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What is a good 6 to 8" Newtonian OTA

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#1 Nippon

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Posted 09 October 2019 - 08:32 PM

I've been living in the refractor world for a long time but thinking of a 6 or 8" f/6 if possible Newtonian. Seems they are all f/4 or faster or come in Dobsonian form which I don't want. But I do want very good optical quality.

 

Thanks, Paul



#2 MalVeauX

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Posted 09 October 2019 - 08:46 PM

For a commercial, non-premium scope, consider:

 

https://www.teleskop...in-Germany.html

 

Where in Florida exactly are you?

 

Very best,


Edited by MalVeauX, 09 October 2019 - 08:46 PM.

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#3 Nippon

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Posted 09 October 2019 - 08:49 PM

Winter Haven. It's just south of I-4 between Tampa and Orlando.


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#4 nicoledoula

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Posted 09 October 2019 - 08:53 PM

https://agenaastro.c...lector-ota.html    https://agenaastro.com/sky-watcher-6-traditional-dobsonian-telescope-s11600.html


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#5 vtornado

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Posted 09 October 2019 - 09:01 PM

I have the celestron xlt f/5 good not great, but the price is right.

 

I don't know if it is good or not, but it is cheap, If I didn't have the f/5 I would get it.

https://optcorp.com/...g-ota-telescope

 

If you don't want a dobsonian, what kind of mount to you want/have?

I had a 8 inch f/5 and it takes quite a mount to hold it steady just the OTA was 16-18 lbs.

I have a sky view pro mount head, and a tripod with two inch legs.  With counter weights,

the thing was a beast, and was at the edge of the mount's capability.

It was orion branded and the mirror was quite good.

 

I just picked up a used orion 6 inch f8 dob.  I am very impressed with the views so far, but I need more time.

It is a dob, but you could not use the base and get some rings for mounting.  It would take quite a mount too

being 1200mm long.   The focuser is stinky, lots of backlash.  I'm looking for a drop in replacement.


Edited by vtornado, 09 October 2019 - 09:10 PM.


#6 Garyth64

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Posted 09 October 2019 - 09:13 PM

Make your own mirror.



#7 Sleep Deprived

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Posted 09 October 2019 - 09:18 PM

Parks Optical makes good Newts with a longer Focal Lengths:

 

http://www.parksoptical.com/

 

They are more spendy, but they have a good rep.  Don't know the price range you are shooting for.

 

Good luck with whatever you decide upon!!!


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#8 Joe1950

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Posted 09 October 2019 - 09:30 PM

I have a 6” f/6 scope I built into a dob using a very good mirror purchased in 1976. It does a great job and is light weight, so that I can carry the whole thing outside as one piece.

 

Anyway, I’m very impressed with the Agena/GSO 6” f/6 OTA at $200. Why? Agena is a great company that I have explicit trust in. To offer a scope that has been checked over by them especially optically is a value I wouldn’t underestimate.

 

I bought a 6” f/8 scope with a well known brand name. The mirror was ok, but friends who know optics evaluated dozens of images of star tests, using a 33% center obstruction, and defocused 10 waves inside and outside the focal point. 

 

Evaluating the differences in the unfocused star images, edge appearance and ring lighting, as well as the relative size of the CO shadow, the consensus was it fell between 1/3 and 1/2 wave, P-V. A center of curvature Foucault and Ronchi test confirmed the evaluation showing a substantial central plateau.

 

In short, it gave decent images to a point but was not a decent figure. I had the mirror refigured and the scope performed very, very well.

 

My point is, when you buy a production scope as I did with the 6” f/8, you may get a good one or you may get a poor one. You just don’t know.

 

Getting an optic that is checked by a competent optician before it is shipped to you is worth it’s weight in gold in today’s world. 

 

Just my opinion. But that benefit alone would seal the deal for me.

 

Good luck, Paul.

All the best,

joe

 

 

 

ADDED:  Just for comparison sake, this as a Foucault image of the same mirror before refiguring (left) and after (right). Note too, an f/8 shows more of a delicate slope if properly figured as does the after image.

 

mirror comp.png

 

I'm certainty not criticizing the other suggestions, as I have no experience with the brands mentioned. Some brands are well known by their owners and have a high percentage of very good scopes sold. I'm just going by my experience which is limited among brands today. 

 

If I were to purchase a new scope, I feel I have a talent to find the lemon among them. So having some kind of qualitative assessment on the particular one I receive is valuable to me.


Edited by Joe1950, 09 October 2019 - 10:04 PM.

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#9 Diana N

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Posted 09 October 2019 - 09:32 PM

You can also look for a “golden oldie.”  Edmund Scientific, Criterion, Parks, Star-Liner, and Cave all made OTAs in that size range. (And it looks like Parks still does.)


Edited by Diana N, 09 October 2019 - 09:36 PM.

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#10 Nippon

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Posted 09 October 2019 - 09:35 PM

Parks Optical makes good Newts with a longer Focal Lengths:

 

http://www.parksoptical.com/

 

They are more spendy, but they have a good rep.  Don't know the price range you are shooting for.

 

Good luck with whatever you decide upon!!!

I thought Parks went belly up years ago.



#11 Nippon

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Posted 09 October 2019 - 09:51 PM

You can also look for a “golden oldie.”  Edmund Scientific, Criterion, Parks, Star-Liner, and Cave all made OTAs in that size range. (And it looks like Parks still does.)

I wish Vixen still made the R150ss. I had the Celestron version, a SPC6 and have fond memories of it. I have seen a few used C6 Newtonian OTAs but usually by the time I do they are sold. Plus since they are likely to be at least 20 years old I wonder how the mirror coatings will be.


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#12 Nippon

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Posted 09 October 2019 - 09:55 PM

Well I clicked on a tube on the Parks site and it says cart is unavailable at this time. I think it's a ghost of the past still haunting the internet.



#13 Sleep Deprived

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Posted 09 October 2019 - 10:13 PM

 

Well I clicked on a tube on the Parks site and it says cart is unavailable at this time. I think it's a ghost of the past still haunting the internet.

Huh.  Look at that.  Maybe you are right.  The website is copyrighted for 2019.  Not that that is a guarantee of anything.  Perhaps they keep the website active, 'just in case'.



#14 25585

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Posted 10 October 2019 - 04:33 AM

F8 is great.


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#15 dmgriff

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Posted 10 October 2019 - 06:10 AM

Orion Opitcs UK offers 6in f/5, f/8, and 8in f/4.5, f/6 newtonian otas in the VX series (choice of 1/6, 1/8, 1/10 wave PV, Zygo interferometer report included). Optics made and assembly in Staffordshire, United Kingdom. 8in carbon fiber otas are available in the CT series.

 

https://www.orionopt...onianrefle.html

 

Good viewing,

 

Dave


Edited by dmgriff, 10 October 2019 - 07:06 AM.

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#16 SandyHouTex

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Posted 10 October 2019 - 10:02 AM

I recently purchased two Skywatcher classic Dobs.  One is a 6 inch f/8 and the other is an 8 inch f/6.  Both are very good.


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#17 scopeboy42

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Posted 10 October 2019 - 11:25 AM

I thought Parks went belly up years ago.

Yes, they are out of business, but I know that up to a few months ago the owner was trying to sell the business. Apparently he has everything packed away in a warehouse somewhere in CA and was looking for a buyer. 


Edited by scopeboy42, 10 October 2019 - 11:26 AM.


#18 scopeboy42

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Posted 10 October 2019 - 11:30 AM

Parks Optical makes good Newts with a longer Focal Lengths:

 

http://www.parksoptical.com/

 

They are more spendy, but they have a good rep.  Don't know the price range you are shooting for.

 

Good luck with whatever you decide upon!!!

Here is a link to the old Parks Optical website that has better/bigger photos of what they use to sell.

 

http://www.parksopti...site/index.html



#19 Garyth64

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Posted 10 October 2019 - 12:12 PM

Our club has an Orion XT8i, 8" f/6. It is a very good scope.  It gives great views and is easy to move around.

 

We also have a TPO 8" f/4 Astrograph, which is also a very good scope.

 

Both are very well made.

 

I have used both of them.



#20 25585

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Posted 10 October 2019 - 12:38 PM

Orion Opitcs UK offers 6in f/5, f/8, and 8in f/4.5, f/6 newtonian otas in the VX series (choice of 1/6, 1/8, 1/10 wave PV, Zygo interferometer report included). Optics made and assembly in Staffordshire, United Kingdom. 8in carbon fiber otas are available in the CT series.

 

https://www.orionopt...onianrefle.html

 

Good viewing,

 

Dave

They can also do "XL" models to special order 6" F11 and 8" F8

 

http://scopeviews.co...ptics200Dob.htm

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Edited by 25585, 10 October 2019 - 12:46 PM.

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#21 Joku_

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Posted 10 October 2019 - 07:55 PM

I've been living in the refractor world for a long time but thinking of a 6 or 8" f/6 if possible Newtonian. Seems they are all f/4 or faster or come in Dobsonian form which I don't want. But I do want very good optical quality.

 

Thanks, Paul

Where do you get the idea that moderately sized reflectors like 6" or 8" are as fast as f/4? confused1.gif

 

Something like HEQ-5 should be fine with 8" f/6 reflectors.



#22 SeattleScott

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Posted 11 October 2019 - 12:59 PM

Generally speaking people don’t want to deal with a newt on a gem for visual anymore, so the higher end newts for gems are around F4. Or they are Dobs. That is what you are seeing. For a Newt OTA to go on a gem, you take your chances with the Chinese stuff, or buy from Germany to get Chinese stuff with a better focuser, or you get a custom order. Orion Optics is by far the most affordable of the higher end custom newts. Brexit probably helped the exchange rate a bit, but you still have expensive international shipping, customs, and foreign exchange fees. And while their products are a clear step above Synta, and MUCH more affordable than Parallax, it is really kind of an upper/middle tier product aimed at being better than the cheap mass produced stuff and cheaper than the top of the line, cost is no object stuff. And their customer service reputation is spotty, although I haven’t had issues myself. Definitely an option for someone who wants a quality product but doesn’t want to drop a few grand on a top of the line model. But the shipping and such does add considerable cost.

Scott
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#23 25585

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Posted 13 October 2019 - 03:26 PM

One solution may be buying the mirrors you want from one seller, then getting a scope built around them by another.   http://apm-telescope...m/item/33353538 are for a good general purpose 8", for example. 


Edited by 25585, 13 October 2019 - 03:27 PM.


#24 iKMN

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Posted 13 October 2019 - 04:12 PM

I've been living in the refractor world for a long time but thinking of a 6 or 8" f/6 if possible Newtonian. Seems they are all f/4 or faster or come in Dobsonian form which I don't want. But I do want very good optical quality.
 
Thanks, Paul


I went through something similar last year and was difficult to find in this size that did not have a cheap focuser or build quality. I went with a 6” Mak-Newt the ES one. Surprisingly it’s very good and is one of my favorite scopes. I just kill it with this scope. A couple things... the flat field OMG, the weight distribution with the mirror in the back and the corrector in the front it balances very nicely on my TWII mount even with big heavy eyepieces. Also u don’t need a CC with it also absolutely color free flat field with almost zero coma. It’s almost refractor like. I could really go on and on how much I like this scope. Unfortunately, I don’t think the QC is there. My first one had to go back and even my 2nd one arrived with a broken dew shield which was replaced by ES. So I am reluctant to recommend and post threads and how good this scope is. However, I live about 90 min south of you and we have star parties at my ranch. The next one is Oct 26 weather permitting. You can come and see for yourself if u like you can use it as much as you want. I’ll also have my 10” dob setup with CC. At times I think an 8” Newt with CC might be just as good. We are on Facebook at Heartland Astronomical Society or send a PM. There is someone in Lake Alfred in our club that usually comes every star party so you can hitch a ride possibly. Some of the people are from FOO in Dade city that hop between FOO and my place. Anyway, good luck finding a scope. I like my 6” MN so much I sold all my refractors.

Kristian

#25 MalVeauX

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Posted 14 October 2019 - 04:40 PM



Winter Haven. It's just south of I-4 between Tampa and Orlando.

Hollar at me if you're ever near Gainesville/Ocala/Trenton/CedarKey and you can look through whatever scope you want. I have a sharp fully Quartz 8" F6 scope from Germany that rides comfortably on a HEQ5 and Twilight 2 you could compare to.

 

33948345908_25b1abfd87_c.jpg

 

48609877387_03c74bc0e3_c.jpg

 

Very best,


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