popular, despite the easy availability of large aberture dobsonians. Both have their strong sides.


Clear skies!
Thomas, Denmark

#13 Jon Isaacs

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Posted 17 July 2012 - 04:57 AM

Inspired by many discussions I've seen over time about how aperture is king and how the impact of the central obstruction on other designs is overstated, I am curious why people spend the extra money on refractors.

Consider that you can get an 8" f/4.9 newt from Orion for $300. You get the relatively wide field of view, no CA, and a lot more aperture for way, way less than even a no-frills 5" ED doublet would run. Heck, throw in the coma corrector too, and you still don't even come close.

I can only speak for myself, but having owned a Newt, and SCT, and now refractors, I find that there is a certain visual aesthetic that decent refractors provide. Very sharp images, high contrast, no diffraction spikes. Bonus: no messing with collimation (not hard, but convenience is worth a lot to me since my observing time is limited... and I might just have two left hands [I'm right handed :lol:]).

I'd love to hear your reasons.


A photographer owns and uses several lenses. As an amateur astronomer I own and use several telescopes. For my smaller telescopes, it's refractors, for my larger telescopes, it's Newtonians.

In general, refractors are small telescopes and make very good small telescopes. The disadvantages to a 3-4-5 inch Newtonian or CAT are significant so a small refractor of high quality is a good choice doing the sorts of things smaller telescopes do best, portable, wide field views, few thermal issues...

But in the larger sizes, a refractor is at some serious disadvantages, color correction is dependent on both aperture and focal ratio so when one moves towards medium sized (8inch-10inch), the focal ratios become quite long, there are no 10 inch F/5 apochromatic refractors, the scopes become physically large as well as heavy and expensive. The efficiency of the refractor is no longer of such importance, there is plenty of light. The portability that was so handy in the smaller refractor is no longer, the SCT and Newtonians are at a definite advantage in the mid sizes. And, such refractors have big chunks of glass so thermal equilibrium issues exist. And of course, there is the expense.

---------------

In my world, it is not a question of one or the other but both.

In my backyard on a work night, it'll be one or the other but on the weekends in the mountains, or on vacation to the black skies of the Navajo reservation, it's both. I almost always setup a 3 or 4 inch apo alongside a Dobsonian that is 12.5 inches or larger... Such pairs compliment each other, provide me with capabilities that exceed those of either scope.

At the eyepiece, brightness, sharpness and contrast...

A 10 inch F/5 with a Paracorr and the same eyepieces it takes to make a 4 inch F/5.4 sharp across the field, this can be essentially perfect. It is tempting to call it "refractor-like" except that most refractors have issues with field curvature...

How sharp and clear is M30 or M80 in a 4 or 5 inch refractor as compared to M30 or M80 in a 12.5 inch, 16 inch or even 25 inch? Not too... How much contrast of the finest planetary details is there in a 4 or 5 inch scope... close doubles, a 10 inch outperforms a 4 or 5 inch.... these are things that are primarily functions of the aperture...

On the other hand, the Veil, it is quite nice in both big and small scopes, the Pleiades, best in small scopes, the California Nebula, best in small scopes.

----

It is important to recognize the tools one has. I use small hammers for jobs that are best done with small hammers, I use big hammers for jobs that are best done with big hammers. I have both, I use both.

Jon

#14 Erskin71

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Posted 17 July 2012 - 05:35 AM

:gotpopcorn:


:funny:

#15 Don Trinko

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Posted 17 July 2012 - 06:18 AM

You have discovered why many of us have more than one scope.
I have a Genesis and for planets it is great but M13 is just a small gray blob. Terrestrial objects look great also.
With my 8" Dob M13 shows individual stars but for Terrestrial objects the central obstruction shows most of the time. All IMO; Don T.

#16 Hanns

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Posted 17 July 2012 - 07:37 AM

:gotpopcorn:

Indeed, but that is the point ;) But I trust we can have a grown-up conversation here (looking good so far). No one needs to defend themselves here. Obviously we all have our reasons and I'm just curious what those might be.

The major point I see being made is "right tool for the job" - but what's interesting is the differences in what people consider the right tool, which (at least for me) comes down to something more basic than aperture. It's how much pleasure I get from using the thing in total. For me, this includes:
  • Setup/breakdown/cooldown time
  • Maintenance (collimation)
  • Looks - yes, let's admit we like to look at our scopes, not just through them. Reference the picture threads in every sub-forum as evidence :smirk:
  • Image quality (obviously)
  • Image aesthetics - Different optical systems will render the same thing differently, even if we can empirically state scope x and scope y of different designs show the same amount of detail. I believe this is one of the reasons we see people going for large refractors despite the cost and loss of convenience that smaller models provide - they want the light bucket with the refractor aesthetics.
For example, this quote by GOLGO13 is interesting:

Have you ever been in a dark sky with a 10 inch telescope? A 16 inch telescope? A 30 inch telescope? I have...and they were not refractors. Did they have disadvantages? sure. But when you can count a ton of Saturn's moons, see crazy views of galaxies, nebulas taking on a whole new meaning, color in planetary nebulas, Globular clusters shimmering like star dust...it's something special.



Yes, that does sound special, and sadly I've not yet had that opportunity. However, I will take you at your word that this is true for the sake of discussion. Is there magic in looking through the eyepiece of a 30" dob? No doubt. Would I want to own one, even if I had a place to store it, a way to move it to a dark site, and money was no issue? Negative - I'm way too lazy to do the setup and breakdown, and way too impatient to wait on that sucker to equalize.

Finally, I think there is the sex appeal factor. It's the reason so many people choose Apple devices over the many competitors out there. They are sleek. They are beautiful. They feel good in your hand. Yes, I could get a $300 8" reflector from Orion. Is it going to have the sex appeal of either of my two current scopes? Doubtful.

I think like many things consumers buy, it's not just about getting from point A to point B (i.e. seeing objects), but getting there in a way that is pleasing to us and in style. Apple has made billions on this idea.

#17 cheapersleeper

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Posted 17 July 2012 - 07:51 AM

There is no debate over the "right tools for the job" philosophy. The debate comes in when anyone from any of the astro sub-sets claims that his/her scope is "better."

#18 jmiele

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Posted 17 July 2012 - 08:08 AM

Hanns, Indeed a grown up conversation would be a pleasure. We may even get one here. You will have to hunt for it through the rest of the:

many tongue in cheek comments
several comments based only on ones personal experience
lots of comments based on limited experience
my dramatic rhetoric :)

You see, most folks like what they own. Not all, but many. As a result many have trouble being completely objective on these type questions. The answers are in there, you just have to find them. Kinda like a telescopic "where's Waldo". <-- dramatic rhetoric, but I'm not helping any more than that. :)

The "aperture is king" statement itself means the those agreeing are automatically limiting themselves. Any knife will cut, but a surgeon uses many to complete his/her task. This is NOT directed at anyone, however, a blanket "aperture is king" statement is....well, ignorant. While looking for the "most" aperture one can get "if" only one instrument is going to be purchased, one needs to consider "how" they will use the instrument. Given their objectives, the biggest "refracted" objective they can afford might be a better choice than a larger "reflected" one.

The biggest puzzle to me is that in the hobby SO many people are more than willing to share access to their scopes at SP's and many people with these type questions don't take advantage of it. A star party is a great place to see many objects, and objectives. :) If you find at the end of the night you want to take home more than one of the instruments you looked through, you've found the answer.

Best,

Joe

#19 russell23

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Posted 17 July 2012 - 08:09 AM

I started a reply several times and cleared it. It boils down to this: I like refractors more than reflectors. Mainly I like the nice flat-field views with my 5.5" refractor, pinpoint stars, no messing with collimation, quick cooldown times. I imagine at some point in the future I might once again add a larger dobsonian to the mix, but for now I just don't think I would use a dob enough to justify the expense.

Dave

#20 PhilCo126

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Posted 17 July 2012 - 08:20 AM

Why refractors?
Portability up to 152 mm aperture, thermal stability, clear images, almost never to be collimated,...

" Gentlemen only ever use Refractors " :refractor: :imawake:

#21 Hanns

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Posted 17 July 2012 - 09:22 AM

There is no debate over the "right tools for the job" philosophy. The debate comes in when anyone from any of the astro sub-sets claims that his/her scope is "better."

I see a lot of disagreement as to what the right tool for any given job is - and I can see how it could get emotional for people who have invested significant resources in certain instruments and don't want to hear that some other instrument might do x better.

The biggest puzzle to me is that in the hobby SO many people are more than willing to share access to their scopes at SP's and many people with these type questions don't take advantage of it. A star party is a great place to see many objects, and objectives. If you find at the end of the night you want to take home more than one of the instruments you looked through, you've found the answer.

I live very near to the Skies Unlimited store (same shopping center I go grocery shopping in - dangerous!). When I walk in there, I want to take everything home :lol: Seriously, Newts, cats, refractors - all potentially beautiful instruments just waiting to show us cool things.

...pinpoint stars, no messing with collimation, quick cooldown times. I imagine at some point in the future I might once again add a larger dobsonian to the mix, but for now I just don't think I would use a dob enough to justify the expense.

Yes... I think this describes my feeling on it as well. I'd love a light bucket, but I don't know that I'd drag it out enough to justify the expense and space it takes up. Maybe a fast newt on my existing mount.

#22 GOLGO13

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Posted 17 July 2012 - 09:40 AM

I find dobsonian reflectors to be quite easy to setup and take down. They are much easier/quicker than an equitorial mounted telescope to me. My 4 inch apo on a porta mount is equivilent to my 6 inch dob (can pick it up and move it all at once). Both are great scopes. The 10 inch requires setting the mount out, then dropping in the tube. A quick check of collimation with a cheshire. Equitorials are a pain to me. I do like the capability they provide. But I rather have a nice alt az for any scope type, unless I need the tracking, thus why I have both options.

Cool down I can agree...but more of an issue in the winter than normal times. Usually I just set my scope on the back porch and no big deal. Or I get out the refractor while the dob is cooling. Cool down can be a bigger issue as the scope sizes grow. And can be a big issue for cassegrains and Maks with closed tubes and no cooling fans. I've read that flourites need a little more cool down than other refractor glasses. My 80 is a flourite.

A 30 inch dob is best left in an observatory or moveable shed. That's a beast. But there are plenty of 12-16 inch truss dobs which are quite managable. They also look great and have great craftmenship. Of course, they also cost a lot with premium mirrors.

Sex appeal with telescopes? That's a new one for me. I mean, among us I agree. But I can tell you that non-astro people are more impressed with my 10 inch (insert joke here) than my sexy apo.

#23 yashi

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Posted 17 July 2012 - 09:43 AM

if you limit your decision by scope size. The refractor can have the upper hand.

if you limit your decision by money...dont even think about a refractor.
all these contrast/ resolution arguments are meaningless if you compare a refractor with a reflector of double the size. the reflector OBLITERATES the refractor.

the point is..it doesnt matter how big your scope is, because all of them show basically nothing.
its only a question of how much you need to see to be satisfied.

i prefer refractors, because i dont like diffraction-spikes. plus they look more like a telescope :p

#24 jmiele

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Posted 17 July 2012 - 09:47 AM

"the point is..it doesnt matter how big your scope is, because all of them show basically nothing."

That may be the most accurate point made yet in this thread. In essence it is true that for all their differences in design and size, a novice moving up to the eyepiece will see little difference. The real work is in learning to interpret and dig into what's there, and that can happen in any instrument - at any size.

Joe

#25 Hanns

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Posted 17 July 2012 - 10:30 AM

the point is..it doesnt matter how big your scope is, because all of them show basically nothing.
its only a question of how much you need to see to be satisfied.

That's pretty thought provoking. It's pretty easy to forget the bigger picture of what's really out there versus the little bits we can see with any instrument an amateur would have access to.

Sex appeal with telescopes? That's a new one for me. I mean, among us I agree. But I can tell you that non-astro people are more impressed with my 10 inch (insert joke here) than my sexy apo.

Haha, I agree. Yes, I was talking specifically about enthusiasts (people willing to drop serious coin on a telescope). I also agree with your other points. In the case of a dob, you are absolutely correct, and I find the GEM to be a pain compared to any alt-az mount. However, since my particular thrill right now is astrophotography, the GEM is kind of a necessary evil and since I live in an apartment, there's no room physically for a big dob. But that's specific to my situation and not a statement on what's better or worse.






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