Which Dob?

[Geoff Barnes]

Hi everyone,

I'm about to take the plunge and upgrade from my current dear old Celestron C4R to something altogether more serious.

I'm inclined towards either a 10 inch or a 12 inch Dobsonian, either of which would introduce me to a whole new world (universe?) from what I've seen so far.

I was really inspired by John's description of seeing the Horsehead Nebula a while ago for the first time with his 12 inch Dob, and would love to see it for myself.

So my question really is simply do folks think I'll be able to see it with a !0 inch Dob or is a 12 inch the minimum required to see it without straining my eyeballs?

Many thanks in advance.

Geoff.

[Stu]

Hi Geoff,

Welcome to the forum.

I think we would all love to see the Horsey, but don’t underestimate how hard it is.

My first question would be how good are your skies at home or can you get the scope somewhere decently dark? It is not so much a question of the scope, I’ve heard of people seeing it in smaller scopes, the darkness and transparency of the sky is a major factor. Even 16” or 18” is no guarantee.

I don’t mean to sound offputting, just setting realistic expectations.

[Geoff Barnes]

Thanks Stu

Yes, it's always hard to quantify just how dark our skies are isn't it.

We live on top of the Dandenong Ranges about 50kms east of Melbourne, Oz. Whilst our area has no street lights and we have no near neighbours, there is still a fair bit of light pollution from Melbourne itself (it is a huge city these days). We do however have the advantage of being 500 metres above sea level which must help with the clarity of our skies.

I'm really jealous of the incredibly black skies at my mothers house up on Bodmin Moor in Cornwall, you feel like you can reach up and touch the stars!

Ours are nowhere near that dark, but probably a lot darker than most peoples.

Having come from Southampton I know only too well how hard it is to get a dark sky there.

[Stu]

Didn’t realize you were down under. That does change things because although Orion is upside down there, it is also significantly higher than here so you are looking through less of the atmosphere. Also, if Melbourne is to your east, then I guess looking south towards where the objects are at their highest should be a little better?

If John can get it from here with 12” then I think you stand a chance from a good dark site near you. Aperture always helps, so go as big as you can manage, and have realistic expectations as to what you will see. I think Olly Penrice gave a good description of it, but it’s a bit like spotting a black cat in a coal bunker  

[Geoff Barnes]

We're lucky down here in that this year all of the four main planets are high in the sky for us to view, one of the main reasons for me wanting to get a big scope very soon. Hopefully someone on the forum who has a 10 inch Dob can give their opinion on seeing the Horse. Size is not really an issue, just the cost difference.

[Ben the Ignorant]

My club had a ten-inch newtonian for many years, and I now have my own twelve-inch dob. I never saw the Horsehead because even our "countryside" site is not good enough, and I didn't buy an H-beta filter since its use is too limited. But for general observing the larger scope shows everything better, especially galaxies. They were fairly good in the 250mm scope, more structured in the 280 Schmidt-Cass that replaces it, and downright obvious in the largest of them.

Difficult targets like the central star in the Eskimo nebula are no problem, thanks to the good polish and almost nonexistent spherical aberration. Lunar detail is way too plentiful to draw, and even difficult to grasp with the eye unless you focus on a very little region, and look carefully for a long time. Sunspots with their penumbra are like sunflowers. All the brighter galaxies are visible in detail from the city. The scope is a GSO.

[Red Dwarfer]

Sounds like perfect astronomy conditions down there . I recently went from 8 inch to 14 inch Dob and the size difference is considerable . Going with the biggest Dob you can manage is probably the best advice .

When I finally figured out how to fit the feet to the 14" last night ( the screws come out and go in the opposite way ) I took a pic beside the 200P and several other scopes for scale and size comparison - might be useful to anyone who reads this 

[LukeSkywatcher]

I'd be more concerned about the size of the Dob and whether I could handle it as opposed to being able to see an object. If you have no issues with moving a big Dob around, then I'd say the bigger the better. 

[LukeSkywatcher]

1 hour ago, Red Dwarfer said:

Sounds like perfect astronomy conditions down there . I recently went from 8 inch to 14 inch Dob and the size difference is considerable . Going with the biggest Dob you can manage is probably the best advice .

When I finally figured out how to fit the feet to the 14" last night ( the screws come out and go in the opposite way ) I took a pic beside the 200P and several other scopes for scale and size comparison - might be useful to anyone who reads this 

Bottom right of image. The SCT/MAK. Is that 8"?. Very nice collection. They all look like they really belong together. 

[Red Dwarfer]

23 minutes ago, LukeSkywatcher said:

The SCT?. Is that 8"?

Thanks - It`s a 127mm/5" 

[LukeSkywatcher]

Ah OK. I can see better now that's its not quite as wide as the 200. I was originally thinking maybe 150mm.

[NGC 1502]

3 hours ago, Geoff Barnes said:

Hi everyone,

I'm about to take the plunge and upgrade from my current dear old Celestron C4R to something altogether more serious.

Hi Geoff.  It’s tough to be sure whether or not you would be able to spot the Horsehead with a 10 or 12 inch Dob under a great sky.  But what is certain is that either would be capable of seeing much fainter than your 4 inch refractor. However, a CR4 would be a good scope to compliment a larger reflector, so if it were myself, I’d hang on to the 4 inch if you can. I like the way refractors give more pinpoint stars. My 10 inch Dob goes a lot fainter than my elderly 80mm f11.4 Vixen, but I like the way the refractor resolves double stars in particular, less resolution but a very pleasing view indeed, and less affected by poor seeing.

Ed.

[Geoff Barnes]

Thanks for all your replies guys.

It does seem that I.m going to need to find slightly darker skies than we have here at home to stand a good chance of seeing targets like the Horsehead. The valley down behind our mountain is largely unpopulated, just a scattering of villages, I'll do a bit of investigating, see how dark it is down there. It would take me further away from the city light pollution for sure. 

If Stu thinks people have seen it with smaller scopes (obviously under very dark skies) then I'm hopeful that a 10 inch Dob will suffice. 

I think I'm right in saying that John saw it from his back garden in Somerset, so Im quite hopeful of getting good results from here.

Getting clear skies here is a lot easier than back home in Blighty that's for sure. Would you believe we've only had three proper days of rain since the end of January! I feel your pain over there with your lack of clear skies believe me, it would drive me mad!

[Geoff Barnes]

Following on from talk of sky darkness, I found this handy website which allows the user to click on any point on the map and instantly see the Bortle Index.....https://www.lightpollutionmap.info/#zoom=2&lat=5223693&lon=-373594&layers=B0FFFFTFFFF.

For my particular location I'm in a Bortle 4 region, so it loks like I need to head 50km further east to get really dark skies.....

[John]

Hi Geoff,

I'm glad my post on seeing the Horsehead has inspired you to consider a larger aperture scope. My typical skies here vary between Bortle 4 and 5 I think. When I did manage to glimpse the HH neb (note the "g" word there !) it was under the best conditions that I'd seen here for quite a while - possibly for a year or more. I've tried many times with the same equipment and not seen a hint of it - but I tend not to report those !

My 12" dob has provided me with my best observational experiences in this hobby however and these have come from the many other targets within the grasp of the 10/12 inch aperture and also that such apertures deliver improved views of objects which can already be seen with smaller aperture scopes while remaining relatively easy to handle instruments.

As an example, the brighter globular clusters with a 10/12 inch aperture and, say, around 150x magnification do (to my eye at least) resemble the images that you see posted of them with star resolution extending right into the heart of the cluster creating an almost 3D effect.

Another example is a galactic group such as Markarian's Chain in Virgo where a wide field low power eyepiece coupled with a reasonably dark sky can deliver a single field of view of 10 or more galaxies - a gorgeous sight !

So, provided that you can store and manage the much larger size of scope, I'd certainly recommend something in the 10/12 inch class, even if the Horsehead never does show itself. There are many other treasures that will be within your grasp 

[25585]

Seconding John, moving to double figure apertures reveals a much more detailed night sky.

You move from Pocket Sky Atlas to Uranometria or deeper detail. Or in a terrestrial allegory from purple OS maps to orange. 

12 inch tubes are about 14 inches diameter, 10 inch tubes 12. Mirror and cel weight are heavier than the extra 2 inches suggests in a 12, so carrying, handling and accommodation require more consideration. A 10 inch F6 has the same focal length as a 12 inch F5. As a first step I would recommend the former. For 12 inch and larger, get to see and examine an OTA physically if possible, Newtonians can become gargantuan very quickly.

[Dragon_Astro]

On 4 May 2018 at 14:24, Red Dwarfer said:

Sounds like perfect astronomy conditions down there . I recently went from 8 inch to 14 inch Dob and the size difference is considerable . Going with the biggest Dob you can manage is probably the best advice .

When I finally figured out how to fit the feet to the 14" last night ( the screws come out and go in the opposite way ) I took a pic beside the 200P and several other scopes for scale and size comparison - might be useful to anyone who reads this 

That many scopes out in the open like that, you can't be married? Lol

[Geoff Barnes]

Many thanks for your response John, your posts are always so well measured and thought out.

And 25585 too, good suggestions, but I'm 62 now and this is intended to be my first and last scope purchase so I want to get it right first time!

I'm a landscape gardener, a big strong boy, so size doesn't worry me, so I think I'm favoring the 12 inch Dob to be honest. I really don't want to spend the rest of my days wishing I'd got the bigger scope if I went for the 10 inch.

I will probably take the plunge very soon, so stay tuned!

Then it will come down to decent eyepieces. Rather than buying a few good quality ones I am considering the Baader Hyperion 8-24mm Mark 1V zoom which seems to be greatly favored on this forum. Does this seem a good option to you guys?

Dragon_Astro, my wife really wouldn't mind if I had all of those beautiful scopes, trouble is I could never afford them, lol!

[25585]

1 hour ago, Geoff Barnes said:

Many thanks for your response John, your posts are always so well measured and thought out.

And 25585 too, good suggestions, but I'm 62 now and this is intended to be my first and last scope purchase so I want to get it right first time!

I'm a landscape gardener, a big strong boy, so size doesn't worry me, so I think I'm favoring the 12 inch Dob to be honest. I really don't want to spend the rest of my days wishing I'd got the bigger scope if I went for the 10 inch.

I will probably take the plunge very soon, so stay tuned!

Then it will come down to decent eyepieces. Rather than buying a few good quality ones I am considering the Baader Hyperion 8-24mm Mark 1V zoom which seems to be greatly favored on this forum. Does this seem a good option to you guys?

Dragon_Astro, my wife really wouldn't mind if I had all of those beautiful scopes, trouble is I could never afford them, lol!

12  inch for you then, solid tube! Orion Optics UK do mounted solid tube Newtonians up to 16 inches in their VX range.

The Pentax SMC XL 8-24mm is the best zoom, but Vixen LV zoom 8-24 is another option - same optics as the Tele Vue 8-24, which was made by Vixen for TV. 

[Louis D]

2 hours ago, 25585 said:

The Pentax SMC XL 8-24mm is the best zoom, but Vixen LV zoom 8-24 is another option - same optics as the Tele Vue 8-24, which was made by Vixen for TV.

The Leica ASPH is generally regarded as the best zoom out there, though the Zeiss 20-75x gets good reports as well.