Planet advice

[Mason76]

Hi there, I am a new owner of a Dob 200p and just starting to explore the sky. What I really need your advice on is focusing on Jupiter. I just can't seem to get a really sharp image using either eyepiece. I can get close but it just isn't that clear and I would expect it to be given the reviews and the comments on here. Stars seem to be quite sharp so it must be something I am doing. Your advice is appreciated

[Uplooker]

Hi Mason,

First off, you sure the scope is properly collimated? I note you say stars are sharp. That means "seeing" is at work. Think of a hot day, when you look at something off in the distance you can see things shimmer or rather a heat shimmer. This is exactly the same thing when you are looking at planets. You are trying to look at the planet through turbulent atmosphere. It means that you think you have gotten good focus, but wait, it seems to drift out of focus again. That is down to seeing. Some nights are better than others, it is just one of those things. Sometimes when you look at the stars with the naked eye you see them "twinkle" again that is seeing. It is influenced by turbulence in the atmosphere. The jetstream certainly does not help, depending where it is located in respect to your location.

When the seeing is not great just get focus the best you can and enjoy the fleeting moments of good views. Seeing can sometimes be best very early in the morning.

Ian

[KarlosFandango]

Yes, I have the same issue - stars seem perfectly focused but Jupiter is just a.. blobby mess, utterly lacking any definition. Accounting for Uplooker's post above, that is, the atmosphere is interfering - it begs the question, what is the resolve?

What is collimated?

I'm strugging right now to figure out even if I have the right eye pieces in and haven't got a clue what the Barlow lense is about - aside that it has "2x" on it, so I'm guessing doubles the eye pieces magnification.

[Qualia]

Dear Mason & Karlos,

From what I've been reading the last couple of days, it seems quite a number of folk are exerienceing soft, mushy, blurry views of Jupiter in the UK, and this okay, seriously. As Uplooker argues, it's mostly down to the unfavorable viewing conditions, especially at this time of the year. So there's no need to blame yourselves and think you're doing something wrong . But we can go over a few boxes to tick off in order to cover our bases.

In principle, collimation could also be an issue. In general, if it's not good, it will affect contrast, resulting in views below the standard to which our scopes were engineered and designed. I know the moons or stars were said to be pinpoint sharp, so it sounds like we're okay on that front. But just to cover our bases, if you guys haven't got the tool already, it is essential to buy a Cheshire and it maybe neceaasry to give your primary mirror (and perhaps the secondary) a little tweaking. There's nothing to be afraid of. I collimate every night I head out and after a little practice it just becomes second nature and over and done with in a jiffy.

Along similar lines, make sure the scope is cooled down sufficiently. If the scope has not stablized thermally, the views are not going to be sharp. Although you can start viewing straight away, give yourself a mental note of an hour for cool down.

Another factor to bear in mind is location. Jupiter could have been low relative to the horizon. If that's so, you're punching through more atmosphere which will soften up the image. Try to view near the zenith whenever possible. Another box to tick off is magnification. Most nights, I'm not pushing the 10" f/5 Dob over 200x without sacrificing sharpness. Bad nights, I'm looking at a boiling, bright blob around 125x. Usually, I'm playing around with magnifications ranging from 150x to 200x.

Accepting that the seeing conditions this evening were not great, it's also worth bearing in mind that there's something about planetary viewing which lends itself toward practice. It's a bit of an art. I'm not being condescending here, but really wanting just to help out.

You see, on another better night, you may still feel you're not seeing that much but what you're seeing just might be pretty close to what you can really see . That's not a play with words. Jupiter has a lot of features, a wealth of information to tweak out, but to see these features takes hours of practice. So, on that other hypothetical evening where you feel you're not seeing that much, you might be seeing more than you realize. Adding to this sentiment, viewing Jupiter also takes patience because the seeing conditions will inevitably ebb and flow; one minute you might not have a view at all and the next moment you could have a view which burns itself into your memory forever .

Give Jupiter another try another night. Sit with him patiently for an hour or so and let us know if things improve. To train the eye, it might be a nice idea to try a sketch or two.

P.S: yes, a Barlow does exactly that. It effectively doubles your scope's focal length and in consequence doubles your eyepiece's magnification.

[jetstream]

Qualia another fantastic informative post.Touches all bases. My routine consists of checking collimation,correcting collimation if needed,thermally stabilizing my optics (cooling) and try to reduce or eliminate tube currents.In general  tube currents caused by the primary holding a bit of heat really can play havoc.Jupiter will "blob" out frequently and be a blurry mess,but coming together,kind of once in a while.Qualia addresses this by stating a good cool down time and this works.I also run a small fan (no vibration at all) to speed cool down and thus reduce thermals.I run across tube currents even when the mirror has cooled....ground sources are common and the fan on my mirror cell really helps-I run it most of the time as there is no drawback.

The fastest way to get good planetary views is to leave the scope in a shed or other place that has the outside temp,quick colli check,fan on if available and use an EP matched for the sky conditions,and then as Rob stated,view the object when high up.Check Qualias sketches to see how well his suggestions work.

Excellent Rob!

[ronin]

Going to suggest you spend £50 on a decent eyepiece.

The 25mm will not really give enough magnification, and combined with the brightness of Jupiter means the bright band will sort of overflow and you get a poor view. The 10mm eyepiece and the barlow are generally just poor.

Lots will say get used to the supplied items, I tend to be more of the opinion that they are bad enough that they can put a person off of astronomy.

Don't know what Hampshire was like last night but here we had a slight layer of moisture that made everything a bit of a hazy view.

[Golfer66]

Going to suggest you spend £50 on a decent eyepiece.

The 25mm will not really give enough magnification, and combined with the brightness of Jupiter means the bright band will sort of overflow and you get a poor view. The 10mm eyepiece and the barlow are generally just poor.

Lots will say get used to the supplied items, I tend to be more of the opinion that they are bad enough that they can put a person off of astronomy.

Don't know what Hampshire was like last night but here we had a slight layer of moisture that made everything a bit of a hazy view.

So what eyepiece would you recommend a beginner to use ??

[AstroJon]

For £50 you can't go wrong with the BST Starguiders, probably the 8mm.

[Moonshane]

the 10mm should give a good image. when using a scope like this you need to put it outside for about 30-40 minutes before you will get sharpest results possible at higher magnifications. you can start observing at lower magnification sooner though.

if Jupiter is low in the sky then this will affect the view as will it being close to heating vents etc.

once you find your best focus point then don't touch the focus again as the seeing will bring sharpness in and out. look for at least 10-20 minutes and detail will start to appear on the surface. with your 10mm at 120x I'd expect you to see the great red spot if it's on our side at the time, at least two main bands and the polar regions and any moon shadows visible at the time. plus of course the moons themselves.

[YouCannotBeSirius]

I've found that stars are at a different focus to Jupiter... when you're on Jupiter, try refocusing gently and slowly and see if it comes into sharper focus; it should.

[Mason76]

Thanks everyone for the advice. Turns out I was rushing things with it being a weekday and not having enough time to do things right. So today I took the scope out to start cooling before getting kids ready for bed then hour or so later went out and got straight to it seeing the two bands and four moons really clearly..so so impressive. Will try again for the Great Red Spot as I don't think it was there when I was looking.

So I guess my lessons learnt are plan ahead, be patient and start saving as I can see a need for better eyepieces!!

Next stop some DSO's which may take time as I learn my way around the sky.

[KarlosFandango]

Thanks to all for the replies. Despite a quick google search on "collimation" it's not a term I'm familiar with. "Parallel lines of light" - I have no idea how to check that on my telescope or how to identify whether it's wrong and assuming it is wrong, I've not an inkling how to correct it... I'm not just a beginner here - I'm the lowest of the low learner!

[KarlosFandango]

I don't seem able to edit my own posts, else I would have edited the above. Instead, I have to create a separate post, hence, this one. 

What is this cooling of the telescope about? I left mine out one of the nights at work for a few hours and one of my colleagues brought it in saying it was beginning to freeze - looking at the bigger lense (I presume there's a fancy word for this), it seemed to have got condensation on it so I left it a few hours to warm-up instead of cool-down.

[Uplooker]

Hi Karlos,

"What is this cooling of the telescope about"  Well, cooling of your scope is all about getting your viewing equipment i.e. you telescope to a similar temperature as the surrounding air. As I and others have posted in this topic about "seeing" in the atmosphere, there is also a similar thing happening with the "atmosphere" within the tube of your telescope.

If you bring your telescope outside, after it has been stored in a centrally heated house, there will be a significant temperature differential between the telescope, the air in the hollow tube of the telescope, and the air in your garden/ viewing location. Because of this thermals will be set up. Essentially the dense cool air of the garden with try and fill the space of the less dense air that is within your telescope tube. This replicates the effect of atmospheric "seeing" that lots of people have mentioned above. There are different times that should be allowed for different types of telescope. There is some rough rule of thumb that people use which says that you should leave X amount of time for X inches of aperture, I can never remember what it is, suffice to say that you should allow your telescope to stand outside with the end cap removed for at least 30 - 40 mins, so that it may acclimatise, before attempting to get reasonable views without the effect of seeing being apparent. It is true to say that you can view with low power / magnification without having too many problems, but as you increase the magnification the views will or most likely deteriorate.

The worst telescope for cool down time are SCts and Maks. This is primarily down to the fact that the tubes of these scopes is closed at both ends, thereby it takes an awful lot longer for them to acclimatise / cool down.

"so I left it a few hours to warm-up instead of cool-down." This is probably the worst thing you could have done - warming the scope up again! There may have been a bit of condensation on the primary but I suspect that may have come from the fact that the scope had come from a warm environment into a cold one. It should be noted that most people have experience their equipment being completed frosted up during or after a good nights viewing / imaging - thats a good night, as it means the skies have been clear and the views - hopefully excellent.

With regards to collimation, it is one of those things that scares the pants off people - it shouldn't. once you understand the principles it is not too difficult. A couple of people who can teach you a thing or two about collimation are Astrobaby and Moonshane. Hopefully Moonshane (Shane) will be along to give you a link to his  collimation guide, but in the meantime Google "Astrobaby's collimation guide"

To answer your other questions, the big mirror at the bottom of your scope is called the "primary", the little mirror that is at 45 deg to the focuser and at the top of the tube is called the "secondary"

Hope that helps,

Ian