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Using D810 for astrophotography

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#1 Waterobert

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Posted 17 September 2019 - 08:02 PM

I just got Stellarvue 80mm /f6 scope and this weekend I would love to try using my D810 Nikon for astrophotography. I should get Nikon T adapter and focusing mask this Friday. Scope and camera will be on Astro-physic's Mach1 mount. I will not be guiding, and polar alignment will be done with help of Polar Master. This will be my first time using D810 camera for AP. I am thinking of M31 as my target. What ISO setting should I start with and how long my subs should be? I am located in red zone, so I don't expect much. Any help would be greatly appreciated.



#2 Jim Waters

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Posted 17 September 2019 - 08:05 PM

What's your light pollution like?



#3 andysea

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Posted 17 September 2019 - 08:09 PM

From dark locations and with the D810a I usually do 1 minute subs at f4 and ISO 800. Have tried 2 minute at f6 and that worked well.

I think that with heavy light pollution you probably want to do shorter subs than that. Maybe try 30 seconds? Theoretically you want to expose to the point that your background swamps the read noise by 10x. With heavy light pollution and a low read noise camera that shouldn't take too long.



#4 bobzeq25

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Posted 17 September 2019 - 08:36 PM

Looking at your posts, it sounds like you haven't actually imaged the deep sky yet.  Forgive me if you already know some of this, OK?  I do see you already have the Deep Sky Imaging Primer, which is great.

 

Your 810, like my D5500 is "ISOless", meaning the read noise does not increase substantially at low ISO.  So low ISO is better, gives better dynamic range.  Nikons can do some funny things at 100, I use 200.

 

Excellent rule of thumb for exposure.  Pull up the histogram on the back of the camera, try something.  30-90 seconds will do.  What you want to do is get the obvious histogram peak about 1/3 over from the left.  About is good, there's no benefit in trying to get it "exact".  The result is you're shooting about the right exposure.  Not doing too many short subs (which are subject to read noise) or too few long ones (which also costs you dynamic range).

 

That procedure automatically compensates for your light pollution level, and the speed of your optics.   It all gets wrapped into the histogram.

 

For your first image I suggest a star cluster instead of either a dimmer nebula or galaxy.  Especially if the Moon is out.  It will allow you to cut your teeth on a target which will give you an image to work with, make problems more obvious.  Even a random starfield will do.   The important thing is to get started in a way which doesn't leave you scratching your head (too much).

 

I trust you realize that stacking multiple subexposures, and processing the data intensively, is what makes this work.  The more subexposures, the longer your total imaging time, the better it works.  Especially in light polluted skies (like I have).  My rule of thumb is one hour minimum, two is better, four good.  One will do for now.

 

Do take the camera calibration frames also; bias flats, darks.  If you don't you're almost surely going to learn some bad habits in processing.  Processing is hard enough without having to unlearn bad habits.  <smile>

 

For stacking/processing software I recommend Astro Pixel Processor.  It does both, which avoids possible trouble transitioning between two programs.   There are advantages to using an astro specific program, this is quite unlike terrestrial photography.

 

Have fun.  But, realistic expectations.  The pretty pictures do not come easy.  <smile>


Edited by bobzeq25, 17 September 2019 - 08:40 PM.

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#5 KLWalsh

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Posted 18 September 2019 - 12:36 PM

I have an 810A.
I recommend downloading and using Backyard Nikon from otelescope.com. The pro version is fairly inexpensive but you can do a free trial.
Makes AP so much easier, letting the pc act as an intervalometer to control the camera and store the images.
There is a YouTube video by the author (Guy Rochon, iirc) which is a good intro. He talks about the original Backyard EOS for Canons; a lot of it applies to Nikons.
I typically start by making a 20 or 30 second shot at the highest ISO setting to make sure the object is framed how I want it. Then I shoot at ISO 200, maybe 400 and 800, for exposures from 60 sec to 300 seconds - but I’m in a Bortle 3 - 4 zone, so my skies are fairly good.

At an fl of 480 mm the full frame will get all of M31. But it’s a difficult object as a first object. You might try globular clusters first. You could waste an entire night on M31 and get nothing usable.

Edit: I always take flat frames. (Sky flats, usually.)
The noise on the 810 is so low, it’s practically a waste of time to take darks or bias frames.

Edited by KLWalsh, 18 September 2019 - 12:40 PM.


#6 bobzeq25

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Posted 18 September 2019 - 04:23 PM

I have an 810A.
I recommend downloading and using Backyard Nikon from otelescope.com. The pro version is fairly inexpensive but you can do a free trial.
Makes AP so much easier, letting the pc act as an intervalometer to control the camera and store the images.
There is a YouTube video by the author (Guy Rochon, iirc) which is a good intro. He talks about the original Backyard EOS for Canons; a lot of it applies to Nikons.
I typically start by making a 20 or 30 second shot at the highest ISO setting to make sure the object is framed how I want it. Then I shoot at ISO 200, maybe 400 and 800, for exposures from 60 sec to 300 seconds - but I’m in a Bortle 3 - 4 zone, so my skies are fairly good.

At an fl of 480 mm the full frame will get all of M31. But it’s a difficult object as a first object. You might try globular clusters first. You could waste an entire night on M31 and get nothing usable.

Edit: I always take flat frames. (Sky flats, usually.)
The noise on the 810 is so low, it’s practically a waste of time to take darks or bias frames.

It's not a waste to shoot bias.  Flats are handled very differently than lights or darks.  They're much higher ADU and you divide by them instead of subtracting.  The math of flat correction doesn't work well without bias being subtracted from both the lights and the flats.  There's a fixed component of bias, that's substantially larger than the noise around it.. 

 

Not to mention that shooting a set is trivial, and you can use a master bias for months.

 

I don't shoot darks with my D5300 (any more, I did at first), for the same reasons as you.  I do recommend beginners do them, they're an essential skill for an imager.  Down the road a CMOS camera waits, and those need darks because of amp glow.


Edited by bobzeq25, 18 September 2019 - 04:25 PM.

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#7 Waterobert

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Posted 19 September 2019 - 07:09 AM

Thank you guys!

I will start with 30s subs at ISO 200 and take it from there. I always thought that M31 would be a good target due to its size. Well I was wrong, lol. 


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