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Astrophotography #79

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void4 opened this issue Jul 9, 2022 · 0 comments
Open

Astrophotography #79

void4 opened this issue Jul 9, 2022 · 0 comments

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@void4
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void4 commented Jul 9, 2022

(work in progress)

Who this is for

Maybe you should only read this if you don't want to go into the hobby yourself. One of the great advantages of newcomers to all fields is their naivete - not knowing what awaits you, a wide-eyed expectancy can give you the momentum to embark on difficult quests and with it the energy to endure their unexpected challenges - which you may not have taken on if you knew their complexity beforehand. But it may be useful to have heard of some problems and solutions before you encounter them. In any case, this hobby can also be very educational and rewarding - there are many many many things you can do.

How it started for me

For me it started when I remembered I liked to see stars, and that I hadn't seen them often so far in my life. Lacking any equipment, even a camera, i tried out some web-based remote controlled telescopes, and was amazed by some results. But they were very expensive.1

The images hooked me and I started my journey of getting into the basics of astronomy and editing. There are overwhelmingly many things to learn. From scaling to alignment and stacking, to astrometry, to filters, to coordinate systems, and many kinds of software. There are hundreds of new terms and concepts you will encounter - unless you have a background in photography or astronomy, they will be completely new to you.
words

And soon I learned, not only the theory, but also the practice is an endeavor that will take not months, but decades to master...

image

A typical progression

1. Making (very) short or long exposures or time lapses with a static camera on a tripod

Install Stellarium and learn how the stars move across the sky. Assuming you already have a camera and a tripod, for this you will probably need a remote shutter release to do long exposures (cameras can usually do only up to 30 seconds themselves) and to avoid shaking the camera when pressing the shutter button. These cost about $20-$40 (relevant terms: intervalometer, bulb mode, polar star, relevant site: https://photographylife.com/remote-shutter-release)

image

image

(source)

2. Getting a star tracker (optional, good if you don't immediately want to go "up" to a telescope)

These allow you to take longer exposures with your camera (typically up to 5-10 minutes), without the stars trailing into lines due to their apparent movement due to the rotation of the earth.

image

This costs about $250-$450 and is also the step where the image editing aspect of the hobby starts. Get ready to not only learn lots of things about the sky, but also the basics of the post-processing process (e.g. registration, alignment, stacking). At this point many exposures may be combined to achieve a better final image.

Recommended guide: https://www.peterzelinka.com/blog/2018/8/which-star-tracker-should-i-get

Getting a fast (low f-value like 1.8, aperture is important) telephoto lens can improve both the amount of light you get and enable you to capture smaller objects.

This is still considered "wide-field" photography, meaning you capture a large portion of the sky. For comparison, while a camera with a 50mm lens might cover 30° of the sky, a telescope that is built for "deep-field" astrophotography will cover only about 0.5-1.5°. That's the difference between the moon being a small circle in the image and it covering the entire image:

Screenshot from 2022-07-09 22-52-24

Screenshot from 2022-07-09 22-52-03

1° (one degree) is about the same as the width of your little finger at an arms length, the moon spans about half a degree, the Andromeda galaxy 3°, but it is much, much fainter - about 3 million times!

image

(from: https://www.timeanddate.com/astronomy/measuring-the-sky-by-hand.html)

Most deep sky objects are much smaller than that, so if you want to image these, you'll need a mount and telescope that can reliably track and collect enough light from this little patch of sky.

3. Buying a telescope

This is were many more concepts become relevant, and the setup and post-processing time more significant (refractor vs reflector, calibration frames, all kinds of software).

If you want to do deep sky object (DSO) astrophotography (planets, galaxies, asteroids, nebulae), this should be a motorized equatorial mount (not alt-azimuth, because those need to rotate on two axes simulatenously to track the stars) that like the star tracker can make the telescope follow the stars.

altazvsequ

(from Alt-Azimuth Mount vs Equatorial Mount)

This will cost >$1000, because astrophotography setups have more and different requirements than those that are only used for visual observing. It's good to learn about and understand these aspects before deciding on which particular telescope+mount you want to purchase.

For example, planets need long focal lengths, nebulae might need filters, deep sky objects like galaxies need a lot of light. A telescope that is excellent for one of these use cases may be completely unsuitable for the others. Depending on the scope it may still be possible to use your camera, more permanent (and especially remote-controlled) setups use dedicated astro cameras.

While a larger star tracker can handle some smaller telescopes, only with the bigger mounts can you mount the larger diameter, heavier telescope tubes that are necessary for deep sky object astrophotography. Important aspects of mounts:

  • motorized/tracker: necessary for long exposures
  • go-to: has motors on both axes and can point to the object/coordinates you want to target itself, controlled by either an external hand controller, some by smartphone or a computer
  • computerized: is or can be controlled by a computer (useful if you need/have to do autoguiding or want a more automated setup)

Telescopes are essentially light buckets, with a larger diameter tube collecting more photons. But with increasing size comes an increased weight, not only for the mount which must support it and all the extra equipment that is attached to it, but also for you all to transport if you can't image from home.

post-217769-0-87311700-1656561349_thumb
(from here)

Larger mirrors also become more expensive.

The longer the focal length, the smaller the patch of sky the telescope 'sees' - this is called the field of view (imagine looking through a toilet paper vs kitchen roll). Many objects are really really tiny in the sky so you need a good focal length to "distribute the pixels" of your camera across that small field. Otherwise some features or objects may be covered by one pixel and you may not be able to see them.

Check out the r/astrophotography telescope guide: https://www.reddit.com/r/astrophotography/wiki/what_telescope

Telescope systems rarely come as a kit, since the different components are from different manufacturers. So it's up to you to find a combination that fits your desired use case.

It may be possible to find a cheaper second-hand telescope, or if you're up for an extreme challenge, you might build your own 2.

If using a dedicated astrocamera, will you use a monochrome camera with filters (and a filter wheel) or a color camera? Each has its own advantages and disadvantages.

image

A filter wheel for monochrome cameras.
image

The longer your exposure time, the more light you collect. However, it also increases the risk of

  • clouds covering or satellites or planes flying through your image
  • tracking errors, causing stars to become trails or larger blobs eventually
  • the telescope accidentally moving (for example by wind or you bumping into it)

For these reasons, exposure times are typically kept between 60 seconds and 5 minutes, and the resulting images aligned and stacked in post processing.

The longer focal length of a telescope also brings its challenges: finding (go-to can help here) and keeping the object you want to capture in the smaller field of view gets harder, where in wide-field images a quick polar alignment may have been sufficient to avoid tracking errors, even small alignment discrepancies will now become noticeable in longer exposures, possibly necessitating Autoguiding - itself requiring more equipment: a guide scope, a guide camera, cables and software.

Screenshot from 2022-07-11 12-40-39

image

The most important thing however will be location, location, location. Depending on where you live, light pollution may be a problem, buildings or trees may obscure the view, or clouds will become your enemy.

image

If where you live is too bad, think about whether you'd be willing to go elsewhere with better conditions, and what implications your setup complexity, size and weight have for such trips. Power supply is also something to consider.

When I started, I very quickly realized that I don't live in Chile or the Australian outback but in an absolutely light polluted city, the only thing I can see here is a hint of color of a single band on Jupiter's surface, a suggestion of the space between Saturn and its rings and when I point it at somewhere else in the sky I see some faint dots, more stars than with the naked eye, but nothing impressive.

The only consistent good thing is the moon, but even its image is always distorted by the heat of the city and turbulence of the atmosphere. Seeing better requires traveling an hour outside of the city, at least there Jupiter seems to be pretty clear. Inside the city, the sky is too bright. In the city, Jupiter is still a blob. I'm happy to see some light of its moons though.

Besides telescopes being pretty bulky and financially painful, I also realized the following:

Aligning mounts can suck, especially when it's cold outside (and winter is unfortunately the darkest - and therefore best time to observe - you might not even see the milky way in a summer night). Focusing, manually aligning and tracking objects is frustrating, with 140x instead of 70x magnification essentially impossible. Also the clouds, the f*cking clouds.

clouds

Nature becomes your enemy in a way you never expected. Depending on your location, you may only get a few cloudless nights per month. And forecasts are unreliable, so planning becomes impossible and the hobby can rob you of a healthy sleep cycle. And it's not just the clouds, atmospheric turbulence (also called astronomical seeing, the reason why stars seem to twinkle, essentially a nightmare for all earthbound/ground based astronomers) which is somewhat independent of cloud coverage can be a major limiting factor of image quality. And the mosquitoes, street lights, obstructing trees, the brightness of the full moon, all these things can stand in the way of an enjoyable experience.

I needed an adapter to be able to use the camera with the telescope. Searched, bought and waited for the adapter for quite a while. Finding the right adapters/spacers can cost quite a bit of money, nerves and time. Since astrophotography has become more popular recently, a few items might be out of stock or take a long time to deliver. Sometimes you get a new piece of equipment and realize you need yet another one to actually or effectively use it.

Some GoTo mounts may not be built for accurate tracking, especially with a heavy camera on it. Exposures longer than a few seconds have trails. Check the mount and motor weight capacities! A good setup requires all parts working well together.

4. A small personal observatory and/or remote controlled telescopes

This very much depends on your style. Some people happen to have a back garden, and want a larger, more permanent setup. A telescope on a steel or concrete pillar, covered from the elements by a roll-off roof wood shed
ezgif-5-a0d448056e

plastic clamshell

image

or rotating dome

image

avoids having to set up and realign the telescope every night.

Some people band together in groups and collectively afford a remote controlled telescope at a very good, dark location somewhere on the planet.

Some rent telescope time (anywhere between minutes and hours) at one of the several web-based providers (e.g. Telescope.Live, iTelescope.net, VirtualTelescope.eu, Telescope.org, Slooh.com).

itelescope

Especially on cloudy days, I occasionally seek comfort in these web telescope pics. But even 40 bucks only get me a half hour of exposure with the good telescopes. And the results are far from what can be considered good images, these simply require longer exposure time (HOURS!). While they provide unparalleled sky conditions, another disadvantage of these remote controlled telescopes is that they simply don't feel the same. If you are a tinkerer, just tapping some buttons to get what you want will feel wrong. If you are more interested in the image editing aspect of it though, or live in a really astro-suboptimal location, it may be the right thing for you. It can obviate the need to own and mess around with any hardware altogether.

As a redditor estimated once, a good automated setup can cost >=$10,000. Don't neglect the software cost as well. I guess this progression exists in many hobbies, but astrophotography especially seems to require a lot of time, patience and moolah before getting any satisfying results. Also, location, location, location.

Other stuff

Astrophotography from $100 to $10,000

I made this list of Astronomy Youtubers, maybe you can learn from some of them.

Some subreddits:

r/astrophotography

r/AskAstrophotography

r/telescopes

r/astrophotogramemes

Footnotes

  1. Like with many hobbies, money is a factor, and may even be a constraint. But more on that later.

  2. The popular Dobsonian-type telescopes, because of their Alt-Az mounts aren't suited for astrophotography though, only for visual observing. Some people are crazy enough to even grind their own mirrors - this level of dexterity, dedication and patience eludes me however...

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