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Occasional Contributor
Posts: 5
Registered: ‎10-23-2017
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T3i night sky continuous 10 sec exposures?

[ Edited ]

I spent this past weekend at my new night job; pressing the remote shutter trigger about 2000 times to capture the night sky and the Orionid meteor shower.  For reference, we bought this camera off of QVC several years ago, but I've only recently started playing with it (I've been busy!)  So, I'm only just now getting familiar with the Canon Rebel EOS T3i; I bought the "for dummies" book so that's helping. My tripod, 10-18mm lens and wireless trigger came in on Friday, just in time for Orionids peak Friday and Saturday night. So I put them all to good use and tried out some settings. FYI: last time I did camera stuff was back in the army and then afterwards at OSU. Hobby only. 20+ years ago.

After spending both nights pressing the remote trigger button seemingly endlessly and listening to the camera, I wondered if there was a way to do these long exposures back to back/continuously automagically, for two reasons:

1) I'd like to do something (anything) else during that time

2) all that internal mirror slap can't be good for the camera. The moving parts must have some type of expected life.  

 

I kinda tried it out. I set the camera in continuous mode and hooked the wired trigger back up.  But it didn't "seem" like it worked i.e. I locked the trigger down, and listened and had it hooked to the external monitor. I didn't understand what it was doing.  So I abandoned that and set it back to single shooting w/the wireless trigger and spent the next 5 hours learning otj how to optimize shutter button half press and full presses for manual semi-continuous shooting. I also learned how to use a hand warmer wrapped around the lens to resist dew, that night sky focusing is a job unto itself, and that f/4.5 isn't going to cut it for meteor shower shots.  (I did a time lapse compilation each night (using Shotcut for the first time...wow) and posted to FB if anyone is interested in seeing the results, I'm joe.balint.6) https://www.facebook.com/joe.balint.6/posts/1920171551331728

 

Seems like it should be possible to do long exposure continuous shooting. Where the shutter trigger is locked down and the camera keeps taking 10 second exposures and recording them back to back. Can anyone verify this for me? And follow-up, if this works, what's the tell tale that the card is full? Just the red LED goes out? Let me know. Much thanks. -Joe

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Esteemed Contributor
Posts: 2,373
Registered: ‎11-14-2012

Re: T3i night sky continuous 10 sec exposures?

I've never owned a Rebel series camera but I suspect you can set a shutter speed of 10 seconds in Tv mode. most of the DSLR's I have owned go to a 30 sec max. Also check your owners manual to see if there is a menu choice for mirror lock up. That will solve another of your questions. 

"A skill is developed through constant practice with a passion to improve, not bought."
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VIP
Posts: 13,169
Registered: ‎12-07-2012

Re: T3i night sky continuous 10 sec exposures?

Here are a few tips to try.  First you don't want a remote trigger, you need an intervalometer.  Second, you didn't pick the best lens for what you are doing.  A lens like the fully manuaRokinon 14mm f/2.8 IF ED UMC Lens For Canon EF or the Rokinon 16mm f/2.0 ED AS UMC CS Lens for Canon EF-S is better.

 

Focusing the night time sky is really easy.  Once you get focus, everything is in focus.  Pick a bright star and focus until it is pin sharp.  Liveview helps if you have it.

 

We used to set up a few common small resisters in a circuit around the front element with a small battery to keep it slightly warmed.  I am sure you can find the schematic on the ole inner web on exactly how to do it.

 

EOS 1DX and 1D Mk IV and several lenses!
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Occasional Contributor
Posts: 5
Registered: ‎10-23-2017

Re: T3i night sky continuous 10 sec exposures?

Focusing: in theory, yep, I get it. Get one get all.  But in practice, even hooking up a 22" TV with the hdmi cable, I can just barely see the stars. And even so, I can tell when they are mostly in focus, just not spot-on.  I could only tell that I was just barely out of focus when I pulled the card and brought the pics up on the PC. Now that I write this, I realize it's probably more to do with the aperture and not getting enough light onto the sensor.

Lens: yep. I went on a spending spree picking up some lenses off of Amazon with larger apertures. I'll look for those rokinons next.  Originally, I was just happy to get any wide-angle in time for the shower.

Intervalometer... I feel like I recognize the term from my engineering days, but not in this context. I'll look it up. Thanks.

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Esteemed Contributor
Posts: 3,849
Registered: ‎06-11-2013

Re: T3i night sky continuous 10 sec exposures?

For night sky & astrophotography the camera has to be on manual everything - no auto-focus, no auto-exposure, etc.

 

Take the aperture to whatever “wide open” is for your lens.

 

If you divide 375 by the focal length of the lens (and that should hopefully be a wide-angle lens) this will give you the longest exposure you can get away with before the stars begin to elongate due to the rotation of the Earth. 

 

E.g. if you had a 14mm lens then it would be 375 / 14 = about 27 seconds.   But that’s the maximum duration.  That sounds like a lot... but suppose you’re using a 50mm lens... suddenly that’s only 7.5 seconds (not so great now).

 

BTW, if you really zoom in, you will see that the stars aren’t perfectly round if you use 375... you could use a lower value to help... e.g. 300 for example would be more conservative.  

 

Next is the ISO... use ISO 800.

 

That’s it... plain and simple... 800 ... don’t even think about using anything else.

 

You might be wondering where that came from.  That’s a magic number for the Canon 18MP sensor (every Canon camera that has that sensor... the T2i, T3i, T4i, 60D, and 7D ... and I’m probably forgetting a few).   That’s the point where the camera stops doing “upstream” amplification and starts doing “downstream” amplification to boost ISO.   “Upstream” is analog gain done in the chip BEFORE it does analalog to digital conversion.  “Downstream” is all digital amplification performed after the analog to digital conversion.

 

The reason it’s a big deal is because when you do “upstream” amplification you’ll get very little loss of dynamic range.  Once a camera starts doing “downstream” amplification you lose dynamic range much faster.

 

So this is a well-known value used by astrophotographers who use any Canon camera with that particular sensor (and it doesn’t matter which model camera it is... just which sensor the camera uses... and Canon uses that sensor in a lot of cameras.)

 

So... wide angle lens.

Manual exposure

ISO 800

Set the shutter speed to whatever you can manage based on focal length.  I do enough astrophotography that I have a pretty good idea of how long an exposure might be based on the focal ratio.  ISO 800, f/4 and 15 seconds (for example) works out fairly well.  Even f/2.8 and 15 seconds probably wont have any over-exposed stars at ISO 800.

 

Manual focus ... and take your time.  This is a tough part of astrophotography because the stars are so very dim and tiny and it’s difficult to be sure you’ve focused well.  To do this, I crank the ISO to max, turn on live view, use the live-view digital zoom feature and set that to 10x zoom ... with the camera pointed at the brightest star I can find in the sky.  Then I very gently adjust focus to try to get that star down to a pinpoint.

 

Take several test exposures... dont’ worry if you’re “wasting” 10 minutes just trying to work out the focus ... this is not “wasted” time, this is “invested” time and your care will be rewarded.  When I started, I often did not spend as much time as I should have refining the focus, the images on the tiny LCD screen on the camera looked pretty good... then I’d get home, import the images, and be disappointed that focus was soft and I hadn’t noticed because I wasn’t zooming in enough and taking enough time.

 

Set the “Drive” mode to continuous burst mode.

Use a “wired” remote shutter release.

Press the shutter button and slide the “lock” ...

 

Walk away, go enjoy some coffee (or your favorite beverage).  Look at your camera and smile from time to time.

 

 

 

 

 

Tim Campbell
5D III, 5D IV, 60Da
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Occasional Contributor
Posts: 5
Registered: ‎10-23-2017

Re: T3i night sky continuous 10 sec exposures?

Ok.  I’ve spent a bit of money and played with settings and set-ups and the like. I now have both of the rokinon lenses that were recommended in this post (the 12mm f/2.8fisheye and the 16mm f/2.0 wide-angle as well as a dew-resistor and some light pollution filters, intervalometer, etc.) I’ve successfully taken several multi-K shots and ShotCut them into time lapse compilations.  I’ve also recently (read that “today”) installed magic lantern.  I saw that I now have 25K shutter actuations already logged. (Seems kinda high since I just really started using it about the time of my first forum post. But believable given a week’s worth of continuous exposures.)  Looking online the expected shutter life is 50-100K...does that sound right?

 

So, my main question now is this:  

Can I lock the shutter open on these continuous shooting nights so that the shutter doesn’t have to actuate with each shot?  I mean, shouldn’t there be a setting where the image is taken off the sensor at whatever interval I set without having the shutter close?  This seems like a smart/pro-type feature that is probably in the camera somewhere but I don’t know where to find it.  (I am using mirror lock-up already). 

 

Also, for any Magic Lantern users: what features besides Magic Zoom and the intervalometer should I be exploring?  

 

Thanks again for for all the help!  Really, really, really helped shorten/reduce the learning curve for me. At 47, I can use all the time-saving shortcuts I can get! Tick-tock.  Trying to learn Magic Lantern, telescope, camera, PixInsight, Deep Sky Stacker, plus Inkscape and my Glowforge all in the last 45 days has been kinda taxing, what with a 3-yr old as well.

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Esteemed Contributor
Posts: 4,241
Registered: ‎02-17-2016

Re: T3i night sky continuous 10 sec exposures?

That is "B" mode. You hit the button once to open the shutter and again to close it.

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Moderator
Posts: 1,702
Registered: ‎10-25-2012

Re: T3i night sky continuous 10 sec exposures?


@kvbarkley wrote:

That is "B" mode. You hit the button once to open the shutter and again to close it.


You'll also want to use a remote or the self timer for best results.

 

If you don't know about remotes, click HERE.

 

For the self timer, click HERE.

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Occasional Contributor
Posts: 5
Registered: ‎10-23-2017

Re: T3i night sky continuous 10 sec exposures?

I don't think we are on the same page.  In your description, is "B" mode the same as "Bulb" mode?

 

If so, I am familiar with Bulb mode.  But that doesn't give me what I am looking for.  As I have used Bulb mode: you press the button, the shutter opens, you let go and it closes the shutter and saves the image and resets the camera sensor.

 

What I am looking for is (e.g. for continuous 10 second exposures):

-Press button

-shutter opens

 

WHILE (Button not re-pressed)

   -Wait 10 secs

   -save image from sensor

   -reset sensor

LOOP back to the WHILE

 

-Close shutter (save last image. reset sensor)

 

In this way you could be taking continous 10 second exposures and the shutter only opens and shuts once.  So, for a 3000 exposure night-long session the shutter only actuates for 1 cycle, saving 2999 cycles on the shutter.  My goal here is to prolong shutter mechanism life.  I think the GoPro operates this way by default.

 

Seems to make sense that there would be a function or advanced feature for this somewhere.  

 

Does this make sense? Does this exist somewhere, officially or in Magic Lantern?

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Esteemed Contributor
Posts: 4,241
Registered: ‎02-17-2016

Re: T3i night sky continuous 10 sec exposures?

You need the TC-80N intervalometer with the cable to let it hook up to the camera.

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