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8 inch newt vs. 5 inch APO

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#1 jonnyastro

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Posted 18 June 2007 - 11:08 AM

Went to my club Saturday nite and happened to set up right next to a gentlemen who was using a 5 inch Takahashi refractor. I was using my 8 inch Orion Intelliscope. We struck up a conversation and soon began swapping scopes on different targets. Now as some of you know, i got the Dob to tide me over while saving fro a premium APO. Well, to make a long story short, my lowly, mas produced mirror beat the state of the art fluorite lens on every single target, planets included. Interestingly, it wasn"t i who first acknowledged this, it was the guy who owned the Tak. He kept bringing his own ortho eyepieces over to my scope, and shaking his head. As a recovering CRF, this was very validating for me. I am really no longer seeing any advantage at all to ultra expensive refractors. Not to mention that, while stunningly beautiful, and well made to say the very least, his scope and mount combo is a boat. Mine was out and ready in under 5 minutes. In conclusion, i am no longer aspiring to get the 4 to 5 inch APO, rather my next upgrade will be a 12 inch newt, which, because of cost, can happen a lot sooner. Personally, at this point, i see refractors as excellent, rugged, grab and go travel scopes. I am quite happy to be in the reflector camp at the moment.

#2 snart

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Posted 18 June 2007 - 12:36 PM

Aperture rules and a lot always depends on the seeing which is the great equalizer, but a well made Newt with a reasonably small secondary mirror can be a great planetary scope. The secondary mirror will always lower contrast compared to the unobstructed Apo, but the higher resolution of an 8” brings something to the view that the 5” telescope can’t.

#3 Covey32

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Posted 18 June 2007 - 01:00 PM

A 5" scope is a 5" scope , adding a pedigree doesn't change the size of the aperture.
Imaging=APO Visual= Aperture

#4 stevek

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Posted 18 June 2007 - 01:03 PM

I just got back from a weekend star party and pretty much had observed the same thing. My wellcollimated DOB showed more and better than anything that had less aperature. Since I cant afford anything in the APO category, it left me pretty pleased with my equipment. Also noticed swapping EPs that mine were as pleasing as any of the topend pieces I put into my scope. VERY encouraging. I guess my homework and the help supplied from CN has led me to the right stuff!
Steve

#5 gordon

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Posted 18 June 2007 - 02:03 PM

The hang up over reflector verses refractor seems to originate in the 1950's-1960's. Even Patrick Moore will say buy a three inch refractor or a six inch reflector.
However times and tech have changed. It just takes time for the astro community to accept this. I own a 14 inch reflector and I also own an 8 inch mak. I have also owned a five inch apo. The most used scope is the 14 inch reflector.
I have been into astronomy for 30 years, I have been very active and I know my stuff.
Don't forget if someone buys an apo for $2000 they want it to out do any other type of scope that costs a third less,their opinion will rely on the cost. It is human nature.

#6 jonnyastro

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Posted 18 June 2007 - 02:13 PM

Gordon, interesting you should bring Patrick Moore into this discussion. In his "Atlas of the Universe", which i own, he sates that Dobs are not suitable for planetary work"!

#7 jonnyastro

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Posted 18 June 2007 - 02:14 PM

It just boggles my mind that a piece of equipment costing in the three hundred dollar range can outdo one costing in excess of 5000 with mount.

#8 snart

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Posted 18 June 2007 - 02:18 PM

he sates that Dobs are not suitable for planetary work



I have to agree with him to a point. A Dob can be a pain in the butt at high power even if the settling time is very short. An equatorial mount is far, far better than a Dob for planetary, however it can be done with the Dob...

#9 jonnyastro

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Posted 18 June 2007 - 02:23 PM

Suprisingly, i am having a great experience viewing the planets with my Dob. The trick for me has been to utilize wide field eyepieces.

#10 Jon Isaacs

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Posted 18 June 2007 - 02:28 PM

It just boggles my mind that a piece of equipment costing in the three hundred dollar range can outdo one costing in excess of 5000 with mount.


I really don't think it is quite that simple...

A 5 inch APO is really best suited for astrophotography. When one pays that much (actually a lot more) for a 5 inch telescope and mount, they are buying optics and capabilities that an 8 inch DOB does not possess.

Visually, a 5 inch APO will provide a wider field view that is better corrected to the edge than a similar newtonian and should be fully illuminated as well.

If you wanted to purchase a mount capable of the sort of precision possible with a TAK, A-P for you 8 inch Newtonian, you would be paying the big bucks too.

Myself, I like Newtonians and I like refractors. A decent 8 inch Newtonian that is cooled down and collimated can provide some wonderful views. But a 5 inch APO can also provide some wonderful views and take some wonderful photographs as well.

Jon

#11 jonnyastro

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Posted 18 June 2007 - 02:33 PM

That is true, i often omit photographic capability, since i have not yet fully gotten into astrophotography. I was coming from a purely visual standpoint. Personally, neiither of us felt that the wider field of the refractor was significant enough to really factor into the visual work we were doing.

#12 snorkler

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Posted 18 June 2007 - 02:58 PM

On the night of Deep Impact on Comet Tempel 1, we set up a 12.5" Portaball between an Astrophysics 155 and a homebuilt 10" reflector on a pipe mount. Farther down the field were a 17.5" Discovery truss Dob, a 14" SCT, and other scopes.

First, to identify the comet, we had to look in the SCT and the truss Dob to see that it was a comet. We had a circular fuzzy in the Portaball. It took the larger scopes to see the tail of the comet in the same star field.

Then, after the impact, we exchanged views with our immediate neighbors. Both larger reflectors easily clobbered the AP 155.

Over the years, my best views of every target have always been through large aperture instruments. I use my refractors pretty much only for extreme widefield views and double stars.

#13 Jon Isaacs

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Posted 18 June 2007 - 05:32 PM

>>>I have to agree with him to a point. A Dob can be a pain in the butt at high power even if the settling time is very short. An equatorial mount is far, far better than a Dob for planetary, however it can be done with the Dob...
----

Tracking is nice when viewing the planets but there is a compromise between the useability of a DOB and a GEM mounted scope and aperture. In my own situation, I prefer the planetary views in a larger DOB over a smaller GEM mounted Newt, the added resolution/brightness makes going to those high magnifications worthwhile.

Jon

#14 erik

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Posted 18 June 2007 - 06:01 PM

Being a newt guy, I'd agree that an 8" reflector can beat a 5" apo refractor. However, I would point out a few things:

The newt may require more cooldown time, and it may be more affected by seeing conditions, tube currents, etc.

The newt will show diffraction spikes around bright objects unless a curved spider is used, while the refractor will obviously not.

The refractor may show a "cleaner" image, but not necessarily more detail. This is especially true if the newtonian has a large central obstruction, isn't flocked, etc.

...The great thing about newtonians is that they're easy to modify. A flocked, collimated, cooled down newt with a curved spider, nice focuser (being perfectly in focus is important on planets!), and good optics will be right on par with an apo refractor of the same aperture minus the secondary obstruction, IMO. :)

#15 John Fitzgerald

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Posted 18 June 2007 - 06:03 PM

Tracking platform for a Dob, a great equalizer.

#16 Almach

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Posted 18 June 2007 - 06:04 PM

I own a 14 inch reflector ...


Gordon, is your 14" Orion UK scope one of those Orion Optics 350mm f4.7 scopes?

If yes, what makes that scope stand out from others in that aperture range?

As and when I make a jump in aperture, that particular scope, the OO UK, is one I will consider.

#17 Almach

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Posted 18 June 2007 - 06:06 PM

It just boggles my mind that a piece of equipment costing in the three hundred dollar range can outdo one costing in excess of 5000 with mount.


... isn't it great! :)

#18 mistyridge

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Posted 18 June 2007 - 06:31 PM

So why would anybody in their right mind spend $5k on a 5" scope? :confused: The answer is me because I am nuts. :crazy:

#19 KWB

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Posted 18 June 2007 - 06:35 PM

I'm not so sure your about about the equal aperture compar-
ison.

I have no way of knowing and probably will never be lucky
enough to find out,but strickly wild guessing from what I've
heard and read from the owners and users of large aperture
ED refractors tells me there may be more to the story.

If all things were equal,a top of the line 8 inch ED scope
that had the same color correction as say the ED 80 Orion
refractor should be able to chew up and spit out the best 8
inch reflector and get a very large piece of the best 10
inchers as well. My wild guess only.

I like reflectors as well as anybody but am not going to get
carried away here. IMO reflectors are the best bang for the
buck but certain comparisons don't hold sway here,at least
to me.

#20 Jon Isaacs

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Posted 18 June 2007 - 06:47 PM

Tracking platform for a Dob, a great equalizer.


The best of both worlds...

Jon

#21 jonnyastro

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Posted 18 June 2007 - 07:32 PM

It just boggles my mind that a piece of equipment costing in the three hundred dollar range can outdo one costing in excess of 5000 with mount.


... isn't it great! :)


Yeah Jim it is!

#22 pstarr

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Posted 18 June 2007 - 08:55 PM

Gordon, interesting you should bring Patrick Moore into this discussion. In his "Atlas of the Universe", which i own, he sates that Dobs are not suitable for planetary work"!



I think this comment goes back to the early days of the dob revolution, when they were know primarily as "light buckets" that used large short focus mirrors often made of porthole glass and questionable wave front quality. A far cry from the high end dobs with premium optics available today.

Paul
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10" F-6 Eq planetary newt. w/Zambuto mirror
fully flocked aluminum tube
curved spider, Antares 1/30 wave secondary
12'x12' roll-off roof observatory
TV Radians 5,6,8,10,12mm
Baader Hyperion 17,21mm
TV 2.5x barlow

#23 erik

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Posted 18 June 2007 - 09:09 PM

I like reflectors as well as anybody but am not going to get
carried away here. IMO reflectors are the best bang for the
buck but certain comparisons don't hold sway here,at least
to me.

Good point. I think refractors can win in lots of areas. The most obvious (and the reason I think many people spend thousands of $$$ on a 5" telescope) is the build quality and pride of ownership. A fine, precision apochromatic refractor is a beautiful piece of gear and workmanship. I can relate to appreciating something like that (but I don't have the money to spend on one! :grin:).

The other thing is that we all see things differently. Perhaps it's bias, our eyes being different, etc. ...But I've compared views between scopes or eyepieces, and had completely different opinions than the guy standing next to me looking through the same gear! Some will insist that open clusters look better in refractors. Some will insist that planets have a more "contrasty" look to them, and they can see more detail. To each their own, I guess.

The great thing is that we can all enjoy this wonderful hobby, whether our scope costs $100 or $5000. I don't think the same can be said about many other hobbies. :)

#24 Covey32

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Posted 18 June 2007 - 09:10 PM

Your 10" with a Zambuto mirror should be giving you very "refractor like" planetary views. I can remeber the first few times with my 12.5 Portaball Zambuto and how surprised I was at just how good things can look. The 5" Televue APO I had did not really deliver anything sharper or with more contrast.
I'm sure the types of reflector optics as are available today are a far cry from the original Dobs, and that, while there is no doubt of the APO's superiority for imaging, the premium Dobs around today don't give away anything to the APO refractors in visual applications.

#25 KWB

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Posted 18 June 2007 - 09:13 PM

I agree Erik. I don't have the money for a top flight large
refractor,either. For me,reflecting scopes are the only
real game in town.
:jump:


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