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Luminance at a dark site, RGB from home

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#1 dx_ron

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Posted 02 March 2021 - 12:41 PM

Camera & strategy planning question:

 

I have a couple of dark(er) sites available - a state park that looks to be at the good edge of Bortle 5 about a 45-minute drive and a dark site owned by the local club (that I shall be joining shortly) that is Bortle 4 about an hour and a quarter drive. (I realize the limitation of estimating darkness from cleardarksky.com, but it is certain both are much darker than home and the farther away one will be darker than the closer state park). Home is at least Bortle 7, but probably more like 8. I expect I would be able and willing to make either drive a couple of nights a month at least. But I am unlikely to stay at either site much past midnight to 1am - I'm old smile.gif  Kind of limiting during summer.

 

As I get close to spending the money on a cooled camera, I'm thinking in a couple of directions.

 

1. The simple answer is to just get OSC, that would let me capture useful signal in a few hours at a time at the dark sites and I would just deal with the limitations of OSC imaging from home. I get by so far with a dslr, so I am aware of the added difficulties of dealing with light pollution gradients during processing (I rarely to never use a filter). This would also be the cheapest, and I can always sell and move up to mono at any time.

 

2. Mono. Can do narrowband at home, but I do like also shooting broadband targets. So my question is - if I use my dark site time for luminance on broadband targets, is it practical to add the color components from the much more polluted home? Would that give a better end result, or will the gradients in the color channels still be just as bad?


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#2 PirateMike

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Posted 02 March 2021 - 02:06 PM

I'm not sure as I don't travel all that much, but I would suspect that you would want to shoot the color at the dark sites and lum at home.The way I see it, you won't upset the color balance so much and the Lum can be corrected for gradience before adding to the image. 

 

Just go mono and be done with it. There are many advantages and having one will open up a lot of doors like NB, something a "small chip, cold DSLR" can't provide... for nearly the same price. You will get a lot more signal in a lot less time with a mono.

 

If the cost of the filters are an issue (as they usually are) just get a cheap LRGB set and add an Ha later, followed by O3 and an S2. Or just get an HA and start with that.

https://www.astrobin.../full/384810/0/

 

 

Miguel   8-)

 

.


Edited by PirateMike, 02 March 2021 - 02:09 PM.

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#3 John Miele

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Posted 02 March 2021 - 07:16 PM

Interesting...I say just the opposite. Shoot the luminance from the dark site and RGB from home. My logic is all the detail comes form luminance so that is the heart of the shot. It deserves the best sky to maximize S/N ratio. RGB is only going to paint color on the luminance and can have aggressive NR applied if needed. There are several ways to remove gradients in the RGB image if they become a problem.

 

cs...John


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#4 dx_ron

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Posted 02 March 2021 - 08:38 PM

That was my logic in posing the original question. If I go mono I rarely would have enough time at the dark sites to complete a substantial LRGB imaging session.

But I'm a beginner, so my "logic" is based on reading forum posts, not on doing.



#5 Stelios

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Posted 02 March 2021 - 09:15 PM

That was my logic in posing the original question. If I go mono I rarely would have enough time at the dark sites to complete a substantial LRGB imaging session.

But I'm a beginner, so my "logic" is based on reading forum posts, not on doing.

If you can afford mono, get mono. It's that simple. There's zero advantage to OSC, other than it simplifies taking flats and (slightly) initial processing. At times OSC comes close to mono, and that's all that can be said of it. Much of the time it's far behind. 

 

Are you going to be imaging someplace dangerous where you can't leave your stuff unattended? Is your car very small? I am 73, and sleep in a rollable mattress in my Toyota Sienna minivan. It's a shame to leave a dark site at 1AM. (My site is reasonably safe).

I haven't actually done it, but I agree with John's logic re RGB from home, as RGB is just for color and *all* the detail in LRGB comes from luminance. The RGB of course can be shot very efficiently with a mono camera. 


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#6 PirateMike

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Posted 02 March 2021 - 10:48 PM

Interesting...I say just the opposite. Shoot the luminance from the dark site and RGB from home. My logic is all the detail comes form luminance so that is the heart of the shot. It deserves the best sky to maximize S/N ratio. RGB is only going to paint color on the luminance and can have aggressive NR applied if needed. There are several ways to remove gradients in the RGB image if they become a problem.

 

cs...John

You are probably right, but I guess there would be only one way to know for sure.

 

I'm just glad that I don't image from a dark site so I don't have to find out which is better. wink.gif

 

 

 

Miguel   8-)


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#7 dx_ron

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Posted 03 March 2021 - 07:57 AM

Are you going to be imaging someplace dangerous where you can't leave your stuff unattended? Is your car very small? I am 73, and sleep in a rollable mattress in my Toyota Sienna minivan. It's a shame to leave a dark site at 1AM. (My site is reasonably safe).
 

That's an interesting question. The state park has a campground, but that's wooded and there's no camping allowed outside of the campground (and it isn't a very large park, most of it is occupied by the small reservoir). I don't have any sense yet for the club dark site, never been there. Somewhere before turning 73 I will retire, that will help too :)
 


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#8 Ron (Lubbock)

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Posted 03 March 2021 - 09:50 AM

I take the opposite approach with my mono setup: RGB at the dark site, and luminance at home.  I find that the light pollution has a more harmful effect on the RGB data, which already have lower S:N ratio.  Shooting RGB data from home gives me lots of work to do with removing gradients and green noise, and the colors are "muddy" after processing compared to dark site data.  Taking luminance from home doesn't hurt the image quality as much overall.  Then again, my home is Bortle 4/5, which is not bad at all as far as LP goes.



#9 imtl

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Posted 03 March 2021 - 10:05 AM

I'm just glad that I don't image from a dark site so I don't have to find out which is better. wink.gif

Miguel 8-)


I'm gonna frame that and make a poster title of it in the next NEAF. THAT is going to get some attention!
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#10 PirateMike

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Posted 03 March 2021 - 10:15 AM

I'm gonna frame that and make a poster title of it in the next NEAF. THAT is going to get some attention!

Do it do it do it! bow.gif


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#11 dx_ron

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Posted 03 March 2021 - 10:16 AM

I seem to recall that Miguel lives some place worth the tradeoff. Canaries, is it? I'd take that...


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#12 PirateMike

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Posted 03 March 2021 - 10:36 AM

Puerto Rico. Not quite the same as the Canaries. undecided.gif

 

They don't call it "The Shining Star of the Caribbean" for nothing.

 

Light pollution mapsm.jpg

 

 

Miguel   8-(

 

.


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#13 imtl

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Posted 03 March 2021 - 10:57 AM

It looks like a fish!

I see some dark sites, you just need a floating mount or a scuba-scope


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