14" Dob - what to expect?

[swamp thing]

Its true that the larger the aperture the brighter the image, which is better for DSO's but the larger the aperture the greater the effects whether in perfect or not so perfect conditions on the larger telescope

Aperture doesn't make extended objects brighter. It's principle purpose is to make them bigger, M42 is the same surface brightness through any scope with the same exit pupil, the difference is image scale. What aperture does is provides a larger image scale at the maximum exit pupil size......basically makes them bigger not brighter.

All extended objects are at their maximum surface brightness when seen with the naked eye alone. Scopes make them bigger not brighter.

Seeing really doesn't effect galaxies and nebulae. Never seen more detail through my smaller scope when it comes to these objects.

[Naemeth]

True, but you  will also  gather/see as much, maybe  more light pollution in that equation, due to the larger capture of the larger aperture.

...........Using a big scope to see the  faintest  objects from a light-polluted city wouldn't make a lot of sense anyway. you'll still gather/see more light pollution.

It makes sense to me......... Its true that the larger the aperture the brighter the image, which is better for DSO's but the larger the aperture  the greater the effects whether in perfect or not so perfect conditions on the larger telescope. I would also have continued that although emadmousssa is looking at an observatory, if the skies were too polluted, then the bigger scopes would be more of an effort to transport to a temporary darker site.

The increase from 130mm to 250mm, both in light polluted skies, allowed me to go from seeing black and white (well, grey and white) to some colour (green on M42 and faint hints of colour on M57). I imagine the jump to 14", while not quite as big, will allow a similar leap in what i can see .

[emadmoussa]

Aperture doesn't make extended objects brighter. It's principle purpose is to make them bigger, M42 is the same surface brightness through any scope with the same exit pupil, the difference is image scale. What aperture does is provides a larger image scale at the maximum exit pupil size......basically makes them bigger not brighter.

All extended objects are at their maximum surface brightness when seen with the naked eye alone. Scopes make them bigger not brighter.

Seeing really doesn't effect galaxies and nebulae. Never seen more detail through my smaller scope when it comes to these objects.

Bigger aperture is also about more resolving power, which automatically brings out more details.

[Naemeth]

Bigger aperture is also about more resolving power, which automatically brings out more details.

AFAIK it's as long as the seeing conditions allow (if the seeing blurs the space between a tight double, then no amount of aperture will split it cleanly). If we were on the Moon (or anywhere with no, or very little atmosphere), I would 100% agree .

[Mike73]

...........Using a big scope to see the  faintest  objects from a light-polluted city wouldn't make a lot of sense anyway. you'll still gather/see more light pollution.

Sure it gathers more light pollution but it still gathers more light from the actual object you are looking at!

Now this is purely my experience....

Looking at M31, my old 8" from my local LM 6.3 dark site gave a VERY similar view to what my 16" does from my light polluted LM 5.2 home. I can split globular clusters into thousands (well maybe hundreds:)) of stars with my 16" from home but my 8" showed a fuzzy ball with a couple outlying stars.

Saying an 16" will be no better under LP skies compared to a 8" just doesn't match what I have experienced.

[Charic]

Aperture doesn't make extended objects brighter. It's principle purpose is to make them bigger, M42 is the same surface brightness through any scope with the same exit pupil, the difference is image scale. What aperture does is provides a larger image scale at the maximum exit pupil size......basically makes them bigger not brighter.

All extended objects are at their maximum surface brightness when seen with the naked eye alone. Scopes make them bigger not brighter.

Seeing really doesn't effect galaxies and nebulae. Never seen more detail through my smaller scope when it comes to these objects.

I was  under the impression from reading  that many deep space objects are very large, but also very faint. In order to see them, you need to make them brighter, not bigger. The larger the aperture, the brighter the image at any given power.  Must be easier to see more detail in a brighter image than one that is dim.

[emadmoussa]

AFAIK it's as long as the seeing conditions allow (if the seeing blurs the space between a tight double, then no amount of aperture will split it cleanly). If we were on the Moon (or anywhere with no, or very little atmosphere), I would 100% agree .

Yep, this will be ideal. My concern will be micro meteorites going through me and my astro kit :D

[Naemeth]

I was  under the impression from reading  that many deep space objects are very large, but also very faint. In order to see them, you need to make them brighter, not bigger. The larger the aperture, the brighter the image at any given power.  Must be easier to see more detail in a brighter image than one that is dim.

I believe it's more accurate to say that at any given exit pupil the image will seem brighter (same brightness from object spread over a larger area) with a larger scope.

[Charic]

Sure it gathers more light pollution but it still gathers more light from the actual object you are looking at!

Now this is purely my experience....

Looking at M31, my old 8" from my local LM 6.3 dark site gave a VERY similar view to what my 16" does from my light polluted LM 5.2 home. I can split globular clusters into thousands (well maybe hundreds:)) of stars with my 16" from home but my 8" showed a fuzzy ball with a couple outlying stars.

Saying an 16" will be no better under LP skies compared to a 8" just doesn't match what I have experienced.

Cant argue with experience, but I'm still seeing snippets in my favour. not that I`m arguing this point. (still cant find the article i read? ) Just trying to learn. I fully agree, aperture is king, but started  believing that  if a bigger aperture will/can improve a telescope, The  opposite is true for light pollution. bigger the scope, the bigger the issues compared to the smaller scope. So in one case the 16" wins hands down under perfect skies, and in another, loses out due to the greater LP  Its all good for debating. and we all learn or have to re-learn, if that's the case.

[NGC 1502]

For what its worth, my own view is that a larger scope will show more detail, fainter nebulae and stars, under light polluted or better skies.

I've never owned a larger scope than my present 10" Dob, but have used 16" and 20" Dobs at nearby light polluted sites, and at my clubs dark site plus Kelling star party.

Aperture wins, but I do think that a larger aperture is more affected by unsteady atmosphere, because it's looking through a larger column of that unsteady atmosphere, but an unsteady sky is not the same as a light polluted one.

You can have an unsteady turbulent atmosphere at a stunning dark site,  a rock steady atmosphere at a light polluted site...........

Definitions -  

Poor seeing = unsteady turbulent atmosphere.

Transparency = how free of dust/haze etc the sky is.

Regards, Ed.

[AlexB67]

The OO UK models are a lot lighter, a 14 inch OTA weights 20 kg according to the website, compare that to my flextube SW 10 inch at 15 kgs, almost grab and go as Swamp would say, I'd say manageable to lift by oneself , alas, costly though.

[Mike73]

I give up! 

[jetstream]

I always see more through my 10" vs 3.5" regardless of LP.On planetary my 10" always betters my 3.5"-under very bad conditions,on planets the 3.5" can do ok but has never bested my VX10.Under good conditions .ie seeing,transparency & dark skies the 10" wins....big time....on everything.If I was Emad I know which one I'd pick...something like mike73,estwing or swampthing did

[Moonshane]

Cant argue with experience, but I'm still seeing snippets in my favour. not that I`m arguing this point. (still cant find the article i read? ) Just trying to learn. I fully agree, aperture is king, but started  believing that  if a bigger aperture will/can improve a telescope, The  opposite is true for light pollution. bigger the scope, the bigger the issues compared to the smaller scope. So in one case the 16" wins hands down under perfect skies, and in another, loses out due to the greater LP  Its all good for debating. and we all learn or have to re-learn, if that's the case.

see http://www.skyandtelescope.com/howto/visualobserving/3305656.html especially p3

http://www.cloudynights.com/ubbthreads/showflat.php/Number/4813640

http://www.cloudynights.com/ubbthreads/showflat.php/Number/5230065

you may find arguments against too but the first of many links I found, and our experience of using various scopes in light pollution, support the view that the disadvantages to aperture have nothing to do with LP.

[YKSE]

Great links!   Moonshane.

[AlexB67]

I always see more through my 10" vs 3.5" regardless of LP.On planetary my 10" always betters my 3.5"-under very bad conditions ,on planets the 3.5" can do ok but has never bested my VX10.Under good conditions .ie seeing,transparency & dark skies the 10" wins....big time....on everything.If I was Emad I know which one I'd pick...something like mike73,estwing or swampthing

I'll second that Gerry. I live in suburban Bristol, a fair bit of LP around but with decent shielding from artificial lights in my garden in one or two spots . Since I upgraded form a 5 inch to a 10 inch I've now bagged more galaxies or other fainties that I previously tried in the 5 inch and they were just not possible. I know improved skill will be part of this as well, so in some cases I went back to see if I could bag them in the 5 inch, in some cases I did detect them ... just, but rarely in most cases, there was still less to see. Mag 9 - 11 fainties are a fairly typical catch in the 10 inch in my garden, that was just dream stuff in the 5 inch from the same spot,  depending on their size ( and therefore resulting surface brightness ) of course, but mostly such targets are doable. 

Unless I am standing in the high street observing, which is portably a bad idea :0) IMHO there is always some benefit to be had from that extra aperture in any sort of half reasonable spot in or near cities where you can reasonably dark adapt. I cannot vouch for the really big instruments never having used them, but the principles/theory are still the same. 

Whatever the conditions, up to a point at least where atmospheric stability does not interfere , the extra resolving power of the bigger instrument will allow you to see more detail in any case, regardless of LP.  M13 for example will always look largely like a fuzzy ball surrounded by stars with a hint of resolved detail near the edges away from the core, but in the 10 inch on the other hand it can be resolved to the core.

Charlic, I can highly recommend to have a read of Roger Clark's book visual astronomy of the deep sky If you can get hold of it,  it touches on this subject in quite a bit of depth, but also the subsequent work by J Torres on understanding visual detection as discussed on this page.

http://www.uv.es/jrtorres/visib.html

I actually implemented the use the threshold method in a program of my own and it works rather quite well I feel.  I wish I had an SQM meter, but interestingly I believe last night for example I worked backwards from this method and using my observations to estimate the sky background darkness within a sort of 0.5 mag/arcsec^2 rnage I feel.  Unfortunately I don't have an SQM  instrument to verify it  ... I'll wil get my hands on one of these meters one day, but buying another eyepiece always seems more attractive right now, since an SQM costs around a 100 pounds. 

In any case, what the calculation did tell me in advance with a good deal of confidence based on what I felt my NELM was at the time,  that the several targets I used would be possible to see in the 10 inch scope, but not in the 5 inch with the eyepieces I have, this turned out to be true.

[estwing]

I wouldn't put a bigish dob in an obsy....

[emadmoussa]

I wouldn't put a bigish dob in an obsy....

Why?

[jetstream]

I wouldn't put a bigish dob in an obsy....

Great point Calvin,great scope too.Your picture shows the mobility of that great truss design,just wheel her out then wheel her back in.Emad could have navigation options with this design too...

[jetstream]

As mods Moonshane and Swampthing have shown,larger aperture show more than a smaller one will.Now the question is why and how to use the bigger scope effectively.AlexB67 is right on the money with his last post,and if members are interested in learning why and how the sites/link he gave will go a long way to explain it.They explain Swampthings thoughts on the DSO/surface brightness issue,with the optimum magnified visual angle being an important concept, as is aperture.http://www.clarkvision.com/visastro/index.html

[Charic]

Charlic, I can highly recommend to have a read of Roger Clark's book visual astronomy of the deep sky If you can get hold of it,  it touches on this subject in quite a bit of depth, but also the subsequent work by J Torres on understanding visual detection as discussed on this page.

http://www.uv.es/jrtorres/visib.html

Cheers AlexB67........... been trying to study  surface brightness and integrated brightness. There's more to this than just  polluted skies? but  I`m nodding!  Ive got to get some sleep first, on the go here over 48 hours?  

[swamp thing]

I was  under the impression from reading  that many deep space objects are very large, but also very faint. In order to see them, you need to make them brighter, not bigger. The larger the aperture, the brighter the image at any given power.  Must be easier to see more detail in a brighter image than one that is dim.

You can't increase surface brightness it's not possible.

Have a read of this

http://www.rocketmime.com/astronomy/Telescope/SurfaceBrightness.html

[Charic]

Cheers Steve. Going back to the OP and my first reply #2 Id like to add,  that the ability to see Celestial objects  is somewhat related to  the Objects brightness and having the right equipment.

Increasing the aperture will always increase detail, provided there is some detail to begin with. If an object is overwhelmed by light pollution and/or poor sky transparency then that object could be invisible at any aperture, and will mean that you will never be able to see the faint DSO's no matter what telescope you use.

Visible objects will benefit from larger apertures, irrespective of light pollution, by virtue of having the bigger aperture, but the larger aperture shouldn't  produce results any worse than the smaller aperture from the same light polluted area.

So regardless of light pollution levels, increasing aperture increases detail in the visible objects, but increasing the aperture won't make  invisible objects, visible under those conditions.

The only reason 'invisible' objects become visible with aperture from darker skies is that your eyes have a minimum threshold for detecting incoming light, which is the reason we use the telescope.

My thought "larger apertures gathering more light =  gathering more light pollution" is plausible, but many folk don't see that with their experiences.  Now more to study from that link.

[John]

Cheers Steve. Going back to the OP and my first reply #2 Id like to add,  that the ability to see Celestial objects  is somewhat related to  the Objects brightness and having the right equipment.

Increasing the aperture will always increase detail, provided there is some detail to begin with. If an object is overwhelmed by light pollution and/or poor sky transparency then that object could be invisible at any aperture, and will mean that you will never be able to see the faint DSO's no matter what telescope you use.

Visible objects will benefit from larger apertures, irrespective of light pollution, by virtue of having the bigger aperture, but the larger aperture shouldn't  produce results any worse than the smaller aperture from the same light polluted area.

So regardless of light pollution levels, increasing aperture increases detail in the visible objects, but increasing the aperture won't make  invisible objects, visible under those conditions.

The only reason 'invisible' objects become visible with aperture from darker skies is that your eyes have a minimum threshold for detecting incoming light, which is the reason we use the telescope.

My thought "larger apertures gathering more light =  gathering more light pollution" is plausible, but many folk don't see that with their experiences.  Now more to study from that link.

I'm not sure I understand this 

My observing site (garden) has some light pollution as you would expect from streetlights, neighbours etc, etc.

Despite this, my 12" scope will show me objects and detail that is simply not visible with my 6", 4.7" and 4" scopes. This is the case for both deep sky objects and the moon and planets.

If viewing conditions are mediocre or poor then the smaller scopes get closer, sometimes much closer to the larger one on planetary and lunar detail but the 12" continues to do proportionately much better on deep sky objects.

Whether this meets "the theory" or not I don't know but thats what I observe happening

[Moonshane]

broadly, if you ignore light pollution, a larger scope will show many objects that are not visible with less aperture. the smaller aperture cannot see them in the same way that our eyes with their even smaller aperture cannot see them. so a larger scope will make 'invisible' objects visible.

if you include light pollution, then the only difference is that the contrast of the object has reduced in comparison with the sky background. this is to a 'standard' level across the sky so relatively speaking the situation is as above but with a different contrast starting point.