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FORUMS Photography Talk by Genre Astronomy & Celestial Talk 
Thread started 30 Aug 2016 (Tuesday) 19:30
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Tried & failed, may not have known too well what to do, could someone help?

 
tnick771
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Aug 30, 2016 19:30 |  #1

So I've done a lot of reading, and last summer I was presented with an infinite blanket of night sky with countless stars and my camera, a tripod and a desire to capture what I saw.

What I had read was to take your lens and turn it just before infinity on the focus dial, set exposure for 30 seconds, crank the ISO up to at least 1600+ and then use a remote to avoid camera shake.

My photos were a disaster.

Does anybody have a near-fool-proof "recipe" for astrophotography?

I use a Canon DSLR, a 10-22mm Lens (could use another if better?), a tripod and a remote.


Canon 6D and a couple lenses, I don't know... just trying the hardest I can :)
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Aug 30, 2016 21:38 |  #2

What camera? What lens exactly (include aperture)? Which direction did you point the camera (Milky Way core is south x southwest this time of year and only visible for a couple hours after dark)? Was the moon up?

I suggest reading this tutorial for the nitty gritty of astrophotography, it's the best series on the internet for everything from equipment through processing:

http://www.clarkvision​.com/articles/nightsca​pes/ (external link)


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Aug 30, 2016 21:58 |  #3

You haven't given much details. What exactly did your photos look like? Can you post them? We're you in a dark sky location? If not, light pollution could have potentially overwhelmed the starlight.


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Aug 31, 2016 00:04 |  #4

Yeah post a sample image. I may be able to help. I can do decent MW images.




  
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Aug 31, 2016 19:58 |  #5

The biggest challenge you will face will be the rotation of the earth and how to deal with that. If you are shooting with your SL1 from a solid tripod, you can get roughly 25seconds of exposure from the 10mm setting of your 10-22mm lens. Thats enough (especially if you stack) to get some nice Milky Way images. Focus is more tricky with wide angle lenses if you are just eyeballing it, but use live view and a bit of patience. Better yet, you could hook up to a laptop and use Canon's tethering software to step focus forward or backward to nail it. Just remember to switch the lens to manual focus after you get it set. Your lens is going to have some visible coma issues toward the border of the frame. Stars there will look a bit distorted even when focus is spot on. (see the link)
http://www.lenstip.com …Coma_and_astigm​atism.html (external link)
If you want to take longer exposures of widefield images, there are a number of good compact tracking devices you can use to counteract the earth's rotation. These cost $300 or more on average, and can run much more if you want to use heavier lenses for telephoto or big prime work. Finally, you will need some decent software for processing the images. There will be a learning curve in processing astrophotos but youtube is a good resource for tutorials. A dew-heater would probably be a good idea to keep from fogging up while you image at night.


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tnick771
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Aug 31, 2016 20:06 |  #6

Pax2You wrote in post #18113053 (external link)
The biggest challenge you will face will be the rotation of the earth and how to deal with that. If you are shooting with your SL1 from a solid tripod, you can get roughly 25seconds of exposure from the 10mm setting of your 10-22mm lens. Thats enough (especially if you stack) to get some nice Milky Way images. Focus is more tricky with wide angle lenses if you are just eyeballing it, but use live view and a bit of patience. Better yet, you could hook up to a laptop and use Canon's tethering software to step focus forward or backward to nail it. Just remember to switch the lens to manual focus after you get it set. Your lens is going to have some visible coma issues toward the border of the frame. Stars there will look a bit distorted even when focus is spot on. (see the link)
http://www.lenstip.com …Coma_and_astigm​atism.html (external link)
If you want to take longer exposures of widefield images, there are a number of good compact tracking devices you can use to counteract the earth's rotation. These cost $300 or more on average, and can run much more if you want to use heavier lenses for telephoto or big prime work. Finally, you will need some decent software for processing the images. There will be a learning curve in processing astrophotos but youtube is a good resource for tutorials. A dew-heater would probably be a good idea to keep from fogging up while you image at night.

Wow, just... wow... thank you for this post. So much great info here.

as for ISO level, I'm sure this varies, but how do I know where to set that? I'm sure Aperture is wide open, correct?

Also is a 10-22mm not preferred? Is there a better option (something telephoto)?


Canon 6D and a couple lenses, I don't know... just trying the hardest I can :)
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Sep 01, 2016 11:31 |  #7

tnick771 wrote in post #18111889 (external link)
So I've done a lot of reading, and last summer I was presented with an infinite blanket of night sky with countless stars and my camera, a tripod and a desire to capture what I saw.

What I had read was to take your lens and turn it just before infinity on the focus dial, set exposure for 30 seconds, crank the ISO up to at least 1600+ and then use a remote to avoid camera shake.

My photos were a disaster.

Does anybody have a near-fool-proof "recipe" for astrophotography?

I use a Canon DSLR, a 10-22mm Lens (could use another if better?), a tripod and a remote.

"Fool proof" is maybe asking a bit much. Honestly if we stated every minute detail, it would be difficult to remember every step. I think I can probably safely state that we all botched quite a few of these as we learned how to do it ("experience" is a great teacher.)

The 10mm focal length is pretty good for your camera on a stationary tripod. It's nearly as wide as you can get without vignetting in the corners. So I think you're good in the lens department.

Focus

Focus is tricky... you cannot trust the "infinity" mark on your focus ring. I switch on live-view, find the brightest star I can find in the night sky and point my camera at it (even if this is NOT the part of the sky I plan to image -- that doesn't matter for focus) Turn OFF the auto-focus. Turn on "live view".

Your camera uses a feature called "exposure simulation" when you use live-view. This means that as long as you are in live-view mode, you'll notice as that as you change the exposure settings you'll see your live-view screen getting brighter or dimmer -- simulating the image it thinks you might get at that exposure setting. Use this feature to your advantage when focusing.

Crank the ISO to max... e.g. ISO 6400 ... or whatever your SL1 will allow.
Crank the exposure time up to 30 seconds (which is the maximum time you can use before having to switch to "bulb" mode.)
Drop the aperture down to the lowest possible setting your lens will allow (this varies by lens).

Even though these are not the settings you will use wen you take the "real" exposure, this will brighten your stars and make it easier to focus.

Now use the live-view zoom button to zoom in... take it up to the 10x zoom live-view with your bright star in the center.

Very gently adjust the focus ring on the lens and you'll notice the star going in and out of focus. Try to focus the star down to the smallest pin-point you can manage.

Having achieved this focus (and make sure that auto-focus is disabled) you can now point the camera to the section of sky you actually want to image.
Also, return the exposure settings to the settings you plan to use when you take the exposure. You can also turn off live-view.

You do not want to "touch" the camera when you take the shot because depending on how solid your tripod is, this will induce a vibration and blur your shot. If you have a remote release, use it. If not, set the camera to use either the 2-second count-down timer or the 10-second count-down timer to give it time to damp the vibrations before the camera takes the shot.

As for settings...

Aperture...

If you have a tripod but do not have a tracking head (a motorized head that tracks the stars as the Earth spins) then you have little choice except to use the lowest possible aperture your lens will allow. You might not get optimally shaped stars (especially if they are bright and near the edges of the frame). Stopping down will improve those stars, but it'll also mean you'll need a longer exposure, which you really cannot do without a tracking head.

Shutter speed...

If you are using a tripod and no tracking head then the your shutter speed is based on the apparent distance that the stars will seem to move during your exposure. Since the Earth is spinning beneath our feet (from west to east) the stars seem to move across the sky (from east to west). How far they move is based on the speed of Earth's spin... it turns we do a completely 360º rotation in one "sidereal day" (about 23 hours, 56 minutes, and 11 seconds -- not the 24 hours you might guess (you can ask me why if you really want to know)). When divide that down to the question of "how far do we rotate in just 1 second?" the answer turns out to be about 15 arc-seconds ("seconds" as in "degrees, minutes, and seconds" of angle... not "seconds" of time. I use the term "arc-seconds" to make it clear I'm describing the angular measurement and not the time measurement). It turns out stars near the poles don't seem to move so much. A star located directly above the pole would appear to not move at all (Polaris, the north star, is actually not above the pole... but it is close.)

The "long" version of the answer on shutter speed is to work out how many arc-seconds of sky fit into just one pixel on your camera and determine how many pixels the image can move before you notice the blur. I'll skip that math and go for the easy stuff.

There's a rule for full-frame cameras and 35mm film cameras that suggests that if you simply divide 600 by the focal length of your lens, the result of will be the number of seconds you can manage to image before you notice the stars seem to be elongated (the stars are no longer "round" in your images ... due to the rotation of the Earth.)

But you don't have a full-frame camera. You have an APS-C size sensor camera with a crop factor of 1.6. So if we divide 600 by 1.6 we get 375. So... YOU can divide 375 by the focal length of your lens. That gives you a max shutter time of 37.5 seconds (you can't set your camera to 37.5 seconds but you could use a remote (wired) shutter release to control it in "bulb" mode. Or... just do the best you can at 30 seconds if you don't have a remote shutter release.

Some astro-imagers think that 600 is too generous... so they use 500 to be a bit more conservative. 500 ÷ 1.6 = 312.5 -- so you could use that as your base.

E.g. at 10mm... 375 ÷ 10 = 37.5 seconds of exposure time. Or using the more conservative 500 rule (which works out to 312.5 on your camera) it's: 312 ÷ 10mm = 31.2 seconds of shutter time.

In either case, you can easily get a 30 second exposure.

REMEMBER: This rule is only for those who have a stationary tripod. If you have a tracking head... you get to ignore this math and you can expose for many minutes.

ISO setting...

ISO is a one of the most important settings to think about. Why? Consider this:

1) If you're limited to a stationary tripod, then you've already set the shutter speed to the maximum value you can possible manage. In other words, your shutter speed is probably locked in based on your camera lens selection. So that's not really a mater of taste or something you get to pick... you do a quick division problem and it is what it is.

2) Also if you're limited to a stationary tripod, then you're probably trying to capture as much light as you possible can during every second of exposure. That means you don't really get to pick your aperture choice either. You set the lowest possible setting your lens will allow. That's pretty much all there is to it.

So...

3) This means the ONLY setting in which you really have any flexibility to adjust exposure... is the ISO setting.

It turns out there is an "optimal" ISO setting for the camera when doing astrophotography, but that may not be the optimal setting if you are limited to a stationary tripod. The stars may be too dim if you use this setting... but here it is...

For YOUR Canon EOS SL1, the "optimal" ISO setting is ISO 800.

The optimal setting has to do with the technical nature of the way the sensor actually works. While you'll hear people saying that changing the ISO on your camera changes the "sensitivity" of the sensor... that's actually not true at all. What it really does is changes how much the camera AMPLIFIES THE SIGNAL received by the sensor.

In other words... if you set your camera to ISO 3200 and took a shot (any shot). And then set your camera to ISO 1600 and took the SAME shot (don't touch any other settings... just the ISO) and then you go into your photo processing software and increase the exposure of your ISO 1600 shot by exactly one full stop.... you will get the IDENTICAL image (pixel for pixel) that you got from your ISO 3200 shot. No kidding. (Ok, full disclosure is that I've somewhat over-simplified this to make the point because there are some nuances... but not much. You pretty much will get the identical exposure.)

You cannot change the sensitivity of your camera sensor... it is what it is. What you change is what the camera does with the data after it captures it on the sensor. It's all post-processing and the only question is "where" did the amplification occur.

Canon cameras that use the 18 megapixel sensor that was extremely popular in the T2i, T3i, T4i, SL1, 60D, and 7D cameras... all do an internal "upstream" signal amplification on the sensor which is an analog amplification... up until somewhere around ISO 800. After ISO 800 they no longer push up-stream amplification ... they digitally amplify the data in what is known as "downstream" amplification. What your photo editing software does when you adjust exposure settings on an image is also considered "downstream" amplification. Canon doesn't publish this information. There are tests that are used to try to derive where the tradeoff between "upstream" vs. "downstream" amplification occurs and, for your camera, it turns out it's somewhere very close to ISO 800 (it's probably not exactly ISO 800).

Having said this... if you are using a tracking head, then YOU should definitely use ISO 800... but this means that you're now free to adjust both your aperture setting and your shutter speed. So you lock in the ISO to 800 ... maybe you decide to stop-down the lens by a stop or two to improve the stars (based on the optical quality of the lens... you tend to get sharper stars if you stop down at least a little) and now you increase the exposure time to compensate for it all.

But if you're on a stationary tripod, then you're probably going to have to adjust the ISO... depending on your skies and how much detail you want to capture, that could be ISO 1600... it could even be ISO 3200.

Yes, you'll get more noise if you increase the ISO. You can use noise-reduction techniques when post-processing to improve your images and there are numerous ways to do this. "Stacking" also reduces noise, but stacking is best for those who have tracking heads so that the sky doesn't shift between the multiple exposures used for stacking.




  
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MalVeauX
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Post edited over 2 years ago by MalVeauX.
     
Sep 01, 2016 18:19 |  #8

tnick771 wrote in post #18111889 (external link)
So I've done a lot of reading, and last summer I was presented with an infinite blanket of night sky with countless stars and my camera, a tripod and a desire to capture what I saw.

What I had read was to take your lens and turn it just before infinity on the focus dial, set exposure for 30 seconds, crank the ISO up to at least 1600+ and then use a remote to avoid camera shake.

My photos were a disaster.

Does anybody have a near-fool-proof "recipe" for astrophotography?

I use a Canon DSLR, a 10-22mm Lens (could use another if better?), a tripod and a remote.

Heya,

Just something else to think of, since a lot has already been covered, here's something that I would call 'fool proof' from experience:

I used to just use a 650D (T4i) with a Tokina 11-16 F2.8 lens on a standard tripod, didn't even use a remote shutter. It didn't matter if I put the Tokina at 11mm or 16mm, or any focal length in between. I simply turned it's focus throw to infinity, left it at F2.8, and set my time to 20 seconds. The only thing I adjusted was ISO. I usually just shot it at ISO 1600 or sometimes ISO 3200. I never had to focus it, never had to worry about exposure beyond using one of those two ISO values. Just pointed it in the general direction I wanted, and hit the shutter button to expose it (I used the built in 10 second timer to avoid shaking it while pressing the shutter).

It was truly bullet proof in the sense of just walking out, setting it up, and exposing. Not having to worry about time, aperture, not worrying about focus at all, etc. Amazingly easy. Really enjoyed it.

++++

Since then, I moved to a tracker and it really changes time for exposure as a limitation, so you can use more lenses (like slower ones) and longer focal lengths, etc. Big time game changer. But it also requires alignment, money, time, etc. It is not fool proof, it just adds complexity, but it also opens a lot of doors to progress forward.

++++

Exposure time is a big deal for the night sky, you have to get enough data to process. But, the longer exposure time is limited based on your focal length & sensor size's relationship (with respect to the time it takes for an object to move a significant amount within an arc; this is where the common 500/focal length(1.6 if aps-c) = seconds of exposure time before trails happen, comes into play). I use 500/focal length(crop factor) because it's a lot safer to avoid trails than 600/focal length(crop factor). But this means you have to use wider angles to get enough exposure time if you want to avoid trails.

Aperture helps a lot, but you don't have to stress getting the widest aperture possible, it helps, but it also can be harder to use (such as achieving focus, and dealing with bad CA around stars, etc).

ISO is your friend, crank it up, don't be afraid to top it out, just test things. You can clean up more than you might think!

Achieving focus is the other big deal, since out of focus stars are just fuzz. Do this in Live View, magnify 10x on a big star, and focus it manually (turn off AF!) until it's as pin point as possible. Another option is to get a Bahtinov mask (they're cheap) and put it over your lens while you focus in live view and focus it that way (google it, it's easy, and works great, takes a lot of guess work out of it; easy $15 accessory that works wonders).

The biggest deal is to practice!

Very best,


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Sep 01, 2016 18:22 |  #9

OP still needs to share a photo. Otherwise, we are just guessing as to what his problem is.


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Sep 05, 2016 19:03 |  #10

Hey guys thank you all for your awesome help and feedback. I understand that I should have uploaded my original attempt but time got away from me prior to my vacation (as expected).

Here's THIS time's attempt... Turned out better but definitely open to some pointers as to helping me the next time I get to escape the light polluted jungle I call home.

Thanks!

IMAGE: https://c3.staticflickr.com/9/8030/29197466010_8738777929_b.jpg
IMAGE LINK: https://flic.kr/p/Lu5D​qo  (external link) The Milkyway (external link) by Tyler Nickel (external link), on Flickr

Canon 6D and a couple lenses, I don't know... just trying the hardest I can :)
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Sep 06, 2016 12:46 |  #11

You have a digital camera which frees you to experiment. Take some initiative. Try different settings, shutter speeds, ISO even lens. It wont cost you a dime. This is one of those instances where doing is better than reading. People can suggest settings, but nobody knows your exact situation. Do you have a clear black sky or a city with reflection street lights. Its dry air or humid hazy air. Dont try one or two settings you read about and then quit if it isnt right. Try 10 or 20 or 30 settings and combos of shutter/iso/aperture. Photography is a DOING sport.

Experiment Experiment Experiment and Learn.




  
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Sep 06, 2016 12:50 |  #12

You will find that it will look better if you cool down the WB and crush the blacks a bit to darken the sky.


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Sep 06, 2016 14:22 as a reply to  @ tnick771's post |  #13

It's got a strong red color-cast that you can back off with a white balance adjustment. The stars are elongated but 30 seconds at 10mm isn't really long enough to cause what I'm seeing in the image. I'm guessing some of this elongation may have been caused by vibration in the camera during the exposure. You may be able to hang a weight on your tripod to help with stability. Also, if you don't have a remote shutter release for your camera, then use the delay timer to allow camera vibrations to calm down before the camera opens the shutter.

If you use an inspector that lets you view the RGB values of the pixels, the background sky should have RGB values where the background is roughly color-neutral. As I hover over areas of background with a color inspector I'm noticing the RGB values aren't neutral and the red values are anywhere from 30-50% stronger than the blue values.




  
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Sep 07, 2016 13:58 as a reply to  @ TCampbell's post |  #14

Thirty seconds is plenty of time to see star movement because of earths rotation, not camera movement.




  
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Sep 07, 2016 21:50 |  #15

kjonnnn wrote in post #18120083 (external link)
Thirty seconds is plenty of time to see star movement because of earths rotation, not camera movement.

It's really not enough to see the amount visible. 500 ÷ 1.6x = 312.5 At 10mm that would mean that even the more conservative 500-rule should show little to no star trails for a 10mm lens with a 30 second exposure (unless the exposure data listed isn't correct -- which does sometimes happen.)




  
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Tried & failed, may not have known too well what to do, could someone help?
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