Definitive method to shooting star trail photos with 20D and TC-80N3 timer remote

Discussion in 'Canon EOS' started by erick_kyogoku, Apr 18, 2005.

  1. I've shot star trails before, but always with film. I'll find myself with a 20D in the southern hemisphere (only slightly, in Tahiti at W149? and S 17?) and want to take star trail photos with the 20D, a Canon TC-80N3 timer remote control, and perhaps a 28/1.8, 50/1.4, or 17-40L/4.0. But I don't know what settings to use. I used 400 speed film in the past, should I set the 20D to 400? Perhaps it's best to use the 28 prime stopped down to 2.8? I also read that with digital it may be better to take several shots rather than keep the shutter open for 4-5 hours. (Could be my imagination but I read of CMOS censor warming up?) I have bits and pieces of information but nothing definitive, and am seeking the right way to do it with a digital SLR. Perhaps I can set the remote to take several one hour exposures (but won't that result in gaps?) or is one contiguous exposure of 3-5 hours possible without the battery dying? Please advise, thank you.
     
  2. I have not found my 20D particularly good at very long exposures of dark things - too much banding noise at any ISO even with the long exp noise reduction turned on. Maybe this is one area where film still has an advantage over digital.
     
  3. Read this

    http://www.photo.net/learn/dark_noise/
     
  4. The Canon Astro Guide is excellent, they use a 10D, but it should be nearly the same advice for a 20D, e.g.,
    "From the Three Stars of the Orion Constellation
    to the Nebulae of the Orion Constellation
    ISO setting at 400, AWB EF200 mm f/2.8L II USM
    Full aperture, 2 mins. 30 secs."
    <p>
    What more can you say?
     
  5. "ISO setting at 400, AWB EF200 mm f/2.8L II USM Full aperture, 2 mins. 30 secs" - what more can you say - well 2min 30sec exp is not very long at all.
     
  6. Searched for info on this the other day and found this

    http://www.photo.net/learn/astro/star-streak

    Great links at the end, and try Dan Heller's site, too.

    From all I've learned over the past week of reading and experimenting with a 10D and 17-35mm zoom...

    Use ISO 100 - I know, it sounds absurd, but it's what everyone uses for low noise, and it looks great.

    Exposure will vary according to how much moonlight (the less the better), but I found 17 to 24 minutes gave good streaks, while a full hour gave longer streaks, but much more background brightness.

    Get away from lights as much as you can.

    Include a foreground element, like a tree or building silhouette.

    Set the lens to infinity (all the way to the left - my lens has an infinity marking, but it's not accurate - I wanted a good quarter inch past it) and stop down one stop from wide open to give a little extra sharpness (though you lose some faint stars - try each and see what you think).

    For processing, shoot RAW, bring up the exposure to where the brightest stars begin to show over-exposure, adjust color to liking, convert to 16 bit Tiff, and, if necessary for a bright sky, move the mid-tone slider in Levels to darken the sky back to a normal-looking night sky.

    Use a sharpening method that doesn't sharpen the blank areas of sky - Fred Miranda's 20D CSPro action (works in Elements and CS) would be an excellent low-cost investment for you to make. The Low ISO / Level 4 / Sharpen Fine Details setting works best.

    http://www.fredmiranda.com/software/

    You'll find all this and more on those sites listed, as well as one at the Luminous Landscape site you linked to (look under Meteor Showers in the Tutorials).

    Good luck, and have fun!
     
  7. Nothing definitive, but this was taken with my 85mm prime, @ f/8, ISO 200, and a 15 minute exposure. Automatic noise reduction was on. It's had slight levels adjustments and normal USM, but that's it.
    [​IMG]
    I believe that the slight breaks in the beginning of some of the trails were caused by the winds that night. They were about 40 knots coming off the glacier. I could only stand two photos before I had to give up and go get warm.
     
  8. Lance - is that from a 20D?
     
  9. Yes, sorry, it was taken with a 20D.
     
  10. I found the Canon guide to be informative, but not very in depth. It is a bit of a marketing piece afterall. I would also suggest http://www.astropix.com/INDEX.HTM
     
  11. (Could be my imagination but I read of CMOS censor warming up?)
    There's good advice here so far; I just want to beat some more on this dead horse for a minute before throwing my two cents in.
    The notion that the sensor heats up during a long exposure (with EOS DSLR's at least) is a myth. Dark noise accumulates over time linearly (twice the time, twice the dark noise), and the warmer the sensor the faster it accumulates. All camera's sensors are not entirely isotropic; there will be "hot spots" where the dark noise is greater, but the existence of these spots doesn't mean the sensor is "heating up," it just means it was warmer in those areas during exposure. During integration, there is no significant, if any, heating of the sensor. Incoming light is converted to electrons not heat; and the sensor isn't powered, it is a passive detector until it is read out.
    A sensor does heat up during a rapid burst of picture taking. The reason is that the readout of the sensor requires that amplifiers do a lot of work, and powering these amplifiers (which are generally on the sensor in CMOS detectors) kicks out some heat. But that situation seems inconsistent with taking long exposures, and dark noise isn't a problem with short exposures. (Dark noise in my 10D is so low that I consider it non-existent at an exposure of under five minutes or so.)
    So the bottom line is don't worry about the sensor heating up. Just worry about the signal and noise level.
    You could use the remote to take several 1-hour exposures and you could combine these exposures, but since you are taking star trails, this will reduce the signal to noise ratio of the trails. That's maybe not the best idea, but you could experiment and see. You won't get gaps if you start the next exposure within a few seconds of the last one with the lenses you are talking about.
    My preference for long-exposure star trails is to use ISO 100, shoot raw, and close the lens down a stop or two from wide open so the star images look good to the edge of the frame. This is one situation where I freely adjust EV in the raw converter if necessary.
    I've taken a 4-hour exposure with the 10D (BP-511) battery without a problem. I've not had the 20D long enough to abuse it similarly. In general, I'd recommend you have a better power source for the camera than a single internal battery. Even using the grip with a second battery on the 20D would be an improvement, but you probably want to get an external battery pack or AC power option if you have AC at the site.
    FWIW.
     
  12. Nice shot, Lance. Those mountains look other-worldly, especially with the colors, and great composition. Erick - took my 10D and 28 mm out for some test shots this morning at 4 AM. Here's 100% crops of what I got for the various ISO settings.
    00Bu2z-22961884.jpg
     
  13. Part II As you can see, the 400 level brings out more stars, but also more background light. In the second row, I adjusted the photos with Levels to match each other, to compare the noise levels. It's easier to see surrounded by black in CS, but ISO 400 has noticeable noise. 200 isn't bad at all, though, especially considering this is a 100% crop. Here's my second test, using various f-stops.
    00Bu3E-22961984.jpg
     
  14. Part III

    In that one you can see (though difficult on a white web page) how the smaller apertures made the brightest star trails sharper.

    They were all taken with 4 minute exposures, and then adjusted in RAW and with Levels to equal each other to compare the final output(originally, of course, the smaller aperture files were much darker than the wide open one).

    What is surprising is the extra amount of noise in the f/5.6 file - kind of blotchy. I guess that's from the extra processing.

    Either way, you can also see, looking right above the numbers, how the fainter stars are much fainter in the 5.6 shot, while better in the others.

    So, to wrap up my test, I'd say go with ISO 100 or 200, and set your lens wide open or closed a stop.

    Finally, for one last tip - when you're all set and have the scene composed, crank up the ISO to 1600, take a ten second picture, and then check out the image on the LCD - it will show you your composition much better than you can see through the viewfinder, and it can save you from taking an hour long picture with a crooked horizon or some limb sticking in from the side.

    Just don't forget to set it back to ISO 100.
     
  15. here are 6 shots, 2 min each, layered in photoshop. The TC remote was used and it's
    minimum time between automated shots is 1 sec, hence the visible gaps in the star trails.
    This was done with a 10D.

    http://www.pbase.com/santa/image/37601424.jpg
     
  16. Good luck. I wired up my own toggle switch for the 20D, it works good enough for what you have in mind. ISO 100-200 and F5.6 is good for 20-30 minutes. Without too much light polution you could go for several hours.
     
  17. Erick, I do not know if you will be close enough to the equater to get a shot like this: http://www.photo.net/photo/3177551 If you are you might want to try it. This picture is VERY cool..
     

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