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8inch f6 Dob vs, 6 inch Orion Max on the moon and planets

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#1 tommy10

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Posted 20 October 2017 - 10:58 PM

I own an Orion 8 inch dob  that I really enjoy, I'm thinking  about getting the Orion 6 inch f12 mac with the star seeker mount for the next Mars opposition season, the dob is easy enough to use and gives good views of the planets Jupiter from 171x to 220x is usually doable sometimes higher power on great seeing nights,Jupiter shows a wealth of detail festoons, white ovals, the GRS has been great lately very reddish. The advantages of the Mac include tracking ,goto,the Mac should be able to achieve higher mags with it longer focal length and the optics on the Mac maybe better then the parabolic mirror on the dob, the Mac has a 30percent central obstruction, the dob has a 23% obstruction,the dob may have more tube currents while the MAC may take longer to cool,the Mac offers the opportunity for astrophotography the undriven dob not so much,anyway what do you guys think? Some folks have gotten very nice plantetary sketches with the Mac, will I be disappointed by buying the Mac and getting worse planetary views then my dob offers.



#2 barbie

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Posted 20 October 2017 - 11:56 PM

Properly cooled and collimated, a Mak can do quite well on the moon and planets.


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#3 fcathell

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Posted 20 October 2017 - 11:56 PM

Assuming a good mirror in the 8" Dob, they should both work well on the planets, however, I think you may find the Mak will give more contrasty images. Maks have always been my favorite for planets. Obviously a good unobstructed refractor would be best, but size, weight, and cost factors for a 6" refractor may be prohibitive.  A Mak is a good compromise. I have had (or tried) the 90mm through the 150mm Orion Maks and they all have been excellent scopes. I really liked the 150mm because it was the best compromise w.r.t. weight and aperture. The 5" (127mm) Mak is also a good planetary scope if you want a real grab and go instrument. One recommendation with these Synta made Maks - flock the primary baffle tube with a thin piece of felt. It can be cut, rolled up and just slipped into the rear of the scope and will usually hold its shape against the inner sides of the baffle tube. The improvement on contrast is significant. For some reason, despite the stock "roughing" of the baffle tube, it is still reflective at shallow grazing angles and the flocking is well worth the effort. I found the felt sheet for 99 cents at an art store.

 

Frank 


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#4 barbie

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Posted 21 October 2017 - 12:02 AM

Flocking the primary baffle made my C90 go from a very good scope to an outstanding scope and it took less than 10 minutes to cut the flocking to size and installment was simple with no need to disassemble the scope.



#5 Eddgie

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Posted 21 October 2017 - 09:42 AM

I disagree that the MCT will be better.

 

There are few telescopes that work as well as an 8" f/6 reflector for planetary use.

 

If you really want better planetary views, here is my strongest advice.  Do not spend your money on a 6" MCT. Instead, here is how I recommend you spend that money.

 

Contact a top tier mirror refinisher and ask them to evaluate, refigure, and recoat the mirror you have. 

 

A 6" MCT at its very best is going to fall far short of the result you can get with a top end 8" mirror with high Strehl.

 

The image in the 6 MCT will be dim at the powers you need, especially for Mars.  Many of these 6" MCTs simply have so-so optics. Want proof of that?  Here:  http://teleskop-spez...eleskope.html  

 

On a night of good seeing, It is almost impossible to beat a good 8" f/6 on planets with anything smaller.  

 

My advice is not to buy some indifferently made 6" MCT with Strehl of maybe .85, when you can have a killer mirror in our own scope for less money. 

 

You will get a brighter high power view (and for Mars, you need high powers), with better color saturation (these MCTs are dim due to transmission losses and large CO), and you will have less cool down issue. 

 

Don't do it..  My advice to everyone wanting better planetary views is  is to always spend money on a better instrument, or make their instrument better than it is.    An 8" f/6 reflector with a high quality mirror is one of the best planetary scopes money can buy.  Period.  Don't be duped into thinking a 6" MCT is going to be better. Physics simply don't permit it.


Edited by Eddgie, 21 October 2017 - 09:43 AM.

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#6 Eddgie

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Posted 21 October 2017 - 09:50 AM

And if you need tracking, do either of these:

 

  1. Get a tracking platform
  2. Sell your scope and buy an 8" f/6 Go2 dob. This will have tracking built in and won't be much more trouble to use than 6" MCT on a suitable mount will be. Then, have the mirrors refinished. 

It is all about the mirror and the clear aperture.  You just can't beat a high quality 8" f/6 mirror with anything smaller that would not cost you $10,000.


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#7 tommy10

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Posted 21 October 2017 - 12:51 PM

Thanks Eddie, the mirror on the dob is very good, maybe not premium good, but does show a wealth of detail planets, usually at outreach the dob shows planets better then most of the other scopes, dobs and Sct ,but cooling and collimation issues may explain that ,your suggestion about getting a tracking platform is interesting ,I may look into that ,thank you for your thoughtful response.


Edited by tommy10, 21 October 2017 - 11:14 PM.

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#8 barbie

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Posted 21 October 2017 - 11:19 PM

Eddie, I very much disagree with most of your post!  My 90 mm Mak has outstanding optics and does quite well on Mars( as well as Jupiter and Saturn)for its respective size! Of course a larger Newtonian will do far better but you quite wrongfully diss the Mak as a planetary scope. I've also looked extensively at that website and have and will also disagree with much of what it says.



#9 Eric63

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Posted 22 October 2017 - 01:14 PM

I took the route Eddgie recommended a few years ago. I have a 127Mak and was going to upgrade to a 6"Mak. I kept the 127 and had the mirror in my 6" reflector re-figured,flocked the tube, added a dew sheild and a two speed focuser . I was not disappointed, this 6"f5 reflector has turned into a amazing all around instrument. The CO is the same as a 6"Mak and it can do low power. I love it.

Eric

Edited by Eric63, 22 October 2017 - 02:26 PM.

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#10 Jon Isaacs

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Posted 22 October 2017 - 01:56 PM

Assuming a good mirror in the 8" Dob, they should both work well on the planets, however, I think you may find the Mak will give more contrasty images.

 

 

I'm not sure why you would expect that.  Smaller aperture, larger central obstruction.. 

 

Orion is a bit tricky with their central obstruction specs, they use the term: secondary mirror obstruction. The 127 mm Orion Starmax I had, the secondary mirror obstruction was spec'd at 31%, same as the 150mm.

 

The problem is that secondary mirror is 39 mm and that computes to 31% but actual secondary obstruction is the 48 mm secondary baffle so the actual CO is close to 40%.. 

 

I think the 8 inch F/6 should be the better planetary scope.. Larger aperture and smaller CO means greater resolution, greater contrast..

 

Jon

 

 


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#11 Planethunter80

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Posted 22 October 2017 - 04:14 PM

Thank you all for you feedback and kindness in the replies.smile.gif 

 

This is another example of threads on this forum benefiting so many other individuals then those who are active in it.

I have used refractors and SCT's with every scope I have looked thru.

 

It seems that if aperature is king then a larger(well made and collimated)mirror would perform better on the planets then any other scope(including a smaller reflector).

I look forward to following this thread as Mars' opposition is my main goal upcoming as well. Thank You All.bow.gif 


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#12 gene 4181

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Posted 22 October 2017 - 04:20 PM

  JMO    , but  seeing is king  .     I would gladly  be  forever   using a 6in f5 under  1 arc second seeing (planetary )   .   


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#13 jgraham

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Posted 22 October 2017 - 04:21 PM

It may come down to the quality of the optics in each scope. Assuming good optics I'd give the edge to the Mak for planetary performance. I own quite a variety of scopes, including a couple of the 90mm Orion Maks, and my Maks consistently give sharp, high contrast images with little fuss (nothing to adjust other than the focus) and my Meade Mak 7 gives the sharpest image that I have seen in a production scope.

 

Soooo, if'n it were me I'd take a hard look at the 6" Mak and give the optics a thorough checkout before accepting it.

 

Food for thought.


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#14 Jon Isaacs

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Posted 22 October 2017 - 06:09 PM

Assuming good optics I'd give the edge to the Mak for planetary performance.

 

Even giving up 2 inches of aperture?  

 

The 7 inch Meade Mak has quite a reputation with a 218 mm primary, F/15 focal ratio and all the rest of it.  It's not clear to me that these Syntax Maks are of similar quality.  The 127 mm does not have the oversized primary .

 

https://www.cloudyni...-maksutov-r1135

 

Jon


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#15 Eric63

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Posted 22 October 2017 - 07:38 PM

Assuming good optics I'd give the edge to the Mak for planetary performance.

Even giving up 2 inches of aperture?

The 7 inch Meade Mak has quite a reputation with a 218 mm primary, F/15 focal ratio and all the rest of it. It's not clear to me that these Syntax Maks are of similar quality. The 127 mm does not have the oversized primary .

https://www.cloudyni...-maksutov-r1135

Jon

Synta never corrected the 127 primary size but I believe that the 150 and 180 are now at full aperture.

Eric

#16 tommy10

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Posted 23 October 2017 - 12:32 PM

So if you get an 8 inch f6 Orion off the shelf dob and place it next to an off the shelf Orion 150mm F12 Max and point both at Jup at 200x will the views be better in the Mac or Dob? Let's add a eq platform to the dob so the price will be more equal,theorically the dob with more aperture and less central obstruction will be better but what about in practice?Will the views be so similar that the scope with the slightly better optics win? Is there still that much variance between the optics of commercially made scope?



#17 mark379

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Posted 23 October 2017 - 01:49 PM

An 8" f6 cooled and colliminated will leave a 6" MAK in the dust.

Grab some 235 mm tube rings and a decent eq mount, balance properly, and you're golden!

 

I own an Orion 8 inch dob  that I really enjoy, I'm thinking  about getting the Orion 6 inch f12 mac with the star seeker mount for the next Mars opposition season, the dob is easy enough to use and gives good views of the planets Jupiter from 171x to 220x is usually doable sometimes higher power on great seeing nights,Jupiter shows a wealth of detail festoons, white ovals, the GRS has been great lately very reddish. The advantages of the Mac include tracking ,goto,the Mac should be able to achieve higher mags with it longer focal length and the optics on the Mac maybe better then the parabolic mirror on the dob, the Mac has a 30percent central obstruction, the dob has a 23% obstruction,the dob may have more tube currents while the MAC may take longer to cool,the Mac offers the opportunity for astrophotography the undriven dob not so much,anyway what do you guys think? Some folks have gotten very nice plantetary sketches with the Mac, will I be disappointed by buying the Mac and getting worse planetary views then my dob offers.


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#18 Ed D

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Posted 23 October 2017 - 02:15 PM

If aperture were the only factor it would be a simple decision, wouldn't it.  How easy is it to take out your 8" Dob compared to how much effort it's going to take to set up a GEM and mount the Mak.  How much time are you willing to spend to let the Mak cool, because they do cool slower than Dobs.  As the temperature falls in your environment, will the Dob or Mak be able to keep up with the changing temperature?  How fast do clouds come rolling in?  How about rain?  How much hassle factor are you willing to put in to use the scope?

 

If you want to observe better detail start by making sure your Dob is well collimated after it has acclimated.  Start sketching planets or the moon.  They don't have to be works of art, but they will surely teach you to eke out fine planetary detail.  How good are your eyepieces?  For planets my best advice are good quality Plossls, such as the Vixen NPL or Tele Vue, or good orthoscopics.  Before doing anything with the primary, have you considered changing out your secondary for a better quality one?  It's the secondary mirrors on production Dobs that are lacking.  The views through my 10" Dob improved quite a bit by simply installing an Antares secondary.  I think you get my point.

 

If you really want a Mak, why not get the 5"/127mm Mak?  I have one and they are light, cool quickly, and give good detail for the aperture.  My 5" Mak gets used way more than my 10" Dob or 6" mak simply because of the convenience.

 

Finally, while I wouldn't recommend it, I have observed a lot of detail on Mars with my 70mm achromatic refractor in the morning hours, and have posted many sketches in the sketching forum over the years.  Yeah, my 10" Dob or 6" Mak out perform the refractor, but I'm not lugging out a monster at 4:30am for a 45min session before getting ready for work.

 

You already have a good scope.  Use it and learn to get the most out of it, and maybe smooth up the Alt-Az motions to make hand tracking more precise and easier.  If you get another scope, get one that compliments the Dob.

 

Ed D


Edited by Ed D, 23 October 2017 - 02:46 PM.

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#19 Ed D

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Posted 23 October 2017 - 02:28 PM

You said in your original post that the Mak should get higher magnification due to the longer focal length.  Well, I can make the toy scope in a kid's meal work at even higher magnification, but the image will be horrific.  The larger the scope aperture the larger the theoretical magnification it can achieve before the image breaks down.  The 8" Dob can be pushed a bit higher than the 6" Mak.  However, local conditions are what will limit your magnification, not so much the scope.  But, the larger aperture will show more fine detail than a smaller aperture at the same magnification.

 

What longer focal length will do is give the higher magnifications with longer focal length eyepieces.  If using Plossls or Orthos this is a very important consideration because the shorter focal length ones will have very short eye relief.  However, modern high quality Barlows can be used with good effect, allowing use of longer focal length eyepieces at high magnifications with good eye relief.  Many modern eyepieces use a barlow lens in the field end.

 

Ed D


Edited by Ed D, 23 October 2017 - 02:47 PM.


#20 Ed D

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Posted 23 October 2017 - 03:01 PM

In your original post you also touch on photography.  A tracking mount will definitely make life a bit simpler.  But, lunar and planetary imaging is way different than deep space.  In lunar and planetary imaging you take thousands of frames in a very short time, and then use maybe 10% of the best frames when processing.  I use my Dob for planetary and lunar imaging by letting the object drift through the field of view, pausing, and repeating the process until I have sufficient frames to stack.  The processing software takes care of aligning and centering the image.  This image of Tycho was taken with a 72mm ED APO with a manual Alt-Az mount using the technique I described.

 

Pic 1 - Full Moon and Tycho 2017 3-10 AT72ED on Alt-Az Mount.jpg

 

Deep space is another matter all together that I don't want to get into.

 

Ed D


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#21 tommy10

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Posted 23 October 2017 - 05:17 PM

Thanks for all of the responses,I often heard folks talk up the high mag make views enough those with modest aperture,the star seeker four looked light and easy to use although the six inch mak maybe pushing it, It seems one has to buy a really expensive scope to beat a eight inch dob in planetary views, the suggestions to improve the dob are helpful and appreciated, I have nice ortho and plossl eyepieces I use to get nice planetary views,I'm nearly always more limited by seeing conditions then aperture with the eight.


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#22 Eric63

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Posted 23 October 2017 - 07:38 PM

Seeing really is the big factor. I have had perfect seeing conditions a few times and both my mak and my reflector have left me breathless. I don't think a perfect 6" Apo under average conditions will come close to what my scopes have shown me under perfect conditions.
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#23 mark379

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Posted 23 October 2017 - 08:43 PM

Given any magnification, your 8 will show more detail, contrast and be brighter. F6 is also very forgivng with collimination.

Thanks for all of the responses,I often heard folks talk up the high mag make views enough those with modest aperture,the star seeker four looked light and easy to use although the six inch mak maybe pushing it, It seems one has to buy a really expensive scope to beat a eight inch dob in planetary views, the suggestions to improve the dob are helpful and appreciated, I have nice ortho and plossl eyepieces I use to get nice planetary views,I'm nearly always more limited by seeing conditions then aperture with the eight.


Edited by mark379, 23 October 2017 - 08:43 PM.

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#24 tommy10

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Posted 30 October 2017 - 01:25 AM

Yeah I think I’ll just concentrate on improving my 8inch dob, flocking, eq platform,maybe even a mirror regrind when I have to recoat it.



#25 Asbytec

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Posted 06 December 2017 - 07:11 PM

JMO , but seeing is king . I would gladly be forever using a 6in f5 under 1 arc second seeing (planetary ) .


I think Gene is spot on. I have a 6" Mak and observed Jupiter intensely over four years. The images are very nice and I sketched them many times. I was enjoying Jove immensly.

I also have no illusions what I was enjoying immensly was fine tropical seeing conditions. They afford the ability to really tweak collimation, and modest ambient temperatures allowed the scope to operate at ambient. The 3 C's allowed the scope to perform: collimation, cooling, and C'ing.

Turns out, when these conditions are met, a 5" or 6" Mak is great on Jove and, disagreeing with Eddgie, also on the higher magnification requred for Mars. I have no trouble at 240x observing Jove. In fact, I prefer it. Same with Mars closer to 400x.

But you have to remember, Jove is both easy and difficult to observe. Everyone can make out the EQ belts, GRS, and polar regions. But it takes good seeing and experience to see much of the more difficult features. Color in a 6" is subtle, but discernable and sketches often embellished to show it better.

The kicker seems to be, given favorable conditions, I'd bet the 8 with descent optics will show more if for no other reason than having the light grasp to magnify the image 300x and a little better resolution. The Mak is no slouch on planets, but a good 8" should outperform it.
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