Light Pollution And Larger Aperture Telescopes?

[Ian McCallum]

If I got a larger Dob than my present 200p, given that I live in a Bortle 6 area - would my seeing/observing be impacted by the larger aperture because of increased sky glow?

[jacobingonzo]

you woulnt get poorer observing- you would definitely improve you experience its just that the bigger aperture wouldn't reach its full potential. And believe me when you take it to a dark site you will really appreciate the bigger light bucket

[Stu]

I agree with @jacobingonzo. It won’t be worse, and you will still see more than with a smaller scope, but there will be bags of potential left on the table. Upping magnification can help cut sky background brightness, but a lot of the better targets for larger Dobs are lower surface brightness (nebulae and galaxies) so will really benefit from a darker sky.

[Ian McCallum]

I'm sure I read somewhere that if you have light pollution issues, then bigger Dobs would show this up more (or something similar).🤔  

[Zermelo]

13 minutes ago, Ian McCallum said:

I'm sure I read somewhere that if you have light pollution issues, then bigger Dobs would show this up more (or something similar).🤔  

I've not heard that one, but there is a line about larger scopes being worse when the seeing is bad, supposedly because their larger apertures are more affected by the moving air cells.
And then I've also read other people saying that's rubbish.

[Ian McCallum]

2 minutes ago, Zermelo said:

I've not heard that one, but there is a line about larger scopes being worse when the seeing is bad, supposedly because their larger apertures are more affected by the moving air cells.
And then I've also read other people saying that's rubbish.

That's probably what I read, as that rings a bell with me.  I hate when I've read something somewhere and either can't remember where or what exactly was said.🙄  Thanks for correcting me.👍

[John]

I've found that my refractors are punching above their weight on the planets because of their low altitude currently. On the deeper sky, the refractors (100mm - 130mm) do very well for their aperture but my 12 inch dob pushes substantially deeper and fainter and resolves globular clusters much more impressively.  

My skies are Bortle 5, generally.

 

Edited October 12, 2021 by John

[Ags]

I am of the school that thinks larger aperture is a mixed blessing in light polluted skies. My situation is Bortle 8-9 (sometimes it seems like Bortle 11 😀 ) and my goal is pretty views in the eyepiece. That goal means the background in the eyepiece needs to be relatively black, not milky white. That in turn means a viewing exit pupil of 2mm or preferrably less. Given a 300mm dob, that would mean a minimum magnification of 150x, which would mean (assuming an 82 degree eyepeice) a field of about half a degree, which is getting a bit tight. 

Edited October 12, 2021 by Ags

[Tiny Clanger]

26 minutes ago, Ian McCallum said:

I'm sure I read somewhere that if you have light pollution issues, then bigger Dobs would show this up more (or something similar).🤔  

I've read something similar in the past too ...

Some discussions and info

https://stargazerslounge.com/topic/271682-biggest-useful-aperture-in-light-polluted-skies/

https://www.cloudynights.com/topic/443936-aperture-vs-light-pollution/

https://astromart.com/reviews-and-articles/reviews/beginners/show/aperture-vs-light-pollution

https://www.astronomics.com/info-library/frequently-asked-questions-about-telescopes/how-big-a-scope-do-i-need/

the upshot of which is ... um, opinions vary .

[Ian McCallum]

28 minutes ago, Ags said:

I am of the school that thinks larger aperture is a mixed blessing in light polluted skies. My situation is Bortle 8-9 (sometimes it seems like Bortle 11 😀 ) and my goal is pretty views in the eyepiece. That goal means the background in the eyepiece needs to be relatively black, not milky white. That in turn means a viewing exit pupil of 2mm or preferrably less. Given a 300mm dob, that would mean a minimum magnification of 150x, which would mean (assuming an 82 degree eyepeice) a field of about half a degree, which is getting a bit tight. 

I've got the full range of BST EP's, minus the 2x Barlow.

[Stu]

55 minutes ago, Ags said:

I am of the school that thinks larger aperture is a mixed blessing in light polluted skies. My situation is Bortle 8-9 (sometimes it seems like Bortle 11 😀 ) and my goal is pretty views in the eyepiece. That goal means the background in the eyepiece needs to be relatively black, not milky white. That in turn means a viewing exit pupil of 2mm or preferrably less. Given a 300mm dob, that would mean a minimum magnification of 150x, which would mean (assuming an 82 degree eyepeice) a field of about half a degree, which is getting a bit tight. 

That’s true enough, but you do have the option of filtering with OIII or UHC for nebulae which can allow you to use larger exit pupils under poorer skies. Doesn’t work for galaxies of course, dark skies are the only answer for those.

 

1 hour ago, Zermelo said:

I've not heard that one, but there is a line about larger scopes being worse when the seeing is bad, supposedly because their larger apertures are more affected by the moving air cells.
And then I've also read other people saying that's rubbish.

Yep, poor seeing definitely affects larger scopes more than smaller. I’ve seen this demonstrated very clearly when observing Jupiter through a 16” dob under fairly poor conditions. We masked the dob down to about 7” and the views became more stable. Ultimately the views were better in the larger scope but we had to wait longer for the better views.