Mars Oppositon - Which telescope for an optimal view

[Profiler]

I was asked today by some friends who are completely new to astronomy what would be the best choice in terms of buying a relatively modest telescope to look at Mars during the pending opposition.

I wasn't too sure what to recommend as I have my own preferences/bias. Also, it needs to be kept in mind they are new to the hobby and want to only spend a modest amount of money (if possible).

The two options which sprang to mind via technical specs would either be a long focal length achromatic refractor (i.e. 100mm x1000FL) which are made by Skywatcher or an 8 inch Dob (also made by Skywatcher). I would be able to lend them some eyepieces and I also have a spare tripod if also needed. So, the only real consideration is the telescope and thus bang for their buck as to what they will get to see of Mars

Consequently, I would like some feedback from those of you who have some experience with both OTAs as to what might be the better option to give them a good view of Mars

All thoughts/perspectives welcomed:)

[Atmos]

8” Dob all the way!

[Wavytone]

Dobs are far from optimal for planetary visual observing ... secondary too big, not enough focal length, the SW mounts are too stiff, and at high power tracking is not easy especially with a stiff mount.

Long focal length (and f/ratio) is required... get a 150 or 180mm mak or 200mm SCT on a GOTO mount - though either will cost more than the dob.

A 150mm mak on a SW All-View mount would do quite nicely on a modest budget, and would eat the 100mm refractor on anything.

[Gundary5]

In the price range you have, go the dob.

[sil]

Or a Newt. Cheap and look impressive to the unknowledgable. And good for a one off event. If there's a chance they may want to continue with the hobby go the dob, good eyepieces and a good barlow in case of good seeing conditions. Better to be prepared to take full advantage on the night than to be unprepared.

A 6 or 8" SCT goto would be good. Great magnification and useful for astrophotography too but maybe too much initial outlay for newbs? Show them Jupiter through what you have and see what their reactions are to that, mars will be half diameter I think roughly but similar brightness. Plus you can should them how the seeing reduces as magnification is increased. Give them some realistic understanding before Mars so any unrealistic expectations can be gotten out of the way.

If they just want to brag about seeing Mars on facebook about the size of their "magnification" a newt would suit.

[glend]

How much money do they have to spend? Anything requiring a mount (Alt/Az or EQ) is going to be fairly expensive compared to a dob. The problem with Dobs, especially larger ones with focal length, is storage and moving them around. A long focal length Achro will work, and if you sit it on a simple Alt Az push to mount (like a SkyTee, etc) then it can be cost effective. The longest focal length budget Achro at the moment is the Bresser 102L which at F13, will have reasonable CA control and good focal length for planets. It only seems to be available through Teleskop Express but they offer great service and will ship to Australia at a fairly reasonable cost, even UPS if your in a hurry. The price of that Bresser is very attractive at 218 Euro, just $340 AUD, add about $50 for DHL shipping, its a real bargain. And no GST on this scope if you import it before 1 July. They will be selling a lot of these in the next month or so I would think.

https://www.teleskop-express.de/shop/product_info.php/info/p9739_Bresser-Refractor-Messier-AR-102L-1350---Optical-Tube-Assembly.html

[Profiler]

Hi Glen

I can certainly lend a tripod and the telescope you have suggested comes with some basic EPs anyway. I can also lend them a few of my own EPs to use. I must admit you don't often come across F13 achros anymore - but do you think they are likely to see more of Mars with this 4' f13 refractor rather than a 8' dob?

[ngcles]

Hi Wavytone & All,



Must say I have to disagree with much of your post. Of the commercially available Schmidt-Cassegrainian telescopes, all have central obstructions in the order of 36-40% and are inherently low-contrast telescopes **when used visually**. Maksotovs generally are better on this front but aren't in the same league as a good Newtonain. Yes, most of the current crop of off-the-shelf Dobson-mounted Newtonians do have what I consider to be over-sized secondary mirrors and are about 25% obstructed, but a much better in that department than all the commercially available S/C and Maks.

A Newtonian optimised for visual work (about 15-20% obstructed) assuming good-quality, well collimated optics are superb planetary performers -- second only to a fine refractor inch-for-inch.

I do share your view on some of the dob-mounts that re not particularly pleasant to use, but they can be tweaked very easily and cheaply to make them adequate performers.

There is an old adage (that so many these days forget): Visually, a good big telescope will beat a good little telescope any day of the week both in light-gathering power and in resolving fine detail.

Recently I had a friend do "first light" on his second-hand Takahashi 150mm f/9 refractor (a gold-standard 6" telescope if ever there was one) side by side with my 18" Newtonian. The Tak cost nearly $10,000 second hand (and that's just the tube) and my 18" cost me about $7,000 including the mount and all the bells and whistles like digital setting circles and servo-cat drive. Guess what? My well-made 18" f/4.9 with a 17% secondary mirror flogged it to death on Jupiter. The image is nine times brighter and three times better resolved (in perfect conditions). In the Tak, the Jovian moons were beautiful little star-like points. IN my Newtonain Ganymede & Callisto were tiny little *globes*. When we looked at just a few deep-sky objects (and were talking bright eye-candy objects), the Tak was a very long way behind.

Yes, *visually* a good big telescope will beat a good little telescope -- every day, in every way.

Best,

L.

[Profiler]

Some good general advice but my friends are newbie's and I don't think they want to buy either a 10k Tak or a 7k Dob. With respect to my actual question would I be correct in understanding that your view would be that although not ideal due to the degree of 2nd mirror obstruction the 8 inch Dob would be a better proposition than a 4' f13 achro refractor?

[ngcles]

Hi Profiler,

In short, yes, it will produce an image that is 4x brighter and twice as well resolved if the conditions are good and it is collimated.

As I said, and this is the point of what I wrote; Used visually, a good big telescope will beat a good little telescope any day of the week. The 8" dob has four times the light gathering power of the 4" and is capable of resolving detail half the size of the refractor.

Best,

L.

[Tropo-Bob]

A 6" or 8" Dob are my recommendations. Having owned both at the same time, I found the view of planets to be 'cleaner' in the 6" Dob, but a little more detail could be seen with the 8" Dob.

The EPs that come with them are barely acceptable, so I would suggest they they buy a good 7 to 11mm EP to enhance their views. Your probably have a good idea of the magnification that your local skies can support.

If your friends are only a little interested in Astronomy, they may prefer storing the smaller and lighter 6" in the corner.

If they would prefer a refractor, even the Skywatcher 70mm (900mm FL) will provide interesting views in this very favourable Opposition. Again, a better EP in the 6 to 9mm range is also recommended.

[pmrid]

A budget OTA will not produce the kind of results they probably expect for planetary viewing. An OTA alone (which probably would not come with tube rings) without a mount will be rather useless on its own unless they were to borrow a mount so buying an OTA alone would be a bit of a waste. And buying a budget scope and mount combo would likely be a compromise-too-far. Both would be sub-standard and quickly get consigned to the garage.

I would be inclined to suggest they contact a local astro club and see whether there are any events planned so they can get a good look at Mars at no cost and, from there, have a better sense of what they want (if anything) for future use. The club may even have some loaners that might be available but I don't really advise it. A first-time user will have a fair bit to learn about setup, alignment, perhaps collimation, appropriate eyepieces and so on. I find that most tend to get lost on their own for a while and would benefit greatly from having some experienced hands available to guide and instruct.

Peter

[Kal]

The best views that I have ever had of mars were through my meade ETX90, a little 3.5" maksutov. Granted that may also be because 15-18 years ago when I made these observations that was the only scope I had, and in the time since when I have obtained larger and better glass mars has not been as good to observe in terms of angular size etc.


If you are looking at the price range of the skywatcher 100mm x1000FL scope, I would instead suggest the skywatcher 4" or 5" (mak tube) star explorer series in the same price range. I know most members will say "aperture aprerture aperture" and pound that message in, but as a newbie into astronomy there was so much benefit to me in having a computerised starter scope that I could set to do a tour fucnction and being able to observe 20 different objects in an hour without having to mess around trying to find them with star charts etc. It will also track the object.

[pmrid]

Here's a good scope for a beginner.

http://www.iceinspace.com.au/forum/showthread.php?t=166553

Peter

[Baza]

I think an 8 to 10 inch dob.
Good eyepiece.
If the dollars permit a 10 goto dob.

For a newbie I think that setting up a tripod correctly aligned, set at the correct angle, power pack etc is overwhelming. You can assist & get everything perfect on any night but when they go to set up alone it is initially difficult and we have another discouraged individual.

[el_draco]

Ah, angular diameter is minute at the best of times. Send them to a star party/ observatory where they might encounter a bigger scope. If interest is piqued, then suggest a scope... IMHO

[astro744]

Do not underestimate the importance of a tracking mount when planetary observing. It is more difficult to concentrate on the detail in the image if it is moving whether it be a 40 degree AFOV or 110 degree AFOV. Stop that motion in the eyepiece and you can take your time to examine and record the detail (whether by sketch or photo).

[Tinderboxsky]

I agree.

[Wavytone]

Then tell them not to buy anything.



Simple answer: Yes.

Personally I'd say DON'T BUY any scope... visit a star party nearby and use their scopes - it's virtually certain that there will be better gear than they can possibly afforded for casual viewing once a month this will suffice.

Only buy when certain this hobby is a long term commitment, not a spur-of-the-moment daydream.

[sil]

:thumbsup:

If you want to give them one as a gift or if they are set on buying something anyway (which will likely be the wrong one) try to steer them towards a tabletop dob. Orion have a 100mm, red aluminium model That I bought and it blew me away how great this model is out of the box and the included eyepieces are great. I bought another for a friend who loves it too. For unknowns or people on the fence this is a great scope (i bought from bintel), small, nothing to set up or screw up really. truelly grab and go. Great views from suburbia, mine gave me my only eyepiece view of neptune. has a threaded hole to mount to a regular camera tripod if you want to stand up to use. Yes its small, yes its specs dont overwhelm, no its not a visual talking piece in the corner of the room, but damn it gives crisp comfortable views from the box with nothing more to buy. Perfect for casual observers and children or as a secondary scope if you have a big rig doing other things.

[dpastern]

I would say go with a 6" mak. The longer f ratio (than either refractors or dobs/newtonians) will help with resolving planetary details. A 4" refractor (doublet) would be my 2nd choice. I personally would avoid a dob because they are a mongrel to move around at high magnifications based on my personal experiences with my admittedly low end 6" Saxon dob.