Difference between 8/10/12 Dob on Andromeda

[Neutrinosoup]

I’m really enjoying my 8 inch Dobsonian, in Bortle 3 skies in SW Scotland it shows a lot on a moonless, cloudless night.

I have a question about larger Dobsonians…using Andromeda as an example, on a clear night I see a brighter core and a smudge outside that with no real detail.

What would it look like through a 10 inch and 12 inch Dobsonian?? And has anyone done live view pictures in the same seeing conditions that they could link me to?

Also does a premium 10 inch Dobsonian with 1/10pv mirror (alledgedly reflects significantly more light??) get close to a more standard 12 inch dobsonian….

 

many thanks,

Niall

[Giles_B]

Not an exact answer, but my own experience in my first year of astronomy when I moved from a 5" (Mass produced, Synta) Celestron Newtonian to a 10" Orion Optics (Hand finished, 1/6 Wave) Newtonian, was that there is a difference, but on galaxies it is a pretty small difference - a bit more brightness overall, a slightly extended visible periphery, and a bit more differentiation between the core and the periphery. But only a bit - a small increment rather than a revolutionary change.

The difference I noticed was on other objects - globular clusters (especially) and open clusters showed noticeably more detail.

My guess would be that you wouldn't notice a change from 8" to 10" at all (on Andromeda).

Edited March 11 by Giles_B

[vlaiv]

I think that you'll benefit more from:

- having a bit more experience in observing

- choosing the right eyepiece

- choosing the right night

- choosing the right time of the year to observe M31

than changing the scope.

I managed to see first dust lane of M31 in 8" scope from Bortle 8 location on particularly transparent night when M31 was at zenith.

[Peter Drew]

The Andromeda Galaxy is a large object, as the telescope is increased in aperture it no longer fits into the field of view.  Using my 30" Dob it looks more impressive in the 80mm finder as there is a fair bit of dark sky surrounding the galaxy.      🙂 

[Neutrinosoup]

16 minutes ago, Peter Drew said:

The Andromeda Galaxy is a large object, as the telescope is increased in aperture it no longer fits into the field of view.  Using my 30" Dob it looks more impressive in the 80mm finder as there is a fair bit of dark sky surrounding the galaxy.      🙂 

The Orion optics UK 10 inch dob can just about manage I think?

[PeterStudz]

42 minutes ago, Peter Drew said:

The Andromeda Galaxy is a large object, as the telescope is increased in aperture it no longer fits into the field of view.  Using my 30" Dob it looks more impressive in the 80mm finder as there is a fair bit of dark sky surrounding the galaxy.      🙂 

This is a very good point. And for me Andromeda looks more impressive in my 10x50 binoculars than my 8” Dob.

[Ratlet]

Don't think you'll see a massive difference going from 8 to 10".  It's pretty diffuse.  I've not seen any detail with my 10" from bortle 4, but that because I've not spent a lot of time trying and as with any issues I have the problem is between the eyepiece and the ground.

For me there are some objects that benefit from a wider fov than my dob provides and my 5" newt does better because the shorter focal length (big fan of Auriga open clusters at low power).   I think Andromeda would benefit from a wider fov than the 10" could provide as you'll gain more context to make spotting the detail easier.

[Zermelo]

M31 is (from our perspective) oval shaped. In a modest scope, especially in a light sky, you're essentially seeing the nucleus, which is also oval shaped. It's easy to imagine that you're seeing more of it than you are.

With a larger scope/better skies/better dark adapted eyes, you see more of the outer regions, though it still looks oval. One thing that will change is the apparent distance to the satellite galaxies, M32 and M110. When I first looked at M31, I was surprised at the gap between it and M110 in particular, having previously seen the photos from Hubble, etc.

[bosun21]

Regarding the mirror quality being 1/6th wave or 1/10th wave lambda I always thought that this has nothing to do with the reflectivity of said mirror. I always thought of the lambda quality would be better for resolving the finer details of an image, ie a 1/10th wave is better than a 1/8th wave. The actual brightness of an image being directly related to the reflectivity of the mirror. Of course eyepieces and other factors will play a part in this. as well as the mirror coatings etc. Am I wrong in these assumptions?

[vlaiv]

2 minutes ago, bosun21 said:

Regarding the mirror quality being 1/6th wave or 1/10th wave lambda I always thought that this has nothing to do with the reflectivity of said mirror. I always thought of the lambda quality would be better for resolving the finer details of an image, ie a 1/10th wave is better than a 1/8th wave. The actual brightness of an image being directly related to the reflectivity of the mirror. Of course eyepieces and other factors will play a part in this. as well as the mirror coatings etc. Am I wrong in these assumptions?

When observing at low power such as M31 requires - difference between 1/6th wave and 1/10th wave is non existent.

Only very discerning observers will tell the difference on the nights of best seeing when observing planets at very high magnification.

[bosun21]

2 minutes ago, vlaiv said:

When observing at low power such as M31 requires - difference between 1/6th wave and 1/10th wave is non existent.

Only very discerning observers will tell the difference on the nights of best seeing when observing planets at very high magnification.

Thanks @vlaiv. That's exactly what I thought.

[John]

I agree with the comments regarding the visibility of M31 above. 

Taking a different type of deep sky object, with the brighter globular clusters, these aperture increases will show noticeable differences in the resolution of stars within the cluster and the depth towards the core that is resolved. With a 10 inch and upwards aperture, M13 starts to look like some of the images you see of it. Quite splendid 🙂 

 

[Mr Spock]

With my 12" globulars are impressive. Galaxies are just grey smudges.

[Xilman]

3 minutes ago, Mr Spock said:

With my 12" globulars are impressive. Galaxies are just grey smudges.

Tried looking at globulars in the Andromeda galaxy?

Mayall-II should not be difficult in your 12".

 

[Ratlet]

4 minutes ago, Mr Spock said:

With my 12" globulars are impressive. Galaxies are just grey smudges.

Whenever I get carried away about astronomy at work I always make it clear that I have absolutely no idea why looking at various flavours of gray smudges brings me such joy, because that's what most of the objects look like, but it does.

But Globular clusters in a big dob is something else.  Just spectacular.

[Piero]

Andromeda is about 6 full moons.

I had the best view of this galaxy with revelation 15x70 binoculars (£50) from the Devon countryside..

Larger dobsons tend to have a longer focal length and therefore higher magnification and smaller field of view. They allow one to see smaller and dimmer targets. Globs, small open clusters, the vast majority of galaxies (not the big ones close to us), planetary nebulae, details in extended galaxies etc..

With larger dobs you might want to spot the brightest globular clusters in Andromeda...

 

Eventually what matters the most is the darkness of your skies. Of course, dark skies+aperture=heaven..

[bosun21]

I am beginning to think that I am one of those rare few individuals who actually gets a lot of satisfaction from the smudges in my eyepiece. I draw a lot of motivation and satisfaction from looking up a given target and learning about the details for example the distance, magnitude and the orientation of the galaxy. The orientation helps me draw out some detail knowing beforehand which shape and angle it is relevant to Earth. Of course I love all the usual targets which I find myself revisiting over and over again as the seasons come and go. Low magnification sweeps around productive regions of the sky like the constellation Virgo during galaxy season can be productive, depending on conditions of course.Having recently taken up planetary imaging and to a lesser degree a bit of EAA, I could easily enough replace the eyepiece with the camera and bring the galaxy clearly into view but I love finding a target with my eyepiece beforehand (if possible at all). Maybe I have a masochistic streak in me. Does anyone else appear to have this streak?

[John]

1 minute ago, bosun21 said:

..... Does anyone else appear to have this streak?

I seem to 🙄

I really enjoy searching out faint targets with rather small aperture scopes. Stuff that is at the edge of what the aperture / conditions / observer can see. Usually it's that last component that is the weak one !

Next clear and dark night I'll be trying to spot the quasar 3C 273 in Virgo with 130mm or smaller apertures 🙂

 

[bosun21]

2 minutes ago, John said:

Next clear and dark night I'll be trying to spot the quasar 3C 273 in Virgo with 130mm or smaller apertures

I have added this to my to do list of things to observe. Thanks, however I'm a bit more conservative than yourself and will probably throw more aperture at it. Once located I then like to reduce the aperture and ascertain whether it remains visible.

[Stu]

19 minutes ago, bosun21 said:

Does anyone else appear to have this streak?

Quite a few of us around! 👍🤣

[Stu]

I’m with Piero and others that actually M31 looks fab in a widefield; for me that means my old Genesis with a 31mm Nagler in it giving a very flat five degree field. From a dark site with proper dark adaptation, you really start to see the full extent of the galaxy and its satellites set in context with the surroundings.

Dobs are great tools, but you won’t fit all of it in, certainly not enough to see the outer edges because it will be largely filling the field of view. Again, as said, with a proper big dob and dark skies you can hunt down globs surrounding it which is crazy, never had the chance myself but would love to give it a go.

[PeterStudz]

24 minutes ago, bosun21 said:

Does anyone else appear to have this streak?

One of my most memorable and satisfying nights included locating the galaxy M81 from my Bortle 7 back garden. This in the early days and my first galaxy. All using a 4.5” reflector on a wobbly EQ1 at near zenith with just a cheap red dot finder. I was over the moon!

[Zermelo]

1 hour ago, bosun21 said:

Does anyone else appear to have this streak?

Me too.  Of course, I love to look at more spectacular sights too, but detecting those barely-visible objects tickles the stamp collector in me.

[Ratlet]

I get a thoroughly indecent feeling when I think back to first seeing the veil with my 5" Newt.  Did it without a filter first and it was almost like one of those magic eye posters.  I could just suddenly see this slight difference in the dark.  Almost like a difference in texture rather than colour or shade.  Dropped in my SV202 Dual Band (doing double duty as an O3) and it just popped right out.  Magnificent.  I can't even remember if I tried the dob on it.

Or M33.  That was a belter.  Did a REALLY rough sketch because I was convinced I could see this faint blob but had a nagging doubt.  I'd star hopped to it so confidence was low.  Came in and checked Stellarium and there it was, the stars lined up.

I also like the thought that the photons from stars have been flying through space, largely unimpeded and ignorant of the universe only to end their enterally brief existence on the retina of some teuchter.  2.73 million years of vacuum and sporadic hydrogen atoms, waiting to make a beardy weirdo smile.

But, uh... back on topic.

Rather than going up by 2 inches for more of the same, have you considered going down a few inches for a wide field view?

Edited March 11 by Ratlet

[vlaiv]

2 minutes ago, Ratlet said:

Rather than going up by 2 inches for more of the same, have you considered going down a few inches for a wide field view?

Something like this:

https://www.firstlightoptics.com/stellamira-telescopes/stellamira-110mm-ed-f6-refractor-telescope.html

(that's my "hope to have M31 and other wide field stuff" scope)