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Visual observing: big APO refractor VS. big Dobson

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#151 naramsin

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Posted 29 September 2020 - 02:07 PM

I'm not sure if it's been suggested already, but I find the following website helpful, and surprisingly realistic:

 

https://stelvision.c...cope-simulator/

 

You need a good computer monitor though (I have a 27" 4K LG).

 

It's interesting how when you compare a 60mm F15 refractor to an 8" f5 newt with Saturn as a target, with a 5.5mm eyepiece, there's not much difference. But with M42 it's a different story.

 

It's also really helpful if you match exit pupils. Then you can appreciate what a huge difference image scale makes.

 

For example, look at M42 with the 60mm F15 with a 32mm (about 2mm exit pupil). Then the 8" newt with an 11mm.

 

It's like ants to elephants. And it's more or less what I see in my actual telescopes.

 

It's one reason why I'm holding off getting a 4-6 inch APO refractor. Well, that and cost. There's not much I can't do already with my smallish refractors (up to 80mm F11) and the old light bucket. Especially when I get out to a dark site. It's astonishing what an 80mm can pull in upstate when seeing permits.


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#152 Peter Natscher

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Posted 29 September 2020 - 02:10 PM

Your 45lbs. C14 is easier to hold and lift onto a lower mount and pier saddle than a 8" f/7 APO would be. Tube dimensions matter. The 60lbs. 8" APO would require a taller pier/mount because of its longer tube.  Lifting 60lbs. shoulder height or higher is tough and dangerous for one person to do. I had a 45lbs. AP 175EDF a few years ago and mounted on a 52" ATS portable pier with a AP1100 mount with a saddle height of 68". I chose that height of ATS pier to keep the eyepiece height high enough for observing overhead objects and still be seated comfortably at the eyepiece.  I don't like lying on the ground to observe.  I'm 6'3' tall and believe me, lifting that 45lbs 175 to my shoulder height into the rings 68" up was a task in strength and mental fortitude.  I would have to focus totally on the task before and after. I was nervous mounting and dismounting it.  All my larger aperture Dob's (14"-24") were a piece of cake to set up and pack up compared to the 175 and it's other heavy accessories.  My 16" f/4.5 Zambuto Dob outperformed the 175 anyway so the 175 got sold.  I've come to realize that I a lot more comfortable observing at the eyepiece position that a Dob offers versus what a refractor does. The Dob's eyepiece location makes more sense to my body mechanics, that is to stand up, or sit on my CatsPerch observing chair, and to and look level headed into the eyepiece rather than looking down.  With a refractor, you're looking down -- bad for your neck, head, and eyes.  Eye floaters appear in your view looking downward more often than when looking level.  At a 45° and higher telescope angle, the Dob's horizontal eyepiece works better for your neck, head, and eyes than looking downward at the end of a refractor for longer periods of time.

 

Well I think the 8 inch APO is unwieldy and I would be hard pressed to put one into my Accord.  But on the other side of this argument I regularly transport 150 lbs of mount, counterweights, and pier.  Mount: two sections of 15 lbs each, counterweights, 18 lbs each, counterweight shaft, 20 lbs, ATS pier (looks big but all aluminum) 30 lbs, OTA C14 45 lbs, battery 50 lbs (that's the worst part of my rig), apo 12 lbs, eyepiece box 30 lbs, observing and two folding chairs, 30 lbs = 30+54+20+ 30+45+50+12+30+30 = ~300 lbs, though I suspect I overestimated a few items and would peg it at 250 lbs.  

 

It's my favorite set up but not when the observing window is short or the forecast is iffy.  It is definitely my wife's favorite setup.   It is so nice to have a spouse who likes astronomy I try to cater to her preferences.  

 

The reason the APO is a problem is that it would likely take up two seats, as I found out when I transported a 10" f/6 Newt.  I had to put the front passenger seat down and slide the tube in from the rear passenger door.  That would leave no room for wife and dog.   The stupid Accord designers decided to save ten bucks by not making the rear seat split 60/40, either the whole thing goes down or it stays up.  But even if it was 60/40 there still would be a problem of a lost seat and lost trunk space, causing some items from trunk to have to move into the rear seat and now room for wife but no dog.  

 

But with a C14 it all works out for wife and dog and a rig worthy of the Normandy invasion.  And with great performance capabilities.  smile.gif

 

Greg N

 

attachicon.gifC14+CFF at Chimney mountain 6-20.jpg


Edited by Peter Natscher, 29 September 2020 - 02:27 PM.


#153 Urbyz

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Posted 30 September 2020 - 05:07 AM

Seeing is not a constant, it varies. The eye can catch moments of good seeing...

...My guess is your backyard isn't that steady...

I have come to realize there are two types of planetary scopes..

- Those that make the best of a very good situation. These are generally large aperture scopes that can take advantage of excellent seeing. Evidence suggests such a scope would be a good fit for my situation.

- Those that make the best of a less than ideal situation. Thermal issues from harsh climates, jet streams overhead, unstable seeing, clouds and short periods of clear skies. You have to be ready and you don't want to wait for your scope. Refractors of moderate size are very often preferred.

I suspect that Ruben's situation is more like the second than the first.

Jon


Yes Jon, you are right about that! Just look up Gouda, the Netherlands on the lightpollution map and go ahead and have a chuckle. It’s one of the worlds biggest bortle 8-9 zones.

On top of that is the fact i’m watching from a roofterrace with cement tiles and furnace vents everywhere. (Typing this i hope some of you realize how lucky you are with your location.)

So all things considered, i think a nice refractor would be the better option. Seeing it’s performance suffers less from my “less than ideal” viewing location.

Would anyone recommend the TEC 140FL? Or is 5,5” a little to large again to benefit from the refractor and should i stick to 5” max?

#154 CHASLX200

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Posted 30 September 2020 - 05:36 AM

lol.gif  You have no idea exactly how odd, almost surreal, that phrase you said that I bolded above is!! lol.gif  It stopped me in my tracks and I had to re-read it several times as just could not figure out what planet you were on!!! lol.gif

FL has not had real winters in years. Many days are seeing around 90f during the winter now and i would guess in another 30 years at the rate of the rapid warm up high 80's will be year round in FL.

 

Feb has always had the most steady nites on very humid and warm nites. I live right on the gulf and with sea fog just offshore and moving onshore i can get some dead still nites.  Summer is never good as i get what i call fast or rushing water effect where it looks like a planet is being viewed in fast moving water. Then i get the slow rolling seeing where a planet will just fuzz over for about 10 secs and then sharpen up in and out.  Nites with fast temp drops are never good. 

 

 


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#155 bobhen

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Posted 30 September 2020 - 06:46 AM

Yes Jon, you are right about that! Just look up Gouda, the Netherlands on the lightpollution map and go ahead and have a chuckle. It’s one of the worlds biggest bortle 8-9 zones.

On top of that is the fact i’m watching from a roofterrace with cement tiles and furnace vents everywhere. (Typing this i hope some of you realize how lucky you are with your location.)

So all things considered, i think a nice refractor would be the better option. Seeing it’s performance suffers less from my “less than ideal” viewing location.

Would anyone recommend the TEC 140FL? Or is 5,5” a little to large again to benefit from the refractor and should i stick to 5” max?

If you are thinking along the lines of a TEC 140, which is excellent, then any of the high quality offerings from CFF, Takahashi, APM (LZOS) and Tele Vue in the 120 to 140mm range might be considered as well, as they all have absolutely first-rate optics. Consider the mechanical and ergonomic differences and pay close attention to weight, size, delivery dates, cost and accessories and mount requirements, etc.

 

Do your homework and call the retailer or the manufacturer with any questions.

 

Along with the wonderful views, any one of the above (with the right accessories) will be versatile enough to meet future solar, imaging, night vision or EAA needs.

 

Have fun.

 

Bob



#156 Jon Isaacs

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Posted 30 September 2020 - 07:12 AM

It's interesting how when you compare a 60mm F15 refractor to an 8" f5 newt with Saturn as a target, with a 5.5mm eyepiece, there's not much difference. But with M42 it's a different story.

 

 

I suspect that is more about the simulator and not about reality. I certainly doesn't match my experiences.  I have owned some very good 60mm scopes, the best being 60mm F/13.3 Asahi-Pentax refractors.  The detail is missing from the 8 inch.

 

Jon


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#157 CHASLX200

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Posted 30 September 2020 - 07:14 AM

I suspect that is more about the simulator and not about reality. I certainly doesn't match my experiences.  I have owned some very good 60mm scopes, the best being 60mm F/13.3 Asahi-Pentax refractors.  The detail is missing from the 8 inch.

 

Jon

Any good 8" Newt kills a 60mm on the planets. Even a so so 8" SCT does better on detail. The 60mm may be sharper but lacks the light needed at higher powers.


Edited by CHASLX200, 30 September 2020 - 07:14 AM.

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#158 Jon Isaacs

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Posted 30 September 2020 - 07:22 AM

Would anyone recommend the TEC 140FL? Or is 5,5” a little to large again to benefit from the refractor and should i stick to 5” max?

 

 

My own thinking is that it's better not put all your eggs in one basket.  A good 120mm -127mm refractor plus a larger mirror based scope will provide more capability than a single slightly larger refractor.  

 

From an urban setting, the important factor is the seeing, the stability of the atmosphere.  I am not sure how stable it is in Gouda.

 

Goodtostargaze.com says it's about 1.5 arc-seconds currently.  If it gets much below that, a bigger scope will definitely show more.

 

And keep in mind, you already have a 6 inch scope.  The refractor will be significantly better optically but the views will be similar in many ways. 

 

Joe Bergeron's review of the 6 inch F/5 Celestron Omni XLT is worth reading.  Joe compares it to his two Astro-Physics refractors, a 155EDT and a 92 mm Stowaway. 

 

 http://www.joebergeron.com/omni150.htm

 

Jon



#159 naramsin

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Posted 30 September 2020 - 08:10 AM

Any good 8" Newt kills a 60mm on the planets. Even a so so 8" SCT does better on detail. The 60mm may be sharper but lacks the light needed at higher powers.

What I meant was that superficially the 60mm F15 view of Saturn versus the 8" newt was more alike than different when compared to M42, which practically disappears in the 60. Plus I was comparing them on Saturn with the same eyepiece, while I was comparing the exit pupils and image scale of M42 using different eyepieces. The 60 and the Newt are similar in focal length so Saturn is about the same size. But it was surprising to me how much of M42's nebulosity disappears even at the same exit pupil.

 

Everything is a little harder to see in such a small scope (in my case a Jason 313 frankensope). I can just see the Cassini division and surface banding. I can just barely split the Double Double on a night of good seeing. Even a slightly bigger scope (a 67mm F4.5 ED Nikkor lens or an 80mm F11) shows these effortlessly.

 

So why bother with the small scope? Well, it's fun to push it as far as it can go. It has little to no CA and its star shapes are beautiful compared to a scope with CO. Also, I'm under the jet stream and LP just outside NYC, and many nights there's just no point in setting up the Newt. This might be a consideration for the OP since he lives under Bortle 8-9 skies, no?

 

But you're absolutely right, the 8" Newt will show everything with more detail, I have no illusions about that. One season I was straining to see Trap E and F with a 4" Mak, never seeing them. When I used the 8" Newt, there they were, plain as anything.



#160 t.r.

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Posted 30 September 2020 - 09:10 AM

A TEC 140FL could go a loooong way as a one scope solution. It will be just enough aperture to at least reveal every class of object there is...easily giving its owner a lifetime of enjoyment.
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#161 BKBrown

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Posted 30 September 2020 - 10:22 AM

Yes Jon, you are right about that! Just look up Gouda, the Netherlands on the lightpollution map and go ahead and have a chuckle. It’s one of the worlds biggest bortle 8-9 zones.

On top of that is the fact i’m watching from a roofterrace with cement tiles and furnace vents everywhere. (Typing this i hope some of you realize how lucky you are with your location.)

So all things considered, i think a nice refractor would be the better option. Seeing it’s performance suffers less from my “less than ideal” viewing location.

Would anyone recommend the TEC 140FL? Or is 5,5” a little to large again to benefit from the refractor and should i stick to 5” max?

Hi Urbyz! I can relate to your Bortle-challenged viewing situation having lived under similar skies for many years. Observing wise I am blessed in two ways: first, I moved out of the city to a country property under Bortle 3 skies and second, I own a TEC 140 (among other scopes). I can recommend the TEC without reservations of any kind. And while the TEC is optimized for the human visual range (the only premium APO that is to the best of my knowledge), it will do great work if and/or when you decide to try your hand at imaging (although I suggest you start with a nice 65mm to 80mm APO first). 

Unlike many others here, I have never cared for the ergonomics of Dob Newts. Despite their many advantages, I am just not a Dob guy. Instead, I like a good sized SCT and have 11" and 14" EdgeHDs at my disposal. The 11" in particular is a very useful size for going deeper than the 5.5" TEC while still being conveniently usable on the same class of mount. At a minimum, you would need something like a Skywatcher EQ6-R Pro to handle these scopes for visual work or lunar and planetary imaging. So stay focused on what it takes to use scopes like these and consider the accessories and support equipment as carefully as you do the telescope. Under no circumstances should you ever under-mount these instruments, the mount is no place to cut corners! With proper dew mitigation and quality fans (maybe even a thermal jacket), an SCT is competitive with any other scope in its class, and more versatile than other designs.

Good luck in your search, I hope this helps smile.png

 

IMG_7638sc.jpg

 

 

Clear Skies,

Brian snoopy2.gif


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#162 Urbyz

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Posted 30 September 2020 - 04:58 PM

If you are thinking along the lines of a TEC 140, which is excellent, then any of the high quality offerings from CFF, Takahashi, APM (LZOS) and Tele Vue in the 120 to 140mm range might be considered as well, as they all have absolutely first-rate optics. Consider the mechanical and ergonomic differences and pay close attention to weight, size, delivery dates, cost and accessories and mount requirements, etc.

I’ll have a look at those. Thanks.

 

How about William Optics? Is their fluorite line any good or comparable to the brands you named? 



#163 N-1

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Posted 30 September 2020 - 06:00 PM

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

 

Out of 10 consecutive and/or random nights, or out of 10 nights that you've selected to use for observing? That's an important difference. Most any site can get a 10/10 average by the latter method, eventually. Not that hard, and certainly nothing to base a decision on aperture on.


Edited by N-1, 30 September 2020 - 06:14 PM.


#164 Mitrovarr

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Posted 30 September 2020 - 08:45 PM

On a side note I finally had a night where my 6" refractor was finally not seeing limited!

It was completely AMAZING! I saw so much detail on Jupiter and Saturn (the magic was over by the time Mars rose, although one of the club's astrophotographers says it came back later and got a stunning shot of Mars).
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#165 Traveler

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Posted 30 September 2020 - 10:22 PM

  • CFF 140mm F/7.5 version = 7690 Euro, includes VAT 23%

 

  • TEC APO 140 f/7 € 7,213.45  includes VAT

 

Orrrrrr.......

 

  • SW Esprit 120: 2875 includes VAT  

 

and

 

  • Skywatcher N 304/1500 PDS Explorer BD EQ-6 Pro SynScan GoTo  € 2340 includes VAT

 

Makes a total of € 5210 ....

 

So, one 140 refractor versus a 120mm ED refractor, and 12 inch Newtonian and a EQ6 mount...and 2K to spare..for buying cheese or send your wife on a shopping tour with her friends....grin.gif

 

Do make your own conclusion...cool.gif


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#166 PowerM3

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Posted 30 September 2020 - 11:44 PM

I own a Meade 178ED and a 16" dob(actually a JMI reverse binoscope but used to have a premium 16" and 18" single dob in the past). Even a 7" APO cant touch a 16" dob on DSO that can actually fit into the FOV of the dob!

 

As others have said you really do want both as they are not rivals they are compliments to eachother;)


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#167 bobhen

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Posted 01 October 2020 - 06:39 AM

 

As others have said you really do want both as they are not rivals they are compliments to eachother;)

I see the “you need both” (larger Dob and apo refractor) posted a lot. But for deep sky observing, using today’s technology, there are other options to the larger Dobsonian.

 

The poster lives in a light polluted location. With that in mind, the options of doing EAA (electronically assisted astronomy) with an astro-video camera or DSLR digital imaging or doing night vision with an image intensifier and a smaller scope has many advantages over the large Dobsonian.

 

Just some of the advantages include…

 

1. Cutting through light pollution
2. No pressing need to travel to a dark sky
3. More observing because you don’t need to pack and travel
4. Less impact by moon phases
5. Will easily deliver more detail than a large Dobsonian
6. The intensifier delivers views in real-time
7. The astro-video camera (with all accessories) is only around $300
8. Can be less expensive than adding another telescope

 

The EAA and Night Vision forums are very active with creative solutions and innovation. 

 

Bob


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#168 Jameshp54

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Posted 01 October 2020 - 03:26 PM

I always set up both a Dob and a refractor! They are such a wonderful complement

to each other-the wide field views of the refractor with the deep sky punch of the Dob.....

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#169 adamckiewicz

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Posted 01 October 2020 - 05:20 PM

 

  • CFF 140mm F/7.5 version = 7690 Euro, includes VAT 23%

 

  • TEC APO 140 f/7 € 7,213.45  includes VAT

 

Orrrrrr.......

 

  • SW Esprit 120: 2875 includes VAT  

 

and

 

  • Skywatcher N 304/1500 PDS Explorer BD EQ-6 Pro SynScan GoTo  € 2340 includes VAT

 

Makes a total of € 5210 ....

 

So, one 140 refractor versus a 120mm ED refractor, and 12 inch Newtonian and a EQ6 mount...and 2K to spare..for buying cheese or send your wife on a shopping tour with her friends....grin.gif

 

Do make your own conclusion...cool.gif

 

Or buy a herschel wedge for the esprit, that cannot go together with the dob. So you can even practice daytime astronomy while your wife is spending the last 1500 dollars!



#170 BillP

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Posted 01 October 2020 - 07:15 PM

A TEC 140FL could go a loooong way as a one scope solution. It will be just enough aperture to at least reveal every class of object there is...easily giving its owner a lifetime of enjoyment.

Remember, beauty is in the eye of the beholder.  My 4" Apo is giving me a lifetime of enjoyment that's for sure.  About the only class of target I have not seen with it would be a quasar I guess, but only because I have no interest in looking for one.


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#171 Jeffmar

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Posted 02 October 2020 - 12:54 AM

Aperture fever is probably the only reason I don’t have a nice 130mm apo refractor. The best views I have had of galaxies, nebulae, and star clusters have always come from large Dobs. Because I also like to take photos of things is the sky, I guess I have found a happy middle ground with my SCT’s. 



#172 therealdmt

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Posted 03 October 2020 - 08:05 AM

I’m just a beginner but I’ve read this whole thread and I’ll throw in my 2 centavos. 140mm seems a bit big to me - which could be cool! Bigger is better. Except, if you can’t leave it permanently mounted, then you’re dealing with carrying it out and setting it up and some cool down time, and then breaking it down and carrying it back in. Part of the beauty of refractors, besides aesthetically pleasing views, is the convenience of use - but that convenience starts to go down as the aperture goes up. I dunno - it would be absolutely great to have the extra aperture, but I’d be tempted to get a 120mm or even 100mm instead. In fact, as convenience was a huge priority for me, I did get the 100mm (f/9 ED doublet) - but I can fully understand the temptation to carry a little more weight and get something a little bigger, gather a bit more light. In fact, I feel it myself! Conversely, I also feel the temptation to get something smaller and shorter for travel and possibly a bit of imaging. 
 

Which comes back to - a guy or gal could really use 2 scopes, one big and one small. If choosing just one like I did, its hard to know what would be ideal without taking a chance and jumping in. Just know there will be tradeoffs regardless and no single scope is likely to be the perfect home run for all situations. Still, it’s better to have something rather than sitting on the sidelines with nothing. I think you’re headed in a good direction, Urbyz - enjoy the hunt and your new scope when it arrives!


Edited by therealdmt, 03 October 2020 - 06:42 PM.

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#173 BKBrown

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Posted 03 October 2020 - 11:25 AM

A TEC 140 weighs 19 pounds clean (two pounds lighter than a Skywatcher Esprit 120ED!), A Takahashi TOA-130 weighs 23 pounds clean...the TEC is not a heavy or unwieldy telescope. One of its great virtues is comparative portability and ease of mounting. I typically use mine on an Orion Atlas AZ/EQ-G mount and Losmandy tripod. It is not grab-n-go, but it is easy enough for most folks in good health to deal with...

 

IMG_7517sc.jpg

 

Clear Skies,

Brian snoopy2.gif


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#174 Praise.M42

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Posted 03 October 2020 - 04:56 PM

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.

 

Until now. 

 

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 :grin: .

 

 

 

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 grin.gif

 

PraiseM42

 

 


Edited by Praise.M42, 03 October 2020 - 04:59 PM.

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#175 tom_fowler

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Posted 04 December 2020 - 05:08 PM

Undoubtedly for straight visual observation of deep sky objects such as clusters, the large Dob will outperform a smaller refractor.  But the refractors are much better at dealing with poor seeing conditions, are far easier to transport, can be put on equatorial mounts, and will in general give sharper views, which is important for planets.  In addition, using EAA, you can trade time for aperture.  A 5min exposure with my 115mm apo will far outstrip anything you can see visually in any Dob, no matter how large.  You'll see lots of detail and great color.  I started with reflectors (back in the 60s) and then moved to SCTs.  I still have an 8" SCT but find myself more drawn to refractors for the above reasons.  Check out this image of M33, taken with a DSLR and a tablet computer, using the 115mm APM/LZOS, which weighs in at 13.5 lb.

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