Author Topic: Focusing on stars (Z)  (Read 516 times)

Ilkka Nissilä

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Focusing on stars (Z)
« on: August 12, 2021, 12:54:46 »
Hi,

I'm planning on shooting the Perseids tonight.

I'm wondering if anyone has had time to do astrophotography (or night landscape photography with stars) with Z lenses yet? What is the recommended approach to focus on the stars; is manual focus realistic with Z lenses such as the 35/1.8 (is the step size fine enough) or should I pack a mechanical manual focus lens? With DSLRs I've managed to manual focus with some struggle by turning the ISO dial way up to 25600 for focusing and then returning it to shooting ISO. However, many autofocus wide angles have a bit too fast manual focus turn and some slop in the mechanism (this isn't the case with Z lenses, but I'm still wondering if the step size is small enough near infinity).

I notice that there is a low-light AF mode in the Z6 II, I guess I can try this.

Thanks for any suggestions.

Ilkka

longzoom

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Re: Focusing on stars (Z)
« Reply #1 on: August 12, 2021, 16:15:39 »
Yeah, that's a real problem, for me, at least. I can't focus manually, so, in the daytime, I do focus my lens at infinity AF, beginning from a minimal distance, to let the mechanics absorb all the "flops". Repeating a couple of times, I do make a small - very small - sign on the lens's barrel, with a thin needle. At the night, I am setting the lens to the mark, beginning manually from the minimal distance, again. This way it is working for me, no problem.  LZ

Ilkka Nissilä

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Re: Focusing on stars (Z)
« Reply #2 on: August 13, 2021, 13:36:34 »
I was able to manually focus on the stars based on the live view image. However, I noticed that my eyesight doesn't correct all that well when it is dark. ;-) It might be time for new eyeglasses. The focus-by-wire was a bit frustrating but not impossible to deal with. I do prefer conventional manual focus. To be on the safe side I stopped the 35/1.8 down to f/2.8.

I also tried the low-light autofocus and it was a bit hit and miss whether it would pick up the star, but once it did, the outcome was OK.

I got plenty of satellite reflection trails and some uncertain meteor trails, will need to take this more seriously to figure it out. I also accidentally overexposed some stars. But I haven't been trying astrophotography in a long time and figured that now is as good a time as any to begin. ;-)

David H. Hartman

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Re: Focusing on stars (Z)
« Reply #3 on: August 13, 2021, 19:11:27 »
I got plenty of satellite reflection trails and some uncertain meteor trails, will need to take this more seriously to figure it out. I also accidentally overexposed some stars. But I haven't been trying astrophotography in a long time and figured that now is as good a time as any to begin. ;-)

Ilkka,

I'm wondering if Astra Noise Reduction and Edge Noise Reduction are useful tools in cleaning up hot pixels, if any, in your current photographs? Do these noise reduction tools remove real stars from the image? I have no idea how these noise reduction tools work.

I haven't attempted to photograph the Perseid meteor shower as the atmospheric conditions and light noise make such an endeavor quit useless where I live. I hope you'll post some images.

Dave
Beatniks are out to make it rich
Oh no, must be the season of the witch!

Ilkka Nissilä

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Re: Focusing on stars (Z)
« Reply #4 on: August 13, 2021, 20:29:47 »
I haven't tried noise-reduction software on astrophotography images yet.

Here is one pic from the place where we parked before going on the hill to find some open sky. I liked the trees in this case. This is with the Z6 II and 8-15 mm AF-S Fisheye Zoom-Nikkor at 8 mm, f/4.5, 25 s, ISO 6400. I focused on the top of the tree in the middle lighting via an LED torch. Unfortunately I had forgotten to turn off VR so that may have affected sharpness (the camera was on a heavy tripod).

I didn't find any Perseids in my photos; all the streaks turned out to be satellites.


Ilkka Nissilä

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Re: Focusing on stars (Z)
« Reply #5 on: August 13, 2021, 20:38:03 »
This first (dark) one is still overexposed for 12 stars at least, but it is otherwise very dim, the treeline is hard to see. Z Nikkor 35mm f/1.8 f/2.8, 4 s, ISO 2500.

It seems that if one wants to see the color in the stars (instead of white stars in blue sky which is a common style in night sky images), the treeline needs some auxiliary lighting or a double exposure and multiple exposures are needed to render the stars with more depth (more stars and nebulae with less noise). However as I was trying to catch meteor trails I didn't do any long exposures. I did do many exposures of the same scene and I could average those. I'll give it a try. Unfortunately the weather forecast is cloudy/rainy for the next 10 days.

There was quite a lot of fog as well so conditions were not ideal. In August during the night, fog is very common here.

The second shot shows an image averaged in PS from 25 frames, with one satellite trail visible. Edit: I changed the color balance to daylight so it would be consistent with the single frame and increased contrast to make it look like the night that it was. I have no idea how it dealt with the area between the stars and treeline but it seems to have dealt with it somehow. ;-)

WGHalvorsen

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Re: Focusing on stars (Z)
« Reply #6 on: September 03, 2021, 14:48:19 »
Ilkka, I have read recently that you should slightly de-focus if you want to see colors in the stars.

/Bill

Ilkka Nissilä

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Re: Focusing on stars (Z)
« Reply #7 on: September 03, 2021, 15:21:33 »
Ilkka, I have read recently that you should slightly de-focus if you want to see colors in the stars.


Thanks for the suggestion. I'll give it a try.

It does make sense that a slight defocus would make the stars dim enough to register without clipping and this would allow the colour to be preserved more easily all the while trying to get something from the nebulae to register as well.

Ilkka Nissilä

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Re: Focusing on stars (Z)
« Reply #8 on: September 05, 2021, 01:12:49 »
This is still a version with focus on the stars (I did take a defocused version but it lost many of the stars (even though there was more colour)).

Z6 II, FTZ, 8-15mm Fisheye Nikkor at 15mm, f/5.6, ISO 12800, 15 s. Nine shots merged in Photoshop automate/photomerge.

I noticed a problem that with this level of darkness, I couldn't really see anything through the LCD or viewfinder, apart from the brightest stars when the view was suitably zoomed in and positioned. The treeline was invisible to the viewfinder. Also the AF, although it did focus, it didn't achieve optimal focus on the stars, I had to do that manually (now the question may be whether it should be the objective, I'll have to do more testing to see that).

Edit: I replaced the image with a lighter version that I adjusted during daytime; after a few hours in the dark my eyes had been adjusted so much that I ended up showing a very dark image that didn't look right after my eyes came back to daylight adaptation

Ilkka Nissilä

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Re: Focusing on stars (Z)
« Reply #9 on: September 05, 2021, 09:18:11 »
I now realize how much eyes adapt to the dark; I should avoid editing during the night. ;) The shots were not intended to appear quite as dark as they do if I view them in daylight. ;-) Have to come up with rules: no editing of astrophotos at night after adaptation of eyes to the dark! This problem is especially evident if viewing on small mobile screens in daylight.

Nasos Kosmas

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Re: Focusing on stars (Z)
« Reply #10 on: September 05, 2021, 12:44:45 »
I’m not a dedicated Astro shooter but I use only manual focus into brighter stars and then I try to keep focus constant
I don’t care if it’s focus by wire in my Z6, I can do the job and here are two shots with the  kit lens on 24 f4
The place was not ideal it’s actually a beach during night and you can see the lights of the small town next to my place
I usually do some PP on LR on iPad , the Colored lines are passing airplanes as I can see  two different colors from the lights that are on the wings
Today I show this interesting article on Nikon rumors,  is actually in my country in Aegean sea where you may find many places with low light pollution areas

https://nikonrumors.com/2021/09/04/from-a-thought-to-a-photograph-astrophotography-in-despotiko-island-with-the-nikon-d850.aspx/

ColinM

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Re: Focusing on stars (Z)
« Reply #11 on: September 14, 2021, 18:32:58 »
Hi Nasos, thanks for the images.

Can you tell use more about the line of lights in the bottom 1/4 of each image, to the right of centre.

I'm curious how they're in a similar position on each image (or is the later one just a continuation of the same flight?)

Nasos Kosmas

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Re: Focusing on stars (Z)
« Reply #12 on: September 14, 2021, 21:30:28 »
Hi Colin!
Must be some minutes apart, I reposition the frame of the camera to get more sky space
It’s not the same plane,  The one is near the surface of the mountain and the other is higher
It must be a usual airplane direction Athens airport is 50km away