I have a 16 inch truss dobsonian, which I call 'big dob'. I know very well its qualities and limits, but I couldn't comment anything on topic 'cause I didn't have the occasion to observe with a refractor, at least for a considerable time.
Meet my new APM 152 ED, my first ever refractor. I found a incredible deal and I couldn't skip the opportunity. I'm SO happy .
In the next weeks I'll be able to compare the 16" to the apm: it's my first time comparing a big dob and a decent sized refractor. Both instruments represent a mid-to-high quality and price range, with the exception of the dob mirrors which aren't so great...
With the appropriate tweaks and attention to both instruments I'll be able to compare them in their best form.
Based on the opinions on this thread and some basics physics, I don't expect one to be better that the other. They're complementary instruments, both shining in what they do best. I think that trying to find the best overall design is a bit of a meaningless challenge. Nonetheless, this thread can be massively helpful to understand the different characteristics and peculiarities of two of the most important and relevant optical design in visual astronomy, especially for beginners.
I'll keep you updated, and clear skies !
Well, here I am!
I took some time to thoroughly evaluate my APM 152 and, long story short... I love it!
But let's remain on topic and confront my previous reflectors (10 inch and 16 inch commercial dobs with GSO optics, 300$ used and 1500$ used respectively) with the refractor rig (APM + neq6 rowan belt mod, 2800$ used)
Disclaimer: I'm no optic expert, and not very experienced with star testing neither. But I'm relatively young (with very good eyesight) and totally new and unbiased in the world of refractor. So it could be interesting. Hope it helps!
So here we go:
The APM wins hands down. The tube, the dew shield, the paint, the rings and handle, the focuser... All are excellent, with a very very high perceived quality and smooth movements. It's also surprisingly light for a 6 inch refractor.
The 10 inch Gso commercial structure was a bit rough, but it had a decent 2 inch focuser and good stability. Couldn't expect more for 300$. The base was sooo heavy tho.
The 16 inch had GSO optics but a well thought structure made by the Italian Rp-Astro. I suggest you read my thread "Saying goodbye to the big dob" for more info. It was surely good and innovative, with smooth movements, but not on par with the APM quality.
Fall and winter temperature is surely not so mild here were I live: during the day it settles down around 6-10 °C, dropping to 0-2 °C during the night. My telescopes are stored inside so they have to adapt to a decent thermal jump.
The APM 152 takes 30 minutes to be acceptable to look through, and a full hour to be perfect for high res work.
The 10 inch dob (with the stock rear fan on) took no more than 15 minutes to be acceptable to look through, and 30 minutes circa to be ready for high res work.
The 16 inch dob (with the stock rear fan on) took about 20 minutes to be acceptable to look through, and a full 40-to-60 minutes to be ready for high res.
A clear win for the simple tube 10 inch dob.
Seeing is not so good for the very majority of fall nights here... But some nights it turns out surprisingly good, and these are the nights to star test my optics. Always use Polaris.
The APM 152 has a very good star test. Very little chromatic aberration intra and out focus, with perfect visual correction in focus. No astigmatism at all, and no zonal errors. There's a bit of spherical aberration: I can't tell you how much, but surely no more than 1/6 wave. Not a textbook-magical-takahashi-perfect star test, but I'm very satisfied.
The 10 inch GSO tube dob turned out a surprisingly good star test. A small bit of spherical, but no turned edge, no astigmatism, no zonal errors, and also surprisingly smooth optics. When properly collimated it was a killer scope.
The 16 inch truss dob with GSO optics... Was surely not good. Considerable amount of spherical (1/4 wave at least), a bit of turned edge and also a bit of astigmatism. At least not so rough surfaces. Not unacceptable optics, but surely not so good...
What I learned: a good refractor with good reputation and manifacturing has a very good chance to have excellent optics. A small commercial mirror can be very good, and it's not so infrequent considering the big amount of food reviews here on CN. with a big commercial mirror... It's a bit of a gamble. You either win or lose, with a good chance of being somewhere in the middle.
Large and medium DSOs (emission and reflection nebulae, open clusters and galaxies):
These are my favorite targets to look at from a dark sky. I am so fascinated by them, I always find them beautiful. This also means this is the category I'm more experienced with.
The APM 152 is soooo good in relation to its aperture. I didn't expected it to be this good, but I'm surely happy! Light throughput is comparable to a 7-to-8 inch reflector. The large fields and clarity of the view render spectacular open clusters observation. I'm not gonna feed the "diamonds on black velvet" myth, but it's surely good. Nebulas are very defined and contrasty, with a pleasant appearance and good stars, surely not so extended tho. Galaxies are very etched on the background sky, but not so extended and resolved again. In conclusion: very good clarity and contrast in relation to its aperture, pleasant views, but it surely lacks a bit in aperture and resolution.
The 10 inch GSO was very good and balanced. Stars were tight and views very good. I couldn't get the extremely large fields I get with the refractor because of the secondary shadow, but it was very good on open clusters: richer fields for sure. Nebulas are more extended and stars very good, with comparable contrast to the APM. Galaxies are surely better than the APM regarding resolution and extension, but they're not easier to identify in the sky. In conclusion: surely better than the APM regarding resolution and extension, but the views are equally pleasant in both, maybe a bit "easier" in the refractor. I'd choose the APM for its larger possible fields without secondary shadow. But let's not forget that I payed 300$ for the dob, more than 9 (9!) times less than the refractor. I got a bit lucky with the 10 inch optics, but the point remains.
Here's were the 16 inch dob shines. It's MARVELOUS. It hasn't the very large fields of the refractor but they are so rich that you forget. The double cluster is an explosion of stars. Nebulas are so extended and detailed: despite the not so good optics they're excellent. Galaxies views are a dream. I'll invite you to read my thread on M51 to see how I think the 16 is on galaxies.
Small DSOs (globulars and planetary):
The APM has very good contrast and the views are pleasant, but it surely lacks in resolution. Globulars are not magnificent like the ones in the bigger reflectors, despite being good.
The 10 inch GSO is very good, with both a good resolution and clarity. Main globulars are resolved at least halfway through, and planetaries start to have easy details.
The 16 inch flexes its light gathering capabilities again, with very resolved globulars and planetaries. The not so good optics starts to give "mushy" views at high mah tho, despite not being so noticeable on DSOs.
High res (double stars and planets):
The APM has a classic clean view on double stars, with a very pleasant and "surgical" appearance. It hasn't the resolving power larger apertures have, but the stars which can be splitted are marvelous to look at. I can also push high mags with good orthos
The 10 inch GSO was also very good, but the prominent diffraction spikes were an obstacles a few times. Despite that, it had clean views, maybe a bit less "surgical" than the refractor ones.
The 16 inch had a special secondary spider which rendered 6 very thin spikes, but the optics couldn't keep up with the high mag.
I won't say anything regarding planet observation, because planets are very very low here in Italy this year. Maybe I can say that the 10 inch and the APM were good, and the 16 inch surely not, but the atmospheric diffraction was a big obstacle. Based on star tests and double star observation, I think it would be a tie between the 10 inch and the APM, with the APM surely rendering a more pleasant view with my seeing.
The APM is very good, with a very balanced white tone and good details. It can be pushed to very high mags and it performs spectaculary, with clinical views and details. Rimae and small craters are easy to discern with good seeing.
The 10 inch is marvelous: the intrinsically very high contrast of the moon mitigates the effects of obstruction and the 10 inch aperture, when there's good seeing, renders spectacular details. I think this is the best instrument I had for lunar observation, despite the APM being very good.
The 16 inch was so bright it forced me to use a filter. The details at low mag was incredibly high, but when I pushed the magnification it all became mushy and less defined. Optics play a very important role in high nag lunar observing.
Ease of use:
The APM is not so easy to set up, but when it's all ready it's surely the best regarding ease of use. Goto is a MASSIVE help for me here in a light polluted city, and tracking is so sweet: when you try it you can't go back. With a good chair you can observe for hours.
The 10 inch GSO was the easiest to set up: drop the tube in the base and done. It took about 20 seconds. The movements were not so good tho: very sticky friction on both direction, despite a good clean to the bearings, and the focuser was sub-par compared to the APM and even the 16 inch. Also, no tracking and no goto. For 300$ you couldn't expect more tho.
The 16 inch was a NIGHTMARE to set up. The mirror box weighs 65lbs, not so good for my back, and the truss process took at least 20 minutes. The movements were good tho, and there was zero flexure and consequently zero miscollimation. The focuser was a simple dual speed crayford but it did a decent job. No goto and no tracking as the 10 inch.
Reading the entire review you can easily discern I globally liked the 10 inch and the APM more: the two instruments trade blows on everything, with the APM slightly pulling ahead on optical quality but the 10 inch doing the same on light gathering. It's a very good news for everyone: a fantastic instrument can be obtained for a very appealing price! It's the same old story: to obtain the last 10% optical greatness you have to pay big money. The 16 inch was a fantastic performer on DSO and light gathering work, but it was a one trick pony: you surely have to be lucky, or pay more, to have an all around capable 16 inch.
But... Let's bust some false myths (with a bit of irony):
"Comparable quality reflectors are 10 times cheaper than refractors, you are so d*mb to think buying a refractor is good". Optically? If you're lucky, it can be true. But you have to be lucky, or you have to be prepared to spend more for a premium mirror. Basic reflectors also lack tracking and goto. If you want that, you either have to use a eq-platform and dsc or something like Servocat. The first option is cheaper (but good eq platform are not so cheap), the second more capable but pricier. There's also the option to eq-mount a newt, but not all people find that manageable without rotating rings and a good mount. Summing up: a reflector is surely cheaper, by if you want all the feature that good refractors and mount have, you have to pay more than what you think, unless being lucky on the used market.
"your puny refractor can't se mag 200000 galaxies and you can't see colors in nebulae. It's useless". It's totally true, but it's not all of the story. I learned that with the 16 inch: to have an all around big reflector you have to pay considerably higher than what you think, especially if you don't want to use a ladder. It's true: at a given price, a reflector will be surely better regarding resolution and light gathering, with maybe comparable optical quality, but it will lack in certain compartments (very large fov for example). It's not always all about "who wins". They're different instruments for different needs.
"Refractor are the best. You can have your mushy and grey view. I always have diamond-on-black-velvet views and you gonna have the clarity of a dusted plastic lens". This is also entirely not true. Refractor are not magical, they won't magically gather more light at a given aperture, and a well thought reflector can easily outperform them, even at a lower price. They're fantastic instrument, but they lack in some compartments.
In conclusion: I love my refractor. It a fantastic instrument, easily the best I've ever had. But I had to pay hard cash for it, that's for sure. A good reflector, with good mechanics and good optics, will outperforms it in many compartments at a given price, or even less, but it would lack other characteristic qualities that refractor have. This is a hobby for the majority of us: we can search for new objects and study variable stars, but we don't have to. We can choose the views and objects we like the most and buy a instrument accordingly. Nowadays we have thousands of instruments to choose from, and in every category there's a fantastic performer for a good price: big 6 inch ED refractors, good mirrors at a lower price, the famous 180 maksutovs, celestron and Meade quality higher than ever, and a myriad of other optical designs. I like newts and refractors the most, but I love the wide choice there's nowadays. It's the right thing to advise someone on the right instrument for their needs, but let's remember there's no magical one. And if we love the sky in its entire mess, we can have more than one scope without breaking the bank. Isn't that beautiful?