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Astronomy is kewl

Which EP to get: 8" Dob, 10mm, 25mm SP

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Hello,

I just bought an 8 Inch Sky-Watcher Collapsible Dobsonian and it comes with its 10mm and 25mm Super Plossls (52 degree fov). I was wondering which ones I should get to expand my arsenal. This may include barlows. Currently, with the 10mm, I do not get "close" enough to Jupiter/Saturn, so I would like something more powerful. Also, I plan to see DSO's and planets. My budget would be $50-$100. 

 

Thanks. 

 

 

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6 hours ago, Astronomy is kewl said:

Currently, with the 10mm, I do not get "close" enough to Jupiter/Saturn, so I would like something more powerful

You may need a another scope?

As you increase the power on the telescope, the image appears closer, the field of view reduces and so does the detail, and when the detail is lost you could be right to think the image is blurry, sort out of focus, on some targets, thats how it appears to me.

If I take my scopes aperture of 200mm and realise that as a practical limit under UK skies, then I have to use an eyepiece of 6mm, but this is far from perfect for some targets,  as I  do find that images are sharper, and more detailed, if I go the other way i.e., lower the magnification, but this has the side  effect of reducing the size of the image, which kind of defeats what I'm trying to achieve?

What I have found though is by using 'better' eyepieces, if thats the right word, but more to the point, more comfortable eyepieces, with reference to more eye-relief, and a wider field of view (up to a limit) then the experience I have with the scope when the seeing and weather conditions allow, give me more  pleasure than using the original supplied eyepieces, but within the confines and limits of the telescope in use.

My only issue with the present telescope is the size of the image! its there' just wish it were bigger. A larger aperture gathers more light producing more detail, and I assume a larger image at the focal point. Take two scopes under the same conditions, Its my assumption that a scope  just 4" wider would provide a better image, with more detail at the focal plane, that would allow me to get 'that much closer to what I wish to see!' rather than 'that much closer' in distance terms, if you know what I mean. That said, I have tried to source a suitable scope for over 12 Months, and have concluded that for now, the 8" is still a great scope to have and behold, with the larger scope becoming a greater burden to use, transport  and store, but the rewards could be far better.

The best for me now is to travel to a darker site from where to observe, this scope is truly  a different beast, especially when you have the right conditions, and get away from street light pollution, yes the images are the same size, but the detail is better? The scope just works better at a different site, away from street light/man-made lighting, any lighting that affects your vision.

And as for eyepieces, whats in my signature are set to remain, they work very well for my needs, I've even tried more exotic premium eyepieces, but still favour what remains.

Welcome to the SGL.

Edited by Charic

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My first 'scope was an 8" Dob.  A member here recommended 6mm as about the maximum magnification I could expect while staying in focus.  I have a Skywatcher 6mm and a Starguider 5mm, both within your price range.  On exceptionally clear nights I can focus the 5mm in the Dob, otherwise the 6mm is max.  Both have good eye relief for me.  Whatever you buy I hope you find the investment worthwhile but, as Charic says, the seeing conditions make all the difference.

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The "problem" with planets and geting closer is that there is no eyepiece for it, now a 5mm, 6mm, 7mm and 8mm will do it but that is 4 eyepieces. What happens is that on one night when all just clicks the 5mm may work, the next the 5mm and the 6mm may not but, the 7mm might.

For planetary viewing I often say think of the Celestron X-Cel LX eyepieces, the reason is simply thay they have a 5mm, 7mm and 9mm. Fairly close step increments and one will work, just you have to find out which one on any particular night. The BST's are as good and often praised but the jump in those is 5mm to 8mm and that is a bit much. But I still prefer them.

Not sure of the cost and availability of the Vixen SLV's but they are available if a selection of close steps at the lower focal lengths.

Presently I would go no lower then 6mm, and you may find that that is a bit high on magnification, so may not deliver every night. An 8mm Paradigm/BST would wor just about every night, it is not pushing things to the extreme. But I suspect you will think 8mm is too close to 10mm.

Is the scope f/6 ??

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When I had an 8" dob I found 6mm (200x) was a pretty good maximum magnification. A 5mm (240x) will be useful on really good nights but the 6mm will be useful more often.

For a decent combination of cost, performance and viewing comfort I think the William Optics SPL 6mm are pretty good at £79, the Skywatcher UWA 6mm is also good at £49 as is the Baader 6mm Classic Ortho at £49.00 although the eye relief (distance you need to get from the top of the eyepiece) is close with 6mm plossls and orthoscopics which might not suit you.

On the used market you can pick these up for around 65% of the retail prices so it's worth keeping an eye out in the classified adverts here and on UK Astro Buy & Sell :icon_biggrin:

 

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I hit a sweet spot with my 8" Dob at 7-8mm, it will go to 6mm, but by 4mm it get unusable in the UK - if you elsewhere in the world maybe the seeing if better, but in the UK, I think you would be best sticking at 7-8mm.  I get a lovely view of the planets with a 15mm 2x barlowed Meade 4000.  NB.  You know you won't get planets to fill the EP don't you? - have you read this: 

At the very least scroll down and look at the pictures on the first page!!  :-D

Edited by JOC

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Alright thanks all for submitting your ideas on what to buy, but do you think that 5/6/7mm, 10mm, 25mm are enough? Should I get a lower powered one (35mm?) or is that not necessary? 

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2 hours ago, JOC said:

I hit a sweet spot with my 8" Dob at 7-8mm, it will go to 6mm, but by 4mm it get unusable in the UK - if you elsewhere in the world maybe the seeing if better, but in the UK, I think you would be best sticking at 7-8mm.  I get a lovely view of the planets with a 15mm 2x barlowed Meade 4000.  NB.  You know you won't get planets to fill the EP don't you? - have you read this: 

At the very least scroll down and look at the pictures on the first page!!  :-D

Thanks a lot for this

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I, too, have a "fast" 200mm Newtonian-Reflector - which is what your Dob is - and I'm happy with a 200X eyepiece, roughly a 6mm. And a 32mm would be nice for giving wider views of expansive objects - like the starfields of Cygnus, which is always a favorite of mine.

Best to cover all the bases. And to know your limitations!

Enjoy!

Dave

Edited by Dave In Vermont
syn.
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30 minutes ago, Astronomy is kewl said:

Alright thanks all for submitting your ideas on what to buy, but do you think that 5/6/7mm, 10mm, 25mm are enough? Should I get a lower powered one (35mm?) or is that not necessary? 

Personally I do like to have a low power and wide angle eyepiece available. A 30 or 32mm plossl does a good job in that role as you already have a 25mm. The Vixen NLP 30mm is a nice example for a decent price. In the 1.25" fitting a 32mm eyepiece can still give a 50 degree apparent field but at longer focal lengths the field narrows so you see no more sky.

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