‘Grey’ space

[Tomjo59]

A bit of sage advice required.

Using my 10” Newt, if I look at a star cluster, or other part of the sky richly populated with stars, I see the individual stars as nice, clear pinpoints, as you would hope, given quality optics (1/10 wave mirror) and accurately collimated.

However, the spaces between the closely separated stars appear to me to be a very dark grey, rather than pitch black. Is this my eyes, or could this due to internal reflections that might be improved by flocking?

Any suggestions would be welcome.

Apologies if this is in the wrong  sub-forum.

[furrysocks2]

What eyepiece were you using, and what else have you got? The higher the magnification and thus smaller the exit pupil, the darker the background will appear. This may not be your answer, but it's a starting point.

Edit: is it perhaps the airy discs overlapping?

[Stu]

First question, what are your skies like in terms of Light Pollution? Any particular targets you notice it more?

The sky is never actually pitch black due to air glow, the Milky Way etc. As said, higher magnifications will darken the sky background, widefield views under brighter skies can seems very washed out.

[Tomjo59]

7 minutes ago, furrysocks2 said:

What eyepiece were you using, and what else have you got? The higher the magnification and thus smaller the exit pupil, the darker the background will appear. This may not be your answer, but it's a starting point.

Edit: is it perhaps the airy discs overlapping?

I was using a 32mm Baader Classic Plossl, giving me a magnification of 49x. I have used a 20mm, but because the stars are more widely separated, it isn’t really noticeable. As I say, the star images are tightly defined, so don’t think it is overlapping Airy discs.

I live in a rural area, and my skies are pretty good (can see the milky way clearly).

[Paz]

I don't know what it is but those symptoms do tally with a bit of light pollution. A 32mm eyepiece in a big reflector is going to bring out any lp by washing out the background a bit. Higher magnifications will stretch the background out bringing it closer to black, as you describe bring the case with a 20mm eyepiece.

[mikeDnight]

On 16/12/2017 at 12:52, Tomjo59 said:

A bit of sage advice required.

Using my 10” Newt, if I look at a star cluster, or other part of the sky richly populated with stars, I see the individual stars as nice, clear pinpoints, as you would hope, given quality optics (1/10 wave mirror) and accurately collimated.

However, the spaces between the closely separated stars appear to me to be a very dark grey, rather than pitch black. Is this my eyes, or could this due to internal reflections that might be improved by flocking?

Any suggestions would be welcome.

Apologies if this is in the wrong  sub-forum.

I'm not sure I'm talking about the same thing as you're seeing, but not all space is black. Looking at milkyway star fields with a low power wide field eyepiece, there are vast swaiths of dark nebulosity visible which do display a dark sooty grey appearance. Perhaps you're detecting this dark interstellar dust among the stars as you observe. If so, its an indication that you are  keen eyed observer, as it is not immediately obvious.

[John]

Sounds like my skies are similar to yours. With a 30mm or longer focal length eyepiece in my F/5.3 12" dobsonian, my background sky is not pitch black either, unless it's a particularly dark night. I find using a an eyepiece of around 20mm focal length does produce a darker sky. I ascribe this effect to the background light pollution and the larger exit pupil that the 30mm or longer eyepiece produces with this scope. Light scatter from the secondary mirror and it's supports might be a contributory factor as well.

With my refractors, which vary from F/6.5 to F/9.2 and apertures from 100mm to 130mm I find the background sky generally darker even with 30mm+ focal length eyepieces. The stars have that "jewels on velvet" look more often as well. But thats what refractors are good at 

[ronin]

If open clusters then quite likely. Open clusters are part of the milky way, enough gas has collected to at some time create a bunch of stars. So they will sit in the milky way, so have stars behind them supplying a "milky" background, and they may still have gas around or behind that add to the illumination. In effect anything that is in the milky way will have an illuminated background to it/them.

Globulars clusters "should" be a little better but they fade out towards the edges in terms of number.

Next is that the scope and eyepieces will still scatter light, more elements in the eyepiece add to this - for "clarity" people will use something like a TV plossl as they are lesser elements and good.

The other is also our sky is not dark, there is scattering of light occuring in it all the time and that creates a very dim background to what you see.

[laowhoo]

Sounds like we have the same skies. We analyze the blueness when we walk the dogs in the morning--light blue will be washed out gray at night often--and the day after a storm is usually our best chance for dark blue day sky and dark skies at night. We have two 2" EPs that we never get to use, though--36mm72 and 31mm72--for about 50-65x w/ 6mm and 5mm exit pupils--and even on our best nights only the 24mm will render that velvet sky. Even under the darkest sky we traveled 5 hours for (and cross country, too), I still couldn't use the 36mm.