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long exposure for astronomy (or what ever) - Photography

went out last night with the astronomers, and i thought i can make pictures... so you can set the d70 to 30 sec. that's it? what if i want to make an 1 hour exposure? I found out that when i set the d70 to bulb, i can start it with the remote and turn it off with the remote. but it stays only open for about 30min. and then it takes another 30 min before i can touch it again. with any film slr you could do that easy, is this where we meet the limit? i also noticed, ...

  1. #1

    Default long exposure for astronomy (or what ever)

    went out last night with the astronomers, and i thought i can make
    pictures...

    so you can set the d70 to 30 sec. that's it? what if i want to make an
    1 hour exposure? I found out that when i set the d70 to bulb, i can
    start it with the remote and turn it off with the remote.

    but it stays only open for about 30min. and then it takes another 30
    min before i can touch it again.

    with any film slr you could do that easy, is this where we meet the
    limit?
    i also noticed, that this is very hard on the batteries. normally i
    don't have to charge them for 1000's of images, and with long exposure
    i can make 2-3 images and the battery is flat.

    cheers
    Dimitri Guest

  2. #2

    Default Re: long exposure for astronomy (or what ever)


    "Dimitri" <com> wrote in message
    news:google.com... 

    I'm not sure why it stops at 30 minutes...

    That second 30 minutes is a dark frame subtraction (Mode 2). Go to Mode 1
    instead. Or, better yet, simply power the camera off after the shutter
    closes (right at the end of the first 30 minutes). At that point, the
    camera has saved a truly raw image, with no despeckling or dark frame
    subtraction, which will be surprisingly sharp. Then turn the camera on and
    take the next one. Take *one* dark frame this way, manually, and subtract
    it using software.

    Disclaimer: This is what I've been told about the D70. I have not yet used
    one.
     

    To make a 1-hour exposure, you should take 10 6-minute exposures and add
    them. This results in far less noise than a single 1-hour exposure. For
    some techniques to do the adding with Photoshop, see
    www.covingtoninnovations.com/dslr.
    You can use software like Images Plus, which is specifically for astronomy,
    to do it more conveniently.
     

    You should be able to go a couple of hours with one battery charge. I
    always bring a spare battery with me. I don't know about Nikon, but Canon
    also makes an external AC power supply, and people are working out ways to
    run it from a 12-volt storage battery.

    I hope to have my hands on a D70 in the next month or two, and then I'll
    greatly expand my coverage of it on my web site.

    --
    Clear skies,

    Michael A. Covington
    Author, Astrophotography for the Amateur
    www.covingtoninnovations.com/astromenu.html


    mc Guest

  3. #3

    Default Re: long exposure for astronomy (or what ever)

    On 16 Jan 2005 04:30:56 -0800, in rec.photo.digital.slr-systems
    com (Dimitri) wrote:
     


    Sounds like you had noise reduction enabled, which takes another shot using
    the same exposure values without the shutter being opened.
    ----------
    Ed Ruf Lifetime AMA# 344007 (Ruf.com)
    See images taken with my CP-990/5700 & D70 at
    http://edwardgruf.com/Digital_Photography/General/index.html
    Ed Guest

  4. #4

    Default Re: long exposure for astronomy (or what ever)

    On 16 Jan 2005 04:30:56 -0800, com (Dimitri) wrote:
     

    You might want to look into a program such as "stacker which lets you
    "stack" shorter exposure images on top of each other. It also gives
    much better resolution than a single long exposure.

    Dark frame subtraction or noise reduction (NR) mode works well, but
    virtually all digital cameras use it for exposures longer than a few
    seconds. You will gain a lot of noise beyond ASA 800 for long
    exposures although I have done 10 minute ones with and without NR that
    came out well. However at ASA 1600 the noise was quite plain when the
    image was n up to full screen size. NR took most of that out, but
    I'd stick with about ASA 400 or even 200 for the long stuff and shoot
    a bunch of 5 minute exposures.

    I use the remote to trigger the camera and it works quite well
    reflecting off the back of the 10" telescope.
     

    In the D-70 I can shoot like that all night without the batter giving
    out. OTOH if I try long exposures with my old E-20N the 2,000 mah AAs
    go flat in an hour or so.

    Roger Halstead (K8RI & ARRL life member)
    (N833R, S# CD-2 Worlds oldest Debonair)
    www.rogerhalstead.com 

    Roger Guest

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