Viewing planets with dobsonian

[Skids72 (Brian)]

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-watc...pe-s11700.html

Thanks for your help.

[Rod66 (Rod)]

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 (Brian)]

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

[renormalised (Carl)]

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....sort=4a&page=1

They'll have what you want, and then some

[mental4astro (Alexander)]

Hi Skids72, welcome to IIS, .

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-conten...tm#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 (Paul)]

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 (Jacquie)]

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 (Alexander)]

Hello Hulloleeds, 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, .

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 (Michael)]

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 (Dave)]

Originally Posted by 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.

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

[mental4astro (Alexander)]

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, .

[Mike21 (Michael)]

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 (Eric)]

Originally Posted by 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! .....

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

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

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

[Mike21 (Michael)]

[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 (Eric)]

[QUOTE=Mike21;472159]

Originally Posted by erick

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.

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 (Michael)]

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 (Eric)]

Oh yes, I remember Brian 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