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150mm Instrument for Planets, Which Type?

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#1 MalVeauX

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Posted 19 August 2019 - 02:07 PM

Hey all,

 

This is one of those types of questions that I'm sure many go through... but I'm curious. I have lots of scopes, but not all sizes and so its hard to compare. I like duality and greater if possible from a scope, so I'm always curious what would be ideal. In this case, I'm considering a smaller 150mm (6") aperture scope, of various designs, for lots of things but also for specifically solar system visual observation, namely Jupiter & Saturn for the most part, and a kiss of Venus & Mars when they're around. I have larger apertures than this. However, the goal is to consider the better design scope at 150mm aperture on a manual alt-az mount (in this case, a Twilight II) for planetary observation. Probably not at the highest magnification possible for the night, but potentially with binoviewers sometimes too. While I have larger apertures and have used them for this, and I also have smaller apertures and have used them for this, I don't have a 150mm APO nor a 150mm reflector. I have had a 150mm F10 SCT (C6) and I currently still have a 150mm F8 Achromatic Doublet Refractor (lots of CA). I'm super curious at this point, would a 150mm F6 reflector (GSO $200) do this job well (similar to the C6 did) compared to the 150mm F8 ED doublet (Skywatcher EVO, $2000). I'm really curious if the 10x price factor is worth it from the standpoint of visual observation of planets. I realize a lot of people are biased and that's why I'm asking. I'm a big fan of refractors in general. But, I can't help but consider that a much less expensive reflector could do this job for next to nothing. Then throw in the other options like a 6" SCT, 6" classical cassegrain, 6" Mak, 6" Mak-Newt, 6" ED refractor, etc, within the constraints of a 25lb capable alt-az manual mount for visual use and the potential use of binoviewers but happy going no farther than around 200x magnification visually since there won't be tracking. Is the contrast of the 150mm F8 ED refractor worth the 10x increase in cost over a 150mm F6 reflector?

 

Very curious to the following experience:

 

Alt-Az mount, manual movement

Binoviewers, going as far as 200x magnification mostly if seeing allows, but not really farther than that

Design: SCT, such as the C6 or Classical Cassegrain ($400)

Design: Reflector, such as the GSO 6" F6 newtonian ($200)

Design: Refractor, such as the Skywatcher EVO 150mm F8 ED doublet ($2000)

Overall easiest, smoothest, best visual experience?

Best value?

 

Last question is... would you rather look at the planets in a 150mm F8 ED refractor or would you rather look at planets in a 250mm F4 reflector, assuming seeing is the same either way, and only going as far as 200x magnification, potentially with binoviewers. Part of me thinks the 250mm F4 with binoviewers will allow a brighter high contrast view potentially. But, I also have to wonder... unobstructed optics, no collimation, faster thermal allimation, high contrast refractor view?

 

Sell it to me!

 

Very best,



#2 vtornado

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Posted 19 August 2019 - 02:47 PM

Hello Marty, I can't answer all your questions, but I did a shoot out between a 150mm f/8 achor and 200mm f/6 dob

on Mars a few years ago at opposition. 

 

The Dob was much better, I suspect it had more to do with no CA vs the increase in aperture.  Mars was smeared

with false color rendering very little detail in the views.  I sold the  Achro because it was too much for me to mount.  And in my light polluted sky, I don't do much low power deep sky. 

I suspect that It would also lose fine detail on Jupiter, but I could not do a side by side compare.

 

I have a 6 inch 150 f/5 newt, and it does a good job on Juipter/Saturn.  I have not had a shoot out between it

and say a 100mm ED, or 120 8.3 acrho for a comparison.  As far as personal tastes, my eyes are getting old

and are light starved, so usually a brighter less crisp image is preferred over a dimmer crisper one.

 

I suspect .... the best scope for viewing the planets at 150mm without going crazy expensive would be the

150 f/8 dob.  I'm looking for one right now in the used market.   A 120 ed I suspect would do a good job too,

but at 4x the price, and a big mount to boot.

 

======

I have an f/5 250 reflector on a dob mount.  Best view of Jupiter I have.  It does take an hour to cool.


Edited by vtornado, 19 August 2019 - 02:56 PM.

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#3 EverlastingSky

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Posted 19 August 2019 - 03:19 PM

I struggled with such a question myself. Which 6" design, optically as superb as possible, with thermal management under control, specialized for planetary and lunar from under bright(er) sub urban skies? I tried a 6" f/5 Japan made Vixen Newtonian, then a 6" f/8 Russian Mak-Newt and finally settled on TEC140.

 

Just before a used TEC140 appeared within Canada (rare) I was all set to build a planet Newt "special". It would be a lightweight 6" f/7 (Custom new mirror by Mike Spooner here on CN) in best mirror cell. With a Blacklite phenolic paper tube by Protostar and have a rear fan. Antares secondary mirror on a curved 2 vane spider. Focuser would be either a helical or low profile light weight Feathertouch. Mounted in Parallax rotating tube rings (too heavy judging from the specs...). I had my doubts though. I was fully aware that... buying a used 6" Classic Newtonian is the sensible path to follow.

 

So on a final note - the evidence is clear: The best bang for the buck is to buy a gently used Newtonian, EQ mounted, even an old venerable RV6. Yes, especially an old RV6. That or a later Parks 6" f/6 fiberglass white tube Newt. Or Optical Craftsman or Cave or Meade. Consider sending mirror to a top notch guy like Spooner and paying him to test it and refigure if necessary then send off to re-coat. Flock the tube. Get a good focuser. Try rear fans. But keep everything super lightweight and preferably on wheels ready to roll out. Light, fast, Mercurial is the ticket to much use and enjoyment waytogo.gif 

 

Just my 2 cent opinion


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#4 M11Mike

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Posted 19 August 2019 - 03:19 PM

Hard to beat a "high-quality"  APO refractor on the planets (no central obstruction) --- they yield the highest level of planetary resolution inch for inch.  You don't need a lot of light gathering power (aperture) here - not for Jupiter, Saturn, etc. 

 

FWIW - recently I had the opportuning to view Saturn with a 16" DOB (the view was "disappointing") --- the view same night same location same time, in a "high-quality" APO was superior.  The image was brighter in the 16, but a lot "fuzzier". Much crisper image in the 4"APO.

 

My recent experience....

 

M11Mike

 

PS: BTW - the view of Saturn that same evening was superior in my 8SE as well.  (16 too much aperture-???-given that night's "seeing" conditions - ???)


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#5 aeajr

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Posted 19 August 2019 - 04:15 PM

Going to listen in on this one.


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#6 MalVeauX

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Posted 19 August 2019 - 05:01 PM

Thanks so far,

 

The argument goes.... does it make sense, or am I nuts, to think a 10" F4 reflector for DSO next to a 6" F8 ED refractor for planets makes sense on a dual-mount for visual? Shouldn't the 10" mop the floor? I just hear so many accounts of the 6" ED refractor being the better visual experience than a bigger reflector, without ideal conditions, high in the sky, thermal acclimation, etc. For casual quick setups, it just seems to make sense than the refractor might truly be superior? Mean while, for a DSO, nothing tops the light gathering of a big mirror. Am I nuts thinking a 10" F4 newt next to a 6" F8 ED frac is a good combo?

 

Very best,


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#7 Thandal

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Posted 19 August 2019 - 06:53 PM

<snip>

    Am I nuts thinking a 10" F4 newt next to a 6" F8 ED frac is a good combo?

 

No, not nuts at all.  Best of both worlds, *if* you can afford it.  wink.gif

 

I would love to add a good-to-very-good 4" refractor to my collection of instruments, (eight-and-counting, five in current use) but that'll have to wait...


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#8 fcathell

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Posted 19 August 2019 - 07:07 PM

I've tried them all over the past 40 years.  Best view of planets was through Newts with good mirrors that were properly collimated. Note the underline, because that (particularly the latter) can be an issue with Newts. For something more compact and lightweight a good 6" Mak is an excellent planetary scope and it won't cost you an arm and leg.  I just picked up a used Orion 150 Mak and the (visual) images of Jupiter and Saturn are superb. My old 127 Mak is also good but the 150 gives more edge on brightness.

 

Frank

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#9 M11Mike

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Posted 20 August 2019 - 09:09 AM

Even with spot on collimation (Newts, DOBs, Maks, SCT's, etc.) - you still have a central obstruction vs. none in a refractor and that reduces contrast and resolution...even if just slightly --- it does. 

 

I too have tried them all over the last 60 years or so....best views I have had of the planets were gotten from quality APO's (AP130, C102F, T/V 101, etc.).  

 

I remember one night I was out with two good friends viewing Mars during the 2003 opposition.  I was using a Celestron C102F, my friends a Meade 10" SCT and the other a F4.5 14.5" Newt.   The only scope that showed surface features was the 4" C102F refractor. Both of my friends could hardly believe it with their big apertures.  Little refractor beat them both. 

 

M11Mike

 

BTW: That night was the best view I have had of Mars in over 60 years of viewing.  4" scope.   


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#10 fcathell

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Posted 20 August 2019 - 11:53 AM

Mike - I once had an old Edmund 4", F/16 refractor and the views I got of Mars during an opposition back in the late 70's was stunning. The darn thing was so long that you could sneeze and it would vibrate! Any air movement and you were finished. I was on an EQ mount which was marginal.

 

Frank


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#11 EverlastingSky

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Posted 20 August 2019 - 01:48 PM

Even with spot on collimation (Newts, DOBs, Maks, SCT's, etc.) - you still have a central obstruction vs. none in a refractor and that reduces contrast and resolution...even if just slightly --- it does. 

 

I too have tried them all over the last 60 years or so....best views I have had of the planets were gotten from quality APO's (AP130, C102F, T/V 101, etc.).  

 

I remember one night I was out with two good friends viewing Mars during the 2003 opposition.  I was using a Celestron C102F, my friends a Meade 10" SCT and the other a F4.5 14.5" Newt.   The only scope that showed surface features was the 4" C102F refractor. Both of my friends could hardly believe it with their big apertures.  Little refractor beat them both. 

 

M11Mike

 

BTW: That night was the best view I have had of Mars in over 60 years of viewing.  4" scope.   

The old "apples and oranges" mixed telescope type shoot-out's are often most interesting / informative. Sometimes excess image brightness from larger apertures can irradiate the eye, so I have read. Absolutely critical collimation on the SCT and fast Newt may not have been present. That and thermal acclimation within the tubes may have been an issue too. So many fascinating variables that a refractor can escape by nature of design. Those old C102F Fluorite's were excellent contrast machines.


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#12 M11Mike

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Posted 20 August 2019 - 08:57 PM

Frank --- YES - some of those old F15, F16, etc. Achro's were every bit as good (or better) than many of the APO's made over the last 10-15 years.  Not easy to find a F5, F6 or F7 ED refractor "doublet" to match them.

 

Other than the C102F (but that was FLUORITE and F9)!!!   :-)   

 

Fluorite and a longer focal ratio - that was a great combo for the planets.     

 

Mike  


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#13 NHRob

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Posted 22 August 2019 - 07:26 AM

I think a 6” f/8 dob, with top notch optics 

(Spooner) would be a great choice and affordable. 


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#14 tomjones

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Posted 22 August 2019 - 07:02 PM

6" mak

6" f/8 newt

4" fpl-53 double Vixen or triple

will all give great planet views.


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#15 azure1961p

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Posted 23 August 2019 - 08:26 AM

6" mak

6" f/8 newt

4" fpl-53 double Vixen or triple

will all give great planet views.

Why add a 4" into this discussion when it's an inferior option?  A good 6" f8 outdoes it.

 

Pete


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#16 Richard Whalen

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Posted 23 August 2019 - 11:34 AM

First choice would be a 6" APO refractor the longer the better

Second choice for me would be a 6" ED at f12 or a 6" MCT at f15 or MNT at f6 or longer depending on the mount you have etc.

Third choice 6" f8 newtonian.

 

What ever you get, buy quality optics. And for planets focal length is your friend.


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#17 MalVeauX

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Posted 23 August 2019 - 12:33 PM

So... to add more to this mix...

 

What would any experienced observers rate a 200mm F6 Quartz reflector to a 150mm F8 ED doublet for planetary views?

 

Would the extra aperture make enough of a difference?
Or would the 150mm F8 ED refractor still throw up the better, higher contrast image?

 

Very best,



#18 EverlastingSky

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Posted 23 August 2019 - 01:42 PM

So... to add more to this mix...

 

What would any experienced observers rate a 200mm F6 Quartz reflector to a 150mm F8 ED doublet for planetary views?

 

Would the extra aperture make enough of a difference?
Or would the 150mm F8 ED refractor still throw up the better, higher contrast image?

 

Very best,

The extra aperture would make enough of a difference if the mirror were superb, the tube material, thermal issues, focuser etc., were all finely tuned and working together. Then there are the ergonomics of viewing position and the question of what type of mount will be used.

 

If one were to buy a used 8" f/6 "classic" EQ mounted Newtonian from a good source, such as someone here on CN, then that would be a very efficient bang for the buck. Especially if the mirror were a known and proven winner. Probably in the Approximately $500 range vs. $2000 for the 150mm f/8 ED.

 

"Would the 150mm F8 ED refractor still throw up the better, higher contrast image?" Yes it could, if the 8" f/6 newt had degraded mirror coating and dust, not collimated perfectly, focuser not smooth, set up on warm surface so that thermals enter the tube and plague the system etc., But in my opinion the Newtonian will win if the details are all taken care of and watched. 

 

I wish I could find a local old classic 8" F/6 EQ mounted Newt to play around with, actually...


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#19 Dave Mitsky

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Posted 23 August 2019 - 02:27 PM

I concur with fcathell, as far as planetary observing with Newtonians when all the necessary conditions are in play.  My very best planetary views have been through large truss-tube Dobsonians with premium mirrors, along with large classical Cassegrains, when the seeing has been excellent. 

I also agree with Richard Whalen's post when the aperture is limited to 6 inches.


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#20 Jon Isaacs

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Posted 23 August 2019 - 06:45 PM

Even with spot on collimation (Newts, DOBs, Maks, SCT's, etc.) - you still have a central obstruction vs. none in a refractor and that reduces contrast and resolution...even if just slightly --- it does

 

 

It's worth keeping in mind that the CO does have a small effect on contrast, not on resolution..

 

This does mean that a scope without an obstruction, when compared to an other equivalent scope of equal aperture will have reduced fine scale contrast.

 

But that's only if the apertures are identical and the optical quality similar. Otherwise, the contrast is affected by the aperture far more than by a central obstruction. This is why large scopes with COs can provide much greater contrast than a scope without a CO.

 

Some years ago I experimented with my 120 Eon by adding a 40% CO, I could see a loss of contrast but it was surprisingly small.

 

In this comparison, unless one went with a high quality Newtonians (Spooner) then a $2500 ED Doublet would likely provide better planetary views.

 

On the other hand, if weight and length were the guidelines, the a good 8 inch Newt would be hard to beat.

 

Jon


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#21 M11Mike

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Posted 23 August 2019 - 07:12 PM

Jon - normally I'm with you 99.9%.  But I have seen numerous times FIRST HAND where a quality 4" refractor beat out much larger apertures on the planets.  And I don't think the guys with these scopes didn't have them properly collimated, etc.  These guys with scopes (like the Meade 10" SCT) were my observing buddies and they concurred.   They were active seasoned observers like myself.

 

Mike


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#22 Jon Isaacs

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Posted 23 August 2019 - 08:15 PM

Jon - normally I'm with you 99.9%.  But I have seen numerous times FIRST HAND where a quality 4" refractor beat out much larger apertures on the planets.  And I don't think the guys with these scopes didn't have them properly collimated, etc.  These guys with scopes (like the Meade 10" SCT) were my observing buddies and they concurred.   They were active seasoned observers like myself.

 

Mike

 

Well.. maybe. But you can't blame that on the CO.  Thermal issues, optical issues, poor seeing..

 

Try adding a 35% CO to a 4 inch Refractor and see how much difference it makes.

 

Jon


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#23 MalVeauX

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Posted 23 August 2019 - 10:53 PM

I looked at Jupiter & Saturn tonight in my 200mm F6 Quartz newtonian and it was a lovely view. I'm curious if a 150mm F8 ED refractor would truly best it easily in all conditions.

 

48609877387_03c74bc0e3_b.jpg

 

48609877882_124868e03a_b.jpg

 

48609878257_0656009a4d_b.jpg

 

48609784676_8150da54ef_b.jpg

 

We compared some scopes tonight. The 200mm F6 Quartz newtonian through up a great image. The refractors did well, but none were ED/APO. The C8 Edge did well and had the benefit of the tracking mount in the observatory, so it was super pleasant. But on the manual mounts, the 200mm F6 did quite nice with a 25mm eyepiece. Things got tricky and fussy at 8mm with it. 

 

It helped me really realize without tracking, I'm not terribly fond of planets over 100x magnification. By the time you focus it, move things, wait for settle, etc, you have to re-do it all. I think my high-mag viewing will be in the observatory. I still can easily discern rings and cassini division at low power with smaller apertures (120mm & 200mm) no problem with very little magnification.

 

But.... I'm still curious for a 150mm F8 ED.... sigh!

 

Very best,



#24 M11Mike

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Posted 24 August 2019 - 06:51 AM

Jon - in the case of Mars (2003) - it was the same night / scopes side by side --- 10" Meade SCT (F10) vs. Celestron C102F F9.

 

The C102F showed MORE surface features and the polar cap while the Meade showed LESS and was not as crisp.  Not just me - my friend couldn't believe it either.  

 

Both scopes were out for at least 2 hours so it had nothing to do with cooldown or seeing.

 

And my friend had the 10 Meade perfectly collimated - guy was no rookie - AP nut.  In it for many years.  Owned several scopes at the time including a 14.5" Newt.

 

As I said in my initial post "hard to beat a really good APO refractor INCH FOR INCH" --- I'll take a 6" AP or TAK over ANY 6" NEWT, DOB, MAK or SCT.    

 

Mike 


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#25 dscarpa

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Posted 24 August 2019 - 11:54 AM

 I've had a 6" F8 newt with 1/8 wave optics and it was excellent for L&P. I've got a IM715D mak and the same can be said of it. Big advantage to the mak is in 8 years I've never had to collimate it.  Either scope would work on my Twilight 2 without a counterweight, I doubt the same could be said of a 6" refractor. I've got an excellent WO ZS110 triplet and it doesn't outperform my mak or C9.25XLT for L&P unless seeings sub par.  David


Edited by dscarpa, 24 August 2019 - 11:55 AM.

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