Viewing planets with dobsonian

[Skids72]

Hi guys, just another newby here. I bought a dobsonian the other day. It's a fair bit better than the ebay nasty I bought for $50 or so last year (and a fair bit more expensive). Anyway, the 2 eyepieces it came with were 25mm and 10 I think. I was just looking at Saturn which appears very small in the 25m (I think that's because the FL is 1200 divided by 25 gives 48x). I tried one of the eyepieces (4mm) from the ebay scope which fit the dob and Saturn appeared much bigger. All good. However, I tried the ebay Barlow with both the 25m and 4m and in both cases was unable to focus and the planet appeared as a large circle with a black center. Is this because the Barlow is dodgy, or because the ebay nasty was a refracting scope that the Barlow won't work with a dob? I'd just like to be able to see planets like Saturn and Jupiter as large as possible to discern details.

Also, is this scope any good for looking at DSO like nebulae? The sales guy said so. If so, what eyepieces would work?

Here's a link to the scope
http://www.opticsplanet.net/sky-watcher-8in-dobsonian-telescope-s11700.html

Thanks for your help.

[Rod66]

Hi Brian,

having just bought a similar sized telescope, I can tell you my experience. I too have a 25mm and 10mm plossl that came with the scope and I bought a 2x barlow for about $45 to go with it. No idea if this is reasonable, cheap or otherwise. I was happy with the 25mm and it was ok with the barlow, but was very unhappy with the 10mm and forget it with the barlow. I did some research and found eyepieces that have good magnification but also wide fields of view, ie things like the Televue Ethos 14mm and a new one called the Explore scientific 100degree 13mm. Of course these babies are $600 and $500 respectively which is more than the scope so no chance. Then I happened on the Orion Stratus 13mm 68 degree wideview. Not too bad a price - $200. I bought one of these babies and it literally blew the plossls apart. The difference in clarity and view was absolutely incredible. I can now combine my barlow with the Orion Stratus and get an incredible view of Jupiter and Saturn.
So whats my experience? - the standard eyepieces with a scope like this are adequate for average viewing, but it you really want to get excitement from your scope, invest in a reasonable quality eyepiece and you will never look back. The scope you have is very very capable and don't let anyone tell you otherwise.

cheers

Rod

[Skids72]

Thanks Rod. Very helpful information. What you say about the 2 eyepieces seems about right. I'll look up the Orion eyepiece.
Cheers :)

[renormalised]

There's an exceptionally (no, pretty much 100%) good chance the ebay barlow was dodgy as. Especially if the whole setup you bought was only $50. That big black dot in the centre of the image of Saturn would've been the off focus image of your scope's secondary!!!!. How long is the barrel of the barlow???. You can get short and long barreled versions of barlows, which will vary your length of travel for focusing...depending on the eyepiece you're using. Sounds like you weren't able to bring the eyepieces to focus using the barlow you had. If you want a barlow, get yourself a decent one to start with...even if it costs $200 or more. At least you'll have a quality optical piece that will do the job you ask of it. Although, you can get reasonable barlows for $80-$150....try these,

http://www.myastroshop.com.au/products/barlow.asp

https://www.bintelshop.com.au/welcome.htm

http://118.127.11.230/catalog/index.php?cPath=33&sort=4a&page=1

They'll have what you want, and then some:D

[mental4astro]

Hi Skids72, welcome to IIS, :hi:.

Your new 8" scope, like Rob66 said, is a fine instrument. It will give you splendid views of the sky. If I may, I'll add a couple of points to help you along in case you may not be aware:

* Scopes have a min & max magnification, with the following rule parameters:
Min. 3.6X per inch of apeture
Max. 50X per inch of apeture

So your scopes min & max would be 30X & 400X respectively ( the ability to use 400X is greatly dictated by atmospheric conditions).

*Eyepieces (EP) giving these values would be 40mm (for min) & 3mm (for max). Any EP you purchase would lie within this range. I'm an advocate for spending pennies on EPs rather than a barlow.

Just be aware that at 400X you will have a hell of a time keeping the object in the field of view. Anyone else who doesn't know how to nudge the scope will have no chance.

I had a chance to view through a dob just like yours last Saturday at a dark site, & compare its image quality with my 17.5" dob. If all I had was your scope, mate, I'd be very, very happy with it. Its slightly slower focal ratio, f/6, compared to f/4.5, my mate's 8" actually gives better images of the planets, using identical EPs.

The following link is to some inexpensive EPs (about halfway down the page). The GSO's EPs do have a following. They are good to start gaining experience with, & not injure the piggy bank:

http://andrewscom.com.au/site-content-section-10-guansheng.htm#accessories

DSO's benefit mainly from a dark sky. A nebula filter will help with nebulae if viewing from light polluted areas, except galaxies.

Be patient with your new scope. If you live in a very light polluted area realise that it will really degrade the image, as will turbulant atmospheric conditions. You will see more with the more you use it, regardless of the EP you use.

The EP forum has lots & lots of info to help out some more.

Mental.

[G1ZmO]

Mental, They are seriously inexpensive EPs! If they're half decent they're definately worth a shot. (If I was in Oz I would lol)

Another small thing to remember with regards to using EPs in preference to EPs with a barlow is that using a barlow is adding extra glass to the light path which will inevitably degrade the image to some extent.

Get a good range of inexpensive EPs, find the magnifications that you like the best then maybe spend some cash on a good EP for that mag.

Cheers

Paul

[Blue Skies]

Well, two things that I think need to be mentioned that haven't as far as can see:

1.Yes, Saturn is going to look small in an 8", thats a fact. Even though the planet is comparable in size to Jupiter it is twice as far away! If you super-duper, large, as-big-as-I-can-see-in-all-those-fantastic-images-on-the-web size you need a much bigger aperture, with quality optics that are well collimated plus the atmosphere needs to play fair and hold nice and steady for you. Good eyepieces will certainly help, but they aren't everything.

2. Give yourself time to learn how to see. Seriously. Learn how to see. Its something that takes time and experience. The more you look at the planets the more you will train your eye to pick out the subtle details, so keep looking. I usually reckon it takes a year for people to learn this (maybe more, depends how often you get out.) If you don't believe me, try this. When you observe the planets, Jupiter and Saturn, in the near future, draw a sketch of what you see. Doesn't have to be art gallery quality, just try and get the main features down. Remember to record the date, time and perhaps a few comments on the sky conditions (still, a bit murky, , partly cloudy, seeing moving about wildly! etc) Hang on to those sketches. Next year, try to sketch them again - then compare the old with the new. You might just be surprised how far you have come!

[hulloleeds]

I have just bought this scope myself. I am now in the process of learning exactly what eyepieces I should purchase. What sort of range of eyepieces would be wise to acquire? As in, you mention the min and max, should one first purchase 3-4 cheap ones along that range, say 3mm, 10mm, 25mm, 40mm? (arbitrary values in between)

There are quite a few different EP's on that site, what brand/ type would you recommend?

(I'm sure I could search this out (and I will), but since there is at least two of us listening I thought perhaps I would ask) .

[mental4astro]

Hello Hulloleeds, :welcome: to you too, mate.

I purchased two EPs from this range, both of the 68 degree variety, one 30mm, the other 15mm. This selection was made with the scope they would be used in, a 17.5" f/4.5 dob, & that I would be rebuilding her, hence the preference for the cheaper EPs for now. They are good enough for my purposes as I'm spending the big bucks on materials for the rebuild. I already have good 5mm & 10mm EPs, purchased long ago.

I couldn't go for a longer focal length EP here because the fast f/ratio would most certainly show horrific edge of field deformation.

The 42mm & 15mm 68degree would be a good low & mid powers for you. A high power maybe look at the 6mm or 4mm 'superplossl'. 3mm any brand is notoriously a difficult EP to use. These EPs would only be for 'gaining experience'. Along with the ones which came with your scope, 'learn' to use your scope, as Jacquie said, :thumbsup:.

The dob can be a tricky beast to move at high power. Be patient with youself. I often place the object just out of the field of view, & allow it to 'drift' into it to view it in a steady scope, ;).

Go to a star party or two, & look through other's scopes with thier better EPs, & maybe use one of them in your scope for comparison. That is ultimately how you will see the benefit of excellent quality EPs. But learn with what you have. You can buy expensive EPs now, only to find you don't use it or them that much.

An after thought: another good reason for having a couple of the cheaper EPs is for showing the sky to inexperienced eyes. You know how to look through a scope, a novice doesn't. The EP will get touched & soiled by stray fingers & eyelases laced with makeup & who knows what. Would you subject your expensive gear to that treatment? There really is alot more going for cheaper EPs than we sometimes think.

[hulloleeds]

Thanks Alexander, I really appreciate that advice. I will get the lens that you suggested.

I'm definitely interested in experiencing the cheaper side first, even if it means that I might want to upgrade later. I agree that it would be wise to get a handle on the cheap gear before making the change, rather than wading in with cash.

Best to take it easy when entering the new hobby money hole :)

[Mike21]

I bought this eyepiece some time ago from Andrews (in General Accessories) when it was only $79. I've used it on a 200mm SW Dob and it feels like you can dive into it and swim about in space - no drugs needed. It's over half a kilo of lenses.

Mike.

[DavidU]

I love mine ! What can you get for this $?

[mental4astro]

I'm glad you brought up such a heavy EP Mike. It is something which someone with a dob needs to think about. There are some EPs out there that push the 1kg mark! You need to know that such an EP won't unbalance your scope, or you'll have to rig up a counter balance for it, which you will then have to reset once you remove the bulky EP. Careful it is not a counter weight that puts your primary at risk, :doh:.

[Mike21]

Valid point Alex,

Well I guess it's valid for those this more refined Dobs than mine. The movement on mine is not silky smooth. I'm sure it can be improved but I haven't taken on that task yet, therefore balance is non too critical either. A 30mm EP on a 1200mm FL is only 40X; and considering the EP is also very wide angle, I don't have to do much "tracking". I merely point the tube at my target and give the tension adjuster a small twist. It takes a good while before I have to chase my target again.

If you are still monitoring the thread Brian (Skids72 - hope your wife didn't give you that nick-name while she was doing the washing), there is a review on this eyepiece in Equipment Reviews: Eyepieces, by Mark Hodson. It looks like he paid $150 for it and still thought is was a beauty. I've just remembered the name of the thread, viewing planets. A 30mm EP will probably not magnify enough for planets with a Dob.

Mike.

[erick]

Yep, put this Explore Scientific 14mm 100 deg eyepiece in a 2" barlow and you'll be there!

http://www.iceinspace.com.au/forum/showthread.php?t=45759

But their 30mm 2" 83 deg eyepiece is quoted at 3.2 lbs (= 1.45Kg) !!!!!

[Mike21]

[QUOTE=erick;472148]Yep, put this Explore Scientific 14mm 100 deg eyepiece in a 2" barlow and you'll be there!

That may not be a heavyweight in the mass dept, but it sure looks a heavyweight in the $$ dept. It must be a yummy EP.

Mike.

[erick]

[QUOTE=Mike21;472159]

It's not actually, compared to others, eg. T$V. On special at US$399 until end of August. I'll wait for other focal lengths and more reviews before I have another look.

[Mike21]

I guess expense is a relative thing. My Andrew's is the heaviest EP I have in terms of mass AND moolah. Brian started the thread looking for an EP for a Dob that "was a fair bit more expensive" than his "$50 Ebay nasty". He might consider a $400 EP overcapitalisation.

After re-reading the opening post, Brian did ask if his 1200mm FL Dob was suitable for DSO's. What's it's apperture Brian? I reckon my first suggestion (the Andrew's 80 deg, 2") is a pearler for DS. May be not so much for detail, but definitely for getting to know the sky.

My only issue for using a scope for orientation is the inside-out, upside-down and back-to-frontedness that mirrors and lenses cause. I reckon the Eric's signature suggests he agrees that binoculars are just about the best tool for learning where everything is.

Mike.

[erick]

Oh yes, I remember Brian :D Sorry mate, I got carried away. You have an 8" Skywatcher reflector on a dobsonian base. A great scope - I started with much the same, but in solid tube. Easy to transport, easy to setup, plenty to see!

Yes, no problem capturing DSOs in that once you can work out where to point it.

I moved fairly quickly to the ultra-wide 80 deg 30mm 2" eyepiece. It was a great improvement on the 26mm eyepiece that came with my scope. There are various clones sold by different suppliers. Andrews version for $99 is well worth a look.

[hulloleeds]

Having just been out with my skywatcher 8 dob for the first time, in the middle of light polluted brisbane, looking at Jupiter I have to say I wasn't overly impressed by the 10mm EP that came with it, either. Jupiter was quite small, you could moderately make out the two main bands, though.
However, currently, it isn't particularly high in the sky and I have not tried to collimate yet - so I might have a bit to go in terms of clarity.

I was jumping the gun a little as I have the EP's suggested by mental coming from Andrew's probably on monday. I read up on the ultrawide andrews piece and decided against it for the moment.

+1 points to Skywatcher for a sturdy finderscope as when I was coming in, I tried to put the cap back on the eyepiece end of the finder and pushed it enough to pop it out of the mount, flying onto the concrete below. No cracks. Phew

[mental4astro]

You must be wriggling something horrid waiting for your package, hulloleeds, :D.

Do yourself & your scope a favour & get to a dark sky site to giv the EPs a fang when you can. You are really, really in for a treat.

High power views can be a hit and miss affair. A steady atmosphere is always a lottery to get. It might seem steady down where we are, but up high can be another story. Good luck. To let you know, seeing last night in Sydney was aweful at 11pm. Jupiter was up high, but couldn't get a steady clear view. I was using my 17.5" too, which three weeks ago blew my socks of with views of Jupiter.

By the way, the telescope gods must be smiling on you mate, to not damage the finder, :lol:, :doh:. You won't be doing that again any time soon.

[hulloleeds]

Hah, yes, the gods were good to me, last night. It wasn't all average - I mean, sitting there observing even a substandard jupiter was quite picturesque in itself.

I'll take a quick look tonight, quite enjoy the crisp air.

[hulloleeds]

So, the EPs came (4 and 15mm superplossl and 42mm superview), Unfortunately I've only really the moon and jupiter to play with so judgement is not based on enough data. The "build quality" certainly is up, compared to the skywatcher included EP's and the 15mm, I quite like, at the moon.

Having said that, I'm continually sort of bummed by lack of detail / size on jupiter. I mean, you can really see the atmospheric turbulence through the 4mm (which was as you might imagine, "fun" to get pointed right :)), barely a moment's pure focus before it was all "humid" again. But.. the main thing really being that aside from faint browish stripes, no detail. Is it currently too bright? It does seem plausible that it is simply too bright to hope for detail, but am I expecting too much?, is being in the middle of brisbane (not far from city centre) killing me?

Don't get me wrong, had great fun and I think the EP's will come into their own when I'm trying to look at more than a couple of things. Needless to say, I'm plotting a journey out to darker skies this weekend. However, I'm just looking for someone to maybe point out what my expectations should be.

[erick]

See what others say, but if you get in 15 or so nights observing Jupiter, I reckon only 2 or 3 might have good enough seeing for detailed views.

That said, check that you are not observing across metal roofs, expanses of bitumen or car parks. Could be some local thermals in the air due to these areas - particularly, of course, in early summer evenings.

You could try popping your Moon filter onto the eyepiece and experiment. Some feel that reducing the brightness can help?

[hulloleeds]

Thanks for that information Eric, I don't own a moon filter, but I certainly feel that it wouldn't go astray.

It wasn't super high at the time, so I will try tomorrow night.

I wouldn't say that there were any local thermals due to the causes you mention, however I assume that a $29 4mm GSO superplossl is likely to be extremely susceptable to "anything" in the atmosphere?

My basic opinion is that the view was "bright", regardless of eyepiece. Whilst I saw less of the humidity type distortion in less magnified views, I never felt like I was gaining any better detail. I mean, essentially, I could look at it through a 25mm and see the same thing.

Could collimation be required, could that be a root cause?

[mental4astro]

I second what Erick has said. Steady seeing is a lottery. This year so far, I've viewed Jupiter about eight times, only once would I say seeing was steady to really see detail.

There is another trick for newtonians to reduce glare. You can cut some stiff cardboard to a diameter smaller than the scope & place the 'mask' over the opening of the scope. This effectively stops down the scope, just like making the diaphram of a camera smaller. This is usually done on larger scopes, but no reason to not give it a go. Start with a 50% reduction of diameter. You can always cut it larger.

Hulloleeds, you can still have a shot at Omega Centuri & the Carina nebula while the moon is up now, then you can compare them under new moon conditions. Both will stand up pretty well to being pushed from low magnification to high. Really striking.

[hulloleeds]

Thanks mate, I'll try that out.

[PCH]

Hi HL,

you'll need one sooner or later - a collimator of some sort that is. There's really no way anyone can comment on your collimation as a cause of lack of clarity until you've checked it out.

Laser collimators are cheap enough from the likes of Bintel or Andrews etc. Get one and make sure your coll is set correctly. At the very least, it will allow you to move ahead with your ep collection once you know your collimation is correct.

Also, have you left your scope out for an hour or so prior to viewing - that will help ensure it's at ambient temp, and this will help with the view also.

I moved up to Televue Plossls at about $150 each as my next step up from the cheapo things that are supplied with these scopes. Your choice of a good quality ep will definitely enhance your viewing pleasure. When you feel you have a bob or two to spare, I recommend a pair of Stellarvue Binoviewers from SDM. The view of Jupe thru these will blow your socks off.

Hope this helps :thumbsup:

[hulloleeds]

I realise this is somewhat impatient, but my feeling is that this happens to be the moment when I can upgrade my scope, guilt free. I know, a week after receiving my 8 I'm already plotting upgrade :). Basically I found out I'm getting tax back, which I wasn't expecting. So, with that in mind, I believe I'm going to get a GSO 12 and sell the Skywatcher.

Not saying that I'm disappointed with the scope, only a fool would make judgements on that regard, I just know I'm in this for the long run and that I won't have an opportunity to reevaluate for quite some time after this so it is either do something now, or don't for another year.

[mental4astro]

Hi HL,

Your upgrade is one of the worst cases of apeture fever I've ever seen! :astron: Man, one week! :rofl:

Just keep in mind, a 12"er is much bigger than an 8". You would need to hitch a trailer to your Charade to tranport it!:driving:.

Mental.

[hulloleeds]

Hah, guilty as charged. To be honest I originally planned to get a 12, it's just that the wallet was not actually equipped for such a plan until now.

You don't think the tube will fit across the back seat?

I definitely won't buy a scope that I can't fit in the car :)

[erick]

Put your money in the bank and wait for the AUD to rise further - your buying power will go up.

Learn a lot more with the 8". Much easier to learn on an 8" then on a 12" - I know.

In my Falcon, I would have to remove one rear internal door trim to fit the tube across the seat. You could buy a Hummer?

A 4mm GSO plossl? Paperweight value only, I think. I found the eye relief in the 6mm too small so you must have your eye jammed against the eyepiece?

Yes, the Televue plossls or Vixen LV (better eye relief) - try the second hand market - put out a "Wanted".

Sounds like you were observing Jupiter too low. It is at opposition on 15th so is directly overhead around midnight. However, with a dobsonian mount, it is a struggle to observe at 90 deg elevation, until you learn some tricks (1. - grab the dob base with your spare hand to rotate in Azi. 2. - prop the base base up on one side so the base points to 70-75 deg elevation). Anywhere above about 70 deg should reduce the air column you are looking through.

Your dob may already have an end cover with a reduced aperture hole. Is there a 5-7cm cap that pulls off to leave a hole? Try that - just move the hole to where it isn't over an arm of the spider.

And you have to check that collimation!

[mental4astro]

HL, since you're wanting to get to a dark sky, why not make it to a local star party (check the forum here in IIS, or the club directory in the 'Resources' heading at left). This way you will see many different scope, how big they are & how they perform, before you drop the big bucks.

But do learn on the 8" first, as Erick said. It is an easier scope to handle than a 12".

& if you do get a Hummer, what 12"? 20" dude, :D:P.

[hulloleeds]

Wait? What is this waiting concept? Free money coming!

I should point out, I wasn't going to drop big bucks, really, by my math I could upgrade for very little outlay - given that I have a brand new skywatcher 8 to sell (that I paid only 500 in the first place for). If I can't get a 12 GSO in my car, though, that might be scuppered as I am not so desperate to part with money for a 10.

I believe I do have an endcover with reduced aperture hole, actually. Now that I think of it. I will try it.

On getting it pointed at 90 degrees, no significant difficulties, I have definitely seen Jupiter when directly above. Didn't help that much, just a bright ball with two faint brown stripes, unfortunately. No real troubles moving the assembly, atall, actually, understandably quite difficult to nail Jupiter in a 4mm eyepiece, but aside from that, I've not suffered too much.

On the eyepiece, I'm sure it would annoy many, but I'm fairly lucky in that sense and I had no significant difficulties looking through it but yes, I'm pretty sure the concept of eye relief doesn't exist, looking through it. It doesn't seem to be an issue with me. Young eyes perhaps?

According to the manual, lack of collimation would show out of focus stars as out of sync decreasingly small circles? I don't really get that, I seem to have centered, as prescribed by the manual, hence, whilst I mention it, as far as I could tell, it wasn't wrong.

Just looking for online hummer store? Anybody got a link? :)

To me, if I'm already grasping for EP's, it would seem I would be better off first upgrading the base assembly (scope)

EDIT: is it possible that I might need a shroud?

[erick]

Envious! :mad2: :(

I would suggest going for improved eyepieces in the 8" first. They will transfer from an 8" f6 to a 12" f5 quite well.

[hulloleeds]

Fortunately, above all, I have X weeks to wait before cash bonanza hits, in this time, I will have at the very least observed through a 10 inch dob. In which case I should have "some" perspective on whether I'm being unreasonable in demanding a better view.

I will continue to try all avenues, to learn more about the issue, of course.

[Paddy]

This will be perhaps the biggest issue. Using a 4mm ep in a 1200 mm fl scope means your mag is 300x which generally requires very good seeing. You will get that at the zenith rather than low on the horizon as you are at present looking through a lot of atmosphere. Certainly a good idea to try again when the planet is higher. No scope or eyepiece will give you a good view at this mag with low altitude.

[Jeeps]

I've never used a dob, but i'm thinking about getting one. How hard are they to make small adjustments/bumps when tracking/re-aligning an object? I'm a bit worried that if i get a dob i'll have trouble lining things up and wish i had gotten an EQ mount. Maybe i'm just too used to the unstable cheap alt./az scope i've been using ;)

cheers

[hulloleeds]

Oh, it didn't look any different in the 10, 15, or 25 mm EP's either (in terms of detail). 4mm was just an extreme example of how blowing it up revealed no more details.

[hulloleeds]

It's fairly "hands on". I can't see why you'd find it that difficult, after a bit of practice.

For me, certainly not even on any list of concerns about buying a dob.

[erick]

Out of the box, these economical dobs can be fine, but it is possible to make DIY improvements:-

http://www.iceinspace.com.au/forum/showthread.php?t=20612

[mental4astro]

Hey Jeeps,

If you are not considering astrophotography, dobs give the biggest bang for your buck.

I too started with a poor alt-az mount, ditching it for a photo tripod for my 2" refractor. I learnt an aweful lot with this set up in the nine or ten years before I got my C5, which then again, I mainly use in alt-az.

I digress. Mate, you will have no problem with a dob coming from a poor alt-az. It will actually proove itself a breeze.

[Jeeps]

Thanks for all the replies. I was hoping for such responses :) I can keep a large dob in the garage or tool shed then use a hand trolley to move it maybe 10 metres to an open spot in the driveway. Out here in the country there's no street lights and limited light pollution so with a large aperture and eventually some nice ep's i hope to get some solid enjoyment from it - and to introduce my kids to it too ;)

I'm thinking about a GS or Skywatcher 12" dob or similar

cheers