Using my a5100 for Astrophotography

Discussion in 'Other Genres' started by slothead, Jul 11, 2015.

  1. slothead

    slothead TalkEmount Top Veteran

    544
    Mar 1, 2015
    Maryland
    Tom
    One of the reasons I acquired my a5100 was to hang it on the a**-end of a telescope and use it for astro-photography collecting the imaging with my iPad (as the a5100 has a great wifi interface). This evening however I stuck my a5100 on the top of a tripod by itself (with the 16mm f/2.8 lens) to capture some star trails. It was not as easy as I expected it would be. First I tried using it wide open (f/2.8) and ISO 25600, and the exposure at "bulb" for about 60 seconds and I got a lot of white! So I reduced the ISO to 100, the aperture to f/22 and got nothing (for about another 60 second exposure), so I increased the aperture to half (f/11) and exposed for about 40 seconds and still didn't get anything.

    Star trails can't be this hard! What am I doing wrong? And how can I lock the shutter open (when in 'bulb') instead of holding my finger on the shutter release for however long?

    Thanks,
     
  2. shotupdave

    shotupdave TalkEmount Regular

    114
    Jul 22, 2014
    Torrance, CA
    Dave
    it takes much longer than 60 seconds to get a star trail, you may need to get a wireless intravoltmeter to get exposures longer than 60 seconds
     
  3. slothead

    slothead TalkEmount Top Veteran

    544
    Mar 1, 2015
    Maryland
    Tom
    A wireless intravoltmeter? I've never heard of that. Is there any chance you mean an intervalometer? (I thought intervalometers were for time-lapse. And the a5100 already has access to a time-lapse app.) In any case can you point me to what you think I would need to use the bulb timing for the a5100 (or any remote actuation - aside from the NFC input)?
     
  4. WoodWorks

    WoodWorks Super Moderator

    Dec 12, 2012
    Ashland, OR, USA
    David
  5. Nexnut

    Nexnut TalkEmount Top Veteran

    Why do you use the A5100 instead of your A7R which has a much better S/N ratio and can be used in 16MP crop mode as well? Just curious ...
     
  6. slothead

    slothead TalkEmount Top Veteran

    544
    Mar 1, 2015
    Maryland
    Tom
    Because: (1) I only got the A7R a week ago, (2) it is bigger and heavier (requires different balancing), and (3) will be used for too many other tasks. And there are probably a few other reasons that I don't want to bother describing.
     
  7. pbizarro

    pbizarro TalkEmount Veteran

    358
    Nov 24, 2014
    Portugal
    Star trails are easy, see the link already posted above. Basically, you can not do it with a single exposure, unless you get a film camera and shoot it in Bulb mode for 4 hours:)

    In short, set the ISO to 1600 or 3200, lens wide open (the faster the lens the better), set exposure time to 30 sec, and shoot 100 - 200 images, plus a couple of dark frames. Then process the pics in StarstaX, a neat and free programme.
     
  8. slothead

    slothead TalkEmount Top Veteran

    544
    Mar 1, 2015
    Maryland
    Tom
    I'll try it out! (I'm glad to see that StarstaX is available for OSX.) Thanks pbizarro.
     
  9. José De Bardi

    José De Bardi Assistant in Virtue

    Aug 31, 2013
    Dorset, UK
    José
    So for my star trails I do multiple image stacks.

    I shoot at F2.8/30 seconds/ISO1600 (ISO may go up or down a couple of notches depending on environment).

    There is a star trails app from the A5100, but I find the Time-Lapse app better and then making the start trail later in StarStaX.

    Basically before you go into the app, take a few test shots around the afore mentioned settings (always keep the aperture wide open). On a 16mm lens 30 sec should be fine to avoid any streaking of the stars, the larger the lens mm the shorter the exposure time you can get away with. So basically it's a case of seeing what the lowest ISO you can get away with is at max aperture and 30 seconds exposure - (assuming 16mm lens).

    Once happy go into the time-lapse app and set it up for 150 shots, 30 seconds interval (which will end up with it continually shooting as you are going to do 30 exposures). This will give you (if my math is correct!) 75 mins of shooting which is probably about right, you can do as short as 30 mins and get good results, but longer than 75 mins and the trails just get silly long.

    I batch edit the files on the Mac to get the best colour etc, export to an image sequence of JPG's (potentially batch cropped to 16:9 if I want to make an animation), and put them in StarStaX. You may also want to delete any odd shots which had passers by headlights etc (depends how in the a***-end of nowhere you are!).

    I set StarStaX to Gap Filling mode as it gives the smoothest trails. I also have it output each step as it stacks the images (this is required if you want to animate it but not if you just want the final still with the trails).

    To animate I open the outputted image sequence that StarStaX gave me in Photoshop and render a vid.

    I've not read the link above but I imagine I've said a lot of the same stuff!

    Here's a quick example of what I got using the above method. This was from the Geminids 2014 - there was one shooting star I caught in the top just left of centre that appears part way through.



    Have fun!!
     
    • Informative Informative x 1
  10. José De Bardi

    José De Bardi Assistant in Virtue

    Aug 31, 2013
    Dorset, UK
    José
    Oh and, facing north you get the above effect of a circle. But facing east/west you get more to outsides of a circle either side. It's worth having a compass with you or knowing your direction based on the stars!