263 replies to this topic

[Mitrovarr]

An 8 inch dob with a good mirror is going to better 99% of the apos out there (since there are few 7 inch or larger apo) since you can get a 10, 12, 14 inch scope for reasonable money the dob is the way to go for deepsky and planets when the sky permits it.

To be totally fair to refractors, when you start going to premium dobs the price goes up a lot. Cheap dobs sometimes have good optics but there's no guarantee, and you'll probably need to tinker on it somewhat to kill tube currents and possibly to remove strain on the secondary mirror.

[Urbyz]

why am i suddenly thinking of cheese

Whahaha. It IS the cheese capitol of the world. So you’re welcome to join the busloads of cheese craving tourists that stampede our town every year. 

[Urbyz]

The refractor views are different and I think that's what most people like about them. The sharp pinpoint stars, crisp contrasty views with deep blacks. It's a different look.
Add to that the simplicity of setting up the small to medium size ones, quick cool down, no collimating and wide-field views. They really are versatile telescopes.
 

These are all points that speak to me and make me excited to go out and look for a good refractor.

 

My sensible side keeps me at bay though and it probably will be smart to own a bigger dob. But i just don’t see myself transporting one to a good dark site and since conditions in my hometown aren’t the best. I’m starting to wonder if maybe a 10” dob aside a high end refractor would be a nice combo to last me.

Edited by Urbyz, 25 September 2020 - 12:37 PM.

[Urbyz]

(PS: good luck with observing objects low to the horizon with a big dob! The 4" refractor is much easier when you get below (say) 15-20 degrees! So if you northerners want to glimpse some of our lovely southern objects a refractor may be the way to go! )

Yes thank you. I’m learning a lot about performance in relationship to location and conditions just through this topic. Seeing my conditions are bortle 8-ish, i would imagine going really big and get a un-transportable dob wouldn’t be smart. If a nice refractor performs better under bad conditions and lower angles, i would definitely be leaning towards getting one over a dob. But since every person seems to aknowledge both are great, a 10-12” dob would still give me options to throw it in a car and go to better sites.

[Urbyz]

Visual observing: big APO (130mm) refractor VS. big (12") Dobson.

 

DEEP SKY:
If you live under a nice dark sky or don’t mind driving to one and want to do visual observing of deep sky objects, consider getting the Dobsonian.

 

If you live in an urban location with mild or heavy light pollution, consider getting the refractor. For deep sky observing use a tracking mount and add an inexpensive astro-video camera ($300) and do some EAA (Electronically Assisted Astronomy). You will see more detail in a few seconds from a light-polluted backyard with the refractor/video camera combination than you will with the larger Dobsonian under a dark sky used visually – albeit on a screen, but the views are really something to see. And you can use your scope in mild to heavy light pollution without traveling – a huge bonus. The more expensive but powerful image intensifier used with a 5” apo is an eye-opening, deep sky observing experience. Again, you can use an intensifier in mild to heavy light pollution but they are costly.

 

Adding modern light gathering technology to the refactor negates the Dobsonian’s (used visually) light gathering advantage and need to travel to dark sky locations.

 

PLANETS:
For the 12” Dobsonian to use it full resolving potential on the planets you will need: excellent seeing, which is (or can be) rare in most locations, aggressive thermal management, perfect collimation, excellent optics (Zambuto) and tracking at high power is nice (maybe a platform).

 

If the above is done and the seeing is very good/excellent and the planets are high in the sky the larger scope (with a good mirror) will definitely deliver the goods.

 

If the above sounds like too much for your location’s seeing or your observing style, consider the refractor. A 5” apo will not disappoint on the moon and planets. They: acclimate reasonably quickly, have excellent thermal stability, excellent contrast and light scatter control, do not need collimation, are more conducive to shorter sessions for a quick looks at the moon, etc. and are a little less fussy with the seeing conditions in most backyards.

 

This is what Sky and Telescope had to say about the SV 130mm refractor when they reviewed that scope…

 

“A 5-inch refractor is ideal for high resolution visual use on the sun, moon, and planets. Its resolving power of 0.9 arcseconds is perfect for sampling the typical seeing of 2 to 3 arcseconds common at most amateur observing locations….”

“…and they (5-inch refractors) aren’t as susceptible to poor seeing as large scopes.”

 

OTHER CONSIDERATIONS:
If planetary imaging is in your future, consider the Dobsonian but with some type of tracking. The refractor will also do nicely but for planetary imaging aperture is better, as one can eliminate poor seeing and add contrast etc. in processing.

 

If long exposure, deep sky imaging is in your future, consider the refractor.

 

If Ha solar observing or imaging of solar prominences and disk features is in your future, consider the refractor.

 

FINAL THOUGHTS:
I’m not going to copout and say get both, I don’t think that’s what you want to hear. I’ll just say that NO scope is the best at all things.  So, if you want “specifically” what the Dob does best, then get it.

 

But with the “right accessories” (video camera, GEM, solar filter, etc.)”, the versatility of a high quality, 5” apo refractor comes pretty close to being a perfect, single scope solution that can grow with you as your observing interests expand. 

 

Bob

Thank you for listing so clearly, all the things that made sway one to get one over the other.

 

What really hit home was when you mentioned all the things that need to be in place for a big dob to actually shine. The fact of the matter is that my seeing conditions are very poor and style of viewing lean heavily on the quick and convenient side of things. Most of the times it won’t be perfect outside. Most of the times i won’t have time to wait for cooling down. Most of the times, if not always, i’d like it to be a hassle free experience.

 

Thank you for also listing ways to enhance the experience with a refractor. I’ll have a look at intensifiers and although i’m not keen at looking at screens too much. (I do this for work all day long already) The EAA option might be a great work around.

[Urbyz]

It may be true that the larger Dob will potentially resolve finer detail, and of course will always give a brighter image, but the sharpness of definition offered by a good refractor is where its strengths lie. I have both 8" and 10" reflectors, both F6, so good planetary scopes, and both can show more, but not always!  And despite having these two great scopes at my fingertips, I prefer using my 4" refractor. The refractor is easier to use and always delivers a punch that exceeds its aperture class. I suppose much depends on where your heart lies, as if your heart is in it, you'll be willing to let a scope prove its worth.  Observing the planet's with a Dob is a chore for me as i love to sketch at the eyepiece, and struggling with the push/pull cumbersome Dob is awkward. The spider diffraction is something I hate and to me is just as distracting and destructive to a planetary view as chromatic aberration in an achromat, if not worse. My little Apo shows nothing but textbook perfection, and on an EQ mount is a glorious planetary scope. Double stars at 500X are perfection on a steady night and the Moon leaves me lost for words. When on a grab and go Altaz' it is the easiest and most pleasant scope to use for gliding through those flawless and awesome milkyway star fields, nebulae and clusters. 

 

Below are two recent sketches of Mars made using the 100mm apo. 

1601051904077_IMG_7722.jpg

 

1601051892765_IMG_7723.jpg

What lovely notes and sketches!

It’s wonderful to see when a person has not lost connection with the pencil, which we all learn at such a young age. (I draw for a living) The convenient and ease of use of the refractors seems to be a big selling point for most users.

[hoof]

I played with a 6-inch off-axis mask with my wife's 14.5-inch equatorial Newtonian on several nights when Saturn and Jupiter were well placed and tossed the mask in the trash. While the full aperture was not reaching its full potential because of seeing, it did reveal more detail and the larger aperture and more vivid colors were greatly appreciate.

Clear skies, Alan

I tried that with my 12.5” F/5 back in 2005. Same results. At no time did the masked down off-axis view appear superior to the full aperture, regardless of seeing or subject. That experiment colored my view of refractors for 15 years, despite getting an 80mm and 127mm apo in the meantime.

It’s only now with my high end Baader acami prism that I’m getting to enjoy my apos. I can see the appeal, less bright stars are little discs, and extended objects are stable. In isolation (not back to back against my dob) the views are aesthetically really nice. Was looking at the double double the other night with my 80mm and Vixen 1.6mm HR, and they were four stable circles in the view, very pretty. Even with perfect seeing my dob would have shown the other diffraction rings degrading the view.

To me that’s the appeal of refeactors, the aesthetics of the view. The views just look nice. Sure the big dob shows more, has more detail, is brighter, etc. But the higher resolution of the instrument shows the aberrations of the air column (seeing plus cooling currents), and the brighter stars show the diffraction rings more, which makes for a lesser aesthetic look.

And isn’t that the point of visual observing, to have a good aesthetic view?

[gnowellsct]

Visual observing: big APO (130mm) refractor VS. big (12") Dobson.

 

 

This is what Sky and Telescope had to say about the SV 130mm refractor when they reviewed that scope…

 

“A 5-inch refractor is ideal for high resolution visual use on the sun, moon, and planets. Its resolving power of 0.9 arcseconds is perfect for sampling the typical seeing of 2 to 3 arcseconds common at most amateur observing locations….”

“…and they (5-inch refractors) aren’t as susceptible to poor seeing as large scopes.”

 

OTHER CONSIDERATIONS:
If planetary imaging is in your future, consider the Dobsonian but with some type of tracking. The refractor will also do nicely but for planetary imaging aperture is better, as one can eliminate poor seeing and add contrast etc. in processing.

 

If long exposure, deep sky imaging is in your future, consider the refractor.

 

If Ha solar observing or imaging of solar prominences and disk features is in your future, consider the refractor.

 

 

And yet thousands of observers here in the NE, not known for its great seeing, have routinely seen large apertures outperform high end apos.  Myself among them.  It doesn't matter that this was published in S&T.  They're wrong.

 

I like my 5" triplet 130mm apo.  But the fact is that two Skywatcher Dobs 10" and 12" licked it in a fair fight.  And my C14 licked my FS128 in a fair fight.  And the 92mm apos (both of them) are outperformed by the c8 that they ride on.  And the c8 gives the 5" apo a run for the money on planets.

 

Some of the best imaging of the sun is now done with SCTs.

 

But anyhow we're talking Dobs here (thank goodness, for a change) vs refractors but the point is the same.  Outlandish claims are outlandish.

 

Greg N

[bobhen]

And yet thousands of observers here in the NE, not known for its great seeing, have routinely seen large apertures outperform high end apos.  Myself among them.  It doesn't matter that this was published in S&T.  They're wrong.

 

I like my 5" triplet 130mm apo.  But the fact is that two Skywatcher Dobs 10" and 12" licked it in a fair fight.  And my C14 licked my FS128 in a fair fight.  And the 92mm apos (both of them) are outperformed by the c8 that they ride on.  And the c8 gives the 5" apo a run for the money on planets.

 

Some of the best imaging of the sun is now done with SCTs.

 

But anyhow we're talking Dobs here (thank goodness, for a change) vs refractors but the point is the same.  Outlandish claims are outlandish.

 

Greg N

 

HERE is a link to very detailed website about astronomical seeing. Below is a relevant statement from that site…

 

“How often do nights of excellent seeing occur? At the William Herschel Telescope site in the Canary Islands, even this superb viewing location, second best in the northern Hemisphere, has many nights of relatively poor seeing: the distribution is positively skewed... and at this excellent site, a 10 inch telescope will experience seeing limitations on 9 out of 10 nights.”

 

If a 10-inch scope is seeing limited 9 out of 10 nights at La Palma, which has some of the best seeing in the world! – What are the odds in your backyard? And if the planets are not well placed, like the past few years, and at many times during an appearance, that will also lower those odds even more.

 

As to imaging, I stated in my earlier post “imaging” is a "different animal", as it is possible to eliminate some seeing issues and add contrast, etc. in data capture and processing.

 

Bob

[gnowellsct]

HERE is a link to very detailed website about astronomical seeing. Below is a relevant statement from that site…

 

“How often do nights of excellent seeing occur? At the William Herschel Telescope site in the Canary Islands, even this superb viewing location, second best in the northern Hemisphere, has many nights of relatively poor seeing: the distribution is positively skewed... and at this excellent site, a 10 inch telescope will experience seeing limitations on 9 out of 10 nights.”

 

If a 10-inch scope is seeing limited 9 out of 10 nights at La Palma, which has some of the best seeing in the world! – What are the odds in your backyard? And if the planets are not well placed, like the past few years, and at many times during an appearance, that will also lower those odds even more.

 

As to imaging, I stated in my earlier post “imaging” is a "different animal", as it is possible to eliminate some seeing issues and add contrast, etc. in data capture and processing.

 

Bob

I am often in an environment with friends where there are big scopes and good refractors.  Good is defined as Tak or AP.  I haven't seen a TEC in my club (yet).  The big scopes bring home the bacon.  Much more often than one night out of ten.

 

Greg N

[Bomber Bob]

OP, out my 50+ years in the hobby, I was a Refractor Snob for the first 44 years.  Then I bought a used 1971 Criterion RV-6... that one Old Newt changed this hobby for me.  A good thing, because that Orion XT12g almost turned me off reflectors... what a big floppy heavy mess it was.  Yes, it pulled in more faint fuzzies, but high-power planetary on that AZ platform?  Nope.  I prefer GEMs for serious observing (30 minutes or more studying 1 object).  So, I meant it about my 1980s Meade 826 -- it does everything well.  It's easy to set up, take down, and use -- easier than my much more $$$$ 2017 APM 152ED.  (In fact, I'm thinking of selling the Big ED.)  A light 8" F6 Newt on a solid GEM with good visual tracking up to 400x... what's not to love??

 

In just a few years, I went from 0 Reflectors to 5... 3 Newts + 2 Casses.  Very happy camper.  Not turning in my Refractor Fan Membership Card, but I'm enjoying this mix of lenses & mirrors.  Just not this one...

 

Edited by Bomber Bob, 25 September 2020 - 05:24 PM.

[junomike]

I'm a believer in Aperture rules (mainly due to larger exit pupil), however last night on Mars my Meade 152ED held it's own and then some against a 10" Orion Newt.

The newt showed the polar caps better but the ED had better Mare (black) detail.

On Lunar Detail the Newt was superior.

[Mitrovarr]

You have to really work out all the details to get a reflector to beat refractors on planets. IMO the biggest problem is tube currents. You really need to mod most large reflectors to get decent thermal performance out of them.

Trying to get still images out of my dobs felt like such an exercise in futulity the only time I ever use them on planets is if I already happen to be out looking at DSOs that night.

[KBHornblower]

snip...

 

In terms of travel, am not tempted to get a bigger dob because my 12" does a great job and is highly portable. It has a home-made truss that I can set it in about 5 minutes, and it takes up about the same room in the car as a 40lt Esky. It cools down a lot quicker than the big dobs too. It also does a great job in city light-pollution: it will always pull in more detail than a smaller scope on DSO's even in polluted skies because you can go higher power (and hence darker sky background) for the same exit pupil as the smaller refractor. (I have never understood the comments that bigger dobs are no good in the city!)   ...snip

 

 

My bold.  I think you are mistaken.  As I understand it, combinations of aperture and magnification that have the same sized exit pupil will have the same sky background brightness.  Perhaps you are having the illusion of a darker sky in the bigger scope because the stars are brighter.  I cannot think of anything else.

[hoof]

HERE is a link to very detailed website about astronomical seeing. Below is a relevant statement from that site…

 

“How often do nights of excellent seeing occur? At the William Herschel Telescope site in the Canary Islands, even this superb viewing location, second best in the northern Hemisphere, has many nights of relatively poor seeing: the distribution is positively skewed... and at this excellent site, a 10 inch telescope will experience seeing limitations on 9 out of 10 nights.”

 

If a 10-inch scope is seeing limited 9 out of 10 nights at La Palma, which has some of the best seeing in the world! – What are the odds in your backyard? And if the planets are not well placed, like the past few years, and at many times during an appearance, that will also lower those odds even more.

 

As to imaging, I stated in my earlier post “imaging” is a "different animal", as it is possible to eliminate some seeing issues and add contrast, etc. in data capture and processing.

 

Bob

Heh, I'm actually glad my bigger dobs are seeing limited all the time.  That way I don't feel that I'm leaving resolution or a higher power view on the table.  

I've owned an 8" F/5.9 dob for over 15 years.  It's my 2nd.  I bought one a year earlier, then sold it when I got my 12.5" f/5 truss dob.  I paired that dob with a 6" F/8 dob for grab 'n' go.  Ended up selling it.  Why?  I kept hitting the 'scope's limit on nights, where the 8" would be largely limited by seeing where I lived then.  I felt every time I maxed out the 6" that I was missing out, because the 8" would have let me see that much more, or use higher powers.  That bothered me to no end, so that 'scope found a new home and I bought another 8".  The bummer was the first 8" had identical diffraction patterns on either side of focus.  The new one doesn't (it still goes up to 400x very nicely, thus a good mirror, but not perfect like the first).  

So I see a dob that can never hits it's limits due to seeing a good thing.  That way I know I'm always at the limit for the current viewing conditions, and not being artificially limited by the 'scope.  But that's just me

[areyoukiddingme]

Most of my observing is from my balcony, and most of that is on the planets.

 

I've tried a 6" Explore Scientific apo, which was fun to play with, but like others I found the trade-off of aperture vs. pain to be beyond what I wanted to deal with. Add in a big mount, counterweights,  . . . so I concluded that the sweet spot for me on a refractor was probably around 5" at maximum.

 

Since then I lucked across parts to assemble an 8" F7 Newtonian. This scope has changed my opinion on the refractor/reflector comparo on planets.

 

The key reason is that the primary is 20mm thick quartz, and it's up and running in a few minutes. You just need to blow the boundary layer off and you are ready to go. It is ready to view faster than my 80mm.

 

So the trade-off for reflectors regarding cooling doesn't have to be a trade off if you get the quartz substrate.

 

And as for views, I didn't have the refractor at the same time, but if my memory serves, it's just no contest. I think you'd need more than 6" of the best refractor goodness to beat it, and even then I'll be observing for an hour before the refractor has cooled.

 

At least that is my experience with 8". I've liked it so much that I've ordered a new 12.5" primary in thin quartz. I anticipate difficulties getting it mounted without inducing astigmatism. But if it cools like the 8", I expect to be a very happy camper.

[daquad]

My bold.  I think you are mistaken.  As I understand it, combinations of aperture and magnification that have the same sized exit pupil will have the same sky background brightness.  Perhaps you are having the illusion of a darker sky in the bigger scope because the stars are brighter.  I cannot think of anything else.

That is not an illusion, but your statement is correct.   Equal exit pupils yield the same sky background. And the sky background becomes darker with increasing magnification, but the stellar images, not being magnified, are brighter due to the increased aperture.  So the larger aperture will always show more stars, regardless of the severity of the light pollution.

 

Light pollution will affect extended objects equally.

 

Dom Q. 

[Jsquared]

One point. A big dob with a 5 nm ha filter and a night vision device can allow nice viewing even in heavy light pollution

[vdog]

Whahaha. It IS the cheese capitol of the world. So you’re welcome to join the busloads of cheese craving tourists that stampede our town every year. 

I love a good Gouda.  Good cheese is one of the finer pleasures in life. 

 

I know too many people who think cheese is what comes out of those packages with individually wrapped slices.  I shudder to think of it.

[Traveler]

Thank you for listing so clearly, all the things that made sway one to get one over the other.

 

What really hit home was when you mentioned all the things that need to be in place for a big dob to actually shine. The fact of the matter is that my seeing conditions are very poor and style of viewing lean heavily on the quick and convenient side of things. Most of the times it won’t be perfect outside. Most of the times i won’t have time to wait for cooling down. Most of the times, if not always, i’d like it to be a hassle free experience.

 

Thank you for also listing ways to enhance the experience with a refractor. I’ll have a look at intensifiers and although i’m not keen at looking at screens too much. (I do this for work all day long already) The EAA option might be a great work around.

Hoi Urbyz,

 

I can recommend you to go to Rijswijk observatory. There in even more light polluted skies you can see for yourself if a large aperture instrument can help you what you are looking for.

Have fun.

[aztrodog]

I appreciate different points of view, so here is mines to balance out some of the earlier postings. Personally I did not find either of my two superb 14” SCT or friend’s high end Dob to provide better, more detailed views than either a 6” or 7” APO. I owned two C14s, both of which I used extensively under South Florida steady skies. I also had access to my friend’s 16” Starstructure / Zambuto mirror. As good as those scopes were, I vastly preferred the views in my 7” APO and my friend’s Tak152. The purity and aesthetically pleasing views in the refractors were simply unmatched by the larger scopes. Trust me, from the financial point of view I would have loved for the SCTs or Dob to blow away, leave in the dust or _______ (fill in disproportionate statement) the 7” APO.

 

I spent many nights with one of the C14s and the 7” trying to see (hoping) if by chance the SCT was a better choice for me as a 95% visual observer. No dice, the purity of the views, sharpness, high contrast and zero light scatter plus being able to go from very low power to stupid high magnifications in a single instrument was simply too much of an advantage. Sure the views were brighter in the larger instruments but there was nothing I ever saw in the 16” or 14” I could not pick up in the 7”, either planetary or deep sky. Oftentimes, specially when looking at Jupiter and the Moon subtle details were easier to make out in the 7” on account of higher contrast. 

 

I do like CATs a lot and own a C11 from 2004 and an orange C8” from 1976. But as a personal preference, nothing compares to the views of the heavens my refractors provide. And yes, I still drag out the C11 just about every night the 7” comes out. And no, not one night have I set aside the APO for the larger aperture SCT. And yes, I still hold out hope my C11 will one day magically start to win the shootouts which will allow me to free up a ton of cash for other hobbies.

 

So it is no myth that a smaller aperture APO refractor can match or better the views of larger mirror based scopes, even under steady skies. But I am glad not everybody arrived at my conclusion. How boring would star parties be just filled with 7” APOs .

 

Clear and steady skies to all, no matter what scope you use. 

 

Angel

[hoof]

One point. A big dob with a 5 nm ha filter and a night vision device can allow nice viewing even in heavy light pollution

So true.  NV opened up the whole h-alpha nebula sky to me, I've seen bigger, better, and more satisfying DSO's with my NV device, 7nm H-alpha filters, and various fast 'scopes than I ever saw in the prior 13 years of observing, even from dark skies.  This aspect of astronomy has been so compelling that I've even got crazy rigs set up, such as an 80mm F/3.75 "finder" scope attached to my 15" F/4.1 main scope, each set up with H-a filters and as low a power eyepieces as I could use, for easy switching from 7.5x to 30x. Awesome views of the Cygnus complex, Veil nebulas, Bubble nebula, Pillars of Life, California Nebula, the list goes on and on.  Mind-blowing views of M42 with structure, detail, and awesomeness.  Horsehead nebula?  Piece of cake with detail on the head itself with direct vision.  And all of this from my yellow-zone property.  Globs?  Resolved to the core, all the big ones, tons of stars.  NV revolutionized my DSO astronomy, prior to that I wouldn't bother because stuff was faint & fuzzy.  With NV? You see details normally reserved for long-exposure astro-photography, but it's in real-time.  Best dang astronomy purchase I've ever made.

[Illinois]

I enjoy my refractor very much for planetary , tight double stars and sharp pinpoint stars. Great for large faint deep sky objects like Veal Nebula and M45’s nebula. Wonderful for medium and large open clusters like M11, M93, M7, etc. Quickly grab and go in early morning to look at Mars.  I love large Dobson I have 16 inch and it’s great for faint galaxies, easy see galaxy near M13, Abell galaxies, faint galaxies around NGC 7331!   I like several telescopes like fishing poles with various lures or several golf clubs for depends on distance ball to the hole.  

[CHASLX200]

A top notch bigger Newt in the 10 to 14.5" range will kill any 6" APO in my super steady seeing.  A world class 6" APO and mount are gonna be $10 to 13k when a used 14.5" Starmaster or other top notch Dob is gonna be around $3 to 5k.

 

Go up to a 8" APO when the cost is around 25 to 35k for the scope and mount and it still won't touch a 14.5" Zambuto in my seeing.

 

 

[ismosi]

 

So it is no myth that a smaller aperture APO refractor can match or better the views of larger mirror based scopes, even under steady skies. But I am glad not everybody arrived at my conclusion. How boring would star parties be just filled with 7” APOs .

 

Clear and steady skies to all, no matter what scope you use. 

 

Angel

This agrees with my post earlier .. in my conditions so far at no time have I had a better view of planets than with my 6-inch refractor. Even if I lived where sub-arcsecond seeing was the norm I'd still not be parting with my refractors

 

When it comes to deep sky I'm fortunate to have the big Dob, though.