Semi-beginner semi-first scope advice

[venerium]

First of all, hi all! :) I’m an almost-postgrad astronomy student, hence the semi-beginner. Of course amateur astronomy is completely different to staring at spectra all day, so perhaps that’s more a hindrance than anything. Aside from a $100 dept. store Newtonian (oh the shame ...), I’ve never owned a “real” telescope.

I've been thinking about buying a telescope for too long now, and my budget is at around $3500-4000 (not necessarily looking to spend it all, but if it means a telescope I’ll use for a lifetime I’m more than willing).

I’ve been mainly looking at short-tube apo refractors, although I’m open to any suggestions otherwise. My main considerations are portability and wide field views (the wider the better). I regularly go camping in remote areas and I’d essentially like a grab and go that I can take with me to browse the skies. I’m not really interested in imaging for now. I’d like enough aperture so as to not *completely* miss out on DSOs (around 4"?).

I have a list of telescopes I’m considering, but I’m interested to see what others suggest without the bias of knowing what I’m leaning towards for now ...

- Vi

[allan gould]

I would suggest a good ED80mm scope. There are some very good and reasonably priced scopes on the market ATM and when you get aperture fever (which you will) it will double as a guide scope. Make sure you test it out first for optical errors and CA and you should be happy with it for a lifetime.

[barx1963]

There are a number of factors that I would consider. When you say you are looking at taking it camping in remote areas, are you planning on carrying it any distance or will it be in a vehicle?
A 4" refractor is a fairly heavy beast and needs a decent mounting to use and would be very hard to transport on foot.

[Poita]

A short 4" refractor is only heavy if you are trekking to your camp site. If you are parking nearby then it is a piece of cake.
As is something like a C8 that gives you so much more aperture and reach and is just as portable. A C8 would give much better views of planets, comets and smaller galaxies, and still allow widefield via a f6.3 reducer.

If I had to carry it a long distance though, then get an ED80 or similar and a GSTAR EX video camera and a small 7" or similar screen.
You will get lovely views of DSOs in realtime that you could never see without a really large aperture scope, and get colour on things like orion etc. Video astronomy gets the best of both worlds, real time viewing just like visual, but detail and colour that is more towards CCD photography, but without the hassle it is the best of both worlds.
If the battery goes flat then just use the scope visually.

Whatever you choose, get a great pair of binoculars for true widefield work.

[venerium]

Thanks for all the suggestions! Video astronomy is something I actually hadn't considered at all and a really cool idea, however I think I have a bit of a bias towards purely visual work. A lot of my enjoyment of amateur astronomy comes from being able to remove the layer of abstraction that a camera/screen brings (I get a fair dose of that every day after all :P).

Although trekking is occasionally involved, it's rarely more than a few ks and I don't have many qualms about carrying ~20kg worth of a backpack/tripod. There will usually be other people with me that can help split the load as well.

Would something like the TV NP101 at 4.5kg be able to be supported by a reasonably sturdy camera tripod and say something like the UniStar? I realise high magnification work might be pushing it, but for just wide field/medium magnification viewing would that sort of setup be adequate? (I haven't found that many sturdy telescope tripods have the ability to collapse down to sub-metre lengths like most camera tripods ...)

[John K]

Looks like you have a great budget and will have lots of options!

I think in my mind the key consideration for you will be if you want tracking in the telecope and to do astrophotography in the future. Do you want to do deep sky stuff from dark sky sites but also some planetary stuff from the city?

In my mind aperture always rules. With your budget you can always simply get a small portable instrument to hike with if you are keen on this (e.g. 80mm -100mm short focus refractor on a tripod). But having hiked for over 20 years, I think you will find that if you want to do astronomy stuff in the bush you are better off camping next to you car and have a bigger telescope that you can simply take out of the car. Then you can do your hiking from there without carrying everything.

My thoughts are you should go no smaller than an 8" telescope, so that means a fast reflector or a good quality SCT. If you go visual, a good quality 8" or 10" dobsonian will give you lifetime views. If you want tracking and in the future do some astrophotography (even pickyback - e.g. this year we will have some nice comets visible) go for a short focus reflector or a good quality 8" SCT.

Refractors are great, but visually an 8" dobsonian will kill even a very good quality 4" refractor in terms of brightness of objects, the colour you will see and the no. of objects (sorry to the refractor lovers out there) and you will soon be wanting more aperture.

But that's just my 2 cents of opiniated views and as always everyone will have different views based on their own journey.

Good luck with your choice and enjoy your astronomy journey!

[madbadgalaxyman]

Hello, Vi,

there is some good Telescope advice from some experienced astronomers, in the thread "Recommendations for a beginner telescope" in this forum.

It is a balanced discussion, in that it somewhat curtails the inevitable desire to get a huge telescope, by means of a discussion of the practicalities of various sizes and designs; the useability and practicality of various telescope sizes and designs is discussed in this thread, enabling the beginner to make an appraisal of whether or not a telescope of a particular size is actually going to be used frequently instead of becoming a "white elephant" gathering dust in the garage ( this does happen, surprisingly often!!!)

cheers, Robert

[Satchmo]

You can get an 8" F6 Dobsonian from a Sydney supplier for $399. they are pretty compact - when i used one I at first thought it was a 6" due to its size. Use it in Sydney and take it camping . Try both places and put an off axis 100mm cardboard stop over the aperture to compare views , and then decide whether it would make much sense to have $3000 invested in a that kind of aperture A 32mm 2" ep will allow you to get down to X38 which gives you a few degrees of sky. At least you will learn a lot for a little outlay. You will see next to nothing exciting in Sydney skies with a 4" telescope but the Moon and planets.

[madbadgalaxyman]

I absolutely agree with Mark that a 4 inch refractor is hardly a mainstream recommendation for beginners these days, when you can get a compact 8 inch Dobsonian for very little money.

Look, there are a handful of "refractor fanatics around", and all of us like to have a refractor handy for quickly throwing out onto the verandah for a "quick look-see", but deep sky performance of even a 5 inch refractor is so modest that one soon tires of the instrument.

Mark is absolutely right that light pollution renders a four inch, even a super-high-quality four inch, completely useless for everything except viewing a small number of very bright objects.

[Varangian]

Personally, I would not want to lug an 8" Newtonian on a Dobsonian mount 200 metres let alone a few kms!

As Allan initially suggested go the ED80mm scope. Performance and portability. If you've got a couple of mates to help you lug it in to your dark site up the aperture, you'll be thankful later. Just don't go expecting to carry a Dob a few kms ANYWHERE!

Whack out a chunk of the rest of your cash on some good Tele Vue :thumbsup:eps. They last forever and hold their resale value.

[venerium]

I definitely realise this, but I'd be mostly observing from dark sky sites - I travel out of Sydney regularly just to stargaze already!

One of the biggest issues I had with my (admittedly horrible) first 6" reflector was it almost always required serious recollimation after a bumpy ride down a dirt road. I got sick of it pretty quickly - after a big drive it was the last thing I'd want to be doing!

I guess I'll have to admit too that I seem to have caught the "refractor bug". The ones I've had the chance to look through at public observing nights have always taken my breath away, I don't think that sort of view is something I'd personally tire of despite the obvious lack of deep sky performance. (perhaps I'm just a beginner with some strange tastes :P)



Yeah, 80/90mm seems to be the way to go. However I recently noticed the WO FLT98 and it seems to be a reasonable compromise between aperture and portability. The only downside is I can't seem to find many reviews. Does anyone have any opinions on it?

(PS cheers everyone, thanks for all your responses! :))

[Larryp]

Hi Vi
I'm a refractorholic too. Where I live has a lot of light pollution, but I find the extra contrast of an apo allows me to see quite a lot of DSOs. I agree with John(Varangian)-get a refractor and spend money on Televue eyepieces. I have all Naglers and they are superb!:)

[madbadgalaxyman]

By all means get a refractor, but the you will spend all of your Deep Sky viewing looking at only a handful of objects:
Omega Centauri, The Orion Nebula, The Tarantula Nebula, The Eta Carinae Nebula, the Lagoon Nebula, and open star clusters.
This is the VERY SHORT list of all the deep sky objects that can be reasonably brightly seen in a three or four inch refractor.
Furthermore, nearly all galaxies look like indistinct blobs in apertures under 5 inches!!

In contrast, an 8 inch Dobsonian is quite portable, and it can show hundreds (or even thousands) of deep sky objects if used in a dark sky.

For most of us, a refractor is a nice scope which we enjoy, but it gets boring very quickly due to the lack of objects that it can show reasonably well.

Me(madbadgalaxyman) and Satchmo (Mark) have some credibility on this issue; we have both observed with and compared numerous telescopes of various apertures, and our observing careers are over 30 years each.
Mark is an optician who has produced many professional-standard telescopes and he has owned and built large numbers of different instruments.
I have owned , in my lifetime, the following telescopes:
20x80 binoculars
20x100 binoculars
a 50mm refractor
a 60mm refractor
a 3 inch Unitron Refractor on alt-az mount
a 4 inch Apochromatic Refractor
a 5 inch Schmidt-Cassegrain
an 8 inch Schmidt-Cassegrain
an 8 inch F6 Newtonian (on german equatorial mount)
a 10 inch F4 Newtonian on a heavy German Equatorial Mount
a 10 inch F6 Newtonian on a german equatorial mount
a 12 inch Dobsonian

If you don't want to listen to the voice of experience, then don't listen.....
For most people, a three or four inch refractor gets boring quite soon.

Look, I like the "image' of a refractor, too. I like seeing my 4 inch Apo refractor sitting out on the patio, every day, as it looks like the 'real' telescopes which we see in cartoons and hollywood movies; but I wouldn't recommend a three or four inch refractor as a primary instrument for an adult.

[venerium]

Robert - you're right, and I've been perhaps unfairly not looking at medium-size reflectors as a possibility. I'll definitely do some more research and widen my considerations a bit - I'm not in any rush to buy. I didn't mean to come off as disregarding your opinion - sorry if it seemed that way! :)

Just to shed some light on why I'm being a bit picky about size: camping aside, most of the year I live at university in a very small room - so small that even an 8" dob would be a bit of a pain to have taking up space if I can't just fit it under my bed. That said, could you suggest any decent small-ish reflectors I could consider?

-- EDIT --
Sorry, didn't notice the last part of your post!


It certainly wouldn't be my primary instrument for too long! I'm planning to buy a nice big reflector once my living circumstances are more stable, but that may not be for several years and I've been waiting too long to get involved in amateur astronomy already :P.

[simmo]

Hi Vi and :welcome:,

Sounds like you have some unique things that make this a little more complicated than usual.

Something helped me when purchasing my first scope was that we have here in Perth a telescope shop that atually allows you to try a scope before you buy it (usually Thursday nights). It gives you an idea of what the scope can do and there is something about actually having it in your hands that allows you to understand it better and how it may fit with your own circumstances.

I'm not sure if Sydney has something like this but maybe it would be worth checking out.

If this is a non event then maybe joining a local astro club might be an option. They usually have loaner scopes that you can try for a modest fee. A great way to see if that scope you have in mind will work. Not only that I'm sure that they'd love to have a budding astronomer like yourself come along and join in! It's remarkable what can happen when you get to know the right people too.

Hope it goes well
Simmo ;)

[ZeroID]

Based on this comment and on the known fact that most astronomers will develop and change their preferences and interests as time passes I would suggest sticking with your original idea of a decent APO, 80 or 100. Long term when circumstances change you will buy something with a bigger aperture and the APO will be used possibly in a photographic role or just grab & go for those hiking adventures.
What some of these guys seem to forget is that they have probably gone through a number of different options as they have developed their preferences astronomically and most will have several scopes of both reflector and refractor as I do. I won't suggest brand names or suppliers but there are several good packages around that will fit inside your budget with room for a few extras and still slide under your bed for storage for the time being.
Keep us posted and keep asking questions.

Good luck.

Brent

[venerium]

This is a great idea, I'll look around and see if there's any similar shops here. If anyone knows of one in Sydney or Melbourne, please let me know!

As for the astro club, I was somewhat involved in ASNSW a year ago (before university got in the way) but never heard anything about loaner scopes! Perhaps it's time to get back into it before I settle on a telescope (or time to take a trip to Perth) :P.


Interesting you should say that - it was actually through ASNSW that I managed to land the astronomy internship that's funding this purchase!

Again, thanks everyone for the input. Looks like I've got a bit more thinking to do and perhaps finding somewhere I can try before I buy. I'll keep you all posted if I have any more questions :).

[madbadgalaxyman]

Hello, Vi,

I honestly don't know anyone, apart from a few very odd people, who would recommend a 3 inch refractor as a primary instrument for an adult. These telescopes are either recommended as a children's telescope, or as a second telescope for ease of use and a "fun and quick look-see". I used a three inch refractor when I was a teenager, and I persisted with it, though a lot of adults would have probably stashed it in the attic very quickly.

The idea that a three inch telescope can show rich planetary detail and show deep sky objects well.....is totally incorrect and bizarre.

I do like a refractor as much as the next man, but the smaller ones, particularly 70mm to 100 mm aperture, have very limited Light Gathering power for nebulae, galaxies, globulars etc.........
A 3 inch (75mm or 80mm) refractor cannot really resolve globular clusters, for instance. Furthermore, even in a dark sky, a four inch refractor shows virtually all galaxies as indistinct blobs without any individuality.
A four inch can (but only in excellent conditions) be OK for viewing nebulae, both bright and dark, but (apart from the Eta Carinae & Orion & Tarantula & Lagoon nebulae), a small aperture like this requires a very dark and very transparent sky to see nebulae well in a four inch.

The slightest light pollution when viewing with a four inch, and you find yourself limited to viewing about two dozen deep sky objects!

Also, even the highest quality 3inch / 80mm refractor can show only very modest detail on the planets, as the best angular resolution that can be achieved is around 1.5 arcseconds. This is quite easy to see, numerically, when we consider that the angular diameter of Jupiter is only 50 arcseconds at best, and the disk of Jupiter is usually larger than that of the other planets, when viewed in the telescope. Thus, the number of resolution elements stretching across a planetary disk is too small for seeing substantial detail when using a three inch (75/80 mm) refractor.

You can't even split a lot of the famous double stars with a three inch! (a three inch refractor is a crazy recommendation as a primary instrument for an adult)

A four inch is substantially better for planetary viewing than a three inch, as it has a nominal Best Angular Resolution of 1 arcsecond. It is probably necessary to put about 60 resolution elements across the disk of Jupiter in order to see a lot of planetary detail, so you need 1 arcsecond resolution, or preferably somewhat better to see substantial planetary detail. A three inch doesn't get anywhere near the angular resolution necessary! Therefore, somewhere within the aperture range 4-6 inches, telescopes begin to show rich and intricate planetary detail. A 5 inch (or preferably a 6 inch) can get below 1 arcsecond resolution, and this is what is necessary to glimpse that fine planetary detail when the seeing is good.

(( In defense of refractors, I would day that Short-tube apochromatic refractors of 4 or 5 inches in aperture are a convenient instrument to use, and can give extremely high contrast images, without the necessity of collimating a reflector; the main reason that some Newtonians have a bad reputation is usually the fact that the owner does not know how to collimate the telescope properly.))

cheers, madbadgalaxyman

[Varangian]

That's all well and good Robert and I agree wholeheartedly with your post but I don't think you've read the OPs original posts nor understood his requirements. Treking back to Vi's original posts he states that he is after someting portable as he sometimes treks a few ks to his dark site. I got the impression that this scope was a bit of a fun scope for him at his dark site until his living arrangements changed. I can't think of another scope that could be walked in a few ks other than a 3 or 4 inch refractor or a tabletop 5 inch dob.

[madbadgalaxyman]

Relative Light Gathering Power of small telescopes, which essentially correlates very well with the performance on deep sky objects:

3 inch ; relative LGP is 9 (LGP is proportional to 9)

4 inch ; relative LGP is 16

5 inch ; LGP is 25

6 inch ; LGP is 36

These figures are estimates which ignore complexities such as relative contrast, relative optical quality, and relative light transmission, but it is surprising how well these figures represent the relative performance of various apertures on deep sky objects

In practise, I have used a lot of different telescopes (mainly refractors and Schmidt-Cassegrains) in the aperture range 3-6 inches, and I would say, from the comparative deep sky performance of these instruments, that 4 inches is absolutely minimal and requires excellent conditions, but 5 or 6 inches of aperture is a whole lot better!

P.S.
I do use a short-tube four inch Apo refractor, from a light polluted site, and I do enjoy it. But it is mainly 'just for fun'. For real observing, I greatly prefer either my Celestron C8 (Schmidt-Cassegrain) or my 12 inch Dob.
If I wanted a portable main instrument, I would settle for a 5 or 6 inch Schmidt-Cassegrain or a 5 inch short-tube Apochromatic refractor perhaps on a Synta AZ-4 mount.

[Varangian]

There you go Vi, a 5" Tabletop collapsible Dob is the way forward. The OTA is 650mm which collapses to half that length (325mm) and can go in a backpack and you can take turns carrying the mount with your friends. Not only that, they can be picked up for $200 and resell well:thumbsup:

I've got one and I use it when I have short walks into camp grounds.

[venerium]

I'm a she :). But yes, this is correct - I'm looking for the largest portable aperture I can get right now, and I'm planning for a much bigger scope later. You mentioned a 5" tabletop dob as an option and I see that you own an SW one - what are your opinions on it in terms of camping convenience/general performance?

EDIT: while I was writing this you answered my question! Thanks, that's definitely something I'll consider. At $200 it's a fairly risk-free option too :).

[madbadgalaxyman]

Yeah, I think 5 inches Aperture sounds a lot better than 4. Definitely can see a lot more on nebulae and globular clusters than you can with a four inch.
I used a 5 inch Schmidt-Cassegrain, which was OK for deep sky work at a dark site.
(But a 6 inch would have given me more light pollution penetrating power)

[Varangian]

Apologies for assuming you were a 'he' :thanx:

As for the tabletop Dobsonian as Robert states you will see everything from galaxies to nebulae to glob clusters. I have done 70% of the Messier list with it (you can actually do all targets on this list with binocs) but the 5" makes things so much brighter.

The 5" fueled my interest for observation and gave me aperture fever, so watch out!

[madbadgalaxyman]

Hi, Vi,

I guess it all depends on how portable you want your 'scope to be.

A Six inch Dobsonian would be an excellent option, if it is light and small enough. However, get a 5 inch if you must.
Also, aside from considering the expensive "5 inch refractor" option, you should seriously consider a 5 inch or 6 inch Schmidt-Cassegrain, before you make your buying decision.

As per the table of relative LGP, you can see that there is a very big jump in deep sky performance between 3 and 4 inches, and another substantial (but somewhat smaller) jump in LGP between 4 and 5 inches. A 5 inch in a good sky gives you decent, though not super-bright, views of most deep sky objects, with the exception of galaxies
(unfortunately, galaxies need all the aperture you can throw at them, and more!!)
You would certainly want to use a 5 inch with good quality eyepieces, to somewhat mitigate the effects of the relatively small aperture!

I used to own a 5 inch Schmidt-Cassegrain (it was a Celestron C5), which is a very portable and very compact and very light-weight Optical Tube Assembly, but the mounting requirements are still a problem, even for a 5 inch telescope; because a decent and stable and precisely-moving mount always adds substantial weight.

I currently use a Synta (Sky-Watcher) AZ-4 mount with my 4 inch F6 apochromatic refractor, the version of the mount that has broad metal tripod legs (the wooden-tripod version of this mount is less stable). This is a well-made (it is stable)(it has precise motions up to 150-200 power) altazimuth mount and tripod that can be adapted for compact telescopes of up to 5-6 inches of aperture. (These mounts come in at about $300-450 depending on where you buy them)
This mount and tripod are easy enough to lift and move around, and a lightweight tube assembly would maintain this portability. However, even the AZ-4 mount does not quite meet the requirements of "grab and go".
Here is a picture of the AZ-4, in the version with the thick tubular metal tripod legs :

131873

This mount uses the Vixen dovetail, making it easily adaptable to many different small telescopes. Careful! as there is another "AZ-4" on the market which is a different mount entirely.

The metal tripod is quite beefy, and the rigidity is good, though this rigidity also adds extra weight.
The altazimuth mounting itself was designed without a counterweight, so it is not suitable for heavy instruments:

131875

131876

NOTE ADDED in EDIT:

There are many different ways to mount a 5 or 6 inch Schmidt-Cassegrain Optical Tube Assembly. The above is just one possibility.
I seem to recall that Satchmo (Mark) had a 5 inch Apochromatic refractor on this AZ4 mount, and the setup worked very well, though his 5 inch refractor had a shortish tube. As Satchmo remarked in this thread, you can spend an awful lot of money on a small telescope, if you go for the "apo" refractor option!! (But apos are pretty cool, anyway)

Best regards,
from Bad Galaxy Man

[madbadgalaxyman]

Regarding the 5 or 6 inch Schmidt-Cassegrain option for a very portable telescope:

I note on the Celestron website that a 6 inch Schmidt-Cassegrain tube assembly weighs only 4.5 kilograms.

According to the Celestron website, these tubes are only 406mm in length and not much wider than the 6 inch aperture of the telescope.

These are about $600 in the USA; not sure what local dealers are charging for them.
Celestron sells these tubes with various mounts, with a discount on the price of the tube assembly.

The views through these tube assemblies are about as bright as those through a 6 inch Newt, because the coatings are optimized to enhance light transmission.

Planetary detail, however, usually suffers , compared to a high quality newtonian of the same aperture.

I have not bought a Schmidt-Cassegrain optic for some time, but traditionally the optics of these instruments used to be of 'commercial' standard, which means - in real terms - a very considerable variation in quality between various examples of the same telescope model. Always best to find somebody at a good dealer who can sell you one that has decent optics.

The good thing is, that these compact telescopes give decent deep sky views.

I am not familiar with Meade's lineup of Schmidt-Cassegrains, but they have them in various sizes.

[Steffen]

For SCT compactness/portability and APO-like views Maksutov-Cassegrains are also to be considered.

Some 12 or 13 years ago, when I got back into observing I faced the same set of conundrums as Vi. I ended up buying an Intes MK67 from Claude at AEC and haven't regretted it for one second. These days we also have an ED80 and Dobs on the house but the Mak is my first pick virtually all the time.

If you want to go down the Mak route I'd advise to forgo the cheap silver-spot secondary types and go for the RuMak design with separate (and collimatable!) secondary, like the Russians make them. They deliver breathtaking, contrasty and flat-field views and seem to punch way above their aperture.

Incidentally, Claude has the Intes-Micro Alter M603 on special right now ;) (no affiliation other than being a happy customer).

If I lived under dark skies I'd have a gigantic Dob in the backyard under a roll-off shed. But as things stand I have to travel to get reasonable skies, and for that a big bucket is not very practical. That said, I'm considering one of those collapsible SkyWatcher GoTo Dobs in 12" or more, but for the two nights per year it would be useful the price is still a bit high…

Cheers
Steffen.

[madbadgalaxyman]

Steffen,

Nice to here from a Maksutov aficionado.
Also, we don't get enough experienced people answering questions in the Beginners' forums (tends to be the same few people answering beginner's questions), so your input is most welcome.

Maksutovs have a very good reputation, but I have little experience with them. While not a beginner myself, I would appreciate some further comment from you regarding the relative optical performance of this design, compared to other designs. I do have some experience with an F15 Classical Cassegrain design , and these are also excellent.

I note that "Astronomy and Electronics Centre" has the 6 inch Maksutov optical tube assembly for about $1400
It appears to be an F10 Maksutov-Cassegrain.
It would have to be an excellent instrument, if I were to justify spending this much on a 6 inch OTA!

With the 4-6 inch Maksutovs and Apochromatic Refractors, we are looking at substantial extra cost, per a certain amount of aperture, and these instruments will suit some people;
but others will wish to go the quick and dirty 'Dobsonian route', and therefore have some money left over in order to save up for a HUGE "Deep Sky telescope.

-Robert

[Steffen]

Totally agree, the value proposition of an 8" GSO Dob is such a good one, there is really no excuse for not owning one (except owning a bigger one :P ).

And yes, Maks are more expensive than Newts or SCTs of similar aperture. On the other hand, they're much less expensive than APOs.

The Russian ones I have experienced first hand (made by Intes and Intes-Micro) are RuMak (Rutten-Maksutov) designs with a separate aspherical secondary mirror in its own cell on the inside of the meniscus. Visually, they offer excellent contrast which helps with finding dim fuzzes under light-polluted skies, no false colour, no coma and pin-point stars to the edge (very flat field). Having slow focal ratios they are very easy on eyepieces, you don't need to spend $300+ to get a decent view. For the same reason they also work well with prism diagonals, which in my humble opinion are the bees knees in compatible scopes (no scatter – more contrast, no degradation over time).

In practical terms, they're short and compact (like SCTs), very solid and ruggedly built, use a simple construction and are easy to service and clean (I can only speak for the MK67 here). They are easy and precise to collimate (with Bob's Knobs fitted to the secondary) using inside and outside defocussed star images. The MK67 I've had for many years holds its collimation very well across travels.

The only (and often cited) downside is their cool-down time due to the enclosed construction and thick meniscus. I haven't found this to be a big hindrance under Australian conditions, even though the MK67 has no ventilation (unlike the Alter M603). I'm usually ready to observe after leaving it for 30 minutes, less with advance planning (where to store it etc). If you take it outside from a heated room into a winter night you may have to wait 90 minutes or so.

Cheers
Steffen.

[madbadgalaxyman]

If I was a planetary observer (which I am not), the 6 inch Maksutov tube assembly, on special at Astronomy and Electronics Centre for $1450, could be a strong contender.

My Celestron C8 (8 inch Schmidt-Cassegrain) has good coatings, and it is therefore good enough for some Deep Sky Work, though planetary views through it are very ordinary ; its optics are not quite as accurate as they should be, plus there is further image degradation due to diffraction from the central obstruction.

Why don't they make these Maks a longer Effective Focal Ratio; would perform even better. I used a Classical Cassegrain once with a smaller central obstruction, at F15; very nice planetary scope.

[Steffen]

But they do! The Alter M615 is f/15 (so are the M715 and M815, in 7" and 8", respectively). My MK67 is f/12.

There is also an 8" f/6, so I'm sure there is a case for faster Maks. I suppose that reason would be imaging, but I don't pretend to understand all the various trade-offs that go into telescope design.

Cheers
Steffen.

[madbadgalaxyman]

The Alter M815 (an 8 inch Maksutov) has a central obstruction of only 0.25

This telescope would , if diffraction limited, absolutely annihalate a 5 inch Apo refractor, when viewing planets. It seems to me to be a much better option for planetary enthusiasts than a smaller apo refractor.

[Varangian]

Robert, great point! Agree more members need to put back into the beginners forum rather than just us novices having to provide what little advice we have attained on our short journey. If it wasn't for a beginner question sitting there without an answer for a day I would never post here to be honest.

This is a call out to all experienced IISers to get involved with those new to the hobby.