AN article

[wookie1965]

Got my AN few days ago I was reading through it came across the article "making light work" in the article it says wider FOV is best for light polluted skies I just cannot get my head around this what do people think, here is the piece.

[lunator]

Interesting idea. I know from experience increasing magnification allows you to spot fainter objects. When I observe double stars mag 11+ stars which are not visible at x70 magnification start to appear once you get into the x100-150 range. 

I guess the only way to find out is to test an ethos against an orthoscopic eyepiece :). 

cheers

Ian

[Adam1234]

Sounds counterintuitive at first, but I think it would make sense - depending on the source of the light pollution perhaps. For a given size of aperture I wouldn't have thought any more light would enter the scope regardless of whether you used a 50 or 100 degree apparent FOV. 

That might be different if the source of light pollution was a street lamp next to your house though, as the wider fov might then bring the lamp into the fov.

Edited January 22, 2020 by Adam1234

[johninderby]

Not noticed the difference myself and wonder if it’s more about perception than reality. 🤔

Perhaps some just don’t notice the light polution as much in an ultrawide eyepiece or might it depend on the amount of local light polution.? 

[John]

The wide, ultra and hyper wide field eyepieces enable you to see a good size chunk of sky while delivering an effective exit pupil and enough magnification to darken the background sky if there is some light pollution around.

I think that is what the article is saying though perhaps the way it is expressed could be better ?

 

 

 

 

[michael.h.f.wilkinson]

I don't see this working. You are simply admitting a larger chunk of the primary image into the field stop of the EP. The magnification is the same, thus the apparent surface brightness is just the same. Suppose I move from 50 deg AFOV (apparent field of view) to 70 AFOV at the same magnification (say the difference between 20 mm SLV and XW EPs). The latter allows twice the field of view (in square degrees), thus letting twice the amount of background light reach the eye, spread over twice the AFOV, so the same surface brightness. If anything, this will make matters worse, as dark adaptation might suffer. Now replace the 20mm XW by a 14mm XW. This gives the same true FOV as the 20mm SLV, thus admitting the same amount of background light to the eye, but spread over twice the AFOV, thus halving the surface brightness of the background. Stars, being point soruces are more easily spotted, therefore. Nebulous objects become a bit more apparent, as the eye picks up slightly larger diffuse structures with a given contrast ratio with the background more easily. I think this is the reasoning Al Nagler used when stating UWA EPs help fight light pollution.

[cotterless45]

Think that the article is overlooking the main problem with light pollution; lack of contrast. I'd say increasing magnification until the view degrades will give you contrast . I can't see any other factors ,with regard to letting more light in ,would affect the light pollution.

Rather similar to light buckets letting in lots of light pollution. There was another gem , air turbulence bubbles are said (!) to be 4" diameter . Using a 4" aparture frac will optimise this ! I'll put that idea next to my cloud busting gun.

Anyway , the only 100 degree eyepiece that l looked through , I could get my eye around the view !

Nick.

[John]

35 minutes ago, cotterless45 said:

...Rather similar to light buckets letting in lots of light pollution. There was another gem , air turbulence bubbles are said (!) to be 4" diameter . Using a 4" aparture frac will optimise this ! I'll put that idea next to my cloud busting gun....

 

To be fair, I have read this theory of atmospheric cell sizes enabling smaller apertures to make the best of the seeing conditions a few times before. Refractors do seem to "punch above their weight" sometimes.