Pictures of the Stars

[MaeHouston]

I have a Canon T5i Rebel. I either use a 75-300 mm lens or a 18-55 mm lens. I am trying to get a good picture of the stars.... What is the best choice for shutter speed, exposure and ISO? Should I use manual focus or auto focus?

[jrhoffman75]

Not AF.

http://www.learn.usa.canon.com/resources/articles/2012/astrophotography_techniques.shtml

[TCampbell]

You will need a tripod.  You will want to be well away from urban light pollution.  Find a dark sky site far from any city or town.  Also, you will want a moonless night.  It's easier within a few days of the "new moon" but the 3rd quarter moon also works (since that moon wont rise until a few hours before dawn).  A 1st quarter moon or full moon will be up as soon as the sun sets -- not what you want (although I have done imaging near the 1st quarter moon... but had to wait several hours for the moon to set before I could start shooting.)  Light pollution will make the background sky look gray/brown and very "muddy" -- which is why you want dark moonless skies.

Switch off the auto-focus on your lens.  You will need to manually focus by finding a bright star.  You can use any star to focus and it need not be the same area of the sky you plan to photograph.  It helps to put the camera into "live view" mode and then use the 10x zoom.  Use "manual" mode or "bulb" modes only.  It also helps to use max ISO, lowest possible focal ratio, and increase the shutter speed to 30 seconds -- even though you are not actualy taking an image.  The camera exposure simulation in live-view mode so by increasing all settings it makes it easier to see faint stars for purposes of focus -- even though you will not use these setting when you capture the image.

Slowly focus the lens to make your stars are as sharp as possible.  Once focused you can switch off live-view and re-compose to the area of the sky you would like to capture.  Be careful not to touch the focus-ring (or zoom ring) on the lens or you will have to re-focus.

You will use the lowest focal ratio the lens has.   This maximizes the amount of light captured while the shutter is open.

Divide 375 by the focal length of your lens.  E.g. if you have a 10mm lens (such as the Canon EF-S 10-22mm f/3.5-5.6 lens at the 10mm focal length... or the EF-S 10-18mm f/4.5-5.6 at the 10mm end) then you would divide 375 ÷ 10 = 37.5.  That result (37.5) is the number of seconds you can expose the shot without the stars starting to elongate and form trails.  But notice that if you use a longer focal length it reduces how long you can shoot.  For example... a 50mm lens only gets 7.5 seconds -- which is not very long to collect starlight.

You will need a fairly high ISO setting... probably at least ISO 1600 to 3200.  It would be nice to shoot at an even higher ISO but that generates a lot of noise.

If you need longer exposures, there are mechanical (motorized) devices called tracking heads that can be attached to a sturdy photo tripod... such as the Vixen Polarie, the iOptron SkyTrakcer, the AstroTrac, or the Losmandy StarLapse.  The Vixen and iOptron devices are the least expensive.  The AstroTrac is a bit better.  The Losmandy StarLapse is extremely good (and not suprirsingly also the most expensive.)  These devices have an axis that rotates at the same speed that the Earth rotates -- and if that axis is aligned to point to the celestial pole (so that the axis of rotation is parallel to the Earth's axis of ration -- basically you point it toward the north star) then as the Earth spins from west to east, the deivce rotates from east to west and this exactly cancels the spin of the Earth -- holding everything steady in your field of view even if you take long images.

[Canonacanon]

TCampbell - This is a beautiful explanation, and I've been doing all this for the last few nights, but all I see is a pitch black Live View LCD, and the same in the viewfinder, and no response at all from the shutter button. I'm using the Japanese equivalent of the t5i. What on earth am i missing?!

[TCampbell]

It helps to have a low focal ratio lens (e.g. f/2.8 or lower).  If you've got a kit lens (e.g. the 18-55mm f/3.5-5.6) then things will be a bit dimmer at f/3.5.  An f/2 lens or an f/1.4 lens would be great.

If auto-focus is enabled (and in one-shot mode) then the camera will refuse to take a shot unless it can confirm that it has focused.  Make sure the switch on the lens is set to disable auto-focus.

As for the stars... 

If "anything" in the night sky is focused, then "everything" in the night sky is focused.  This means you don't have to point the camera at your intended subject to focus.  Find a BRIGHT star.  Currently that's probably going to be Vega (it will be in the west just after sunset and should easily be visible -- prior to around 8pm or so local time).  Vega has a visual magnitude of about .5.    After that, Vega is starting to get too low in the west to be a good star for focus... switch to Capella which will start to climb high in the northeast.  Capella has a visual magnitude near 0.   Each full point of difference in magnitude represents a difference of about 2.5x the brightness.  So if Vega is .5 and Capella is near 0, then Capella is more than twice as bright.

But in the very late evening you can use Sirius.  Sirius is the BRIGHTEST star in the sky (apart from our Sun) with a magnitude of around -1.45 (that makes it more than 4 times brighter than Capella and more than 8 times brighter than vega.)

Remember to switch to MANUAL focus.  

Switch the mode dial to manual.

Switch on live-view

Crank up the ISO to max.

Crank the shutter speed up to 30 seconds (not 1/30th and it's easy to make that mistake).

Point the camera to one of these bight stars.  

Depending on your lens you only *might* see the star through the viewfinder (but often the viewfinder is too dim) but you SHOULD see the star in the "live view" mode because Canon uses "exposure simulation" in live view and since you've cranked up the ISO and shutter speed it should brighten up the star.

Important note... if the lens is far out of focus, you'll see absolutely nothing (the star is blurred to the point that there's no light). If that happens, just look at your lens and run the focus out near "infinity" and you should being to see the circles of light concentrate into a star.

Once you can see the stars and they appear focused... you're not done.  Now bump up the digital zoom on the live-view screen to 10x and very very slowly adjust the focus in and out until you're convinced that you've got that star down to the tiniest pinpoint of light possible.  

Having done all of this, return the ISO and shutter speeds to more reasonable settings (we no longer need to boost them for "exposure simulation")  and point the camera to the area of the sky you want to focus (being careful not to touch the focus ring on your camera.)

If you're in "manual" exposure mode and and the lens is in "manual" focus mode then the camera should take the exposure when you press the shutter button.  If you do not have a remote shutter release, then I suggest using either the 2 second or 10 second self-timer to avoid any camera vibration when you take the shot (even on a solid tripod the camera will move slightly when you press the shutter).

There are ways to perfect focus even better using a special focusing mask (an accessory).  Lonely Speck makes a nice one called the "SharpStar" and it slides in (a square filter) using the same filter bracket that you'd use for Lee Filters or Cokin filters (square slide-in filters).  The make has etched lines on it which causes bright stars to throw diffraction spikes in a particular pattern.  Each star throws 3 spikes.  When all 3 spikes meet at a common center, you've nailed focus.  Also if you really can't see anything and you know you've focused somewhere "near" infinitity, you can take test exposures and you should definintely see the diffraction spikes (just don't forget to remove the focusing mask before you start taking real images or you'll end up with wonky spikes all over your stars -- not that I'd ever make that mistake myself (as I wistle innocently)).

[Canonacanon]

Man, you are a legend. I will try this tonight if it's clear. Thank you so much for your patience and knowledge!

[ebiggs1]

Not much to add to Tim's outstanding, as usual, reply but don't fall into the mistaken belief by novices that you need a telephoto lens to shoot stars.  You don't.  You want a wide angle lens.  Even a very wide angle lens.  This pretty much eliminates your 75-300mm.  You will want to use your 18-55mm at the 18mm side.  The suggestion of the ef-s 10-22mm is a fantastic idea.

The Rokinon 14mm f/2.8 IF ED UMC Lens is considered among the very best lens for shooting the sky at night.  It is totally manual and as sharp as a lens can be.  Plus it won't break the bank either.

[Waddizzle]

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The suggestion of the ef-s 10-22mm is a fantastic idea.

The Rokinon 14mm f/2.8 IF ED UMC Lens is considered among the very best lens for shooting the sky at night.  It is totally manual and as sharp as a lens can be.  Plus it won't break the bank either.

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I purchased the Rokinon 16mm T2.2 Cine Lens to take pictures of stars, and for video.  The Bower version sells for less than $300.