Doughnut shapes & eyepieces - help please

[Ptolemy]

Hello all, as absolute newbies (first ever scope, Skymax 127, bought just over a month ago!) we're floundering a bit with knowing if what we're seeing is as good as it gets or if we're doing something wrong or need another piece of kit etc. Some help/advice would be greatly appreciated.

We've seen some great views of the Moon but can't seem to get much else. We've been out last couple of nights looking at Mars, we managed to see it resolved as a bright disc using a 25mm eyepiece (the one that came with the scope) but as soon as we pop in the Celestron X-Cel 8mm eyepiece (the one that didn't come with the scope but did cost us a fair bit!) then everything goes pear shaped, actually that should be doughnut shaped We seem to lose the night sky completely and instead get a white circle with a black circle in the middle, exactly like a doughnut, that fills the scope. After much twiddling of the focus knob we manage to resolve the doughnut image to a slightly out of focus disc of light that dances around the eyepiece and won't stay still, any further twidling of the focus knob just turns it back into a doughnut:confused:.

As total beginers are we just being plain stupid and the answer is obvious to anyone who knows what they are doing ? Are we being unrealsitc - we know our scope isn't designed for DSO but we did expect to get something more than the Moon (beautiful though it is). Or are we missing an essential piece of kit/got the wrong kit?

Any thoughts or advice would be much appreciated, thanks.

PS. although our scope isn't supposed to do DSO we have bought an Antares focul reducer and we're really pleased with the glimpses we get of DSO using that with our 32mm eyepice ......maybe we just have a planetary scope that really wants to be a DSO scope:icon_eek: Why isn't this hobby simly, straightforward .....and less expensive:icon_scratch:

[Capricorn]

This may be an equally stupid question but please tell me that when you change eyepieces that you then refocus the scope?

To remain in focus when you change eyepieces the eyepieces need to be parfocal AND they have to be of the same make and model set. the ones that came with the scope will not be parfocal.

I am guessing that you have simply swapped eyepieces and not refocused as an out of focus star will give a doughnut.

P.S. A 127 should show up a good few DSO's.

[Capricorn]

Sorry, just reread the original and I see that you have adjusted the focus. That leaves collimation.

Have you a collimator? and have you set the collimation?

What focal length is the scope?

Just wondering if 8mm would give too much magnification but I doubt it.

What mount is the scope on?

Update:

127 mm dia, 1500mm focal length, f/11, type = Mak, mount EQ3-2.

8mm EP should be OK but is getting about as small as makes sense. Simply there is a limit to a scopes usful magnification and an 8mm EP is probably it for yours. You may get more but only if everything is good. Ignore theoretical maximum.

Maks have a thick lump of glass at the front and need to cool down, was yours left for 30 minutes to cool down? Preferably longer but people are impatient. They also attract dew/condensation.

They still need collimating at times and if you have only had yours a month then it may have arrived out of collimation. No idea how you collimate a Mak.

The shake is probably due to the high magnification 187x with the 8mm.

Is the mount firmly set, is the scope balanced.

[Cornelius Varley]

Using an 8mm eyepiece will give you 187.5x magnification. Although Skywatcher and many other telescope makers will state amximum magnification of 50x per inch aperture (254x in your case) 30x per inch is more realistic in the UK due to atmosheric conditions. 150x is probably the best you will achieve before the image starts to degrade. Other factors can affect the viewing quality, MCTs and SCTs need at least 1 - 2 hours to cool down before they give their best. Collimation can also be a cause, you can check if the telescope needs colimating by centring a star in the diagonal and defocusing untill the star becomes a series of concentric circles, if they are not concentric you will need to collimate the telescope. As yours is new it shouldn't need collimating and MCTs tend to hold their collimation well.

Unless your eyepieces are parfocal you will need to refocus the telescope when changing eyepieces.

The "dancing around" could be due to either simply knocking or touching the telescope or the telescope being moved by the wind. You can add weights (powertank hung from bungee cords or bags of sand suspended under the accessory tray to help stabilize the mount.

Peter

[John]

The "doughnut" that you are describing is what you should see when the scope is not focussed - it looks like that either side of correct focus. As long as the small black circle is in the centre of the bright circle (ie; not noticably off to one side) then the collimation of the scope is OK.

The image of Mars that you describe as a slightly out of focus disk sounds to me typical of the image you would see through a scope that has not had time to cool down fully. Maksutov's (the optical design of your scope) take quite a long time to cool down if bought from a warm house - up to an hour or more - and this is much more noticable when you try and use high magnification.

Another thing you will need, if you don't already have it, is a dew shield. The Maksutov design is prone to dewing because the front lens of the scope (called the meniscus) is directly exposed to the night air. Dew was probably not a factor in the issues that you desicribe though.

So have another go and give the scope a good long time to cool. I find removing the cap from the star diagonal, not putting an eyepiece in, and tilting the scope to point down (ie: eyepiece end up) allows the warm air to escape from the tube more quickly - it's warm air currents in the tube that mess up the image you see.

The stuff is expensive because you need precision made optical intstuments to get good views of astro objects - that sort of quality takes time and effort to produce.

Hope the experience gets better for you.

[hunterknox]

In my skymax 102 (maksutov) I see the same doughnut shapes when it's out of focus, so don't worry!

You should be able to make the doughnuts contract by turning the focuser. Keep going and they should become recognisable as stars. It's easy to go through the best focussed point and start making expanding doughnuts again, so just take it slow. If you still get smushy stars then check for dew: everything will look smushy and unfocusable if the front of your scope is covered in dew. A blast with a hairdryer will clear it, but prevention is better than cure. I've heard that a rolled up camping mat makes a fine dew shield.

[brantuk]

You will get a little shake on some higher magnifications. To reduce this make sure both axes are firmly tightened up (but not overtight) and that there's no undue movement on the tripod or mount. You can weight the tripod down to help reduce shaking.

It's worth waiting a moment or two for any movement to settle down after changing ep's

[Ptolemy]

Thanks all for your help and advice.

We think we haven't allowed enough for the "reality vs theory" aspect of the performance of the eyepiece magnification. We'd done the 50 x per inch of aperture calc (Skymax 127 (5inch) gives 250x) and the 8mm eyepiece gives us 187x so as you point out, by the time we factor in all the seeing conditions we're probably at the limit.

The doughnut shape is a perfect circle so think we’re OK on collimation - will do the star and concentric circles check just to make sure though.

We're just about OK on the cool down time - normally set up about an hour before use but we'll increase that. We've got a dewshield too. We hadn't come across tipping the scope down though so thanks for the hint about that John - we will give it a go

Do think we definitely need to stabilise the tripod more. It's the one that came with the scope so it's OK but quite light. We've also been standing it on the patio - will migrate to the grass (may as well get wet as well as cold feet ) and stick the legs in the ground to give it more stability.

We think as you’ve all advised that we need to get to know the scope more as well, getting the feel for the focus knob, seeing how it works in different conditions and so on - but so far we love it! Not sure what the neighbours make us though - middleaged couple shrieking with glee at the sight of the Moon at 11.30 at night

Really reassured by all your advice and that no one has come back and "it's terminal"! Also reassured that no one has said "rubbish eyepiece". As true newbies though we are still getting used to the terminology - what does parfocal mean in practice? .....the 8mm EP is parfocal but don’t see how that means the scope will need little or no focusing when changing from one EP to the other?

We do want to get some good quality eyepieces that are appropriate to our scope and we thought the Celestron X Cell range probably fitted the bill (especially as we need LER for glasses) . We've seen several others that get rave reviews and appear to give magnificent viewing but we think we could potentially be overdoing it for our scope. Any thoughts anyone about the Celestron range? or any views on good eyepieces for our level scope?

We've also heard that the star diagonal that comes with the 127 isn't the best and on the basis that the best view will only be as good as the weakest link in the optical chain (does that make sense? ) we will look at getting another one. Any recommendations?

We're really enjoying our new hobby but as beginners do find it difficult at times to know what's good/bad/indifferent. Many thanks in advance for your replies and fingers crossed for good seeing!

PS. This site is excellent and it's full of useful info and helpful folks - apologies if we're repeating questions - just point us in the right direction if we need to be somewhere else on the site, there are soooo many threads!

[LukeSkywatcher]

I'll just add my name to the list of people who see donuts (well just one donut) when my scope (SW130P) is out of focus. Its not a problem really because i tend not to observe with the scope out of focus.

[Ptolemy]

Hi Paul ....... what, not even as a newbie you don't know how relieved we are to find that "donuts=out of focus" and nothing more sinister starting out in astronomy is almost as bad as first time parenting.....but that's another web site altogether:confused:

..............anything useful on EP's or star diagonals would be appreciated

[LukeSkywatcher]

Haha as a newbie (i still am), i'm having a really good night if i remember to take the dust cap off the scope.

[Cornelius Varley]

Parfocal means of equal focus. If, for example, you had a number of the Celestron X-Cell eyepieces you can change the eyepiece for another X-Cell without having to refocus the telescope. I have a number of X-Cells and they are good value. Diagonals are one of the things that get replaced fairly quickly and a good diagonal will help. The latest Skywatcher Maks now come with a 2" diagonal I think, so it might be worth following suit and getting a 2" diagonal.

You will need this adapter Adaptors - Skywatcher Maksutov to SCT adapter to allow a standard SCT diagonal to be fitted to your telescope. After that all standard SCT accessories can be used.

Peter

[DannyL]

Im using a 127 on an eq3-2 and I get the same movement. In my case I have traced most of it to the joints where the legs are attached to the top of the tripod and no amount of wing nut tightening seems to help.

I am currently constructing a pier from the stump of an apple tree to get some weight into it.

As to views, I find the 10mm (150x) gives the most pleasing high mag views, though I do also have a 9mm and a 6.5mm none of which are 'quality' EPs

Best accessory was one I made from a pice of rolled up black card, a dew shield, made all the diff in the world and cost almost nowt!