Does bigger aperture = more light polution

[Kevdan]

Hi all,

Im about to make the move up from my trusted old 150p to hopefully a 250p ds on an neq6, but was wondering,

If the light gathering is 77% more on a 200p to a 150p and 177% more on a 250 pds to a 150p then does the lightpolution also increase or do lp filters solve the problem leaving just better images/views ?

Also what other kit do I need to use the neq6 syntreck with my laptop to make it a fully goto mount?

I may have around £1000 to spend give or take a little so its decision time.

Thanks,

Kev.

[knobby]

now that IS a good question

[Moonshane]

in a word no.

I have a 16" f4 newt which according to the hype is not worth bothering with in a light polluted area like that in which I live - close to Stockport and Manchester.

try telling that to my eyes when looking at the moon, the planets, the doubles, the open and globular clusters, the galaxies, the nebulae both planetary and diffuse......you get the drift.

obviously a dark site would make all the difference but the light pollution is all relative and to a large extent controlled by more magnification.

[Tinker1947]

I don't think you will, but you will well pleased with the 250mm tube.

[Jiggy 67]

That has never even crossed my mind, great question.......no idea!?!?

[jamespels]

I GUESS it's down to the LP being reasonably bright so you are not capturing much extra information (noise) by using a bigger scope. By comparison, a small scope will only capture a little light (signal) from a faint fuzzy; increasing the aperture will collect a lot more light so the definition on the faint object increases. In short, the signal : noise ratio improves, even if the overall amount of LP getting into the scope increases.

Of course, this could be utter twaddle but it seems a reasonable explanation to me

[Tim]

Mmmmm, good question.

Background light pollution reduces contrast in views and images, but my understanding, which is only based on presumption and experience, is that the ratio of contrast between the DSO target and the prevailing background skyglow will remain the same.

While in theory more background light is reaching your eye/camera, more DSO light is too.

For imaging purposes, you will likely find that less time is needed for each exposure than with a smaller scope for a given target.

But where you see a definite plus will be in resolution of the target, and whereas that will increase, the background skyglow shouldn't.

I don't think.

Because of the way they work, blocking certain wavelengths of light, LP filters should be just as effective at 10" F4, as they are at 6" f8. In fact you might even have more to gain.

Not a very scientific answer I know, but bigger scopes with a LP filter get/give better images than a smaller scope with a LP filter in general terms.

This link might also have some interest for you, calculating limiting magnitude for a given skyglow.

Telescope Limiting Magnitude Calculator

Hope that helps a bit and doesn't confuse more. Just based on what I have found from a very light polluted garden in the Midlands.

Tim

[RikM]

I have both a 150P and a 250PX and suffer from a moderate amount of light pollution. The bigger scope gives the better views

[ollypenrice]

You can't beat the direct practical experience related on this thread. Get your cheque book out!

Oly

[spaceboy]

I don't think the larger scope would suffer more from the light pollution but the views will be no better than travelling to dark skies with a smaller scope. Some may say there is no point having large aperture under LP skies and I think the reason for this is based solely on the extra effort and time required to setup, cool down times for one are longer and may often take more journeys in and out of the house to set up. I do agree that there are some night sky objects that are simply beyond LP skies and there is question to the worth of having a large telescope at home but I'm sure these questions could soon be put to rest by all the other night sky objects that do show an improvement.

What I have found is that the larger the scope the brighter the object is. We all know this scope catches 33% more than this scope and all the other but until you experience a real gain in that light grabbing power you cannot truly appreciate the advantages of using a larger scope. The brighter the object the easier it is to see with out using averted vision and the easier it is to pick out detail as you are looking straight at the object as apposed to using you peripheral vision. This added brightness would also mean that the background sky glow will increase but as the exit pupil at any given magnification remains the same there should not be a noticeable effect on the view in relation to the improvement of aperture has on the night sky object. All this said storage and portability can be an issue for a lot of people and when increasing aperture you are not just adding an inch or two on the width but also a significant amount on the length. You also have to take into consideration that larger often means faster and the faster the scope the more demanding it is on eyepieces.

HTH

[RikM]

I don't think the larger scope would suffer more from the light pollution but the views will be no better than travelling to dark skies with a smaller scope. Some may say there is no point having large aperture under LP skies and I think the reason for this is based solely on the extra effort and time required to setup, cool down times for one are longer and may often take more journeys in and out of the house to set up. I do agree that there are some night sky objects that are simply beyond LP skies and there is question to the worth of having a large telescope at home but I'm sure these questions could soon be put to rest by all the other night sky objects that do show an improvement.

What I have found is that the larger the scope the brighter the object is. We all know this scope catches 33% more than this scope and all the other but until you experience a real gain in that light grabbing power you cannot truly appreciate the advantages of using a larger scope. The brighter the object the easier it is to see with out using averted vision and the easier it is to pick out detail as you are looking straight at the object as apposed to using you peripheral vision. This added brightness would also mean that the background sky glow will increase but as the exit pupil at any given magnification remains the same there should not be a noticeable effect on the view in relation to the improvement of aperture has on the night sky object. All this said storage and portability can be an issue for a lot of people and when increasing aperture you are not just adding an inch or two on the width but also a significant amount on the length. You also have to take into consideration that larger often means faster and the faster the scope the more demanding it is on eyepieces.

HTH

Wise words

[acey]

The effect of light pollution doesn't change as aperture increases. But if light pollution is very bad then the benefits of increasing aperture are less pronounced. For deep sky viewing, a small scope at a dark site is better than a big one at a bright site.

For extended DSOs (galaxies and nebulae), visibility is dependent on contrast, which is effectively the surface brightness of the object minus the surface brightness of the sky. When you magnify in a telescope, the surface brightnesses of object and sky are both decreased by the same amount, so the contrast remains the same.

If light pollution is very bad (i.e. the surface brightness of the sky is very large) then there may not be sufficient contrast to see the object to begin with. In that case no amount of aperture is going to make it visible. You can't see galaxies in daytime.

All the above is relevant to galaxies and nebulae. For stars, increasing aperture will always increase the limiting magnitude of the scope.

For planets, increasing aperture might give better resolution, though the limit of resolution in typical atmospheric conditions can generally be reached with a 4-inch scope.

In summary, don't be afraid to increase aperture. But if you're presently using a 6-inch at a light polluted site and are thinking of getting a 10", also consider if you are able to transport the 6" to a darker site: that will give you better deep-sky views than a 10" at the light-polluted site.

Or best of all, get the 10" and take it to the dark site. But you might find the 6" easier to move.

[Kevdan]

Thanks for all the replies, Im 16miles east of birmingham but southern and western skies are reasonable, looking north is okish due to streetlamps.

Thanks,

Kev.

[spaceboy]

Bish is from Dudley and he has the dob version 250PX it may be worth you PM him and see what feedback he has to offer.

[assasincz]

In my oponion - no

The level of light pollutionto the image will remain the same, comparatively speaking. The background will seem brighter when compared to smaller amertures, but so will the stars and DSOs. It will be similar to taking the image produced by a small aperture scope in an light-pollute area and turning the brightness up a bit.

Or am I wrong?

[RogerTheDodger]

Kev, I'm down the road in Halesowen (western edge near A456) and the LP looks no worse in my 8" newt than my ST80, but the object I'm looking at is much brighter.

[Ags]

The background brightness is determined by the exit pupil not the aperture. It will never be brighter than the naked-eye sky. Extended object brightness is also determined by exit pupil, so they will not be brighter in a larger scope, but they will be much bigger and easier to see. Only star brightness is proportional to aperture.

[Kevdan]

Thanks again guys,

Kev, I'm down the road in Halesowen (western edge near A456)

Hi, Its posh there ay it Lol

Looking east as you know is just no good unless its something very high up, I've had a glitch in my funds so I may be only going up to an 8" but I want to stick with the NEQ6 so that if I decide to upgrade further the mount will cope, that way the misses wont moan in 2 years time when I tell her Im upgrading again.(ask very nicely if its ok for me to have an upgrade.)

Kev.

[jamespels]

Thanks again guys,

Hi, Its posh there ay it Lol

Sounds like I drive past both of you quite a lot! I'm getting very familiar with the A456 from the M5 to Kidderminster twice a week (lucky I like my job with this commute form the Peaks!).

I've taken the route down to Kidd on the other side from Bridgnorth once or twice when the M6 has been blocked - some quite dark skies out that way?

J.

[LukeSkywatcher]

Interesting topic.

I have found that the higher i go in aperture the LP remains the same, however bigger aperture allows for more magnification and this is when you could run into problems as the higher magnification also magnifies atmospheric conditions.

But its all relative. So i would say "NO".

Not forgetting the fact that you do get better views with bigger aperture.

[S1m0n]

One place I put my scope is right next to a street lamp and surprising the light doesn't get in the way too much compared to the darker area where I use the scope the most which is obviously better.

I suppose this is one of those questions that will have many different answers and as a new user I can only give you an answer to my own experience.

[LukeSkywatcher]

One place I put my scope is right next to a street lamp and surprising the light doesn't get in the way too much compared to the darker area where I use the scope the most which is obviously better.

I suppose this is one of those questions that will have many different answers and as a new user I can only give you an answer to my own experience.

Have you tried using a light pollution filter?

Try it and that will show you just how much that streetlight is messing with your view.

[jamespels]

OK, thinking this through a bit more, it has to be related to magnification. The LP density across the FOV isn't going to change with magnification; however, larger apertures are going to gather more light from the fuzzies so they will support more magnification.

As a result, the relative light density from the fuzzy (signal) increases relative to the unchanging LP (noise) so there is a direct relationship between aperture and the ability to negate the impact of LP.

(At least in my head, where it is sharing the space with half a bottle of Turner Road cab. zinfandel so there is the teensiest chance of error )

[S1m0n]

Have you tried using a light pollution filter?

Try it and that will show you just how much that streetlight is messing with your view.

Not tried a lp filter but I may try one many thanks for the info

What's the name of the filter ?

[LukeSkywatcher]

The one i use is this:1.25" model

First Light Optics - Skywatcher Light Pollution Filter

I can point my scope right between 2 streetlights and the orange glow is seriously reduced.

I use it in my back garden (no streetlights).............but to test it i have pointed it right between 2 streetlights out the front.