Semi-beginner semi-first scope advice

[Varangian (John)]

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

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

[venerium (Vi)]

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.

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 (Robert)]

Originally Posted by 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.

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 (John)]

Originally Posted by 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 .

Apologies for assuming you were a 'he'

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 (Robert)]

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 :



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:





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 (Robert)]

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 (Robert)]

Originally Posted by Steffen

For SCT compactness/portability and APO-like views Maksutov-Cassegrains are also to be considered.
If you want to go down the Maksutov 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
Steffen.

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 ).

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 (Robert)]

Originally Posted by Steffen

And yes, Maks are more expensive than Newts or SCTs of similar aperture(.....)

The Russian ones I have experienced first hand (made by Intes and Intes-Micro) are RuMak (Rutten-Maksutov)
...... 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).

Steffen.

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]

Originally Posted by madbadgalaxyman

Why don't they make these Maks a longer Effective Focal Ratio

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 (Robert)]

Originally Posted by 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.

Cheers
Steffen.

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 (John)]

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.

Originally Posted by 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