Astrophotography Essentials
Feb 28, 2021 12:36:29 GMT
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Post by BrƎИsꓘi on Feb 28, 2021 12:36:29 GMT
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Hopefully this thread may help a few who (like myself) are just starting out in astrophotography. It can be a sink-hole for money, I've made mistakes but find I'm learning one key maxim: Not everything being advertised as a "must have" really is. Work out what you want to do, work out what you can afford and and ensure your "purchase" do meet your needs.
Before we start: One Essential: A Tripod. In all instances you're taking images where the camera shutter will be open for extended periods - and certainly much longer than daytime shots. Even the slightest movement and your night time image is trashed. If you don't have a tripod, YOU WILL need something strudy to place your camera on. A shutter trigger - or timed release will also be essential.
CAMERA:
DSLR: Any DSLR will do a great job. I'm biased but the Canon EOS range are really user-friendly cameras - and all EOS kit is compatible.
The key here is lenses. Most night targets require lots of light and for extended periods of time. Any lens with an aperture setting from F/4 upto F/2 will give great results. Most camera kit lenses have a widest aperture of around F/3.5 - which should be good enough when starting out.
However, as you advance and - if you have money to spend - the best for astrophotography will be brands like Samyang (Rokinon). In particular, the 135mm F/2 which has a really nice sweet spot at F/2.8. An important pointer is that because of the earth's rotational axis, an untracked camera (see below for tracking info) will be limited by the amount of time the shutter can be left open before star trails begin to appear. Star trails images are great - and very easy to achieve - usually a shutter open for 10+ mins will acquire plenty. However, if you're desire is for crisp, sharp, round star imaging, then we need to adhere to either NPF Rule or 500-Rule. This dictates how long a shutter can be open for (in seconds) dependent upon the focal length of the lens. The NFP Rule is camera/lens make/model specific, but the 500-Rule (see table below) is an excellent starting point for anyone.
At the moment, refurbed DSLRs can be picked up for around £120. Word of warning: you get what you pay for - check the shutter count before buying, as extremely high counts could indicate a Camera Supernova any day soon.
Currently, there appears to be an increase in Astrophotography-Modified DSLRs. There's two kind to look out for: those actually manufactured for the purpose; the Canon EOS Ra is an example of these - but you pay a premium for the tech. Those modified (and usually sold on ebay) because of the internal adjustment made to the camera, will render them only usable for astrophotgraphy - daytime shots will not really be possible. Some of the more expensive Ra cameras will be manufactured in such a way as to be dual-function.
A quick mention of vibration due to mirror shake. Many people don't think this is a thing, but the reality bites. Every DSLR with a viewfinder - by default - has a mirror. Firing the shutter (either manually, or remotely) requires the mirror to shift in order to reflect the image onto the sensor. The result of this process will be a "clunk" as the mirror hits the damper. The damper itself is designed to absorb most of this "clunk" - but the residual vibration can have an effect and create a mini-earthquake within the camera itself. This will vary from camera to camera and will depend upon the quality of build and materials used for construction of both the camera itself and the damper. so the choice here is buy a quality camera or go mirrorless.
BRIDGE CAMERA: Some bridge cameras can be used for night imaging - but it really depends upon what your target is. You'll get nice constellation/milkyway type images. As bridge cameras have a fixed lens, you'll be relying on how programmable the camera is. A key issue will be the ability to program ISO and aperture separately. If you're lucky enough to own a bridge camera with external shutter release access, then all the better. Anything that helps you avoid touching the camera will greatly reduce the risk of shake when the shutter button is fired.
MOBILE PHONE CAMERA: These used to sniffed at, but the last five years or so, the mobile camera has really advanced. Some manufacturers like Xiaomi actually promote their camera's ability in this field. It's worth checking out the camera apps in the online store, as the more control options an app boasts, then the better chances of getting good results.
TRACKING:
I won't get into the science - our planet's movement around the sky makes it appear from earth that the sky is moving. Any images taken of the night sky will start to show drift (depending upon the camera focal length (lens) this can start after a few seconds. Even with the shortest focal length (lenses of 20mm and below) max exposure time is 30secs before stars start to lose their roundness and form commas. If the lens is left open long enough star trails form.
The very best shots will be those that use some form of tracker. There are two types of tracker - they both perform the same function, but in a different way.
♦ Alt-AZ: are computerised trackers that "know" where everything should be in the sky and navigate to a chosen target accordingly. They're convenient - and great for observing with a scope - or taking short exposure images. The downside is that the manner of computerised adjustment (done in steps up/down and left/right) tracking an item across the sky involves steps on both axis - not great for long-exposures as the field of view will turn on its side after a few minutes.
♦ EQ: Equatorial mounts rotate on an axis parallel to that of Earth. An object will stay fixed in position and long exposures can be obtained once the device has been aligned to Polaris at setup.
Aside from Telescope mounts there are several EQ mounts out there that make standalone long-exposure nightsky imaging a piece of cake. I have two:
♦ Skywatcher Star Adventurer Pro - expensive (around £300) with a huge choice of speed settings for tracking sun, moon, planets, stars and more besides. Skywatcher have updated their Star Adventurer Pro for 2021. It now has wifi and a phone app, adding remote tracking and camera control.
♦ Omegon Minitrack LX-2 - much cheaper (£140) option. This is utterly convenient, sling it in your backpack with a portable tripod and astro-imaging can be done wherever you are in the world. No need to lug loads of bulky equipment around. The Minitrack is the size of a large TV remote, attach it to your camera tripod, attach camera, align to Polaris (30secs), point and program camera, wind up clockwork motor for 1 hour of precise tracking.
♦ Bresser Startracker Astronomical Photo Mount Kit - heading towards the top end of tripod/camera mounts. Again an EQ tracker, with a compact, but top-spec design. You won't get much change from £500, but - for that, you'll get precise tracking and extremely reliable German engineering.
IMAGE PROCESSING SOFTWARE:
Almost everything you need is free. Including Photoshop, yes. As any hobby can quite easily become expensive very quickly, I'll try and refer to free/freeware or inexpensive software - suitable for astrophoto processing. So, once you've captured your image(s) they'll require processing in order to achieve a desired result. Processing falls into three distinct categories:
PRE-PROCESSING: Some images do require an element of pre-processing. In many instances calibration, debayering, cropping and applying gain and gamma correction can all be done as a batch process. An example of this type of app is PIPP (Planetary Imaging PreProcessor).
STACKING: So, you've captured 100 images of the Andromeda Galaxy, before you can move on to processing, you'll need to copy all 100 into a single image. This process is called stacking and is (more or less) fully automated. Freeware examples: Deep Sky Stacker, AUTOSTAKKERT!, Sequator and Registax are all very user-friendly.
IMAGE PROCESSING: Now to the tricky bit. Don't worry - there's site after site dedicated to this aspect. Each piece of software has it's own tutorials and guides. Packages like GIMP and Pixlr E are examples of what's out there - but each will require the user learning many familiar processes in unfamiliar ways. The same too applies to Affinity Photo - an excellent Photoshop clone - it's reasonably priced @ £24/$24 (limited time offer - usually £49). Affinity's big + is that many of the filters and plugins used in photoshop are compatible.
I suppose I should now get to the "elephant in the room": Photoshop. It's the industry standard - and to most the buttons, icons, tools and processes are very familiar. So how come it's free? Well - several years ago Adobe deactivated their registration/update servers for one edition of Photoshop. At that time they declared that no future support would be provided and even went so far as to provide a universal serial number for those installing. The only catch? Several years later it's hard to find the complete install file for it as it's no longer on their servers.
Some will say "ah but Photoshop CS2 is very old, what will I want with that?" Well, yes CS2 is old - but it still works quite nicely on win10, all of the functionality for serious image processing is there to be had and - the filters and actions required for astro-imaging are good to go with CS2. The difficult part will be finding CS2 (and the legit universal license) online. If you need help PM me
ONLINE TUTORIALS:
Astro-Imaging can be quite daunting - but needn't be. I'm a complete novice, but an improving novice. This is thanks to the multitude of tutorials out there. Even a simple google search for "Astrophotography Beginners Guide" turns up dozens and dozens of really useful pages.
I've deliberately not included CCD/CMOS Astro Cameras - reason being that (timelapse functionality aside) their chief design is for in-telescope use. these are a whole new ball game, and certainly sink-hole for your hard-earned cash.
So, there you have it, a simple what's what. Now, what's keeping you? time to take the plunge. Good luck and clear skies.
Note: although I've created this table for my own camera, the full frame figures should work for most camera makes. With regard to the Canon 1.6 crop figures, you can calculate your own shutter times if you know the crop size of your own camera's sensor. Nikon (for example) are usually 1.5 - so the figures in this table will work fine for Nikon Crop-Sensor cameras and any other DSLR with a crop sensor of 1.6 or less.
For mobile phone and bridge cameras - the above table will also present a safe "maximum" exposure time.
Hopefully this thread may help a few who (like myself) are just starting out in astrophotography. It can be a sink-hole for money, I've made mistakes but find I'm learning one key maxim: Not everything being advertised as a "must have" really is. Work out what you want to do, work out what you can afford and and ensure your "purchase" do meet your needs.
Before we start: One Essential: A Tripod. In all instances you're taking images where the camera shutter will be open for extended periods - and certainly much longer than daytime shots. Even the slightest movement and your night time image is trashed. If you don't have a tripod, YOU WILL need something strudy to place your camera on. A shutter trigger - or timed release will also be essential.
CAMERA:
DSLR: Any DSLR will do a great job. I'm biased but the Canon EOS range are really user-friendly cameras - and all EOS kit is compatible.
The key here is lenses. Most night targets require lots of light and for extended periods of time. Any lens with an aperture setting from F/4 upto F/2 will give great results. Most camera kit lenses have a widest aperture of around F/3.5 - which should be good enough when starting out.
However, as you advance and - if you have money to spend - the best for astrophotography will be brands like Samyang (Rokinon). In particular, the 135mm F/2 which has a really nice sweet spot at F/2.8. An important pointer is that because of the earth's rotational axis, an untracked camera (see below for tracking info) will be limited by the amount of time the shutter can be left open before star trails begin to appear. Star trails images are great - and very easy to achieve - usually a shutter open for 10+ mins will acquire plenty. However, if you're desire is for crisp, sharp, round star imaging, then we need to adhere to either NPF Rule or 500-Rule. This dictates how long a shutter can be open for (in seconds) dependent upon the focal length of the lens. The NFP Rule is camera/lens make/model specific, but the 500-Rule (see table below) is an excellent starting point for anyone.
At the moment, refurbed DSLRs can be picked up for around £120. Word of warning: you get what you pay for - check the shutter count before buying, as extremely high counts could indicate a Camera Supernova any day soon.
Currently, there appears to be an increase in Astrophotography-Modified DSLRs. There's two kind to look out for: those actually manufactured for the purpose; the Canon EOS Ra is an example of these - but you pay a premium for the tech. Those modified (and usually sold on ebay) because of the internal adjustment made to the camera, will render them only usable for astrophotgraphy - daytime shots will not really be possible. Some of the more expensive Ra cameras will be manufactured in such a way as to be dual-function.
A quick mention of vibration due to mirror shake. Many people don't think this is a thing, but the reality bites. Every DSLR with a viewfinder - by default - has a mirror. Firing the shutter (either manually, or remotely) requires the mirror to shift in order to reflect the image onto the sensor. The result of this process will be a "clunk" as the mirror hits the damper. The damper itself is designed to absorb most of this "clunk" - but the residual vibration can have an effect and create a mini-earthquake within the camera itself. This will vary from camera to camera and will depend upon the quality of build and materials used for construction of both the camera itself and the damper. so the choice here is buy a quality camera or go mirrorless.
BRIDGE CAMERA: Some bridge cameras can be used for night imaging - but it really depends upon what your target is. You'll get nice constellation/milkyway type images. As bridge cameras have a fixed lens, you'll be relying on how programmable the camera is. A key issue will be the ability to program ISO and aperture separately. If you're lucky enough to own a bridge camera with external shutter release access, then all the better. Anything that helps you avoid touching the camera will greatly reduce the risk of shake when the shutter button is fired.
MOBILE PHONE CAMERA: These used to sniffed at, but the last five years or so, the mobile camera has really advanced. Some manufacturers like Xiaomi actually promote their camera's ability in this field. It's worth checking out the camera apps in the online store, as the more control options an app boasts, then the better chances of getting good results.
TRACKING:
I won't get into the science - our planet's movement around the sky makes it appear from earth that the sky is moving. Any images taken of the night sky will start to show drift (depending upon the camera focal length (lens) this can start after a few seconds. Even with the shortest focal length (lenses of 20mm and below) max exposure time is 30secs before stars start to lose their roundness and form commas. If the lens is left open long enough star trails form.
The very best shots will be those that use some form of tracker. There are two types of tracker - they both perform the same function, but in a different way.
♦ Alt-AZ: are computerised trackers that "know" where everything should be in the sky and navigate to a chosen target accordingly. They're convenient - and great for observing with a scope - or taking short exposure images. The downside is that the manner of computerised adjustment (done in steps up/down and left/right) tracking an item across the sky involves steps on both axis - not great for long-exposures as the field of view will turn on its side after a few minutes.
♦ EQ: Equatorial mounts rotate on an axis parallel to that of Earth. An object will stay fixed in position and long exposures can be obtained once the device has been aligned to Polaris at setup.
Aside from Telescope mounts there are several EQ mounts out there that make standalone long-exposure nightsky imaging a piece of cake. I have two:
♦ Skywatcher Star Adventurer Pro - expensive (around £300) with a huge choice of speed settings for tracking sun, moon, planets, stars and more besides. Skywatcher have updated their Star Adventurer Pro for 2021. It now has wifi and a phone app, adding remote tracking and camera control.
♦ Omegon Minitrack LX-2 - much cheaper (£140) option. This is utterly convenient, sling it in your backpack with a portable tripod and astro-imaging can be done wherever you are in the world. No need to lug loads of bulky equipment around. The Minitrack is the size of a large TV remote, attach it to your camera tripod, attach camera, align to Polaris (30secs), point and program camera, wind up clockwork motor for 1 hour of precise tracking.
♦ Bresser Startracker Astronomical Photo Mount Kit - heading towards the top end of tripod/camera mounts. Again an EQ tracker, with a compact, but top-spec design. You won't get much change from £500, but - for that, you'll get precise tracking and extremely reliable German engineering.
IMAGE PROCESSING SOFTWARE:
Almost everything you need is free. Including Photoshop, yes. As any hobby can quite easily become expensive very quickly, I'll try and refer to free/freeware or inexpensive software - suitable for astrophoto processing. So, once you've captured your image(s) they'll require processing in order to achieve a desired result. Processing falls into three distinct categories:
PRE-PROCESSING: Some images do require an element of pre-processing. In many instances calibration, debayering, cropping and applying gain and gamma correction can all be done as a batch process. An example of this type of app is PIPP (Planetary Imaging PreProcessor).
STACKING: So, you've captured 100 images of the Andromeda Galaxy, before you can move on to processing, you'll need to copy all 100 into a single image. This process is called stacking and is (more or less) fully automated. Freeware examples: Deep Sky Stacker, AUTOSTAKKERT!, Sequator and Registax are all very user-friendly.
IMAGE PROCESSING: Now to the tricky bit. Don't worry - there's site after site dedicated to this aspect. Each piece of software has it's own tutorials and guides. Packages like GIMP and Pixlr E are examples of what's out there - but each will require the user learning many familiar processes in unfamiliar ways. The same too applies to Affinity Photo - an excellent Photoshop clone - it's reasonably priced @ £24/$24 (limited time offer - usually £49). Affinity's big + is that many of the filters and plugins used in photoshop are compatible.
I suppose I should now get to the "elephant in the room": Photoshop. It's the industry standard - and to most the buttons, icons, tools and processes are very familiar. So how come it's free? Well - several years ago Adobe deactivated their registration/update servers for one edition of Photoshop. At that time they declared that no future support would be provided and even went so far as to provide a universal serial number for those installing. The only catch? Several years later it's hard to find the complete install file for it as it's no longer on their servers.
Some will say "ah but Photoshop CS2 is very old, what will I want with that?" Well, yes CS2 is old - but it still works quite nicely on win10, all of the functionality for serious image processing is there to be had and - the filters and actions required for astro-imaging are good to go with CS2. The difficult part will be finding CS2 (and the legit universal license) online. If you need help PM me
ONLINE TUTORIALS:
Astro-Imaging can be quite daunting - but needn't be. I'm a complete novice, but an improving novice. This is thanks to the multitude of tutorials out there. Even a simple google search for "Astrophotography Beginners Guide" turns up dozens and dozens of really useful pages.
I've deliberately not included CCD/CMOS Astro Cameras - reason being that (timelapse functionality aside) their chief design is for in-telescope use. these are a whole new ball game, and certainly sink-hole for your hard-earned cash.
So, there you have it, a simple what's what. Now, what's keeping you? time to take the plunge. Good luck and clear skies.
Note: although I've created this table for my own camera, the full frame figures should work for most camera makes. With regard to the Canon 1.6 crop figures, you can calculate your own shutter times if you know the crop size of your own camera's sensor. Nikon (for example) are usually 1.5 - so the figures in this table will work fine for Nikon Crop-Sensor cameras and any other DSLR with a crop sensor of 1.6 or less.
For mobile phone and bridge cameras - the above table will also present a safe "maximum" exposure time.
