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8 inch newt vs. 5 inch APO

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#26 mistyridge

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Posted 18 June 2007 - 11:57 PM

Aperture always wins regardless what kind of scope it is. High quality reflectors and smaller refractors all have their place and specialty that they excel at. Granted there are overlap areas where they seem to compete with each other. IMO when you get over 7" in aperture newtonians are a better choice. The Apo refractor is the better performer inch for inch when you get below 6", but it will cost. If you don't or can't pay the price there are good compromises such as Achros, SCTs and MCTs that cost far less, but with less performance. The 3* to 4* wide field veiw of open clusters through a 5" Apo at low mag. is as as mind blowing as the 0.5* veiw of globular clusters through a 8" or larger newtonian reflector. On planets when the seeing is not sub arc second the Apo may actully beat the 8" reflector due the ablity to give a more contrasty image. If you want to walk out the door on a cold night to for a quick view the smaller refractor is hard to beat.

#27 dave b

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Posted 19 June 2007 - 12:41 AM

like i always show my students; a 6" unobstructed, perfect optic is creamed in resolution by a 10" 20% obstruction 1/10 wave newt:

http://www.astromart...?article_id=473 (thanks darren!)


this is why i always wonder when people say refractors are best on planets.....

#28 snorkler

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Posted 19 June 2007 - 01:06 AM

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.

No doubt, but an 8" apo refractor is going to cost $50,000 to $100,000, and a 10" reflector can be bought for $500. For well under $5000, you can buy a 16" Dobsonian reflector that will blow the doors off of the 8" refractor.

#29 KWB

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Posted 19 June 2007 - 01:28 AM

If I ever hit the jackpot,I'll bite and let you know. Having
stated hypothetically,I don't know. The TMB 203mm F/7 ED,
may not have the correction of the ED80 Orion,but my guess
is it's one awesome refractor and will chew my 8 inch F/6
to bits and it's not 50,000 to 100,000 dollars.

I do know about 8 and 10 inch Dobs,I've owned a number of them
and have an example of each at the present. I don't know
about large well corrected refractors,only speculation on my part.

#30 chris charen

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Posted 19 June 2007 - 01:41 AM

Its funny how people see things differently. My Orion ED100 gives planetary views far superior then my 8" F/6 well collimated Newt. I mainly use the Newt. for dark sky deepsky stuff. The CO of the Newt just takes the detail away on planets. I started with Newts 35 years ago and still love them but for planetary detail I use the 4" APO every time.

#31 KWB

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Posted 19 June 2007 - 01:51 AM

like i always show my students; a 6" unobstructed, perfect optic is creamed in resolution by a 10" 20% obstruction 1/10 wave newt:
----------------
That's fine,Dave but your skirting the issue. I've now been painted into the corner. Can you give the nod to a 6 inch
F/8 reflector against a 150mm Tak,AP,TMB,etc,?

#32 dave b

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Posted 19 June 2007 - 02:52 AM

like i always show my students; a 6" unobstructed, perfect optic is creamed in resolution by a 10" 20% obstruction 1/10 wave newt:
----------------
That's fine,Dave but your skirting the issue. I've now been painted into the corner. Can you give the nod to a 6 inch
F/8 reflector against a 150mm Tak,AP,TMB,etc,?



if they both cost the same, i would take the 155mm AP.

if the 155mm AP and an 1/8 wave 8" newt both cost the same, i would of course take the 8" newt.

#33 gordon

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Posted 19 June 2007 - 03:28 AM

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.


------------------------------------------------------------
Yes it is, the best features are the fantastic optics and the mount design, it is as easy to balance the scope as using an EQ.

#34 pstarr

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Posted 19 June 2007 - 08:22 AM

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.


On nights of good seeing, my scope will leave little to be desired in the way of high resolution views. I especially like using it to spit double stars at the limit of the scopes resolution using 700x with no image breakdown. With an 18% central obstruction, excellent baffling and curved spider, IMO, it does give refractor like views.

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

#35 Daniel Mounsey

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Posted 19 June 2007 - 10:12 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.


http://www.cloudynig...ll/fpart/1/vc/1



I would agree with you only up to a certain point. I've pasted the refractor vs. reflector post to help you see that you have no trouble convincing me, but there are times when a refractor is more convenient. Just the other night, Ridwan and myself set up my 250 Mewlon against my FS152 6" flourite refractor. The refractor gave more detail, crsiper and sharper images the entire night. In other words, it creamed the the Mewlon. The reasons however were obvious. There was little moisture and the 250 Mewlon was obviously hindered by a boundary layer which also proved to be so during my star tests. Does this mean the FS152 is always going to be better? no, but it does mean that refractors are typically ideal at dealing with these situations.

Ridwan, who admits that he is still learning about all this was left with an impression that refractors can sometimes be convenient under these circumstances. I still explained to him not to be fooled. There will be nights that would make you wonder why you bought a refractor.

You happened to view on a night when your Orion reflector was probably thermally stable and that, along with other things granted you a winning image. BTW, I am a reflector fan and I know a great reflector will kill any apo, but that is not said without proper consideration. I've had nights where I set up my planetary starmaster to my friends 8" apo and I've seen both outperform eachother on different nights depending on the temperature, factors, etc.

Refractor usually provide a reliable image. That means you don't have to collimate them or worry "as much" about thermals etc. You just set them up and they work. That's why I got the FS152 for those nights where the Mewlon can't cool fast enough. A refractor that is not cooled will usually be undercorrected before it reaches better spherical correction, but can still provide pretty decent images when its cooling while a reflector must me dealt with in other ways.

and BTW, aperture doesn't rule. "Aperture rules some places some of the time but not all places all of the time" :lol:

#36 jonnyastro

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Posted 19 June 2007 - 10:22 AM

Great points Daniel. I totally understand and agree with all that you have said. The main thing that i got out of this experience was that i now view refractors in a different light. To be exact, the one you just pointed out.

#37 jonnyastro

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Posted 19 June 2007 - 10:27 AM


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. :)


I used to be one of those guys standing at the eyepiece of a refractor trying to convince myself that the views of planets were contrastier. I also agree with you that pride of ownership plays a big role in the refractor market. These are stunningly beautiful instruments. And to be sure, i am not refractor bashing, im pretty sure my next scope is going to be a 66 or 80 ed. I'm just beginning to see them in a different light.

#38 ScottW

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Posted 19 June 2007 - 12:08 PM

Well what about a 5" refractor, achro or apo, vs. 5.1" DMG reflector at 1800.00 or a 1600.00 D&G for that matter.
There are also the reported high quality 8" reflectors at 2500.00 to 3000.00 OTAs.

Many ways to look at this debate, is anyone or any one right?

Scott

#39 mistyridge

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Posted 19 June 2007 - 05:09 PM

I agree with what Daniel said. For example, last week I had my 18" out to look at Jupiter. Collimated it, and let it cool. The veiw of Jupiter was a bright shimmering blob with some color. The condition were just to poor to use that much aperture. So I set up my lowly Mead 102ED. The view was just great I could see cloud bands etc. Under good conditions the view through the big scope are breathtakeing, but that does not happen very often in my area.

#40 KMB

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Posted 19 June 2007 - 06:53 PM

Couldn't agree more with Steve.

I did research for a year before getting my first equipment. CN was a BIG help. Very pleased with my choices.

It's also more satisfying to do well on a budget then to just splurge on the expensive stuff. Of course you can get a good refractor for 8k--of course you can get a good eyepiece for 500 bucks--a great mount for 4k.

And jonnyastro, a twelve inch newt? You ARE a steely eyed missle man!

Best...

#41 tboss70

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Posted 19 June 2007 - 07:30 PM

I agree with what Daniel said. For example, last week I had my 18" out to look at Jupiter. Collimated it, and let it cool. The veiw of Jupiter was a bright shimmering blob with some color. The condition were just to poor to use that much aperture...under good conditions the view through the big scope are breathtakeing, but that does not happen very often in my area.


This is close to the exact question I asked in the reflector forum not to long ago and a although I didnt take count it seems like I remember a majority of the replies saying something similar to, "with a good mirror, and being properly cooled, aperture always wins".

I honestly cannot say as I dont have enough experience looking through both. Im trying to figure out why some agree with this observation and other do not.

What did you use to measure the temperature of the mirror in the 18" to make sure it was properly cooled?

#42 Jon Isaacs

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Posted 20 June 2007 - 08:32 AM

>>>like i always show my students; a 6" unobstructed, perfect optic is creamed in resolution by a 10" 20% obstruction 1/10 wave newt:
-----

There are some things to remember here. First, the "diffraction limited" field of view of a Newtonian is limited so that only applies at the center of the field of view. In a 10 inch F/5 Newtonian, that diffraction limited FOV is about 5 arcminutes. Of course one can improve things with a Paracorr or a slower focal ratio...

And too, a 1/10th wave mirror put into a system does not necessarily result in a 1/10wave optic p-v optic. When Peter Ceravolo was happy with an a 1/8th wave optic in his small and legendary Mak-Newts that he hand figured with an interferometer, I really do have a hard time with claims of better with larger less carefully configured telescopes.

This is not to say I don't love reflectors, rather, it is to say that things are not quite so simple.

Jon

#43 snart

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Posted 20 June 2007 - 09:38 AM

trying to convince myself that the views of planets were contrastier



I agree. Sometimes this is very hard to do. Cloud covered planets look pretty much the same whether the contrast is great or just average. The area that convinced me of the contrast increase is looking at the shadow of a moon transiting Jupiter. If it is barely detectable and gray in color then your contrast is suffering. If the moon's shadow is well defined and black then you’re on the other end of the contrast curve.

#44 jonnyastro

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Posted 20 June 2007 - 11:29 AM

>>>like i always show my students; a 6" unobstructed, perfect optic is creamed in resolution by a 10" 20% obstruction 1/10 wave newt:
-----

But it is this type of thing i remember debating in the refractor forum. FPL53 vs. Fluorite, triplet vs. doublet, level of color correction vs. contrast. The beauty of the experience that i had on saturday night was that we were both just drawing conclusions based on the end result at the eyepiece visually.

There are some things to remember here. First, the "diffraction limited" field of view of a Newtonian is limited so that only applies at the center of the field of view. In a 10 inch F/5 Newtonian, that diffraction limited FOV is about 5 arcminutes. Of course one can improve things with a Paracorr or a slower focal ratio...

And too, a 1/10th wave mirror put into a system does not necessarily result in a 1/10wave optic p-v optic. When Peter Ceravolo was happy with an a 1/8th wave optic in his small and legendary Mak-Newts that he hand figured with an interferometer, I really do have a hard time with claims of better with larger less carefully configured telescopes.

This is not to say I don't love reflectors, rather, it is to say that things are not quite so simple.

Jon



#45 Jon Isaacs

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Posted 20 June 2007 - 01:21 PM

>>>But it is this type of thing i remember debating in the refractor forum. FPL53 vs. Fluorite, triplet vs. doublet, level of color correction vs. contrast. The beauty of the experience that i had on saturday night was that we were both just drawing conclusions based on the end result at the eyepiece visually.
---

Well, thats one of the reasons I like Newtonians... But at the same time, as one's eye becomes more critical, a wide, well corrected field of view is something special.

Jon

#46 jonnyastro

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Posted 20 June 2007 - 01:56 PM

yeah i have thought of that too, and suppose that i have not yet achieved this critical eye, it is a good point

#47 Daniel Mounsey

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Posted 20 June 2007 - 04:30 PM

Im trying to figure out why some agree with this observation and other do not.



It's simply experience with testing optics and different scopes and watching how they behave. Some telescopes perform better than others on certain nights and vice versa. Aperture has it's advantages but like I implied before, it's not a free ride. There's a huge learning curve with reflectors when your starting out, while refractors are practically dummy proof. I've met observers who have been in this hobby for many years and don't even know how to evaluate their own optics, so I wouldn't take everything they say too much to heart. If one observer is telling you something and the other is telling you something else, what does that tell you? It means that there are a variety of scopes that have the potential to perform well on any given night.

Last night I viewed for five hours through the 6" Tak under pretty decent seeing, but we have plans to head up to Charlton this Saturday and the 6" Tak will be the last thing anyone will want to look through, the competition is staggering with a crowed that's highly skilled in optics and planets. With that said, I may just bring up my 12.5" Zambuto since the seeing and conditions there usually allow me to exploit the full potential of that scope. When you're able to see a clean airy disc in your medium size Newt, that's when you know it's time to party.

Here's another example. My friend just brought his new Mewlon 300 up to Pinos and couldn't cool it down, thus, the images of Jupiter were undesirable. I told him to wait until we head up to Charlton, and he'll understand what that thing can do. If he had used his 6" apo that night at Pinos as a beginner, he would have concluded that the optics in the Mewlon 300 were not as good as the 300 like most beginners. Unless someone was there to explain to him why, he might of just given up or sold the 300, not realizing why it couldn't perform. I deal with observers like the all the time. There's too may observers who have too little patience that don't even know what it is they don't know. It takes a long time to realize the full potential of your scope because you have to expose yourself to those nights where the scope is granted an opportunity to show you what it's got. For that reason, I "usually" spend a couple of years finding that out with each scope bfore letting it go. I've seen way too many observers switching one scope for another without truly understanding why.

Learning can be covered in three steps.

Step 1) You don't even know what you don't know.
Step 2) Now you know what you didn't know.
Step 3) Now you know what you know. :lol:

#48 jonnyastro

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Posted 20 June 2007 - 04:33 PM

I can kind of confirm this point in that the night we used these scopes i was immediately taken a back by how sharp Saturn was at 150X when the scope had not even cooled down yet. In all fairness we were dealing with some exceptional seeing conditions on this particular night.


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