no detail in saturn with 10" dobs - sorted now!

[rikyuu]

hi all,

this is my first post as I'm new to the forum and to astronomy, but leaning quickly! I recently purchased a Skywatcher 10" (1200mm focal length) dobs and have been looking at Saturn over the past few weeks. I was initially impressed to see it, but a friend reckons I should be able to see much more detail. The image is sharp and bright, but basically all I can see (with a 10mm lens or with a 2x barlow) is a bright yellowy/orange disc with bright yellow rings, no particular detail. My friend says he can clearly see the shadows of the discs and their separation in his 6" refractor. What is causing all the detail to be washed out with my scope? I've tried blocking off some of the aperture with a cardboard disc, the image gets darker but no clearer detail.

Many thanks for any help.

[Andrew1972]

try using a filter (polarizing/planetary). These should reduce glare and enhance details.

Sorry, forgot to say hello and welcome to SGL!

[George]

Have you checked your scopes collimation? Fine detail can be lost if its slightly out.

[ianporter13]

I'm guessing the scope is out of collimation.

have a look at this site for detail and examples.

http://legault.club.fr/collim.html

Ian

[Rob]

I agree Ian... check the collimation. Then look to pick up a Baader Nyodium filter to enhance the details

Rob

[barkis]

It depends what you expect to see. I am sure you know that Saturn is a gas planet, and the only detail is limited to zonal bands of subtle colouring. You may, if lucky see an odd weather feature, but as stated, unless your optics are precisely collimated, and seeing conditions are excellent, most of this will be denied to you. If the Cassini ring division is seen, you are in possession of a good instrument. As for the rest of the details, pray for excellent seeing. You have to persist too, this detail can be fleeting, and can appear and disappear as the earths atmosphere dictates.

Ron.

[russ]

You are very much at the mercy of the seeing. But also collimation of the scope and whether the scope has cooled sufficiently. Combine all 3 and your view will certainly be lacking any detail. You can do something about two of those things but the seeing is beyond our control.

I highly recommend picking up the Baader Neodymium filter. It really helps to pick out subtle planetary detail.

Russ

[rikyuu]

hi, thanks for your responses so far. I was suspecting the collimation, I have done it using a hole in the centre of a lens cap, I don't know how accurate this is, but stars appear sharp and bright - is this any indication? I have receiving one of the neobinum (spelling) moon and light pollution filters today so will try it when I next get chance. Probably best invest in a collimating device. The hardest part I found was collimating the secondary as it can move in 3 dimensions, in/out, twist and tilt!

[russ]

but stars appear sharp and bright

You'll need to defocus the star until you see a donut (big white disk with a black hole). The donut should be nice and symmetrical.

Nothing wrong with the lens cap method. I use an old film canister with a hole drilled through it. The hard part is working out what you are looking at and what needs to be where. Here's a link to a video tutorial on how to collimate a Newtonian like yours (he's collimating an Orion which is identical to your scope). It describes methods using a cap like you do and a laser. Hope it helps:

http://www.andysshotglass.com/Collimating.html

Don't forget to give the scope ample cooling down time, especially if you bring out of the house.

Regards

Russ

[John]

With all astronomical viewing you will find that the more you look, the more you see. What I mean by this is that, as you get more experienced with observing technique and the objects get more familliar to you then you will gradually to pick out more detail when the seeing allows. Saturn is a prime example of this.

It's entirely possible that an experienced observer with a 6 inch scope could see more detail than someone relatively new to observing with a larger scope. To get the maximium performance out of a scope needs optimum conditions and a resonably experienced eye.

So keep on using your scope and keep coming back to the same objects and spend more time on them - the finer details will start to emerge

John

[Astronut]

If it's any consolation, I haven't seen the Cassini division either in my 12" dob. I've checked and re-checked collimation until I'm blue in the face but I haven't had chance to do a proper star test yet.

I'm beginning to worry if the mirror's centre spot is at the optical centre (as it should be) so until I can do a star test (need a short FL eyepiece and good seeing - fat chance of that at the moment) I can only be 99.9% sure that it's well collimated.

[rikyuu]

Thanks for both links, shall particularly give the 'out of focus' star adjustment a try as I haven't used this method yet.

[Casus belli]

I've got a 10" dob too (Lightbridge) The Dobs are better for deep space objects than planetary work but occasionally I can see the cassini division, ring shadow and subtle hints of banding.

I view saturn every time I'm out with the scope and most nights I dont see much more than the rings and a disc. Collimation in these fast scopes must be spot on for any detail. I splashed out for a laser collimator and though expensive I think it was well worth it.

Conditions play a big part too. If you cant see much swap targets then try again later.

Where you will score over your friend is in the amount of moons you can see. You'll beat him hands down there.

Mars is even more difficult to see surface detail on with a fast scope but perseverance and collimation is the key.

Nebulae and galaxies are where the Dobs excel. Your friend may see more planetary detail but I bet he cant get 5 galaxies in the same FOV.

[rikyuu]

Well, it was a very clear night tonight so I collimated my scope with the out-of-focus star method and it seems to have worked pretty well. I still couldn't quite see the Cassini ring division on 240x mag, but I could definately see more detail and colour and at least 4 of the moons which I haven't seen before. The filter seemed to help too. I managed to get a few pics with my afocal digi cam (not easy with a dobs!) and stacked about 6 of them with registax, result attached. I know it's not great, but I hope it's reasonable for my simple set up, it looks better if you zoom out a bit!! Is anyone clever enough to tidy up the image a bit? And another image of some of saturn's moons. Looks a bit out of focus, but unfortunately with my set up I have to focus with the camera attached and whilst Saturn is whizzing by! Not ideal.

Looking at my mirror with a torch, I noticed it's quite dusty and looks a bit grimey. Will this have a big affect on the image? I suspect it's not been cleaned by the previous owner, so for about 3-4 years!

Thanks

(click to enlarge)

(click to enlarge)

[russ]

Excellent, that sounds far more promising

You may find a laser collimator a good addition to your arsenal. They make fine tuning the collimation in the dark a real doddle.

Don't worry about your mirror, they have to be really caked up before loss of performance. It's not worth the risk of damaging the coating unless you really have too.

Great image. My Saturn image was done the same way back in 2002 using an Orion XT10 dob and an Olympus C1 digicam.

Russ

[acey]

I agree with the other posts - if Saturn isn't showing enough detail then first thing to check is collimation, then make sure you're viewing in steady seeing, and take time to look for detail. Only thing I'd add is to think about your eyepiece. Have you tried using your friend's? A good eyepiece can make a big difference. But don't go thinking you need to spend lots on a new one until you've checked the other things.

Andrew

[Richyboy24]

i have the same telescope and each time i go out to observe i have a look at saturn and some nights are good, some bad. it's just the luck of the draw really!!

i'm fairly well collimated although some nights it's not spot on. last night for example i could clearly see a cloud belt and in between some dodgy upper atmosphere conditions i could see the cassini division quite nicely.

dont panic though just keep waiting and make sure your scope is well collimated and at the right temperature and you'll definately see the detail you're looking for!

[rikyuu]

Got a laser collimator on order, so that should make regular adjustments of the primary more easy. Took plunge and removed the primary for a clean, it had lots or dust, grease and hairs on it, I shall be VERY careful and have read plenty of advice about cleaning!! Also sent the zoom lens back that I received yesterday (Rigel 7-21mm) as viewing just wasn't comfortable, but decided to order a half decent Meade 4000 6.3mm plossill instead (only £35 of ebay). My current 10mm lens came with the scope so I expect it's a cheap kelner. Just waiting for some clear skies again, possibly Friday according to the weather (which is always wrong!).

Thanks for all the advice so far, I look forward to posting on the forum in the future.

(PS. well it's cleaned now, although I also read a lot of advice not to do it!! I took great care only to rinse and soak it so I hope all is well. It does appear to be gleaming now where-as before it has a definate film over the surface with losts of dust. I guess the proof is in the pudding when the sky is next clear!).

[Sam]

I think the cleaning the mirror can make quite a difference as my reflector arrived with quite a dirty mirror and I have noticed since cleaning it the views have been a bit better - collimation makes a huge difference as well. The other problem, already mentioned, is seeing. Sometimes seeing is just rubbish - not much you can do except persevere and wait for the glimpse of good seeing.

[russ]

Congrats on taking the plunge with the cleaning. It's the first thing i did when i got the 12" newt last year. Looked a bit dirty and when i took it out, found there was Golden Retriever hairs all over it, plus the usual grime.

I really didn't want to recommend you doing it though. Rather you made that decision. Wouldn't want to be responsible for you tarnishing the mirror.

I think you'll find the laser a great help. Some people don't like them but i always found it a great asset.

Fingers crossed for some clear skies so you can put all this to the test.

Regards

Russ

[Kaptain Klevtsov]

One thing I found with the standard 10mm Skywatcher eyepiece is that they work just as well if you use a centre punch and knock all the glass out before using them. (Joking, don't try this at home kids, you'll end up with glass in your eye ). The one that came with my 'scope is rubbish. The 20mm or 25mm ones are better, so you'll see the detail but have a smaller image to look at.

I expect that when your new eyepieces are used you'll get a lot better result.

Kaptain Klevtsov

[rikyuu]

One thing I found with the standard 10mm Skywatcher eyepiece is that they work just as well if you use a centre punch and knock all the glass out before using them. (Joking, don't try this at home kids, you'll end up with glass in your eye ). The one that came with my 'scope is rubbish. The 20mm or 25mm ones are better, so you'll see the detail but have a smaller image to look at.

I expect that when your new eyepieces are used you'll get a lot better result.

Kaptain Klevtsov

It that case I'm looking forward to getting the Meade EP even more then! Can't wait to compare them.

I used the laser collimator tonight to recollimate after the wash. How easy is it with that!! It's so much quicker and found that it more accurately positions the secondary to view the whole primary than I could by eye. It allowed much finer adjustments. Also I can't reach the back of the dob whilst looking in the focuser so it's ideal to allow fine adjustment of the primary too. I went for the Revelation collimator, although cheaper it seems to be a substantial bit of kit, very solid metal casing. I hope it's done the job.

[Cloudwatcher]

Well,you have had a good response from the techno-boys which I'm sure is very helpful. Never having owned a 'Dob' I'm not qualified to comment so having read in your post of the 1st April ...... "Is anyone clever enough to tidy up the image a bit?" ........... I thought I'd contribute under that heading. Unfortunately it appears I'm not clever enough.

There are some strange diagonal and horizontal lines on the original that show up more on enhancement (see first image) and as I try to maintain the integrity of an image I left these in but they did tend to spoil the result. So,in the interests of a reasonable 'picture' I went in heavy handed with the Blur tool.(see second image) Not a prize winner but it's a bit brighter and some detail is visible in the rings if you squint.

Cheers

CW

(click as usual)

[rikyuu]

Wow, I am seriously impressed with those images, thank you for spending time to do them. At first I though they must have been from someone else's scope before I read your post! I've read bits of info about tidying up images in PSP and photoshop and have used these packages in a limited way some time ago. Would you be able to give a brief summary of the techniques you tried (if not already posted elsewhere). I presume it was tools like 'shapen mask' etc.

Any ideas what the lines could be? There is a scratch just visible on the primary mirror, would this cause such a line?

PS. apparently not according to my optics expert friend, probably just dirt on my lens or camera lens

PPS. got some wonderful viewing of Saturn during a gap in the clouds tonight, despite a slight haze. Used my new Meade 6.4mm with a 2x barlow (375x) and despite only getting about 5secs before it went out of shot each time with the dobs, the image was pin sharp, I could see some red banding and just glimpsed the Cassini division, I think.

Attached is a single photo of Saturn, not stacked or processed, with an Afocal standard digital camera, 1/8th sec, ISO800, F5.4. It doesn't quite do justice to what can be seen by eye (which is much sharper), but I'm pretty pleased with it.

(click to enlarge)

I am seriously thinking about building an equatorial platform and have drawn up the plans. I've purchased the bearings and just need to get some wood. Even if it's not accurate enough for long exposure imaging, I think it would be very usefull just for extended viewing by eye. And it won't cost too much in materials. Maplins also do 1:1000 ratio motors and it's easy to make a PWM controller. I'll still have the point and shoot ease of the dobs, but once pointed at least I'll be able to view for longer at high mags.

Unfortunately though, I also have to keep on top of the home improvements too, at least to keep the other half happy!

Now I've got the viewing sorted, I think this thread is now moving more onto imaging! I think I will post future photos there.

Thanks Lee