The quest for my first telescope (beginner needing advice)

[Scorpius51 (John)]

Originally Posted by Jowel

Chris, that's bloody awesome!

What about planets? For instance, how big is Jupiter in an 8 inch scope? Got any pics? If not, know where I can view some pics to get an idea of what a planet looks like in an 8 incher?

Hi Jowel

Here is a link to a pic of Jupiter by an IIS member.

http://www.iceinspace.com.au/forum/s...ad.php?t=63453

It's rather good for an 8" and could get better with very good seeing and post processing.

John

[Screwdriverone (Chris)]

Hi Jowel,

Thanks for the comments, I am pretty happy with those early shots so far. I havent tried the new scope on planets yet, although will be doing this as soon as I can as I want to try the 5x Powermate with the webcam now that I have reliable tracking. I have done some Jupiter and Saturn shots with my 12" dob which shows more details than the 8" should (depending on the barlow used).

Here is one of my better Jupiters with the 12" link

And my favourite Saturn here

Now I know you cant really compare these to what you would see with the 8" so hopefully on the weekend I can get some clear skies and try out a few Saturn and Jupiter shots with the new scope to show you the difference (if the seeing allows)

Cheers

Chris

[Mountain_Wanderer]

Originally Posted by Scorpius51

Hi Jowel

Here is a link to a pic of Jupiter by an IIS member.

http://www.iceinspace.com.au/forum/s...ad.php?t=63453

It's rather good for an 8" and could get better with very good seeing and post processing.

John

Thanks guys. That Jupiter shot now raises my expectations in terms of what an 8" telescope can do. I was expecting a small dot of a planet after using that website that compares telescope sizes!

Is the above photo what you'd typically see by looking straight into the telescope, or does that photo show a lot of colour and detail because the camera shot was exposed for a long period of time? I'm trying to get an idea of the exact size, colour, brightness and detail I'd be able to see if I were to simply look into the 8" scope towards Jupiter.

[Screwdriverone (Chris)]

Hi Jowel,

No, the colour is NOT due to long exposures when taking pictures of planets - because they are SOOOO bright we need to take REALLY short pictures, as many as you can to "freeze" the atmospheric seeing. (technical term for the big column of air between YOU and outer space which is turbulent and moving). This is why we use a webcam which can take videos at 30 or 60 frames per second which in reality equates to 60 pictures every second. Once you capture say, 30 seconds of video, then this equates to 30 x 60 frames = 1800 pictures. These are then stacked on top of each other (after throwing away the not so good ones - done by software like Registax) and then you get LOTS more details than just a single exposure which may be blurred when you take it because the atmosphere at the time is moving.

We dont see as much colour on a planet through the eyepiece because our eyes are not as sensitive as say a CCD on a camera or webcam. You CAN still see vague colours and you can definitely see bands on Jupiter and the Great Red Spot etc, but nowhere near as vibrant or detailed as a camera can do. For example, my Saturn pic looks like it has a rainbow of bands on Saturn, but through the eyepiece, it looks creamy white or even beige as my eyes (in the dark) are NOT as sensitive to colours as the camera. Mars however, does look red and you can make out surface details in the eyepiece, depending on how big it is at the time (how close Mars and Earth are to each other in space)

You have to be careful not to expect what you see in pictures here, as it is DEFINITELY NOT what you will see in the eyepiece. My M20 Trifid pic is a prime example of this, a nebula often only looks like a grey wispy blob with your eye, but as you can see in the astrophoto, its red AND blue in reality. However, what you DO see, often blows you away even without all the colour as you are seeing it "live" through your OWN EYES with your very own telescope and often in your own backyard. Humbling and cool all at the same time. AND, very worth it. The first time you see Jupiter or Saturn in your scope will blow your mind and be a memorable moment for you.

Cheers

Chris

[Mountain_Wanderer]

Thanks Chris. Always good advice you offer!

In terms of the SIZE of Jupiter you see when looking through an 8", can I expect the same as in that image? Or is that image a super magnified crop of Jupiter that in reality is a VERY SMALL object when viewed?

[Screwdriverone (Chris)]

Hi Jowel,

The size of ANY object is determined by the magnification. Typically, the more you magnify something, the bigger it gets, BUT the dimmer it gets also.

What this means is that you can use say a 5x powermate like mine on an 8" scope to BLOW up Jupiter to a larger size, but the limiting factor to how bright it will be is the aperture of the scope. BIGGER opening means MORE light and therefore brighter and more detailed image. If I use my 5x barlow on my 130mm scope the planet is too dark to see anything.

In general terms, magnification limit is approximately 2 x the aperture in mm of your scope. Therefore, with my 130mm reflector, the max is 260x magnification, my 200mm reflector is 400x and my 300mm reflector is 600x. To work out the magnification of an eyepiece, you divide the focal length of the telescope by the focal length of the eyepiece. So, for example, on my 8" (FL=1000mm) a 10mm eyepiece gives: 1000 / 10 = 100X magnification. A barlow (magnifying lens) MULTIPLIES this by whatever factor it is. eg. a 10mm EP with a 5x barlow gives 500X magnification!!! This is pushing it a bit for my 8" scope. Therefore I also have a 2.5x barlow which gives me a more usable magnification on the 10mm of 250X. (my 300mm scope has a FL of 1500mm so the 10mm EP gives 150x, 375x (2.5x barlow) and 750x (5x powermate).

However, the maximum you can view is also dependant on the seeing conditions and the transparency of the sky. Bad seeing shows up as wobbly planet (looks like the planet is underwater and is like jelly in the eyepiece - sort of like heat haze) and this makes things like details, difficult to see. Bad transparency means that the planet looks stable and round but its hard to make anything out as its almost like there is a mist obscuring things.

If you are looking at a 8 inch scope - solid dobsonian (which you can use the tube to mount to an EQ platform later) then you will have either 1000mm focal length or even 1200mm, depending on the brand.
What this means is that you normally get a 10mm and a 20 or 25mm eyepiece with the telescope. Assuming its a dob with 1200mm FL, then the 10mm will give you a 120x mag, the 25mm will give you 48x mag. Rather than buying other eyepieces, you can simply get a 2 x barlow (get an APO one, they are better than ED in my opinion) for about $60 and then you will also be able to double the mag on the 10mm to 240x and 96x on the 25mm.

This will give you FOUR magnification levels; 48x, 96x, 120x and 240x which is PLENTY to get you started. and gives you a good range to work with. As I said, the conditions generally dont let you use REALLY high magnification often, so anything too high is a bit of a waste of money.

Looking at say Jupiter at 48x will show you some banding on the planet and perhaps the GRS but also be wide enough to easily make out probably all of the Galilean moons in the one view (depending on where they are). Switch to say the 10mm with the 2x barlow and you will be at 240x and then you should be MUCH closer and hopefully see more details in the cloud belts and make out more of the GRS and some of the closer moons will also be bigger.

By the way, the easy way I remember the four closest Galilean moons for Jupiter is "I Eat Green Cheese" which refers to (in order from closer to farther away) Io, Europa, Ganymede and Callisto.

When you do end up buying a scope, keep in mind that 2 eyepieces and an 2 x APO barlow will probably suffice for at LEAST 12 months and will enable you to see most of the planets as well as some really cool galaxies, nebulae, open and globular clusters as there are literally thousands of things within reach of an 8" scope and the primary reason most people on IIS say to start with an 8", its a great place to start.

Whew!~ another essay from me....hope your eyes arent too tired...

Cheers

Chris

[Mountain_Wanderer]

Dude. Another bloody ripper of a post there. Thanks!

So, it looks like I'm likely to see a large jupiter in an 8" scope, similar to the size in that photo posted earlier. I won't just be limited to a small dot of a planet. Good times!

[Brian W (Brian)]

Jowel, hi my primary scope is an 8" LightBridge and once you get in a little experience there's is lots out there to keep you amazed. However it is good to remember that 'large' is not going to happen with Jupiter or any of the planets. You will certainly be able to fill your ep, on a good night with high magnification, but 'large' it won't be.

Detail galore including the GRS but not what I would call large. The moon is large and you can spend hours or a lifetime exploring all the nooks and crannies. But Jupiter, or Saturn while you will see incredible detail with an 8 ie. a couple of weeks back I saw the shadow that was cast on Saturn by the rings you will not appear really large.

Brian

[Mountain_Wanderer]

Dude, I feel ashamed to ask but...

What is an "Ep"?

[mbo (Pat and Kirk)]

Eye Piece. Oddly enough, it's not mentioned in the glossary here either.
Apparently poms sometimes call them 'Oculars' too. The bit you look into.
To me (a mug beginner) they seem to be the most confusing and debatable part of a hobby that has probably the greatest variety of confusing and debatable aspects to it

[Brian W (Brian)]

Hi Jowel, shorthand for eye piece. Don't let my cautionary post discourage you. 8 is great and however you define 'large' you are about to enter the realm of infinity.http://www.iceinspace.com.au/vbiis/i...eyepopping.gif
Brian

[Brian W (Brian)]

okay, now I am confused... what's a 'pom'?
Brian

[mbo (Pat and Kirk)]

Sorry :-), pommies, as in the British
Also, having thought about it, maybe opinions on Art and Music are slightly more subjective than opinions on astronomy equipment

[Brian W (Brian)]

maybe yes maybe no... we hear the music of the spheres and see the art work of the gods and we all have an opinion about what best helps us to hear and see the dance.
B.

[mbo (Pat and Kirk)]

I hear you Brian, my jokes about eyepiece choices come from spending too much time Googling the pro's and cons, it's starting to drive me a bit batty!. On the other hand, last night I saw Jupiter and the faintest flicker of Callisto, and what I believe was Neptune through a rifle scope. For me that's a bit like hearing Louis Armstrong wafting through the window from a club down the street ... gotta get more of that.

[Brian W (Brian)]

Through a rifle scope takes one right back to one of the driving forces of telescope development... the need for captains of war ships to see the enemy first.

As for sorting out the best ep collection for your needs... I wish you luck!
B.

[Mountain_Wanderer]

Just looking at the specifications for the Sky Watcher 200mm dobsonian, solid tube (SW680)...

Focal length is 1200mm. Is that decent? Some other 8" telescopes have it more? Would more be any better?

Eyepieces listed are: S20, S10(31.7mm). What the hell does this mean? And are these decent eyepiece sizes to start off with?

Focal ratio is "f/6". I have no idea what this means?

Finderscope is 9 x 50. What?

Barrel diameter is 50mm/31.7mm. What?

Also, would this dobsonian telescope easily connect to an equatorial mount if I buy one later?

Yes, I'm definately a beginner Any help guys?

[Colin_Fraser]

Also, would this dobsonian telescope easily connect to an equatorial mount if I buy one later?

I don't know about that model but Andrews have a 10" Skywatcher on an EQ6PRO mount

[Screwdriverone (Chris)]

Hi Jowel,

Hmmm, looks like those answers require my services again, please see below;

Originally Posted by Jowel

Just looking at the specifications for the Sky Watcher 200mm dobsonian, solid tube (SW680)...

Focal length is 1200mm. Is that decent? Some other 8" telescopes have it more? Would more be any better? This is fine, more than I have with my 200mm BDN200, which is only 1000mm.

Eyepieces listed are: S20, S10(31.7mm). What the hell does this mean? And are these decent eyepiece sizes to start off with? They are a 20mm and a 10mm eyepiece. Which in this scope give you magnifications of 60x and 120x respectively. The 31.7mm refers to the barrel size which equals 1 and 1/4 inches (standard focuser size).

Focal ratio is "f/6". I have no idea what this means? Focal ratio is the result of the equation FL of scope divided by the aperture. In this case 1200mm/200mm equals 6. Therefore F6. Small Focal ratios of F6 and below mean the scope is "fast" which gives bright images in a WIDER field than in a longer FL scope such as a compund scope or refractor where the FL can be F7, to F15 (normally a Schmidt Cassegrain). MORE focal length means you can theoretically magnify much more, BUT the view is narrower.

Finderscope is 9 x 50. What? This is the little telescope mounted on the main barrel of the scope which you look through to point the mainscope to the object in the sky you want to "find" in the main scope. Hence the name "Finderscope". The 9 x 50 refers to the magnification level (9x) and the aperture (size of the scope - 50mm). This is a good finderscope.

Barrel diameter is 50mm/31.7mm. What? The focuser accepts 2 inch (50mm) as well as 1 and 1/4 inch (31.7mm) eyepieces. This is normal and good also.

Also, would this dobsonian telescope easily connect to an equatorial mount if I buy one later? Yes, you take the tube off the base (unscrew the two handles - thats it.) You will have to buy some tube rings later (which wrap around the tube and hold it) and a dovetail bar which these two rings screw into and then the dovetail bar is held onto the EQ mount head. When you do get to that stage, an HEQ5 is perfect for this (what I have)

Yes, I'm definately a beginner Any help guys?

Also, dont get too hung up on the details and worry that this 8" scope may not be the BEST one you can get now. There is ALWAYS going to be a better scope or a different scope which you will understand later is referred to as "scope envy" and this manifests itself in you also as "aperture fever" which means you are always on the lookout for a larger and larger scope.

The main reason that the 8" dobsonian has been recommended so highly to you is that its is REALLY easy to use for a beginner. The Skywatcher brand is great quality and value for money. Also, as explained, it is doubly good to be able to upgrade this to mount it on an EQ mount later.

Dont sweat it, you'll be fine.

Cheers

Chris

[Mountain_Wanderer]

Mate, once again thanx for your wonderful advice!