Is Astrophotography Without Tracking Possible? (2022) | Hacker News Reader

Is Astrophotography Without Tracking Possible? (2022)

astroimagery.com

36 pointskarlperera25 comments

Nowadays, most people who say astrophotography don't mean Deep Sky photography, hunting planets, nebula and galaxies. It's mostly the sky over a wide-angle landscape. "Astrophotography" happens at < 20mm.

Totally viable untracked. The classic 14mm prime has gone from f2.8 to f1.8 to f1.4, and sensors have become really good at high sensitivity for a 15 second exposure. Quite often, that's enough.

The hairy part is when it's not quite enough, and exposures have to be stacked. I have a crop sensor camera (canon 1.6x, so 40% area) with an f/2 lens that I like to step down further, and a good Starscape this way will take 10-40 exposures. I can stack those no problem, but it's trees on the horizon that are problematic. The ground stack and the sky stack have to clash, and a complex shaped border will always look photoshopped, because it is.

Old school Deep Sky is losing its appeal due to a) pictures being available online, meaning that you've already seen the better version of the same photo, and b) the images being sterile and without context, with no relation to the photographer's story. Milky Way in a national park says "I've been there!" in a way that a shot of the Whirlpool Galaxy just can't.

Old school Deep Sky is losing its appeal due to C) too many ruined images from man made objects floating through the shot, D) a helluva lot more equipment required than just a camera and a lens

I love the wide angle astro stuff, but I'm more into timelapse. But I do love "trying" shooting DSO as well, but tracking is obviously required.

> Old school Deep Sky is losing its appeal due to a) pictures being available online, meaning that you've already seen the better version of the same photo

I find deep sky astrophotography compelling because there's still a huge difference between _my_ image of a galaxy and the many "better" ones already available. The difference is that I went through the experience of taking it so it feels more like it's really there. It's the closest I can get to actually experiencing seeing the galaxy with my naked eyes. The ideal would be visual astronomy of DSOs but that'll never be possible.

I mean, there are also still radio amateurs out there, but the hobby has seriously lost appeal with the arrival of the internet. And the crowd that you're a part of is not growing either.

Yes, and it is already happening in professional astronomy. For example, the "Antarctic Tianmu Plan" [0] have shown that you can successfully capture non-trailed images without using tracking mounts by using drift-scanning CCDs—basically letting the sky move across your sensor while the detector is read out at the same rate.

[0] - https://doi.org/10.1117/12.3019468

You can, but dark noise is a problem with this technique as your SNR per bucket ends up being low. The purpose of long exposures with tracking is to maximise your SNR.

Also, it helps significantly to be in Antarctica, where the relative movement is much slower than it is at lower latitudes — and to have multiple telescopes - and low noise CCDs, in a cold, dry environment.

Sadly, most of us don’t have those luxuries.

what about computational methods? i have always wondered how stacking many short exposures without tracking compares to deconvolution of a single long exposure. it seems that there is software able to do this by taking into account both motion blur and the PSF of the imaging system:

https://siril.readthedocs.io/en/stable/processing/deconvolut...

The problem is that the noise can swamp the signal. Another example of this would be doing astrophotography during the day. The sun doesn't block anything, it just makes the sky glow with "noise". Theoretically it has exactly as much signal from space as it does at night, but because the sun adds so much noise it's completely lost.

> "because the sun adds so much noise it's completely lost."

Do you mean that it would be conceptually possible to image planets or even deep-sky objects during the day with incredibly efficient denoising software? (I am a noob in astronomy)

I would be, yes. As early as the 1950’s, several avionics companies made daylight-capable star trackers (for jam-resistant long-distance airplane navigation) using chopper techniques. Those trackers were mostly mechanical, except for electronics to demodulate the star signal from the single pixel sensor.

I suspect diffusion models can shine at denoising single shot deep sky images. Will be attempting when I find bandwidth. I do a lot of deep sky landscape photography (IG: @dheeranet) and I want to do them in one go instead of stacking ground (untracked) and sky (tracked) separately.

I also don't agree that deep sky astro is losing its appeal and that is indeed what I am interested in. I think that each astrophotgrapher has his own style which is totally unique and if you check some of my image then you'll see what I mean. https://astroimagery.com/astrophotography-deep-sky-images/

Isn't trackerless astrophotography one of the main use cases for software that can do stacking like Siril [0] and similar tools [1] out there?

0. https://siril.org/

1. https://www.reddit.com/r/AskAstrophotography/comments/1b7fz3...

Siril is for integrating a lot of images together that are tracked and then removing the background. While you may be able to use it untracked it is primarily for tracked images.

Yes those software do align the images based on the stars so it can compensate for movement.

Tracking is needed for when you want to do say 15 second exposures.

The new technique for astrophotography isnt long exposures. Its about fast exposures in an attempt to maximize good atmospheric wobble.

That's called lucky imaging, yes. It's not particcularly new btw. Also, for capturing very faint deep sky objects like galaxies and nebulae you need long exposures of several minutes to get the deeper detail.

What about using a reflector telescope like a Dobsonian? Would it be able to capture more light lowering the requirement for exposure time?

The conventional wisdom is "Dobbies are not designed for photography" but that assumes tracking is necessary for photography. I'd expect that for untracked photography a Dobbie would work fine provided you could lock it down in alt/az and the whole assembly was robust enough not to vibrate for a few seconds. That might be a tall order.

I guess it would need some experimenting. I was thinking of getting something like Apertura AD8 for visual observation, but I was wondering if photography with it is feasible.

Don't buy a dob to do untracked astrophotography. It will be hard, and you will be disappointed with the results. I would pick between visual observation and astrophotography. They are almost separate hobbies that require separate kits. Get the Apertura AD8 for visual or a smart telescope like the Seestar S50 or S30 for astrophotography. The dob would provide great views of the Moon, Saturn, Jupiter, and decent views of some deep sky objects. The smart telescopes provide decent images of the Moon, Saturn, Jupiter, and great images of many deep-sky objects with image stacking build into the software. The smart telescopes are automated, and the dob requires learning the sky for manual tracking.

I mostly want it for visual observation, but if photography with it is possible - then why not try it. It's not the primary goal.

That conventional wisdom is because a Dobsonian is a Newtonian telescope on an altaz mount.

The altaz mount, not lack of tracking, is what makes it difficult for conventional astrophotography because the image rotates as you track the star. That prevents using a single long exposure. Equatorial mounts keep the image stationary.

What about short exposure which is the point of the above post?

That was my point.

1. Long exposures require tracking.

2. Dobbies can't track because they have altaz mounts [0].

3. But short exposures don't require tracking. Therefore a Dobbie might work for short exposures iff you can lock down the altaz axes and sufficiently reduce vibration.

[0] It is possible -- and fairly common -- to track with altaz mounts. Both axes require coordinated, computer-controlled stepper motors. In addition you need a third motor to rotate the tube. This was not possible before digitally-controlled motors. So some Dobbies do track but that kind of defeats the purpose of a Dobbie as a cheap light bucket anybody can afford.

In contrast tracking with an equatorial mount only needs a single motor and that motor doesn't need to be digitally-controlled.

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