Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 69,895   Posts: 1,520,953   Online: 897
      
Page 1 of 2 12 LastLast
Results 1 to 10 of 11
  1. #1
    raucousimages's Avatar
    Join Date
    May 2003
    Location
    Salt Lake
    Shooter
    Large Format
    Posts
    825

    Lunar exposure time @ f10/ISO 100

    I am helping on a technical project involving photographing the moon. The telescope being used is a fixed f10. The film body (camera) is adjustable in 1/3 stops for shutter speed but once a roll is started I may not be able to adjust or bracket the shutter speed. So given IOS 100 film and f10 what would I use as a shutter speed? Useing the "Sunny 16 Rule " for reflected light I come up with 1/250, am I close?

    Thanks for any help.

    John
    DIGITAL IS FOR THOSE AFRAID OF THE DARK.

  2. #2
    raucousimages's Avatar
    Join Date
    May 2003
    Location
    Salt Lake
    Shooter
    Large Format
    Posts
    825
    BTW. I am helping on this because digital is not giving enough detail in the shadows from the lunar mountains. Good old T-max 100 works better!
    DIGITAL IS FOR THOSE AFRAID OF THE DARK.

  3. #3
    Lee L's Avatar
    Join Date
    Nov 2004
    Shooter
    Multi Format
    Posts
    3,239
    From Covington's Astrophotography for the Amateur
    Appendix A.5

    f:10 and 100 ISO

    thin crescent 1/8
    wide crescent 1/15
    quarter moon 1/30
    gibbous 1/60
    full 1/125

    So about a stop more exposure than f:16 sunny, most likely because of atmospheric extinction and variations. Bracketing a little is also a good idea.

    Other important considerations are to balance the scope/camera combination on the mount carefully and use the mirror lockup if using an SLR. I've seen some instances in which making the scope slightly tail-heavy can help damp vibrations, mostly when the camera shutter/mirror excites the system's resonant frequency. If it's f:10, there's a good chance it's a Schmidt-Cass and you often can't adjust balance on those common fork mounts very effectively without a slide bar and some weights.

    Lee
    Last edited by Lee L; 01-02-2007 at 10:34 AM. Click to view previous post history.

  4. #4

    Join Date
    Apr 2005
    Location
    Naestved, Denmark
    Shooter
    Multi Format
    Posts
    146
    Sunny rule 16 will work. And for technical use it will give useful pictures.

    But I'm not sure how much details in the shadows, you will get with this exposure time. As the shadows apparently are important for your project, I would consider one or two stops overexposure.

    Tom

  5. #5
    Jim Jones's Avatar
    Join Date
    Jan 2006
    Location
    Rural NW Missouri
    Shooter
    4x5 Format
    Posts
    1,775
    I agree with Lee and Tom. The surface of the moon is actually a fairly dark grey. Yet, we percieve the full moon to be quite bright. Instead of the Sunny 16 rule, I suggest the Looney 11 or, better yet, the Looney 8 rule. More exposure is usually required when the moon is close to the horizon.

    The full moon lacks contrast. A good B&W film to compensate for this was Kodak Tech Pan developed for fairly high contrast. This will emphasize detail. The contrast can always be reduced when printing, if desired. I always bracketed when using Tech Pan.

  6. #6
    David A. Goldfarb's Avatar
    Join Date
    Sep 2002
    Location
    Honolulu, Hawai'i
    Shooter
    Large Format
    Posts
    17,158
    Images
    20
    Looney 11 is what I use for the full moon.
    flickr--http://www.flickr.com/photos/davidagoldfarb/
    Photography (not as up to date as the flickr site)--http://www.davidagoldfarb.com/photo
    Academic (Slavic and Comparative Literature)--http://www.davidagoldfarb.com

  7. #7

    Join Date
    Nov 2004
    Shooter
    Multi Format
    Posts
    278
    Full moon - 125 at f/8 has always done it for me.

  8. #8
    c6h6o3's Avatar
    Join Date
    Oct 2002
    Shooter
    Large Format
    Posts
    3,161
    Images
    6
    Quote Originally Posted by raucousimages View Post
    So given IOS 100 film and f10 what would I use as a shutter speed?
    Ansel Adams describes in The Making of 40 Photographs how he computed the correct exposure for the moon in his "Moonrise, Hernandez, NM" photograph. He couldn't find his meter and a cloud was about to obscure the moon so he had to think fast.

    He knew the luminance of the moon to be 250 c/sq.ft. At a shutter speed equal to the luminance of a subject in c/sq. ft. the correct aperture is equal to the square root of the film speed. In your case, that would be the square root of 100, or 10. Therefore f10 at 1/250 sec. will give you a Zone V moon. Adams wanted a Zone VII moon, so you need to open it up two stops, yielding a final exposure of f10 at 1/60th.

    Of course this doesn't take into account any filters you may be using. The phases of the moon are irrelevant as its luminance is uniform over the illuminated surface, no matter how much illuminated surface there happens to be.

  9. #9
    Lee L's Avatar
    Join Date
    Nov 2004
    Shooter
    Multi Format
    Posts
    3,239
    Quote Originally Posted by c6h6o3 View Post
    The phases of the moon are irrelevant as its luminance is uniform over the illuminated surface, no matter how much illuminated surface there happens to be.
    This page contains a rather technical explanation of why this is not the case:
    Lunar Albedo

    Albedo is the general term for percent reflectance by an object.

    Albedo is given in a variety of definitions, and the blacktop analogy is the result of the abuse of a couple of such definitions. Without knowing the definition that is used, its impossible to be sure you are comparing apples to apples. The simplest version of albedo is the Lambert albedo. A Lambert surface is one which scatters light isotropically - in other words, an equal intensity of light is scattered in all directions; it doesn't matter whether you measure it from directly above the surface or off to the side. The photometer will give you the same reading.

    For a lambert planetary surface, the illumination effects are entirely geometric. The brightest illumination is directly below the sun, and the amount of light reflected diminishes the farther you get from this point, simply because the sunlight is played along a greater arc of the surface. The illumination isophotes will be round. Unfortunately, the moon is not a Lambert surface.

    For one thing, the subsolar point does not provide the brightest reflection - the limb does. And the phase curve has a sharp peak in brightness during full moon - the moon is extra reflective at full compared to first quarter. Attempts were once made to explain this in terms of a Lambert surface with various kinds of topography, but this does not work out.

    It is now known that this departure from a Lambert surface is caused by the very porous first few millimeters of the lunar regolith. Sunlight can penetrate the surface and illuminate subsurface grains, the scattered light from which can make its way back out in any direction. At full phase, all such grains cover their own shadows; the dark shadows being covered by bright grains, the surface is brighter than normal.
    This is why all well written astrophotography books suggest longer exposures for partial phases.

    Further reading on "Moonrise, Hernandez, NM" will also reveal that the negative was one or two stops underexposed given what Adams intended, and it took him several years to coax the print he wanted out of it.

    Lee
    Last edited by Lee L; 01-03-2007 at 07:52 AM. Click to view previous post history.

  10. #10
    raucousimages's Avatar
    Join Date
    May 2003
    Location
    Salt Lake
    Shooter
    Large Format
    Posts
    825
    Thanks for the help. Everything is ready to go. Telescope, camera (gave up on the film body, it won't allow bracketing), tripod. Now if I can just get the clouds to help. Utah has about 60 heavy overcast days a year and it is looking like this year they are all this winter.
    DIGITAL IS FOR THOSE AFRAID OF THE DARK.

Page 1 of 2 12 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin