Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

stargazine_ep33_banner.thumb.jpg.75d09b4b1b4e5bdb1393e57ce45e6a32.jpg

Brainstorm

10" Skywatcher Dob, no better than my Orion 6" EQ

Recommended Posts

After reading a few posts regarding upgrades, it has often been recommended to upgrade by about 4" a time for the best 'wow' factor. However, my new Skywatcher 10" Dob doesn't seem any improvement over my Orion 6" EQ.

In fact, Peiades looked 'dimmer' in the 10" dob, Andromeda about the same (an oval fuzz), Jupiter was useless, I may as well been looking at a white ball (absolutely no 'stripe' definition, compared what can be seen through the Orion scope). Ironically, Orion was about the only object that showed up better in the Dob. Although I couldn't find any other nebulosity or galaxies in the sky with the Dob (I tried looking for the Horsehead Nebula, but nothing).

I'm not disappointed, just surprised that a 10" telescope (much bigger than the little 6" Orion), is not bringing in any better results.

Share this post


Link to post
Share on other sites

I'm surprised you have found no improvement with a larger aperture. I recently changed from a 6" to an 8" and the difference was quite amazing. Have you compared the views simultaneously? Presumably the dob is clean and collimated?

Share this post


Link to post
Share on other sites

A 10" scope will show much brighter images than a 6" - you should check your collimation and adjust if required. Also cooldown will take longer in the 10".

Share this post


Link to post
Share on other sites

You're dob is f4.7 and will be less tollerant of low quality eye pieces - so it's worth investing in some good glass. As Pauly says - collimation will have a big effect too so make sure you have it right. For the moon and planets you may need a filter cos they are very bright. Be sure you are looking high up and not being confused by the seeing at lower elevations. If you're in a light polluted area make sure you have stray light blocked out with a dew shield (and/or shroud if it's an open truss dob). And remember dobs work best in total darkness.

Get all that right and you will be well on for much better, contrasty, brighter, viewing which will way surpass the 6". Oh and M31 will allways be a fuzzy blob in anything smaller than 16"+ apertures, where better definition just begins to show. :)

Edited by brantuk

Share this post


Link to post
Share on other sites

If jupiter was a "white ball" in the 10" then i would say you have a problem with the 10

Share this post


Link to post
Share on other sites

I would also add that you would be lucky to see the horsehead nebula at all, i used to 12" newt in the past and couldnt see it, i believe (although i could be wrong), that to see that you really need to image it as that gives the best results. Also i think you would need to use filters when looking at it due to the bright star Alnitak.

Share this post


Link to post
Share on other sites

I agree - the Horse Head is an LE camera only object - far too faint to be seen in most scopes - possibly larger dobs of 20"+ but not really sure about those :)

Share this post


Link to post
Share on other sites

I've seen the Horsehead in a 12" f5 from a dark sky site in northern Victoria.

Share this post


Link to post
Share on other sites

Wow Merlin - that gives me hope for my 12" then - very glad to hear that :)

Share this post


Link to post
Share on other sites

You have to remember that the images you see of the Horsehead make it look big and bold, whereas visually it's just a very small notch against the brighter background.

Practise........

Share this post


Link to post
Share on other sites

do your scopes have the same focal length? if not then using the same eyepiece in one then the other will of course create a dimmer image in one than the other (potentially - aperture of the 10" might create no difference of course.)

I suspect with Jupiter it might be cooling time or collimation that's the culprit but as others have said a filter might help. If you have a Baader Neodymium then this works well on Jupiter.

I have no doubt that you'll see a big improvement in light gathering with the 10" but hubble images they will not be with any scope.

Share this post


Link to post
Share on other sites

I used to have a Skywatcher 250mm f1200mm. There was fine detail visible in Jupiter's belts. The 6" should not even come close, so I'd say you have a major problem.

Share this post


Link to post
Share on other sites

This really does sound like a collimation and cooldown problem.

There are lots of online tutorials on collimation, have a look until you find one you can understand, some are very complex.

For cooling, you either put your scope out and wait, or fit a fan. Storing the scope somewhere cool helps a lot.

Or how about contacting Astronomical Society of Edinburgh most clubs are willing to help.

Hope you sort it, Ed.

Share this post


Link to post
Share on other sites
Wow Merlin - that gives me hope for my 12" then - very glad to hear that :)

I've seen the Horsehead in a 9x50 viewfinder before <here>.

You need dark, clear skies and big exit-pupil. I was nr. Bideford at the time. I was very excited to find it...

Share this post


Link to post
Share on other sites
This really does sound like a collimation and cooldown problem.

And you need to check the Jet Stream conditions too.

With this 10" scope under good conditions with the right eyepiece, the surface of Jupiter should appear very slightly grainy - as if it were made of silk - and you should also be able to detect wisps of cloud, moon shadows, and jagged detail at the edge of the bands.

Share this post


Link to post
Share on other sites

Collimation, cool-down time, poor seeing, comparing at different magnifications, light pollution, all these things could contribute.

I have both a 6" f/5 and a 10" f/4.7 and the view through the 10" is miles better, when everything is set up right and the sky conditions are favourable.

Faint fuzzies are always faint fuzzies and planets are always very small through any scope I have looked through.

Share this post


Link to post
Share on other sites

Thanks for all your replies. I drove out to the Scottish Borders to ensure absolutely no light pollution, and the telescope is 'bang on' collimation.

The eyepieces I used are the Orion Plossl's (25mm & 9mm) that I got with the 6" Orion, and I also have a Japanese Meade 6.4mm Plossl (which was totally useless).

I'm not sure what the 'cooldown' issues people are referring to? Could it be that the mirrors may have gathered condensation after being in a warm car? And if that is the case, how long does it take to de-condensate them?

On the bottom of the scope under the primary mirror, it appears there's a space which would possibly fit a computer case fan.. Would it help if I fitted one and attached a 9v battery?

Also, if there is a 'problem' with my telescope, what could it be? There's not much to go wrong with these things, surely? I mean the mirrors are immaculate and well collimated. I would have presumed that's all there is to it...

Where can I find more info on 'cooldown', and how to deal with it?

Edited by Brainstorm

Share this post


Link to post
Share on other sites

I recently moved from a 6" to a 10". I thought the difference was amazing, more especially on some objects more than others. Funnily enough, I got up early this orning for some 'dark' viewing, but before I went to bed I whipped out the 6" just for a peek at Jupiter. The scope is well collimated and I was frankly surprised at the difference in Jupiter. Very difficult to obtain the level of detail I have grown used to over the last few weeks. I have grown used to spotting the GRS and I could tell last night with the 6" I wasn't going to make it, wheter it was there or not. If you're not seeing a difference, something is not right. Another example is Andromeda, with the 10" M32 and M1somethingsomething (you can tell I'm an expert) are pretty easy to spot, not so in the 6"

Bart

Share this post


Link to post
Share on other sites

A fine piece of mesh or a Ronchi grating.....

Held over the focuser while focusing on a bright star...

This will immediately show if there are issues with your optics/ scope - it also shows thermal currents associated with cooling down.

A good investment, well worth having in the box.

HTH

Share this post


Link to post
Share on other sites
A fine piece of mesh or a Ronchi grating.....

Held over the focuser while focusing on a bright star...

This will immediately show if there are issues with your optics/ scope - it also shows thermal currents associated with cooling down.

A good investment, well worth having in the box.

HTH

I just looked on ebay for a "Ronchi grating", but it returned zero results. What is it, what do I do with it, where do I get one, and what exactly am I looking for once it is attached to my telescope? :)

I'm not sure what sort of 'fine mesh' to buy either, there seems to be a lot of different types of 'fine mesh' on ebay, from gardening resources to fishing nets. Or do I get this specifically from dedicated astronomy shops?

I'm still stumped about this 'cooling' issue too, can't find what it is exactly, or how to deal with it.

Seems I've opened a large can of worms by buying a bigger scope.. ;)

Edited by Brainstorm

Share this post


Link to post
Share on other sites

A grating with 100 to 150 lines per inch is normally called a "Ronchi" grating.

You can achieve similar results with a fine mesh - something like a tea strainer, fine fly mesh etc.

While the mirror is cooling down towards ambient it tends to change its shape and is not as optically accurate as is it will be at a steady temperature....

Share this post


Link to post
Share on other sites

My 10" scope needs about 40 min to cool down after I take it outside before it gives the sharpest views at high magnification. You can start with a low power eyepiece straight away as it's cooled down a bit by the time I have checked the collimation and made a brew.

Being a bigger lump of glass, it takes longer to reach ambient temperature than the 6" does.

Edited by RikM

Share this post


Link to post
Share on other sites

Could it be the eyepieces?

Plossl's start to "fail" at around f/5 and being at f/4.7 perhaps what is being asked of them is too much.

I have no idea how good or bad Orion plossl's are.

An f/4.7 scope will have a curved primary image, it will not be flat. Also for the curvature on the actual mirror you may be getting coma.

You may have to experiment with additional equipment. Sky's the Limit and TS do Flat Field eyepieces that are intended for these fast newonians - I believe thay compensate for the curved image. Others may be able to say if a coma corrector is useful.

Edited by ronin

Share this post


Link to post
Share on other sites
A grating with 100 to 150 lines per inch is normally called a "Ronchi" grating.

You can achieve similar results with a fine mesh - something like a tea strainer, fine fly mesh etc.

While the mirror is cooling down towards ambient it tends to change its shape and is not as optically accurate as is it will be at a steady temperature....

I have a tea strainer, do I put this over the empty eyepiece focuser, or do I have the eyepiece attached, if so which size eyepiece is optimal?

Secondly, what would I be looking for, and how would I know what I see is a problem or normal? Do you know of any illustrations available online? Or any books that might help with this?

Sorry for all the questions, this is all new to me.

Edited by Brainstorm

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.