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8" reflector vs 10" reflector vs. 12" reflector

emadmoussa

By emadmoussa
in Observing - Discussion

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emadmoussa

emadmoussa

Posted
Posted

I had a 8" reflector for a while, and it was optically great. However, I always wondered as far as DSOs are concerned, what a reflector of 2" or 4" extra will tangibly give you.

Let me put it this way, for example:

Objects:  M82, M81, M51 and M13

Light Pollution: Moderate to Low

Seeing conditions: average (average differs I understand, but I'm talking good to very good seeing conditions).

Realistically what will the 10" show you that the 8" won't? What will the 12"  show you that 10" won't?

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michael.h.f.wilkinson

michael.h.f.wilkinson

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For DSOs the bigger the scope, the better the results.

Having said that: more important than the absolute size of the instrument perhaps are observing skills. I am pretty sure I have spotted things through my nearly 18 year old C8 that novices, and even some fairly seasoned observers would miss. Buying more and more stuff without finding time to really come to grips with your kit and pushing the scopes to their limits, you wont get the most out of the bigger instrument, and it may well disappoint, because you are not in a position to make the most of it (yet).

I learnt to observe with a 70mm frac and 6" Newtonian. I moved to a C8 because I wanted more aperture, and was feeling the limits of the 6" Newtonian, especially in terms of ease of use and transport. I am now beginning to push the boundaries of what can be observed with my C8, having tallied up nearly 800 DSOs, including 396 galaxies. My Sky-Atlas 2000.0 is riddled with pencil marks showing which objects I have found. Only now I am eyeing bigger scopes seriously (I have drooled over catalogues before, of course). Just like my rule for changing EPs, I will get a new scope only when I feel the current set-up is limiting me.

The other observation is that the best scope is the scope you use most. For me there is a tie between the C8 and Helios 15x70 bins. A bigger scope that rarely gets out under the stars is pretty useless.

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acey

acey

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A 10" reflector shows stars 0.48 mag fainter than an 8", a 12" shows 0.4 mag fainter than 10". So the 12" shows stars 0.88 mag fainter than an 8".

What does this mean in practice? Depends on your level of experience and the quality of the sky. If you're an experienced observer then a 0.4 mag difference is noticeable but probably not a "wow", a 0.88 mag difference is a "wow". If you're an inexperienced observer then a 0.88 difference may not look much and you'll wish you had a 16" (which shows stars 0.6 mag fainter than a 12", 1.5 mag fainter than 8").

The limit of surface brightness depends on the sky, not the aperture. If the sky is so light polluted that M31 is just a little fuzzy blob in an 8" then it will be a bigger fuzzy blob in a 16".

So the main thing that improves DSO views is taking the scope to a darker site. To compare magnitude limits with different apertures the magic formula is 5log(aperture1/aperture2). What this means as an actual magnitude limit depends on your naked eye limiting magnitude - the darker that is, the further your scope will reach.

12" is sufficient aperture to see any NGC object above your horizon, if the sky is dark enough. If the sky isn't dark enough then you may struggle to see Messiers with a 16".

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webboid

webboid

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Posted

I have both an 8" & recently a 12" reflector & have made comparisons from both my back garden with mag 4 skies & moderate sky glow as well as from a dark site with 5+ mag skies(milkyway clearly visible)

M13 at home 12" revealed considerably more stars but not to the core compared with the 8" & resolved to the core at dark sky with the 12"

M51 at dark sky showed dim halo around cores in 12" put only cores in 8"

M81 & M82 at dark sky showed detail more in 12" & could hold higher magnification well

NGC 6331 at home was barely detectable in 8" but quite obvious in 12"

M31,M32 & M110 at home M110 only visible with averted vision in 8" but obvious in 12" & magnificent at dark sky

M57 at home considerably brighter in 12" & could hold higher magnification well

NGC 891 dark lane apparent in 12" at dark sky but not with 8"

Veil nebular at home completely invisible with UHC filter in 8" but quite clear with UHC in 12" & visible with out filter at dark sky in 12"

Hope that helps

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jetstream

jetstream

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Emad,I'm not sure the differences in aperture steps,but I went with as big of scope that I can get to a dark sky.So right now my 10" is loaded and I'm heading for a break in the clouds 50 miles away.The CMC Sat imaging shows a nice "hole" in the clouds starting around 10:00pm,for about 2-3 hours,average transparency forecast.So I'll have to carry this stuff about 100 meters to set up,but it is still do-able.Last time to dark site with the 10" I saw  M31 dust lane,M82 light structure and so on.       

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John

John

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The general rule of thumb for medium aperture newtonians used to be that, assuming equal optical quality, a 4" jump in aperture is needed to show a really noticeable improvement in the views. So 6" > 10", 8" > 12", 10" > 14" and so on. That seems to ring broadly true with me although my last upgrade was just a 2" jump from 10" to 12". The 12" has better quality optics in it than the 10" did so it's not quite a level playing field and I notice quite an improvement especially on lunar and planetary views. Deep sky is a bit "hit and miss" from my back garden where I do 99% of my observing so the improvements there I've found more subtle.

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laser_jock99

laser_jock99

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Emad,I'm not sure the differences in aperture steps,but I went with as big of scope that I can get to a dark sky.So right now my 10" is loaded and I'm heading for a break in the clouds 50 miles away.The CMC Sat imaging shows a nice "hole" in the clouds starting around 10:00pm,for about 2-3 hours,average transparency forecast.So I'll have to carry this stuff about 100 meters to set up,but it is still do-able.Last time to dark site with the 10" I saw  M31 dust lane,M82 light structure and so on.        attachicon.gif003.JPG

What flavour are 'Ranch' Pringles then?

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Naemeth

Naemeth

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Don't know how many times I've said this, but go for the 10". It's the best balance of aperture vs portability, and it should be fine for your back :) - unless lifting 15kg is a problem for you... (the weight of the base, the OTA is 13kg)

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emadmoussa

emadmoussa

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I was thinking that actually - from what I see and read, a 12" - unless stored outside in a shed and simply rolled out and in - it'll be quite a cumbersome to manage . 10" will be the most suitable solution. I just observe from my back garden, and don't have the luxury of a car to drive to dark skies I'm afraid. The other solution is to buy a new house for the 12" :D  Let alone, 2" jump in aperture will not, I assume, show dramatic difference in observed objects. Probably planets will have a little bit of extra details, but not quite a planetary observer myself. :)

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AlexB67

AlexB67

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While I can't say, not being an experienced observer, it actually amazes me how many people upgrade their scopes quickly without exhausting a bit more what current equipment can give at times. When I read the posts by Michael for example with the C8 and the amount of observing he has done it shows what is possible.  No who am I to talk just having bought a 10 inch Dob after 5 months owning the Heritage :D  More it was a case of that I had a bit of cash for various reasons, partly a belated presents from family, cheaper holiday as expected, so all of a sudden I had that cash saying DOb Dob Dob :evil: .  I know the opportunity will not present itself for at least another year to have bigger spares till other things are out of the way and I can invest more in the future,  so it was a treat as much as anything. 

That being said I know full well that even in my small 5 inch there was so much more stuff to be seen.  The stuff  I could see with the few trips to a darker site I've had is astonishing in the 5 inch. Of course the one benefit I do have that even from my garden I will be able to find more stuff under less good skies with the 10 inch, but in all honesty I could say the 5 inch could have lasted me several years alone before I think I could really say, it is really necessary to upgrade ?   

How satisfying would it have been if I had observed the entire collection of the messier catalogue just in the Heritage before upgrading, now of course that will be much easier from less good skies when they come around in the 10 inch and increase the count of other object too.  Anyway, the heritage got me almost half there in that space of time from May to now on the Messier list, not to mentioned buckets of NGC I've added on  the list. I still intend to make that a mission over time to do so with the 5 inch, but some of the last few Messier objects may not be easy depending on location and time of year. 

Scopes cost, but buying skill comes for free, apart from filling up the fuel tank :smiley:

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John

John

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An 8" scope could last a person a lifetimes observing and a couple of decades ago it would have done in many cases I reckon. These days there is so much choice and the prices, relatively speaking, really are low. So 12", 14" and even 16" scopes are readily available "off the shelf" at the click of a mouse. And then there is the vibrant used astro equipment market.

It's hard to be disciplined when it's so easy and relatively cheap to get access to aperture that would be the preserve of the astro society or University observatory a couple of decades ago. When you have a look at, say, M13 through a 16" scope at a Star Party it's quite hard to go back to the views through your perfectly decent 8" scope with the knowledge that for a few hundred quid all those extra photons could be yours  :evil:

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emadmoussa

emadmoussa

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An 8" scope could last a person a lifetimes observing and a couple of decades ago it would have done in many cases I reckon. These days there is so much choice and the prices, relatively speaking, really are low. So 12", 14" and even 16" scopes are readily available "off the shelf" at the click of a mouse. And then there is the vibrant used astro equipment market.

It's hard to be disciplined when it's so easy and relatively cheap to get access to aperture that would be the preserve of the astro society or University observatory a couple of decades ago. When you have a look at, say, M13 through a 16" scope at a Star Party it's quite hard to go back to the views through your perfectly decent 8" scope with the knowledge that for a few hundred quid all those extra photons could be yours  :evil:

Or few hundred thousand quid to accommodate the 16" in a reasonably sized house :D

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laser_jock99

laser_jock99

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An 8" scope could last a person a lifetimes observing and a couple of decades ago it would have done in many cases I reckon. These days there is so much choice and the prices, relatively speaking, really are low. So 12", 14" and even 16" scopes are readily available "off the shelf" at the click of a mouse. And then there is the vibrant used astro equipment market.

 

It's hard to be disciplined when it's so easy and relatively cheap to get access to aperture that would be the preserve of the astro society or University observatory a couple of decades ago. When you have a look at, say, M13 through a 16" scope at a Star Party it's quite hard to go back to the views through your perfectly decent 8" scope with the knowledge that for a few hundred quid all those extra photons could be yours  :evil:

I know what you mean there- big scopes and other gear seem to be relatively cheap these days. Indeed I can hardly believe how far this hobby has advanced in the last two decades with the coming of digital imaging, powerful computers and cheap Far Eastern optics. Some of the pictures we see posted here daily were the realm of professionals not that long ago!

Compare my 15 minute exposure of NGC7000 in 1990......

NA_NEBULA_004.jpg

.....to a 3 minute sub of the nebula today

DSIR6917_1024_zps2cd06cff.jpg

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