Can't decide on planetary scope...

[parallaxerr]

I'm having another analysis paralysis scope dilemma! It really should be easier than this, especially considering the simple criteria.....

A visual planetary only scope, under £1k, to sit on an EQ5 mount....easy right? So why am I fussing so much!?!?

I narrowed it down to a 102mm F11 ED refractor or a 150 maksutov...at least I though so. The only dilemma here is that I prefer refractors, but worry the length of the frac will cause the wobbles - I hate vibrations when observing. The Mak is likely to be far better in this respect being physically shorter despite the additional focal length.

Of course, I've also considered a 6" SCT and Classical Cassegrain....Then I start looking at the 8" versions thereof and either the weight or the price becomes an issue. Now a 180 Mak just scrapes in price wise, but may be at the mounts limit and reportedly is poor at reaching thermal equilibrium.

I'm also reading that people are preferring the view through a CC to a Mak, though I'm not sure why that should be the case. Especially with the 6" versions, the CC's CO is quite significant. Then there's the fact that atmospheric conditions often dictate the quality of the view, which leans me back towards the frac which will likely perform excellently 99% of the time....darn it.

I will say that in my own personal experience, aperture and thus resolution have proven to give me the best planetary views, which makes me reconsider the frac......and so the cycle starts again 🙄

So, you have an EQ5. Do you mount a relatively cheap, long but lightweight 4" frac on it, a mid-priced best compromise 6" Maksutov, or a more expensive and heavier 180Mak or 8" CC???

 

Edited July 28, 2021 by parallaxerr

[johninderby]

I have owned a 6”CC as well as the 8” CC. Sold the 6” to fund an APO and have regretted selling it ever since. Planning to get another when I can afford it. Just light enough for a grab’n’go setup. The actual aperture of the 6” CC is a few mm bigger than the Skymax 150 so the difference in CO isn’t that great in percentage terms. 

Have owned an 8” SCT as well as a Skymax 180 before moving onto the 8” CC and now wouldn’t want to go back to the SCT or Mak. Now the SCT and Mak are very good scopes but the CC just fits my requirements better. Besides the obvious advantages of no dewing problems, quick cool down  and a proper focuser find the CC has great on axis sharpness and contrast. Holds collimation extremely well. Haven’t had to collimate mine since I bought it over a year ago. Build quality of the CC is superb. When I sold the Skymax 180 the buyer had a look at the CC and was impressed by the build quality and he also owns a Tak Mewlon. He wanted the mak for visual while he was imaging with the Mewlon.

The 8” CC is at the very limit of what an EQ5 will handle for visual. Forget imaging. An HEQ5 at a minimum for the 8” is more suited.

So for me while the CC has been the right choice you need to to consider if would be the best chooce for you.🤔

Edited July 28, 2021 by johninderby

[nfotis]

I have a HEQ5 mount, and I am quite happy with my Skymax 180 on it. The Skymax 150 should be nice with the Eq5 mount.

I live in a rather warm place, so I haven't been troubled by thermal equilibrium etc (but I received it at the end of spring, and I move it out before I start hauling anything, so it has more than a half hour to acclimate)

 

N.F.

[John]

For visual only on the EQ5 I'd go for a lightly pre-owned ED120.

 

 

[dweller25]

Another vote for a 120mm ED refractor….

Good resolution, fairly light and quick to cool, giving maximum contrast for the aperture.

[Nik271]

I use a 180mm Skymax on manual EQ5 and the mount can handle it, especially if you don't extend the legs. But with all the accessories on it the EQ5 is on the limit, I take care to balance it perfectly. Cooldown time is (I estimate for the 180mm Skymax) about 1 hour for each 10 degree temperature difference. You don't need a perfectly cool scope for x100  but if you want to go to x300 then it must be in perfect thermal equilibrium. Bear in mind that during a clear night the temperature keeps falling and the Mak may not be able to catch up for a long time  if it starts warm.

From personal experience  90% of the time the seeing conditions will dictate how much detail you can see  and  a 4 inch scope will be able to show you just as much in all except very good seeing condition. When I expect seeing to be poor or average I  use my 120mm (officially the 127mm) Mak, very compact and capable.

My advice is that both of your options - 4 inch refractor or 6 inch Mak are good, the refractor is quicker to set up but at F11 a bit unwieldy. The Mak sometimes will show more due to its aperture (seeing dependent) and is more compact but needs cooldown.

I say just go for one of them and don't feel you are committing too much. If you buy quality you can sell it later if you decide to switch to something else.

People bought a lot of stuff during the pandemic (myself included!) so you may find some good and hardly used scopes in the sell section.

Edited July 28, 2021 by Nik271

[parallaxerr]

Thanks everyone for the responses, I have found them very insightful.

@johninderbyyour experience with all three cassegrain types helps a lot. You have confirmed my suspicions that optically there's not really a bad choice but the CC wins on practicality. One question....spider vanes during planetary obs, any diffraction spikes?

@Johnand @dweller25 I had discounted the ED120 based on my experiences with the 120 F8 achro, I found the objective mass at distance from the mount to be the primary cause of wobble woes, hence I bought an F5 120mm achro for DSO and am now considering the lighter objective of the 102mm for planetary.

@nfotisand @Nik271nice info on the Maks there, thanks. It sounds like the EQ5 is capable but the 150 would be a better fit.

All things considered, I really "fancy" the 150mak, but the 150 CC is making lots of sense. I'm not sure there's any point overloading the EQ5 with an 8" scope when conditions will often prevent it delivering the best views.

There are a few 6"CC options now, I see Altair have added it to their inventory too along side FLO and TS etc. Maks are a little thinner on the ground, though Orion list them as due very soon. So a little time to ponder, but I think it's going to be a 6" Mak or CC.

[johninderby]

Diffraction spikes aren’t a problem with the CC planets and the moon.. Long focal length newtonians are recommended for planetary observing after all and they have spider vanes. 

Takahashi Mewlons are very highly regarded for planetary observing and they have spider vanes.

Edited July 29, 2021 by johninderby

[nfotis]

For me, the closed tube construction of the Maksutov and SCT is an advantage in the long term (less worry about the primary mirror getting exposed to the weather elements). And no diffraction spikes.

On the other hand, the front glass element introduces a bit of chromatic aberration while the CC is a pure mirror system.

Regarding collimation, the Maksutov seem to be the least troublesome. And these seem to offer refractor like views, with high contrast thanks to their long focal length.

All these designs are well suited for planetary and lunar observation thanks to their long focal length. Due to their mass production variations, it's possible to get a better C9.25 than a Skymax 180 or the reverse (same for the CC8), but it's my understanding that Synta produces the Skymax 180 at a very consistent quality.

 

N.F.

[Alan64]

Indeed, among all reflectors, the Maksutov is considered to be the nearest equivalent to a refractor.  My 127mm f/15 Maksutov...

...is a simulation of a 102mm f/19 to 115mm f/17 achromatic-refractor.

I knew about the problems with a 180mm Maksutov, but I couldn't put that much outlay into one anyway.  I did think about a 150mm, but then read of acclimating issues of its own.  

I feel that a 127mm is the "sweet spot" among the varying apertures of the design; not too small, not too big, just right rather. 

Maksutovs are the least likely among reflectors to require collimation, either upon arrival or over the course of ownership.  But if and when time comes to collimate one, it can just as difficult as that of a Newtonian, if not more so.  Schmidt-Cassegrains are the easiest of reflectors to collimate, but I'm not particularly fond of their secondary-obstructions, and will most likely never own one as a result.

Although, I would most definitely give a classical-cassegrain a whirl round the celestial dance-floor.

There is one thing about Maksutovs that I've noticed, personally.  I can sense the meniscus whilst observing.  I can almost "see" it.  They are rather thick.

Edited July 30, 2021 by Alan64

[michael.h.f.wilkinson]

I rather like my Celestron C8, both for planetary and DSO observing. Very light OTA for its aperture. It sits very nicely on my Vixen Great Polaris mount (the EQ-5 is a clone of that mount). It should work very well on your EQ-5. 

[nfotis]

You may be interested in my impressions from my Skymax 180 (added some sample photos as well)

 

 

 

[davidc135]

Although the 6 and 8'' CCs have had good reviews one 6'' owner said that he had difficulty in splitting the double-double in Lyra and put it down to the hefty 2ndry obstruction- which I doubt. I expect there is some quality variation, as with other non-premium scopes, and you might be unlucky. In good conditions my decent quality 4'' sct easily splits E Lyrae and has a co of 38%+.

The 4'' in turn is always outgunned by the 8'' Meade on the moon and planets. In particular, Jupiter's spot was obviously red (back in 2018) in the 8'' but only grey in the 4. 

Many swear that reflectix insulation wrapped around scts and Maks very much reduces cooling problems and I tend to believe them. Certainly the Meade seems to benefit from its two layers.

A 180 Mak plus Reflectix versus an 8'' sct or 5'' ED refractor, each of similar quality? I don't know, small margins.

It may be that local seeing conditions have some bearing on the most useful aperture. Mine are quite good; very rural at 550feet with the ground sloping gently to the south. 

David

[johninderby]

With the CC6” I would suspect it had been knocked about during shipping. Although the scope holds collimation very well it could have been knocked out of collimation. 

[Cosmic Geoff]

I briefly mounted my C8 on my EQ-5 mount and it worked fine, even for planetary imaging.  It should be well within the EQ-5 weight limits, whereas the 8" CC is I understand significantly heavier.  Note that used C8 SCTs quite often appear second hand, and they sometimes went for a lot less than the ~£1000 price of a new one.

[johninderby]

C8s used to go for £400.00 or so not that long ago but now have seen them going for £700.00 to £800.00 now that the OTA new has shot up to £1;300.00.

[CraigT82]

My choice would probably be a used SW ED120. Yes it's quite long for the EQ5 but with an RA motor and one of the cheap SW motor focusers you won't need to touch it at all whilst observing and so no issues with vibration. 

[garryblueboy]

Used C8 Edge portable light and great contrast views 

[johninderby]

Big problem nowadays there is so much choice. 😁

Edited July 31, 2021 by johninderby

[CraigT82]

27 minutes ago, johninderby said:

Big problem nowadays there is so much choice. 😁

Not a bad situation to be in tbh! 😄

[johninderby]

[Alkaid]

Can confirm the C8 is a good match with the EQ5 for visual, it’s quite a light tube when pitted against the 7” maks. 

[michael.h.f.wilkinson]

The C8 on a Vixen Great Polaris is also great for planetary imaging 

[parallaxerr]

Some great conversation and input in this thread, thanks to everyone that has contributed! I was worried another this scope vs that scope thread would be a dud. The information about how the EQ5 (or Orion SVP in my case) handles the various OTA's is especially helpful.

Strong arguments for all types of scope but also little to chose between them I think, at least from an optical performance point of view. I don't think I can make a "bad" choice here.

It all comes down to the readies now really. I have found NEW barebones C8 OTA's for £1099 which is top of budget but would need to add a visual back, or more likely a focuser knowing myself. That's pushing the cost up to roughly twice that of a 150mak or more in the case of the CC.

A 180 mak sits in the middle then at ~ £800-900, I do rather like the look of the Celestron version, though stock is nil. Should have bought one from David Hinds before they shut shop.

Then there's the cheaper 150mak & 6" CC. Both very safe options with respect to how the mount will handle them.

Now for a curveball question.....I have found few definitive (if there's such a thing in astronomy) answers to this, just some OLD posts on CN......

Recent MEADE vs SYNTA Maks (specifically the 150mm) - Any difference (Synta vs JOC maybe?)? And if so, any ranking with respect to quality and optics?

 

Edited August 1, 2021 by parallaxerr

[parallaxerr]

On 31/07/2021 at 18:15, johninderby said:

Haha, "a solution, must I find".