Why the haze and noise?

[peabrain]

Been an long time since i last went out after getting on night shift and selling my z50, and with my new gear i have run into something i need to figure out.

My question is 2 parts

My new gear list
Nikon Z7II full spectrum modified (have astronomik L2 filter and more)
Nikon z 24-70 F4 (temporary until i get a  z20mm F.1.8)
Sigma 60-600 sport
ioptron sky guider pro with ipolar

first the easy one.
A former co worker keeps comparing my Z7II with his Z5, and makes it sound like my sensor noise is going an EV or 2 up in iso, and my shutter time has to be almost double of his even using the same lens.

The second one is what keeps me wondering for the time being.  

When shooting landscape or tele i find my pictures getting a haze?
I have tried lower or higher iso or exposure time, i get the normal lower or higher normal iso noise but the darn haze is what is troubling me.
When trying to process the shots it is like the haze is "linking" the pixels, so that even small changes like changing a saturation on the red will affect the blues or other stuff.

(i know i must be doing something wrong, since with this equipment i should be able to make at least some decent shots.)

here is an example of a recent shoot. (have tried higher iso lower time same result)
24mm F4
iso 1600
120 seconds

example 2 (slightly over exposed for test purpose)
24mm F4
iso 1600
240 second exposure

[AstroMuni]

1 hour ago, peabrain said:

When shooting landscape or tele i find my pictures getting a haze?

Could it be because of light pollution. Are you close to city lights?

[peabrain]

was very dark at the site dark enough for my eyes to see a rough silhouette of the alleyway on the horizon.
 

[vlaiv]

3 hours ago, peabrain said:

A former co worker keeps comparing my Z7II with his Z5, and makes it sound like my sensor noise is going an EV or 2 up in iso, and my shutter time has to be almost double of his even using the same lens.

Just forget everything about EVs and ISO and all of that - that you use in daytime photography, when shooting astrophotography.

It is counterproductive and often confusing.

Noise is complex topic, but here is important part - you don't worry about the noise on its own - you worry about signal to noise ratio. If you want to have cleaner looking image - you need longer exposure to gather more signal - as signal grows faster than noise.

If is often not feasible to keep aperture open for say half an hour or hour - and that is what stacking is used for. Stacking is method of "adding" multiple exposures to form one long exposure that is (almost) the same as taking one long exposure of same total duration.

If you wish - we can go deeper into topic of noise and how it works, but for the time being - stronger the signal (that even includes transparent skies and position of the target) and longer total exposure - better SNR of the image (so expose for longer by taking many images and then stack them).

3 hours ago, peabrain said:

When shooting landscape or tele i find my pictures getting a haze?

That is perfectly normal. Atmosphere is not transparent - it acts almost as ND filter. More dust and particles there is in atmosphere - stronger the filter. Clearest sky is at zenith.

When you look down towards the horizon - stronger ND filter becomes and it simply attenuates light from target. You can see this effect every sunset / sunrise. You will be able to look at the sun when it is just about to set without any filtration. It will be red and light will not be strong at all. Contrary to that - you better not try to look at the sun at zenith - it will be painfully bright and it can even hurt/damage your eyes seriously if you do that.

There is second part to haze - and that is light scatter. Sky is blue because it scatters light - otherwise it would be transparent. Same thing happens at night - except there are fewer light sources. In heavy light pollution, sky will look orange (because of type of light pollution) - and it has to do again with density of the sky - when you look towards horizon - there is much more of the sky in that direction (thicker filter) and also dust tends to stay low (air density thing). This means that low down towards the horizon, LP scatter is the strongest.

Those two effects combined - strong ND filter and strong LP scatter - produce that grayish looking murk when your shot includes part of the sky that is close to horizon.

 

[peabrain]

Thank you for the answer it makes sense. and i somewhat already knew some of it.

Is there a way to remove the "haze" in a single shot for processing?

[vlaiv]

2 minutes ago, peabrain said:

Thank you for the answer it makes sense. and i somewhat already knew some of it.

Is there a way to remove the "haze" in a single shot for processing?

Probably not.

In principle, mathematics of what is happening is "known" - signal is weakened as you move down and there is LP gradient as well - so in theory, you could do it with some clever math, but the problem is SNR part of things. If light from target is blocked too much  - you simply won't record enough signal in single exposure to be able to "reveal" it. When you subtract the LP signal and boost back attenuated target signal - all you'll get is just noise.

 

[alacant]

4 hours ago, peabrain said:

doing something wrong,

Hi

I don't think so. They're lovely shots.

Maybe simply take the raw frame from the camera, but don't stretch it as much? Even the .jpg responds to a bit of tweaking. On the raw, you should be able to do a better job. 

Even better, take loadsa 240s frames and stack them with flat and bias frames. Stop the lens to say, f8 to tame the stars?

Full spectrum (fs)? So, one last thing, Use a strong ir cut. On a fs eos, this one worked well. The one-filter-does-it-all approach doesn't seem to work well with fs. 

Cheers and HTH

 

 

Edited August 12, 2021 by alacant

[peabrain]

I currently use Astronomiks L2 (IR cut filter) although mine is suspected of having some issues.

next time i will try and take at least 20 and a few dark frames. 

comparing my milky way landscape i seem to get a ton of extra stars, any tip for reducing the number of stars?

[peabrain]

Here are a few results from attempting to edit one of the shot. (got very noise very fast )
Next time i ill try and get more shots and try a few stacking software.

Still wondering how to capture and do good landscape milky way and stack em.

[vlaiv]

12 minutes ago, peabrain said:

Still wondering how to capture and do good landscape milky way and stack em.

You can do simple trick. Make your landscape close to you and make your landscape in such way that it hides horizon from you.

If you make landscape close to you - like few hundred meters - it will not get chance to get attenuated by atmosphere. If you look at mountain in a distance versus some object that is close in daylight - you'll notice that mountain is hidden in haze, often desaturated in color and without much contrast, while close object will look normal.

You don't want the "mountain" to be your landscape - you want "grass" to be your landscape.

There is much less atmosphere between you taking the shot and nearby object than it is between you and distant object.

Next part of trick is to make landscape cover part of the sky near horizon. Shoot "up" and not "down".

Even in desert where air is dry and clear and there is no much light pollution - you'll get murk if you shoot it so that distant objects make your landscape and horizon is visible:

But look what happens if you choose your landscape to be close and to cover horizon part - (like when you stand at the foot of the hill so that hill covers horizon):

Left half of image - no haze, right half of image - haze. Difference? Well, left part of the image has landscape that is close and it's hiding horizon.

Hope this helps

[peabrain]

That second to last one intrigues me, as my goal is to get the milky way to pop like that.
one thing though is that the center is not high enough where i live to ever get it that high.

the plan with my original landscape shot last time was to make panorama going up the milky way, then make a shot from low pointing up to hide the horizon. 
But kind of got frustrated since my shots til now, kind of blocked any attempt to process them.
It is kind of like something is blocking what ever i try to do in process.