Difference between 8/10/12 Dob on Andromeda

[IB20]

M51 and M104 are the two galaxies I’ve most been impressed with in the 8” dob. I’ve always preferred Andromeda in binoculars for some reason, maybe it’s the scale or framing of it that just resonates more with me.

[John]

I always felt that Messier 81 and 82 were more interesting through a scope than Messier 31 is. I guess I'm biased, though because those were the first galaxies that I ever saw with a scope. I found M31 later with binoculars.

 

[Stu]

13 minutes ago, vlaiv said:

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)

That would do it 👍

I used to have a 106mm f6.5 triplet apo which framed the Veil beautifully with a 31mm Nagler. I basically copied John’s Vixen 102 f6.5 setup after reading of his observations 👍

[Ags]

Using a big dob on M31 is a little like using a magnifying glass to examine an elephant. It is a big object and doesn't need magnification so a bigger scope doesn't help. Also the brightness of an extended object depends only on the exit pupil and not on aperture, so M31 will be just as bright in 7x50 binoculars as it would be in a dob with an exotic low power eyepiece, with the exception that the galaxy will fit in the FOV of the binoculars. By far the best view I have ever had of M31 was with a pair of cheap and very rubbishy binoculars.

[bosun21]

1 hour ago, John said:

I always felt that Messier 81 and 82 were more interesting through a scope than Messier 31 is. I guess I'm biased, though because those were the first galaxies that I ever saw with a scope. I found M31 later with binoculars.

 

Ditto.

[Stu]

Back in the days when I knew nothing about anything really, including fields of view and object sizes, I tried observing M31 with my OMC200. This was an 8” f20 Mak, so had a 4000mm focal length! Even with a 31mm Nag it gave x129 and a 0.63 degree field of view, likely vignetted a fair amount.

Needless to say I didn’t see much! Just the bright fuzzy glow of the core filling most of the field of view. Even M32 was out of view. Took me a while to work all this out; it was before the time I was active on here so had few sources of information. Once I got my 106mm triplet I understood!

[Ratlet]

A 130mm F5 newt would be another winner for a wide field scope at a lower price.  Heritage 130p would do well but (I think) be limited to 1.25" eyepieces.  130pds would be more expensive and require a mount, but let you use 2" eyepieces.

[dweller25]

I have looked at M31 with a 5” APO, a C9.25 SCT and a Skywatcher 10” Newtonian.

To be honest none of the views impressed me.

I recently looked at M31 again and got that “wow” factor - trust me that does not happen often after 50 years of night sky observing.

The sharpness, relative brightness and above all the contrast of the view really caught me out by surprise.

The scope was a Mewlon 180C

 

Edited March 12 by dweller25

[Mr Spock]

The bigger and wider you go, the bigger the exit pupil. My 8" f4 can cover over 3°, but with a ludicrous 8.8mm exit pupil...

[vlaiv]

2 hours ago, Ratlet said:

A 130mm F5 newt would be another winner for a wide field scope at a lower price.  Heritage 130p would do well but (I think) be limited to 1.25" eyepieces.  130pds would be more expensive and require a mount, but let you use 2" eyepieces.

It has a downside though. Such scope has to have really big secondary to avoid vignetting on 2" eyepieces.

If you do a little search, I'm sure you'll find someone posting a flat field of their 130PDS with APS-C sensor - and it will show vignetting even on 28mm diagonal.

[Neutrinosoup]

Sadly can’t use binoculars, lazy eye after a childhood squint operation. I do have a WO Megrez 72mm scope which is kind of like a big monocular….. and WO FLT98mm than I want to sell because I rarely use it. It sounds like I should be using the 72mm scope on andromeda?

[vlaiv]

1 hour ago, Neutrinosoup said:

and WO FLT98mm than I want to sell because I rarely use it.

Maybe you should try it first with ~40mm 2" eyepiece and a good 2" diagonal?

But you really want to wait for autumn for that target. It can be very high in the sky - near zenith (depending on your location).

For best results - wait for it to be near zenith and also check this website:

https://atmosphere.copernicus.eu/charts/packages/cams/products/aerosol-forecasts

This gives you forecast of transparency - you want "white" to be over your observing location for the evening you plan to observe. That is for best results of course.

Observing when dark gray is overhead is like observing with 8" telescope instead of 9" telescope - you loose one whole inch (going into yellow territory is even worse and can have effect of loosing 2" or more of aperture size!).