Big problems with a new 12" dob

[iceman (Mike)]

You're on the central coast? Excellent! Come to our meet on the 8th December. I've got a 12" newt and I absolutely love it.

I can easily take a look through yours and tell you if there's anything wrong with it, and I can help you collimate it and/or check collimation.

[Satchmo]

Originally Posted by Terran

Note that even though the collimation is closer, the focuser ring is way off no matter how collimated it is.

Terran

Your collimation looks almost perfect .

Note how the refelection of the focusser/eyepiece is well centred in the reflection of the primary mirror and all is centred on the actual base of your focusser. The reflection of the eypiece base looks slightly offset in the outline of the secondary because of 'secondary offset' needed in an F5 scope. It will always look this way when you have correct offset. The fact that the physical edge of the diagonal mirror is a little offset is of no consequence to your image sharpness, that only has a slight effect on the eveness of lighting at the edge of the field in long exposure photograpghy.

You probably owe it to yourself to read up more about collimation so you can undersatnd what you are seeing when you look down the barrel.

When you look at a star image and slightly defocus it in and out , does it look round and symmetrical with the secondary shadow centred ? That is about all you need to verify your collimation.

Perhaps the problem is one of your expectations of what you will see on the Moon. You need to get together with another amateur and look through another scope. Why not look for your closest astronomy club.

Mark

[tileys]

I'd concur with the post that said check out other scopes - preferably in the same location you're viewing from so you can compare.

I too had little frame of reference when I bought my 8" Dob recently (also my first scope). I was concerned about the colimation issue - especially since I was buying a scope that had little after sales support and was relying on the collimation direct from the factory. I was lucky - the out of focus 'bokeh' is well centered around the centre point when I defocus on a star or planet.

I have done all my viewing so far from a garden in a North Western Sydney suburb and even then the views of Jupiter last night - low in the sky and towards the areas of higher light polution (for me) - were stunning. A bit shimmery at times but occaisionly I'd get enough to see two distinct bands of clouds and the four moons. That's just with a 9mm eyepiece with no Barlow lens at all i.e. magnification about 133x. The moon is amazing through this scope - you feel like you can reach out and touch it - it looks like a concrete football I've also viewed the Orion Nebula and the dust clouds are well defined. The other night I viewed M41 - a nice open cluster fairly low in the sky. Mars is a bit small in my 9mm - really need a bit of magnification.

I think you need to double check with other scopes and get someone experienced to go through some fine tuning with you at your viewing possie (or theirs) - don't give up though - I'm sure you're close to getting some great views - a 12" improvement over an 8" will give you more detail and resolution (my scope is from the same manufacturer I believe (Guan Sheng Optical)).

All the best,

Steve

[tileys]

...something I've found is that I need a bit of extension to get a decent focal range - i.e. don't seat the eyepieces all the way into the focusser before you tighten down.

Steve

[janoskiss (Steve H)]

Originally Posted by tileys

...something I've found is that I need a bit of extension to get a decent focal range - i.e. don't seat the eyepieces all the way into the focusser before you tighten down.

... you mean your EPs don't quite reach focus and need to come out a little more than the focuser allows. That's more so with the 8" GSO Dobs - unlikely to be an issue with the 12".

You can try raise the mirror by undoing the collimation screws some of the way (and then recollimating of course) and that should get you to focus without having to pull EPs out of the barrel.

[tileys]

Steve,

Thanks for that - thought I might need to get an extension tube at some point.

I don't mind the situation for the time being - only really an issue on one of the EPs from memory.

Since the scope is collimated well and I don't have a tool to assist with recollimation I might leave it as is for the time being... and make a note to extend the secondary mirror out later down the track.

As a side note - will Uranus resolve to a disk at appx 133x mag ? or will it just look like another star ? I'm trying to 'tick off' the planets

Cheers,

Steve

[erick (Eric)]

Originally Posted by tileys

Since the scope is collimated well and I don't have a tool to assist with recollimation I might leave it as is for the time being... and make a note to extend the secondary mirror out later down the track.

Please get a tool and practice collimation. Well worth doing this.

Steve (janoskiss) means the primary mirror.

[cahullian]

Terran it might be your ep's that are the problem. Doesn't matter how good the scope is if the ep's are second rate you will never get a great view of anything. Have you gave them a clean? A 9mm ep with a x2 barlow especially a cheap barlow in never going to do your scope justice.
You will get lots of different tips on how to clean ep's but a cotton bud and windex should make it better.

Gazz

[tileys]

...collimation...yes, I should look at getting that laser collimator the next time I'm in Andrews...

OK - thanks for clarifying the point about the PRIMARY mirror. So that will shorten the focal length slightly ?

Cheers,

Steve

[erick (Eric)]

Originally Posted by tileys

OK - thanks for clarifying the point about the PRIMARY mirror. So that will shorten the focal length slightly ?

As I understand it, the focal length doesn't change - that is dependent on the physical characteristics of your primary mirror. But it does move the point at which the rays from the primary mirror, bounced off the secondary and through the focusser, come into focus, to a point further away from the tube. This means that your eyepiece can now be placed further away from the tube to do its magnification job. So an eyepiece that didn't come into focus when your focusser draw tube reached its maximum in-travel, may now come into focus before that position is reached.

[Terran]

My chances are very thin for being able to take this telescope anywhere often. I don't have a way to transport it, and the only chance I have is on a rare occasion through my brother, who isn't nearby and works night-shift anyway. I would really like to take it down to an observing night, but that doesn't look like a possibility for a while. I might be lucky though, who knows.

Regarding collimation - comparing it to Bintel's collimation and some important info I've recieved here, it SEEMS that the idea I had in the first place was right and very simple, and my original manual collimation was fine. I should be able to make it better than it currently is, especially with my new sight tube. If I can get this scope to work, I'll consider unscrewing the eye-hole piece from my sight tube so that its just an empty tube with a crosshair, then taping a webcam to the sight tube and putting it into the focuser. It seems a lot easier to get a stable and centered view through a webcam, and you can adjust the screws while watching its alignment on a computer screen.

Sorry for even more questions -

1. Are faint shadows in a pitch black environment all I can expect from this thing? Bintel told me I should easily see structures everywhere, yet I see nothing, not even the faintest outline of a shadow, nothing at all. Just a few more stars than the finderscope. My eye pieces all say Bintel on them. I have a 32mm wide view, and plossl in 9mm, 12mm, and 15mm. I dont know how good they are, but Bintel did recommend the 12mm for image quality reasons (cost about $40 I think). The quality and brightness of Orions nebula is about same on all eye pieces.

2. I don't have issues with lights close by affecting my views of the dark. My eyes adjust fast and it's not a problem. I've been covering my head in a shroud while viewing anyway to make sure no other light is getting into the eyepiece. But the light pollution from my suburb (The Entrance) as well as nearby suburbs, do glow up the horizon like a full moon does. So using a full moon as an example - Should the glow from a full moon make it impossible to see structures in the sky?

Also, there wouldn't be anyone here who lives at or nearby The Entrance would there? Some first hand comments on the light pollution around here might "clear" some things up. I have no reference to light pollution levels and how much it interferes with the view.

[janoskiss (Steve H)]

tiley, sorry, correction to what i wrote earlier: If you haven't got enough out-focus, you need to tighten the primary collimation screws, not loosen them. This will move the primary mirror further down the tube (away from the focuser).

Terran, sounds like you are not using and/or setting up the scope correctly. Your finder is probably not aligned for starters... though it's hard to tell exactly what's going on without seeing the scope. I suggest you follow up on Mike's and others' offer and go along to a viewing night. Take your scope if you can so others with more experience can check it out.

[tileys]

Terran,

I imagine the Entrance has some light spill but not as much overall as a suburb so close to Sydney as mine is. The light pollution you get from a full moon destroys any great visibility for quite a distance around it. In fact - you get so much light coming off the moon (luminescence/magnitude rating at -13 ?) that I can find it in the sky without using a finder and using a 9mm eyepiece - just by navigating towards the brightening glow. I found it hard to pinpoint +6 magnitude objects even a few 'moon spans' away.

There's a large image you can download of the light pollution in Australia and you can apply it to Google Earth as a layer (it's a bit fiddly to get it to scale and lined up though). - see http://www.iceinspace.com.au/index.p...63,404,0,0,1,0

Cheers,

Steve

[erick (Eric)]

Terran

You need a visit from a friendly amateur astronomer. Someone relatively local to you will surely respond if you ask. As you describe it, you are not getting the results you should be getting - something is not right, somewhere - but it's hard to identify the problem without getting hands-on. However, we are running into full Moon so galaxies and nebulae are more difficult for a while - but your eyepiece should be full of stars!


And tileys, I was back to front on the previous outfocus/infocus discussion, sorry, but the eyepiece will "follow" the primary mirror - futher out of the focusser, if the mirror is moved up the tube and futher into the focusser if the mirror is moved down the tube.

[cahullian]

Terran I have the 8" version of your scope and it viewing objects are in their thousands and yours should be too. The 12" is a bugger to collimate I have seen seasoned amateurs tinkering around for ages and still not be overly happy with the result. Keep trying though because once you get it right you will be stoked.

Gazz

[anthony2302749]

Hi Terran

Here is some info that may clarify you understanding of light pollution and its effects on observing from the suburbs.

I live in Melbourne and of course we have how share of light pollution, ask any IIS's living in Melbourne. The effect of light pollution will rob you of some detail in deep space objects. For example I was trying to obseving the Ringtail/Antennae Galaxies in Corvus (this was during new moon), the mag of these object is 10.3 : 11.2 well in the reach of a 12.5" reflector but due to several factors such as light pollution, thin high cloud which traps light in and reflects it back towards the ground, pollutents in the air (and as you have describe it can be like a full moon) I was not able to discern any detail what so ever. It took me three whole night of observing until I was able to view this object, transparence was a lot better and I was able to see a faint centre to this galaxy but no spirl/tail structure.

I have had other observing session which yield the similar results you just have to pick your nights anyway just summing up light pollution can have an effect on what you can see through a telescope.

Originally Posted by Terran

2. I don't have issues with lights close by affecting my views of the dark. My eyes adjust fast and it's not a problem. I've been covering my head in a shroud while viewing anyway to make sure no other light is getting into the eyepiece. But the light pollution from my suburb (The Entrance) as well as nearby suburbs, do glow up the horizon like a full moon does. So using a full moon as an example - Should the glow from a full moon make it impossible to see structures in the sky?

[astronut (John)]

I hate to disagree Gazz I have a LB12".
I collimate the secondary before leaving home. The scope is assembled on site, and then it takes me approx 1 minute to collimate the primary.
I use the Orion Cheshire E/p from Bintel.
With the optics being the same in the LB and solid tube G.S.O's (mine are great) the other things that can be ruining the views are poorly figured primary or secondary mirrors.
The main thing is to eliminate each step as the culprit, it won't take long.
Good Luck!!

[janoskiss (Steve H)]

Originally Posted by cahullian

Terran I have the 8" version of your scope and it viewing objects are in their thousands and yours should be too. The 12" is a bugger to collimate I have seen seasoned amateurs tinkering around for ages and still not be overly happy with the result.

I had both scopes. The 12" is not that different i.t.o. collimation. The main difference is that the springs sag more so you need to rely on the locking screws more. But even a fairly rough collimation is enough to give a reasonable view of things like M42, eta Carina.

[Aster]

Originally Posted by Satchmo

Hi Alex

Emails are not a reliable way to deal with serious issues: Bintel may receive hundreds each day and its easy for just one to get lost or overlooked.

Why not just just get on the phone and speak to them in Sydney directly. I've been dealing with Bintel for 20 years and always found them dedicated, and an experienced bunch ( mostly keen amateur astronomers ) and heart always in the right place.

Look out for a PM from me about the old days at AOS

Mark

Hi Mark,

This little story is not even half of my experience with Bintels since March this year.

Roger Davis, of Melbourne Bintel received a copy of the email I send to Sydney acknowled receipt and I have spoken personally with him on numerous occations about that subject. Even He can not get a satisfactory answer from Sydney. As I purchased the Instrument from Bintels Melbourne Store I thought Melbourne Management would and should be quite capable of taken care of this problem. But every time I ring Bintels in Melbourne I get the same answer, "Haven't received any reply from Sydney as yet"

But maybe I have to start wasting my money on STD calls, as some others have done, only to be told that Mike Smith is not available.

Looking forward to your PM

[Satchmo]

Terran

Reading back through your posts , and assuming your sky is not too bad up at the Entrance , it sounds like a classic case of too high expectations, and not enough appreciation of the subtle art of observing. Maybe if you had worked your way up from a pair of binoculars to say a 6 " scope, you would be celebrating what you can see, rather than stressing out that you can't see stuff just like the photos, or whatever your problem is. If you don't think you have the patence then just sell your scope, astronomy is not for everyone...

Relax, spend some time to appreciate the subtleties of what you can see and the Universe will reveal itself, in its own way in its own time. Don't be in such a hurry. Sorry to sound harsh, but theres been too much molycoddling in this thread allready IMHO .