Eyepieces, magnification or something else?

[Thiink]

I have a question for you seasoned astro-jedis. Ever since I got my telescope I have been trying to get decent views of jupiter (saturn is gone, jupiter is all I am able to view plantry wise at the moment). When I first got my telescope jupiter was still low in the sky, 138x was possible and was about the range of my EP collection at the time (thats with a 9mm GSO EP with no barlow, the 4mm Andrews EP supplied is a waste of time). Then I got a 2x barlow, and thought that possibly 277x would be possible with the 2x and 9mm, but alas the image will never come to focus. At first I put this down to possibly collimation, and jupiter not being high enough, but now with jupiter fairly high (I have been trying for the last 2 months), I thought I would have a chance of it, but it still wont come to focus.

Thinking it may still have been collimation, I spent a few hours last week and stripped my focuser down, cleaned, lubricating and reassembling it. I then went about trying to square it, then grabbed a cheap laser (again GSO branded, tested and collimated at 10ft [I'm waiting to get an Ez Collimator]), reduced the focuser slop as much as I could (by adjusting the focuser tension, and adding a thin layer of sticky tape around the end of the laser) checked the focuser was square again using the laser and then collimated as best I could (checked afterwards with the Cheshire). Phew!

I then took the telescope out on Sunday night when the seeing conditions were fairly good (and no clouds!) and tried again; I still cant get the thing to focus at 277x. Its fine at 100x, 138x but anything higher just isnt going to happen (I only have a 9mm GSO, 25mm GSO, 30mm GSO SV 2" and a 40mm Andrews 500). So I have a question: is this a case of possibly bad seeing, collimation, poor EP quality or expecting too much out of visual views of jupiter? Is anything around 250+ possible with decent EP's? Perhaps its time to spend some money and grab a decent planetry EP, but I am really unsure of what to expect. I see images of jupiter all the time (on this forum) and I can't see anywhere near the detail because I can't get the image size. I realise the GSO EP's are average, but are they that average? At this stage I dont think I could get approval to spend any more than $200 on an EP.

Any advice appreciated, sorry about the novel. :)

[iceman]

Hey simon.

I have the exact same scope, and mostly the same eyepieces (I have 9, 15, 25 and 32mm GSO plossls), with the same 2x GSO barlow.

First conclusion: It's seeing.
Like you, I can't get my 9mm barlowed to focus properly *most* of the time, that is, when the seeing is any less than great.

I've been looking at getting a planetary eyepiece around the 7mm focal length, because it'll give a bit more mag than the 9, but not as much as the 9 barlowed. So when the seeing is fairly good, I can use a 7, and when it's GREAT, I can use the 9 barlowed. I also have the option of using my 15 barlowed, which gives me the equivalent of a 7.5mm to use when seeing is above average.

Collimation is definitely something to look at - squaring your focuser etc is all well and good, but what about your secondary and primary mirrors?

What does a startest reveal? Have you gone inside and outside focus in a startest to check for astigmatism?

Have you checked for pinching on your primary and/or secondary mirrors?

A good eyepiece will also make a slight difference but it won't make the seeing better, and it won't make your collimation or astigmatism better. They're the things to check first before spending money on a new eyepiece.

And finally, don't expect to see visually what I (for example) produce with a webcam. Even with the "ok" images I produce, I don't see that sort of detail (or image scale) through the eyepiece. The webcam is just so much better at capturing the moments of good seeing because of the frame rate, and you throw away the blurry ones when you process it. Unfortunately when looking through an eyepiece, you'll only get the tiny-est of glimpses of detail in good seeing - you don't have the benefit of throwing away the memory of all those bad blurry frames and keeping the memory of the good ones :)

Hope that helps.

PS: Sorry about the novel :)

[iceman]

Also, an addendum, the best view of Jupiter i've seen through a 10" scope like ours was through John Bambury's, at Kulnura a few months ago. He was using a 2.5x powermate with a 10mm pentax XW (I think that was the combination) giving around 300x, but the seeing was very good that night.

I couldn't get the quite the same quality views through my scope at the same time because at that time, my secondary had astigmatism and my collimation was probably not as accurate as John's. Plus, I wasn't using the good quality barlow and eyepiece.

So it all makes a difference, but seeing is #1 priority.

[h0ughy]

JohnB did a eyepiece review about 1 or 2 months ago. as for your problems could be a number of things and the fact that there would be a cross over point at which magnification would be useless. Remember the more glass the light has to pass through the more likely the degridation. Don't forget Mr Icemans link for jet stream winds, that doesn't help either! :D

[h0ughy]

that would be right start to type something and get interupted and finally post it. And mike beats me to the punch.
:poke:

[rmcpb]

The problem may be a combination of the quality of both your eyepiece and barlow. Do you know anyone with an Orion Shorty Plus or a Celestron Ultima Barlow then try combining it with your 9mm? Both of these barlows are fully apochromatic and of high quality so your image should improve. Of course it would be great if you could try one of these with something like a Meade 9mm as this would represent a significant improvement in the quality of the optics.

Another thought is that, while we talk about the advantages of barlows ie. virtually doubling your eyepiece collection, they introduce more glass into the light train and as a result reduce the image quality. While this is not such a problem at lower power this effect becomes more evident at higher powers. Its for this reason that people often buy an eyepiece for planetary work and don't simply barlow a larger lense. In this case then eye relief comes into play so your planetary eyepieces are often quite expensive bits of glass and metal.

Hope this helps.

[ving]

I have the same EP and barlow. I have rarely been able to barlow the 9mm for planetary viewing. the seeing has to be pretty darn good for that. I bought a TV 10.5mm plossl and I can barlow that sometimes as it is better than the GSO 9mm, but still the seeing has to be very good.
my guess is that you just need to wait for good seeing....

the reason I say its not the barlow and EP is that if you use it on a bright DSO you will get a good image even in average to good seeing. but to get detail on planets at that magnification you will need v/good to exeptional seeing :)

[asimov]

Yes. I agree it could be a lot of little problems rolled into one.. On most nights I can't even use a 7.5mm EP with the 6" achro or the 12.5" reflector on jupiter. 12mm is the lowest I go. PERFECT seeing is another story...twice so far for this year..

[Thiink]

Thanks very much to those that replied, its appreciated. I guess it's pretty much what I was expecting. I might look at purchasing a decent EP for planetary use; I never really thought the barlow could be half the issue.

The biggest problem is that I have never really read anywhere what to expect visually when looking at planets, only what people have said about imaging them. I've read that the optics should be (conservatively) good for around 25-30x per inch of aperture, which is around 300x max. It's more the image scale that I was trying to get, detail is visible at lower powers but its harder to see.

I really need to get to a meet or something so I can look through a few other newts/dobs, and EP's.

Ice: I might need to check my secondary for astigmatism, stars arent appearing quite round, they are slightly skewed. I noticed this on Sunday night when I was star testing. The primary is fine, its been checked several times when I've had it out. I should really have checked the secondary when I had it out to square the focuser. How much difference can astimatism of the secondary make to plantary images? I might have a go at getting the secondary out during this week.

Ving: that's where I am at as well, the 9mm with 2x barlow works fine on doubles (at least it did when I was testing on Sunday night), I havent tried anything else.

[asimov]

I've read (somewhere) that jupiter does not take well to magnification...I've yet to read an explaination as to WHY this would be the case. :confused:

[[1ponders]]

Simon with todays quality of optics even at the lower end you should be able to achieve around 50X per inch of aperture. Except of course for the real cheap and nasty optics. For some really good mirrors and lenses available for the amateur today even 60 - 70X is realistic. For your DOb I would be very surprised if you couldn't get at least 50X/", allowing for seeing conditions, temperature equalization of mirror etc of course.

[Mick]

Simon, I have had a lot of viewing nights with bad seeing. I use to think my Meade 9mm ep was a dud until one night of good seeing, I viewed Saturn at 414x with that 9mm barlowed in my lx90. I've only had two good viewing nights like that in the last 5 years; normally I can only use up to 150x. The sky conditions can be very deceiving and cause this kind of problem. :)

[ausastronomer]

John,

I can tell you why that is and I will post a detailed reply about it later tonight when I have more time.

CS-John B

[ausastronomer]

Simon,

I think most of your problems relate to seeing conditions as others have mentioned. 50% of nights you will struggle to go much over 200X on Jupiter with a 10" scope. Its rare that you can go over 250X and very rare 300X. As you also note however collimation is important as is checking your scope for astigmatism. This is easily detected with a star test at medium power. Your 9mm eyepiece should show any astigmatism if present. These scopes are notorius for having a tight secondary holder.

CS-John B

[Starkler]

Step one Simon is to check your optics via a star test . GS dobs are well known for not always being assembled with proper attention to the mounting of the optics.

Check out the GS optics checking how-to for details.
http://www.iceinspace.com.au/index.php?id=63,206,0,0,1,0

I find on Jupiter 200x is as much as I can use. My most used planetary viewing combo is a 14mm pentax xl with a celestron ultima 2x barlow (which i measured at 2.2x).

[ausastronomer]

John,

This phenomenon relates as much as anything to visual perception of the observer.

With Jupiter you are trying to resolve smaller, non-linear, low contrast details. With Saturn, other than the dull bands that appear on the surface, Saturn's details are more sharply defined (higher contrast) and linear, thus will "apparently" stand higher magnification. In fact, this is only an illusion. The ability to resolve is the same. It is only the nature of the details that creates the notion that Saturn will take a higher magnification. The human brain is just better at defining and realizing lines. This is why features at the terminator of the moon look so good under high magnification.

The above explanation was actually provided to me a few years ago in an email from Bob Royce, noted optician and planetary observer.

CS-John B

[cahullian]

Simon I think it may be your eyepieces as I have the 8" Dob and have used my GS 9mm Barlowed with the Orion shorty plus several times on Jupiter in the last month or so and have been able to focus on it easily. Saying that if flies through my FOV and it's nudge nudge nudge every few seconds. I do lose a little detail with the Barlow on but not much and having Jupiter looking so much bigger is still quite a buzz. I'm still a novice at this Astronomy stuff and not too sure what is good seeing and not too good seeing(to me good seeing is no clouds in the sky and not good is overcast). I always start looking at Jupiter with my GS 25mm then I barlow that to give me 12.5 mm then try the 9mm and so on. This gives me the most enjoyment as each time the planet is getting bigger and more detail is viewable. Seeing you have 2" more aperture than me it really does sound as though your ep's arn't what they could be. Saying that John B told me that my mirror was a little beauty and I was able to hunt down the NGC5128 Centaurus A when Anthony couldn't with his 12" light bucket. Sorry Anthony I will be telling that one to my great great grandkids. I also have a Seben 8mm to 24mm zoom lens and have Barlowed it at 8mm looking at Jupiter but with less detail. This eyepiece is for the wow factor with kids. Omega Centuri onfocused at the 24mm looks like a snowball but when brought into focus to the 8mm setting it looks like the cluster if flying right at you. Sorry for going off topic near the end there.

[Thiink]

Thanks for the hints guys! I think its time for the secondary to come out, might do that later this week. Hopefully I can get a star test to show perfectly rounded circles afterwards, would make it well worth the time (thanks for the guide!).

A decent planetary EP is on the cards now too.

Thanks again for the replies!

[Dave47tuc]

Hi All,
I would like to add more to this. Viewing conditions make all the difference. Yes your scope must be of good quality and stable mount, eyepieces etc.
But optimum viewing conditions make all the difference. You have on most nights a part of the sky that is optimal for viewing. That is at you zenith and a few degrees around it. Also in what part of the sky the planets are located.

I remember in 1986 Mars been better to observe than in 2003. Why is this as Mars was a little bigger in 2003 than 86. I put this down to my viewing location has changed a lot over the years. In 1986 Mornington and the Mornington Peninsula was less populated. It has nearly doubled in that time. So the heat generated from all these houses make a difference.

Again I look at Jupiter and Saturn, when they where in the Southern constellations I had a much better view than I do now. I remember using 300x plus on both Planets.
Now and over the past few years I have not been able to.
Also I have found many times viewing the planets is much better between 3am and morning twilight. The air is much steadier and people have turned their heaters of and lights off.

Another case in point, last night I was looking for the Comet, no luck.
I however was able to see the double of Antares at 140x the seeing was very steady at the zenith. BUT Jupiter lower in the West was hopeless. I was looking over many houses and mine also and the heaters would have been on in most of them.
I could not get a decent Image at any magnification. So that small hole at the Zenith is really only the good place for high Mag.

On the brighter side both the big Planets are on there way south once again. So stick around the Viewing will get better as they head south.

Hope this helps. :D

[asimov]

Thanks John B