8" or 10" Dobsonian? (My first telescope)

[Charic]

Im led to believe that with this kind of aperture diffrence you will only really notice the results of yhe larger aperture in dark skies and low light pollution. I may be wrong tho!

Ive been reading too, but not only that, Im sure in one of my threads, sometime back,  I was  also corrected?

My understanding is that all telescopes work at their best under perfect seeing and dark skies, but under light polluted skies,  you will see more with a 10"  or 12" Newtonian than say a 6" or 8"  Newtonian.

Its physics, despite  the atmospheric conditions and light pollution having  the  larger aperture  captures  more, under the same conditions ?

Thats my understanding of having  the larger aperture.

[Luke]

For DSO's I find the step up in aperture from 8 to 10 inches pretty noticeable. The gain is about 56% as you say whereas if you look at say 14 inches versus 12, it's more like 36%. So though it's "just two inches", that's quite a big two inches

If I was picking one DSO scope to last me for a very long time, I would probably pick a 10 or 12 inch solid tube dob. I would want the scope that gives the most aperture without weighing too much or being too much hassle to put out. I had a 12 inch flextube and found that a little bit on the heavy side as a scope that I find close to zero hassle, but I wonder if the much more expensive 12 inch Orion UK dob, which I think weighs similar to my GSO 10 inch, is my long term plan (I'll have to go second hand as brand new it's over my budget).

A solid tube tends to be less prone to dew and me personally, I find I always have to collimate flextube dobs (I had the 12 and now have the 16). Some people seem to have the knack of getting it back in the right place but I don't think it's been spot on once for me!

A flextube on the other hand can be handy for storage or for squeezing the scope into a car (my 16 inch just gets into my car boot, thanks to being a flextube).

Weight-wise I find my 10 inch dob (the GSO 880, which I think is a similar weight to the Skywatcher) to be bang on the money. Pretty much a breeze for me to carry out. I take it out in two parts, base and then tube. Could be that some folks move both together, but I am lazy and it doesn't take long to disconnect them.

The 8 Skywatcher should cool faster and be a bit more forgiving with some eyepieces. Eyepieces like the Hyperions will tend to show distortion on stars towards the edge of the view in "fast" scopes. e.g. F5 or lower. This bothers some people more than others, it didn't actually used to bother me that much as I tended to focus in the centre of the view at the time, so the distortion/blur was in my peripheral vision anyway...

For me there would be a lifetime of viewing with a 10 inch dob, I feel very spoilt with the 16 inch but really the 10 is a very powerful scope indeed, while still being reasonably portable (perhaps not if you have flights of stairs to contend with).

The main downside is cool down time. Ideal would be if you can store it in a shed or garage or outbuilding, already cooled, ready to use in a few minutes

My skies are okay (can just make out Milky Way), nothing special, with a few annoying street lights shining right in. Aperture definitely makes a difference here, and my skies are quite a way off being as dark as star parties.

An 8 is a very nice scope too, I sometimes observe with my 8 inch scope and really all the way down to a 60mm scope. But if better DSO views is high up your list, I'd go the 10 if the size and weight are okay.

[jetstream]

All this talk of big scopes suffering from light pollution....

Surely the focal ratio of a telescope dictates how it suffers, not the aperture?

An 8" and 10" of the same focal ratio will suffer the same amount, won't they?

I read that a slow focal ratio "dampens" seeing conditions resulting in better views, but having played with an aperture mask on my dob found no difference. The slow ratio does help depth of focus though which can improve views and a slow dob will have a bigger coma free area which can also help.

You see more of everything with a larger aperture, even under LP skies, regardless of focal ratio- up to some level where the sky gets a bit too light, greyish I guess, exit pupil considered. It is the "seeing" that can limit big scopes in their ability to give good views, along with thermal issues. This is just my opinion however and as always subject to change lol!

[buzzlightyear]

Ive been reading too, but not only that, Im sure in one of my threads, sometime back,  I was  also corrected?

My understanding is that all telescopes work at their best under perfect seeing and dark skies, but under light polluted skies,  you will see more with a 10"  or 12" Newtonian than say a 6" or 8"  Newtonian.

Its physics, despite  the atmospheric conditions and light pollution having  the  larger aperture  captures  more, under the same conditions ?

Thats my understanding of having  the larger aperture.

Hi charic

I wasn't saying I read that you would not get a better visual with the 10inch compared to the 8inch, that question is obviouse. But the way I read the couple of magazine articles I seen it was merely saying if you are viewing in a light pollution area constant then the visual difference between the two would be far less than under good seeing conditions skies.

The advice I read was if my LP area was not great then the 8inch would be the better option with some good quality EPs bought with the savings from not going for the 10inch.

This is not my advice but just quotes I have read on a few occasions.

Personly if I had the money to chuck at this hobby then I would do a deal with nasa and buy the Hubble from them and have lots of fun. Astronomy eh! Bloodyell! Lol

[Charic]

Hi charic

I wasn't saying I read that you would not get a better visual with the 10inch compared to the 8inch, that question is obviouse. But the way I read the couple of magazine articles I seen it was merely saying if you are viewing in a light pollution area constant then the visual difference between the two would be far less than under good seeing conditions skies.

The advice I read was if my LP area was not great then the 8inch would be the better option with some good quality EPs bought with the savings from not going for the 10inch.

This is not my advice but just quotes I have read on a few occasions.

Personly if I had the money to chuck at this hobby then I would do a deal with nasa and buy the Hubble from them and have lots of fun. Astronomy eh! Bloodyell! Lol

I've just read that the difference is more apparent  seen under light pollution than no pollution at all, with having the bigger aperture?

Just had a read of this article.........  http://uncle-rods.blogspot.co.uk/2011/01/uncle-rods-telescope-academy-how-big.html

A mind blowing subject, Astronomy, as you so rightly mention!

[John]

As I've compared scopes from 4" to 12" in scope aperture over the years I've noticed that the difference that additional aperture makes seems to vary quite considerably depending on the object type. On the Moon and planets I've found the differences to be less marked and the overall quality of views dependant on seeing conditions more than perhaps anything else. On deep sky objects the larger aperture scopes always show a noticable difference, even if the aperture difference is just an inch or two. On globular clusters for example, the appearence in the eyepiece as aperture increases is really obvious in terms of the resolution of stars in the cluster.

Thats why I made my input earlier in this thread to reccommend a 10" scope because the original posters main interests seem to be deep sky objects. The two inches of extra aperture do make a worthwhile difference to the views. For the observer more interested in the Moon and Planets the 8" F/6 dob with it's smaller central obstruction and more error tolerant collimation would be a better choice I feel.

Etiher choice will provide a lot of enjoyment though and probably deliver the best "performance per £ spent" of any scopes on the market today.

[buzzlightyear]

Hope we have not confused the poor chap but you cant beat lots of opinions presented on this forum, its what makes it great. Also not forgetting great advice and tips.

Now wheres these ruddy clear skies?

[buzzlightyear]

Just to add though, would the 8inch with quality ep not out perform a 10inc with stock ep?

This ones not a debate lol but just interested in the answer as I dont know. (I am a novice by the way)

[Liquid360]

With Dobs I'm not sure that high end EPs make a huge difference. I think aperture wins over EP quality, but IMO everything's better with an ethos [emoji6]

[Paul73]

It is safe to say that. The faster the Dob the more you need to spend on eyepieces yo get the same quality of image.

Unfortunatally my f4.7 likes Delos (can't afford Mr Ethos).

My scope grumbles but still gives more than OK views with £50 BST's, it perks up a lot when presented with the £100 SLV's, positively purrs with the £80-£110 MV's and I'm not going to tell you what it does when the £250 Deloses come out to play.

Re. The question about 8" + Premium eypiece vs 10" with stock eypiece. The 8" would win. This is a purely hypothetical question as the vast majority of the 10" owners spend a couple of weeks getting to know the scope & their requirements. Then upgrade eyepieces PDQ. Improvements can be made at most price levels.

Paul

[buzzlightyear]

One thing I was wondering is, what size and make refractor telescope would give simalar views to a8 or 10inch relector, or anyother type of scope for that matter.i guess price wise would be significantly higherTwin Health living juice extractor for a guess?

[buzzlightyear]

One thing I was wondering is, what size and make refractor telescope would give simalar views to a8 or 10inch relector, or anyother type of scope for that matter.i guess price wise would be significantly higherTwin Health living juice extractor for a guess?

God knows where the twin health juicer text came from, please ignore it. Predictive text can be odd if not read through first lol

[Moonshane]

It was a subliminal message placed in you pc memory by your wife to ensure you get the right Christmas gift :0)

I dont agree that more aperture with basic eyepieces is less effective than less aperture with better eyepieces. Think (or rather look) objectively when comparing different set ups and you will see that more aperture reveals more detail. Better eyepieces make the view more aesthetically pleasing and on the edge of visibility might occasionally reveal more detail. The latter point assumes equal aperture and optical quality of scope. Even the worst eyepieces will, on axis, provide the same details and features as the best eyepieces - the best quality brands are not magical. Don't get me wrong I love my case of Televue. A larger aperture will always beat a smaller aperture for detail - ye cannae change the laws of physics Jim.

[umadog]

All this talk of big scopes suffering from light pollution....

Surely the focal ratio of a telescope dictates how it suffers, not the aperture?

An 8" and 10" of the same focal ratio will suffer the same amount, won't they?

I think of it differently. All scopes suffer equally from light pollution. Light pollution just decreases contrast between the DSO and the sky background. This isn't worse at larger apertures, it's a constant. So if an object is visible, then under LP skies the larger scope still shows more. However, LP washes out the fainter stuff first and larger scopes are able to pick up fainter stuff than smaller scopes. Consequently, larger scopes have more unused potential in LP skies. In other words, the difference between an 8" and 12" scope would be more prominent if you're viewing somewhere dark than if you're viewing in suburbia.

[buzzlightyear]

I think of it differently. All scopes suffer equally from light pollution. Light pollution just decreases contrast between the DSO and the sky background. This isn't worse at larger apertures, it's a constant. So if an object is visible, then under LP skies the larger scope still shows more. However, LP washes out the fainter stuff first and larger scopes are able to pick up fainter stuff than smaller scopes. Consequently, larger scopes have more unused potential in LP skies. In other words, the difference between an 8" and 12" scope would be more prominent if you're viewing somewhere dark than if you're viewing in suburbia.

Thats life jim but not as we know it!

So I will now have to buy the mrs a juice for crimbo it seems lol, hope the prices don't eat into my astronomy bits and bobs fundage!

[AndyWB]

... Thread after thread , post after post about the issue, but coma is an inherent aberration with a fast dob, mine shows it.

Yeah, well I still wonder about that. I mean, mine shows a touch at the edges, but not so much that it bothers me (or even really notice), and only with certain eyepieces (I.e. the 28mm MaxVision. Lovely eyepiece, but my scope makes demands on it). I do wonder about if he got a duff mirror or something.

... Eyepieces like the Hyperions will tend to show distortion on stars towards the edge of the view in "fast" scopes. e.g. F5 or lower. This bothers some people more than others, it didn't actually used to bother me that much as I tended to focus in the centre of the view at the time, so the distortion/blur was in my peripheral vision anyway...

On that note, I did recently get a chance to try each of the Hyperion 5, 10, 17 and 24 mm eyepieces in my f4.7 Skyliner 250px. Now THAT was coma. They were dreadful. All of them, and the 17mm was curiously worse. However, stick them in my f12 or so hydrogen-alpha scope - lovely views.

So no, I'm not in a rush to use Hyperions at that speed. 

... 

But the way I read the couple of magazine articles I seen it was merely saying if you are viewing in a light pollution area constant then the visual difference between the two would be far less than under good seeing conditions skies.

My experience with my 5" and 10" dobs is that the 10" still has much better resolution (for splitting doubles), but for DSOs there's a lot less in it, at home under LP. Somewhere dark, though, and the 10" is much better. I think Umadog's reasoning is on the money with this one. 

My scope grumbles but still gives more than OK views with £50 BST's, it perks up a lot when presented with the £100 SLV's, positively purrs with the £80-£110 MV's and I'm not going to tell you what it does when the £250 Deloses come out to play.

I've not tried the Delo's but this matches my experience pretty well. And I know they're narrow, but I do like my SLV a lot.

[Astro Imp]

It has been mentioned a couple of times that a 10" solid tube will cool slower than a similar 8". Was wondering is this significant when viewing DSOs as the name of the game is collecting as much light as possible and not obtaining fine resolution? 

[John]

I find that I can start viewing deep sky objects at low or medium power quite soon after putting my 12" dob out to cool but high power viewing requires 40-50 minutes of cool down to get a steady image.

[Moonshane]

as always it depends. if you are observing planetary nebulae at 200x or galaxies at 150x then this needs different time compared with larger objects at 50x. as always just choose your objects depending on the prevailing conditions.

[Astro Imp]

Thanks John and Shane for the clarification. 

[Charic]

It was a subliminal message placed in you pc memory by your wife to ensure you get the right Christmas gift :0)

I dont agree that more aperture with basic eyepieces is less effective than less aperture with better eyepieces. Think (or rather look) objectively when comparing different set ups and you will see that more aperture reveals more detail. Better eyepieces make the view more aesthetically pleasing and on the edge of visibility might occasionally reveal more detail. The latter point assumes equal aperture and optical quality of scope. Even the worst eyepieces will, on axis, provide the same details and features as the best eyepieces - the best quality brands are not magical. Don't get me wrong I love my case of Televue. A larger aperture will always beat a smaller aperture for detail - ye cannae change the laws of physics Jim.

This is another issue I considered, should I ever upgrade to the 12" solid tube. On axis, the views should be normal,  and off-axis, acceptable, but as I dont record imagery  and everything is 'on the move' I`ve no real issues with anything  coma related or off-axis.

If I went to a 10" I think with the lower focal ratio, this could become an issue/annoyance for my Starguiders, as good as they are, without further possible correction and more in the optical train.  So my jump in aperture would be to miss out on the 10"  and opt for the 12"

[Sporadic Dobstronomer]

Throwing in my 2p worth: my jump was from 8" to 16" in light polluted skies, which is a bigger aperture difference, but my experience is clear: bigger is better BUT ONLY IF you are not so inconvenienced by weight that it stops you from using the thing.  So get the 10" if you are sure you will continue to be bothered to carry all that weight after the novelty has worn off, and get the 8" if not.

This conflicts with what the much-pilloried Buzzlightyear had been told (sympathy beam activated) but I have found that while it is true that aperture does not cut through light pollution, bigger images the same brightness are nicer to look at.

[buzzlightyear]

Throwing in my 2p worth: my jump was from 8" to 16" in light polluted skies, which is a bigger aperture difference, but my experience is clear: bigger is better BUT ONLY IF you are not so inconvenienced by weight that it stops you from using the thing.  So get the 10" if you are sure you will continue to be bothered to carry all that weight after the novelty has worn off, and get the 8" if not.

This conflicts with what the much-pilloried Buzzlightyear had been told (sympathy beam activated) but I have found that while it is true that aperture does not cut through light pollution, bigger images the same brightness are nicer to look at.

No sympathy needed matey. I was trying to say that the difference from 8 to 10 inch is lp area is not that great but you are on about a 16inch that obviously is twice the size and will show visual better..but at a masive cost difference

[nwink]

Throwing in my 2p worth: my jump was from 8" to 16" in light polluted skies, which is a bigger aperture difference, but my experience is clear: bigger is better BUT ONLY IF you are not so inconvenienced by weight that it stops you from using the thing.  So get the 10" if you are sure you will continue to be bothered to carry all that weight after the novelty has worn off, and get the 8" if not.

What 16" Dob do you have?  What you've described is a very similar scenario to something I've tossed around in my mind.  Maybe I might get an 8" now for my first telescope...it would always be useful to me since it is a lighter and portable telescope, and it's what I'd use to really learn the night sky.  Then after several years, I could then (if I'd want a larger Dob) do a big upgrade to like a 16".

[nwink]

10" is / was my first scope. If you can easily fit it in the car and not give yourself a hernia putting it together - go for the 10".

This is especially true if you are heading for dark sky.

However...... If you need to carry the thing down a few flights of stairs to get to the car..... This might be oK once or twice but you will soon get bored of it and start making excuses not to go out.

Paul73, thank you for the comment.  I'm in my 20's...and I've seen that a 10" OTA typically weighs around 30lb (I'll let you convert that to kilos), and the base is about the same weight.  The tube is around 4ft long.  So, it sounds like the tube is more bulky than actually heavy??  I mean, isn't the OTA just a tube with a couple mirrors and an eyepiece attachment?  The comparison I think of is that I have no problem carrying one of my screaming kids (when he's throwing the occasional tantrum)...and he's 30lb and 3' long.  Just saying!