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Visual observing: big APO refractor VS. big Dobson

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#26 Urbyz

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Posted 24 September 2020 - 03:43 PM

Welcome to Cloudy Nights! Are you in dark skies? A light bucket will also scoop up light pollution. If you are a urban viewer, it limits what you can see...


I do live in very polluted skies. (Mid-west of the Netherlands) Bortle 4 skies are about an hour away, but i don’t make the drive very often to say the least. Would a big dob be a waste of money in such polluted skies?

#27 Urbyz

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Posted 24 September 2020 - 03:47 PM

Add a location for yourself, it really helps.
A big newtonian will gather more light, but a good refractor will deliver sharper images.
It is all a balance and very much personal.

The two are different instruments and are maybe oddly "measured" by different qualities often.


I just added a location on my profile. Not sure if people are able to see it now. Anyway, it’s Gouda in The Netherlands.
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#28 Bomber Bob

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Posted 24 September 2020 - 03:49 PM

Haha if that isn’t a flex I don’t know what is wink.gif We do live in very polluted skies actually. Looking at the LP world map it almost looks like one of the worst in the world.. Mid-west of the Netherlands. People are making me believe a big dob wouldn’t fare very well over here.

I'm 2 miles from city center, so my back yard is Bortle 6/7.  A 35 minute drive NE, and I get Bortle 4 skies; 45 minutes SW, and the skies are Bortle 3 -- but I don't know any farmers / landowners out that way...  I briefly owned a 12" Dob -- can't imagine all it would take to pack it in our VW Touareg... no, thanks!  Much easier to tote a 6" F8 ED + mount out to the country -- or, in fairness, my 8" F6 Newt + GEM would be just as easy.

 

In my back yard:  That Orion XT12g was more trouble than it was worth, so it's gone.  My 8" Newt could easily become my Swiss Army Knife Scope -- but I'm a lifelong Refractor Fan...

 

Meade 826 Restore S01 - Lumicon 125 HF.jpg

 

Easier to set up than my APM 152ED.


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#29 delgado39

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Posted 24 September 2020 - 03:52 PM

This seems to be the consensus. I’m starting to realize that one cannot replace the other.

That was my conclusion too after many years in the hobby.  Each telescope still has their pluses and minuses.  Of course, we each have our favorite.  Mine is a TAK128.  Easy setup and no collimation to worry about.  But when the seeing is above average  my Dob and SCT get some time too.  Enjoy the choices. 


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#30 Urbyz

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Posted 24 September 2020 - 03:56 PM

To put it more concretely, I was out last summer, maybe two summers ago at a local event that our club provided some scopes to. I took my 5" apo.
Behind me I had a 10" Newtonian and a 12" Newtonian, both by Skywatcher, and both lovingly tended to by their respective owners. And the two of them together not worth even a quarter what I paid for the apo. The views their scopes were providing blew mine away. There was just no way it could keep up. It was very had to say that it was good value for the money as the mythical "planetary scope" that so often gets posted about in this forum.


Thank you for this great example of a real life experience. Due to covid these kind of things are hard to come by first hand and unlike with AP, you can’t just compare pics on the web for results. Direct in person, honest, comparisons like this make all the difference forming an opinion. Thank you again.

#31 Urbyz

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Posted 24 September 2020 - 04:03 PM

The number of stars spilling out of the globular was breathtaking. The big dob was just a better scope for that type of object.

On this night the planets actually looked better in the AT102ED. The seeing wasn't good enough for the big dob to gain an advantage. At 200x the views in the AT102 were stable and sharp with nice contrast. At 250x they were swimming in the dob.


Most people seem to think a big don would just outright blow any refractor half it’s size out of the water. The only thing i see mentioned a couple of times is that when the seeing is bad, a small refractor might be a nice piece to have handy. I might just have to get both then ;)
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#32 Urbyz

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Posted 24 September 2020 - 04:09 PM

Planets are far better in a 12" when seeing permits which is not a rare thing, though it is not a common thing either. I have had the best planetary results in my 35 years of observing with a 12", and I have owned scopes up to a C14.


For us living in polluted skies. Would you thinka 12” dob would still be way better performing? Would i actually be able to see much more faint objects than with my 6” dob? Or would the pollution kill all the benefits?

#33 Mitrovarr

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Posted 24 September 2020 - 04:22 PM

Light pollution affects what you look at, but aperture always helps. Like, I generally don't galaxy gaze from my Bortle 7 ish balcony. I won't see much. But my larger telescopes do still work better at it when I do it for testing, etc.

#34 NYJohn S

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Posted 24 September 2020 - 04:24 PM

Most people seem to think a big don would just outright blow any refractor half it’s size out of the water. The only thing i see mentioned a couple of times is that when the seeing is bad, a small refractor might be a nice piece to have handy. I might just have to get both then wink.gif

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.

I also prefer splitting double stars with them. It's just a nicer view and I enjoy the challenge, even with my little 72mm.

Edited by NYJohn S, 24 September 2020 - 07:17 PM.

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#35 Kunama

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Posted 24 September 2020 - 05:05 PM

Hi ........................................................

Purely visually. What will be the difference looking at planets and dso’s through a 6k, let’s say 130-140mm, APO refractor compared to a good 12-16” dobson?
............................................................

Best,

Ruben

While the big Dobs are capable of providing more resolution, and brighter views, there are many times when a good refractor will give a better view of planets.

The big Dobs often have thick mirrors that require hours of acclimation, in fact many will never keep up with fast dropping temperatures, this often results in fuzzy stars and  less than ideal details.

 

It really isn't a case of x versus y...... the two instruments complement each other well.  I have a nice refractor and a medium sized Dob which work well together.  I often setup both if time permits and will look at a target in both scopes.


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#36 Jon Isaacs

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Posted 24 September 2020 - 06:28 PM

Now my question is: (And forget about the cost for a minute. I realize it can costs thousands on top of the scope for a big refractor) Purely visually. What will be the difference looking at planets and dso’s through a 6k, let’s say 130-140mm, APO refractor compared to a good 12-16” dobson?

 

 

Here's the way I look at:

 

- You can buy a nice 6 inch refractor for about $6000.  Compared to your 6 inch Dob, the views will be similar but just about as perfect as is possible.

 

- if you spend $6000 on a 12-16 inch Dob, it will be like making your 6 inch Dob as perfect as it can be while gathering 4 to 7 times more light and increasing the resolution 2x to 2.6x.

 

Both the refractor and the Dob will be more effort to setup and not too much different from one another, depending on the mount and the particular Dob.

 

The Dob will require a more hands on approach, more attention to detail. The refractor will be just use it..  in the Netherlands, currently Jupiter and Saturn are low on the horizon, reaching about 15 degrees elevation, Mars is better at 45 degrees but short lived.

 

The big Dob's potential for superior planetary views will not be realized. Deep space.. it'll shine.

 

Jon


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#37 Echolight

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Posted 24 September 2020 - 07:00 PM

I got my big refractor. But it aint no apo. Myself, I can't imagine spending that kind of money on a 6 inch apo. Although I'm sure there are many happy customers who own them. And the view is surely fantastic.

 

Some day I'd like to have a 12 inch dob though. 14 if I could manage it. And I expect either would be great to look through.


Edited by Echolight, 24 September 2020 - 07:12 PM.

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#38 weis14

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Posted 24 September 2020 - 07:18 PM

I'll echo the general wisdom here.  I don't have a big dob, but my C11 is a completely different animal than my Stowaway when looking at the same targets.  I had both under reasonably dark skies last weekend and while the views in the Stowaway were very good for a 92mm scope, the 279mm C11 showed much more detail on every target (as would be expected).

 

The only drawbacks for the C11 are weight, cooldown and collimation.  These three things alone mean that the Stowaway gets more use.  But when the C11 gets brought out under dark skies, it shows its light gathering power.


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#39 gnowellsct

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Posted 24 September 2020 - 07:42 PM

I got my big refractor. But it aint no apo. Myself, I can't imagine spending that kind of money on a 6 inch apo. Although I'm sure there are many happy customers who own them. And the view is surely fantastic.

 

Some day I'd like to have a 12 inch dob though. 14 if I could manage it. And I expect either would be great to look through.

Not THAT many.  Just enough to keep a handful of  boutique producers in business.  A TEC 160 excluding mount costs $12,500.  Double that for a mount to put it on.  

 

People spend more on boats.  And over the course of 5 or 10 years people spend more on bowling or golf.   Golfing once a week on public golf course will run you maybe $2500 a year for example, excluding what you spend on clubs and having lunch before or after or whatever.  Five years of that put you into TEC 160 territory, and of course later in life you can sell the TEC and get 70 or 80% of the money back.  Which you can't with those golfing fees.

 

But you're going to have significant logistical issues moving that TEC 160 around.  If you have to buy a piece of land for an observatory specifically for your TEC well, that's up to you to factor (or not) that into the cost of "the telescope."

 

Anyhow the reason there aren't that many 160 to 180 mm apos out there is because the cost curve of the telescope runs up against the income distribution of the country in which it is sold.

 

Greg N


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#40 Jon Isaacs

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Posted 24 September 2020 - 08:15 PM

 

Anyhow the reason there aren't that many 160 to 180 mm apos out there is because the cost curve of the telescope runs up against the income distribution of the country in which it is sold.

 

I think there are several reasons... this thread points to some of them. Refractors are bestvas small scopes and as their aperture increases, their advantages are less and their liabilities greater. Reflectors are just the opposite, their liabilities become less and less, their advantages are more important. 

 

Chromatic aberration scales with focal ratio divided by aperture. Double the aperture, the focal length increases by a factor of four. 

 

Jon


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#41 Ihtegla Sar

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Posted 24 September 2020 - 08:20 PM

Yep. Thats why my largest refractor is 4". That seems to be a sweet spot for apo refractors considering cost, cooling time, mount requirements, field of view and overall portability.
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#42 DeanD

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Posted 24 September 2020 - 09:10 PM

I often go to club astro camps (at least pre-COVID!), and I usually take my 12" dob and 4" apo. Like a number of people above I often swap between them for a different view of the same object. At the camps there is usually at least one 18" dob, and sometimes a 24". I find that I can see detail in the big dobs that I have missed in the refractor, but often I go back and search for the detail: it is a great way of increasing my observing skills.

 

An example is observing the "homunculus" nebula in Eta Carina (sadly for you northerners not visible!). This is a small nebula that benefits from high power and lots of aperture. The 24" dob gave detail that I had only seen before in Hubble images, but when I went back to my 4" I could see some of the same details, but super faint.

 

The 4" gives wonderful wide field views that the big dobs can't compete with though, and the view is always pristine: a big dob can't match a nice refractor for the beauty of the field and the sharpness of the star images. And for emission nebulae like M42 or Eta Carina the 4" with a UHC filter can even give the 12" dob a run for its money.

 

For planetary, the big dobs will give better views at higher power (on a good seeing night) than the refractor can. The caveat is "good seeing", and the other points above re collimation, cooling down etc. I have made direct comparisons on Jupiter and Saturn at 200+x. The 4" apo gives sharp and beautiful views but it can't match the colour, contrast and resolution (and therefore greater detail) of a big dob at similar power, especially when you go over 200x. At those powers the exit pupil of the 4" is simply too small, and you can't beat the physics of resolution vs aperture.

 

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!)

 

Bottom line for me: both scopes are terrific at what they do- so both are "keepers", but if had to have only one scope I would stick with the refractor simply because of the beauty of the view. (And I would steal views whenever I could through other peoples' big dobs! wink.gif  )

 

All the best,

 

Dean

 

(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! ;) )


Edited by DeanD, 24 September 2020 - 09:13 PM.

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#43 coopman

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Posted 24 September 2020 - 09:25 PM

More aperture is better for just about everything except low power wide field viewing, IMO.  For planetary observing, the atmosphere will be a major factor in what you can see.  Globular clusters will explode with many more stars visible with big aperture.  Faint galaxies will be brighter with more aperture.  Double stars will be more separated with the extra resolution that big aperture offers. 


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#44 ismosi

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Posted 24 September 2020 - 09:47 PM

(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 

Big Dobs can go low. At the Winter Star Party in the Florida Keys we looked at Omega Centauri shortly after it had risen. It was refreshing kneeling to look through a friend's 20-inch f/5 instead of perilously clinging to a ladder :) Eta Carina is *just* visible as well.

 

I compared views in my Stowaway and 18-inch Dob last night on Jupiter, Saturn, and the Moon. I'm a refractor weenie; the 18-inch Dob is new territory for me. In average seeing last night, the level of detail in the 92mm and the big scope was comparable on Jupiter. It was obviously easier to see in the big scope, but the image was just so sharp in the smaller. The big scope got the nod for Saturn .. moons everywhere! On the Moon, it's a toss up - do you prefer the pristine, whole-disk view or the I'm-orbiting the Moon feeling?

 

The Stowaway is showing me the best possible image a scope its aperture can. The Dob needs a night of better seeing so it's still idling, but those nights are rare in these parts.

 

So far the best view of the planets I've had is through my 6-inch TMB152. I'll set it up against the 18-inch one night and point them both at Mars ..


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#45 DeanD

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Posted 24 September 2020 - 11:54 PM

Big Dobs can go low. At the Winter Star Party in the Florida Keys we looked at Omega Centauri shortly after it had risen. It was refreshing kneeling to look through a friend's 20-inch f/5 instead of perilously clinging to a ladder smile.gif Eta Carina is *just* visible as well.

 

I guess it depends how good your knees are: or whether you have brought along a rubber kneeling pad! For some objects I have had to pretty much lie on the ground...  (just goes to show how crazy we astronomers can be!)


Edited by DeanD, 24 September 2020 - 11:58 PM.


#46 Jon Isaacs

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Posted 25 September 2020 - 06:00 AM

I guess it depends how good your knees are: or whether you have brought along a rubber kneeling pad! For some objects I have had to pretty much lie on the ground...  (just goes to show how crazy we astronomers can be!)

 

That really depends on the Dob and how it's setup.  My 22 inch has a horizontal focuser so the eyepiece is quite low at the horizon, about 2 feet.  Doable with the Starbound chair but basically I am sitting on the ground bent over to my left.  But at 10 degrees, the eyepiece is already 3 feet off the ground and it's quite comfortable.  

 

My 16 inch has the focuser at about 30 degrees and I can view objects near the horizon is relative comfort because I am looking down from above rather than from the side.

 

Jon


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#47 bobhen

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Posted 25 September 2020 - 06:50 AM

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


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#48 mikeDnight

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Posted 25 September 2020 - 10:48 AM

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, both 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

 


Edited by mikeDnight, 25 September 2020 - 02:54 PM.

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#49 RichA

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Posted 25 September 2020 - 10:51 AM

Hi there,

I’ve been a proud owner of a small 6” dobson and enjoy using it very much. Being a little smaller and looking at other scopes online, naturally the mind starts to wonder what a bigger scope might reveal through the lens. I might’ve caught some aperture envy!

Looking online i started developing an interest for refractors. Not exactly sure why, but something draws me to their form factor and it might be due to the stories about crisp, contrasty views you’ll only get with a high end APO triplet refractor. Visually as wel as for AP.

I’m very aware that larger dobsons deliver the best bang for buck views and aperture possibilities. Their big aperture lends well for viewing both DSO and planets and the dob mount lends itself perfectly for easy visual observing. But when i read high-end APO triplet refractor (~6k $) product descriptions, it tells me they are capable of also showing details in faint DSO’s and sharp images of planets at very high magnification.

Now my question is: (And forget about the cost for a minute. I realize it can costs thousands on top of the scope for a big refractor) Purely visually. What will be the difference looking at planets and dso’s through a 6k, let’s say 130-140mm, APO refractor compared to a good 12-16” dobson?

I only observe visually so far, but might take up AP in the future.

Best,

Ruben

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.



#50 gnowellsct

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Posted 25 September 2020 - 12:15 PM

I just added a location on my profile. Not sure if people are able to see it now. Anyway, it’s Gouda in The Netherlands.

why am i suddenly thinking of cheese


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