How fast does the moon move through the sky

Discussion in 'Exposure Discussion' started by michael_r, Jun 16, 2011.

  1. michael_r

    michael_r Subscriber

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    I'm working on a picture that will include the moon. I'm using an 85mm lens on 35mm film. Problem is the exposure on TMAX 100 will need to be 15-20 seconds. TMY2 would obviously help, but I would really rather use TMX for finer grain. As fine grained as TMY2 is, I would really rather use TMX if I can. So my question is, how short does an exposure have to be to keep the moon sharp? It seems to move pretty damn fast, especially when I'm setting up and it speeds up so I miss the shot :smile:

    I guess ideally I'd make a first exposure for the scene before the moon is in frame, and then just add a short second exposure when the moon is in place. But I can never rely on double exposures with a roll film camera. Too bad I won't be able to use sheet film for this one.
     
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  2. tkamiya

    tkamiya Member

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    Moon orbits around the earth in 27 days. So I'd imagine most of the "movement" of the moon is actually the rotation of the earth itself... which will be 24 hours per cycle.

    According to the ever reliable wiki page, it says it moves at around 0.5 degrees per hour.

    http://en.wikipedia.org/wiki/Orbit_of_the_Moon
     
  3. michael_r

    michael_r Subscriber

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    I'm ok on the physics. But I'm not sure how to translate it to photography and how long one could keep the shutter open with an 85mm lens (probably can assume 50mm or "0 magnification") before blurring would become visible.
     
  4. ann

    ann Subscriber

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    The moon is quite bright, remember it is lite from the sun. Frankly I have my students rate the film at ISO 200, a shutter speed of 250 at f5.6 or F8; so, just reduce one of those by 1stop to reflex a reduction of 1 stop of ISO
     
  5. tkamiya

    tkamiya Member

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    With 85mm lens, the moon will basically appear as a dot. There won't be much detail to speak of at all. Also, moon is very bright. Depending on your aperture setting, it will bloom quite a bit further obscuring details.

    According to the Wiki page, it moves just about its diameter per hour. That means if you kept the shutter open for a whole minute, it will move 60th of its diameter.

    How large are you going to print this?
     
  6. brucemuir

    brucemuir Member

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    I once did a setup where I wanted to have the moon traverse most of the diagonal of the 135 frame. I didn't have a long lens so I was tring to get creative :whistling:

    I cant remember the specifics but I think the exposures were in the 20 minute range.

    I screwed around with the whole roll and remember I surprised how much it did move even with shorter exposures. The shorter exposures didn't work too well, the moon was just blurred with no detail.

    I'm sorry I can't help more but at least you recongnize there will be some movement.
    Good luck and share your results.
     
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  7. michael_r

    michael_r Subscriber

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    Likely not larger than 8x10". With a normal lens it will be more than a dot. Detail is definitely visible and it is larger than one might expect in the frame. The luminance of the moon will fall initially on zone X with the exposure I'm giving because the foreground elements are quite dark. Even with exposure on zone X there won't be much bloom and full detail will be recorded.
     
  8. coigach

    coigach Member

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    This free photography planning tool might be useful? I use it all the time planning my landscape photos. It has loads of info about the position of the sun and moon position:
    http://photoephemeris.com/
     
  9. michael_r

    michael_r Subscriber

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    Thanks. Yes it does move quite fast. I might have to experiment with a scrap roll and just try some exposures at various times between 4 seconds and 20 seconds. I guess that's the only way to know for sure whether I need to use TMY2 or can stick with TMX.
     
  10. Francis in VT

    Francis in VT Member

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    Kodak had an article in one of their photo-guides about shooting a series of just the full moon. The moon was always in the upper right portion of the frame. Later the film was reloaded making a double exposure to have a large moon in the scene.
    Their top camera at the time was the Retina Reflex IV. The 200 mm f 4 was the lens used for the moon and a 50 or 35 for the second exposure. The film was Kodachrome 64 and the exposure on a full moon was 1/60 @ f4. The maximum on the 200 lens.

    Francis in VT
     
  11. Ian Grant

    Ian Grant Subscriber

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    Often people fudge(d) a night time landscape including a moon with double exposure, and these days more obvious and easier trickery :D

    The moon moves fast enough to see an obvious movement when you shoot a moon lit scene with LF at f22, exposure times tend to be in the order of a minute or longer. But you should be OK with Tmax 100 and a fast lens with 35mm working around f4/f5.6

    Ideally you need to shoot at dusk before it gets totally dark so taht the exposures balance for the moon & the scene, it's a very short threshold 10 mins maybe here in the UK but less further south maybe only 2 mins where we live in Turkey.

    The secret with night shots & the moon is the twi-light zone :smile:

    Ian
     
  12. tkamiya

    tkamiya Member

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    Just for your consideration....

    I am looking at an image taken via my cropped sensor digital with 200mm lens. On this frame, the moon occupies 1/13th of diagonal distance. This is equivalent of using 300mm lens on full frame camera. If I used 85mm lens, the size will be 1/3.5 of that. That would mean it will be 1/45 of the diagonal distance. If I printed this on 8x12 paper (to keep the aspect ratio intact and it has 14.5 inch diagonal distance), the moon will be about 1/3" in diameter.

    My exposure was 1/500th at f/5.6, ISO=200.

    Good luck.
     
  13. Lee L

    Lee L Member

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    The moon moves 360 degrees eastward against the background stars in about 27.3 days. So that's about 13 degrees per day. The earth also spins at 15 degrees per hour, much more rapidly than the moon's apparent progress against the stars. That's the motion that you're really concerned with.

    After the calculations are done, the short answer is this:

    The longest exposure in seconds that you can use to freeze the moon with no apparent motion blur on the film is 250/focal length of the lens.

    See Astrophotography for the Amateur, 2nd. ed., Michael A. Covington.

    This of course, assumes that you're using a fixed tripod. A driven camera or telescope mount will allow longer exposures.

    The diameter of the moon subtends about 0.5 degrees of arc. That's small.

    Lee
     
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  15. michael_r

    michael_r Subscriber

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    That's interesting Ian. On TMX I will need 20 seconds (including reciprocity adjustment) at f5.6 (can't open up wider or won't have sufficient depth of field). And that's really the minimum exposure I can get away with, since that will place most of the picture area and subject matter on zones III-IV.

    Ideally I'd be able to do the whole thing at twilight but in this case I cannot. It's one of those scenes that strikes you out of nowhere as you drive by. I noticed it by accident but the moon has to be in just the right place within the picture, and in fact the moon is hidden behind other subject matter until it rises to just that spot. All this currently occurs at around 10:30pm, well after dark.

    Anyhow I wonder if 20 seconds will cause blur, or if I should just go with a faster film. With TMY2 I could probably get it down to 4-5 seconds.
     
  16. Diapositivo

    Diapositivo Subscriber

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    I suppose you can leave your shutter open, and use a cardboard in front of the lens as shutter. This way you don't have to recock the shutter and don't have alignment problems with the two exposures.

    Do a first exposure by opening 20 seconds, then cover the lens with the cardboard, cloth, whatever, then re-expose for the moon.

    I see this as something that will need several attempts before getting it right. The moon is much brighter than the surrounding area you are going to include in the composition (I infer this from your stated 20" exposure at 100 ISO). I suppose you can go down to 1/4" with the cardboard method.

    The full moon is around EV 14 or EV 15 at ISO 100. That means 1/8 or 1/4 at f/64. You could apply the cap to a ND filter, and screw it to the lens with the cap on, then put the cardboard in front of the lens, and take the cap away, use the cardboard as a "shutter" with a rapid hand gesture (1/4" or so).

    So the sequence would be:
    Open shutter with cardboard over lens (no necessity of mirror lock-up);
    Take cardboard away for 20 seconds or desired exposure, without moon;
    Put cardboard in front of lens;
    While keeping the cardboard in front of the lens, screw ND filter with cap on it;
    Wait for the moon to rise and to go in position;
    While keeping the cardboard in front of the lens, take the lens cap away;
    Do a short exposure for moon details using the cardboard, that's something like 1/4 or 1/8 and is not going to produce a blurred moon;
    Close shutter.

    Repeat until result is satisfying.

    As an alternative: just make two exposures and sandwich them while printing, the moon exposure will have density only on the small part occupied by the moon, no disturb to the first exposure.

    Fabrizio

    PS A camera with a mechanical B shutter is necessary because you'll have to wait for hours with the shutter opened.
     
  17. michael_r

    michael_r Subscriber

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    Yikes that would mean 250/85 so we're talking 3 seconds. Wow that is not much at all.
     
  18. Ian Grant

    Ian Grant Subscriber

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    This is why you need to shoot at dusk, in that twilight zone, effectively depending on the exposure for the rest of the scene you can make the image appear to have been taken at night, or in daylight, anyway if the ambient lights too low the moon will be very over exposed anyway.

    It's easier to do than explain. Think of the famous AA shot that's twilight.

    Ian
     
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  19. Vaughn

    Vaughn Subscriber

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    Something wrong there -- I have photographed lunar eclipses, taking one image every 10 minutes -- and the moon has moved several diameters in that time. Plus it would never get across the night sky at that rate. I do not know how many diameters it is across the sky, but it is far more than the number of hours of darkness.
     
  20. Lee L

    Lee L Member

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    tkamiya is quoting the wikipedia description of the motion against the background stars, caused by the moon's orbital motion about the earth, and not considering other motions. What caused nearly all of the offset in your series is the rotation of the earth, not the moon moving in its orbit. Two separate causes of apparent motion being confused/conflated/ignored with false conclusions on tkamiya's part.

    Lee

    And so we don't dwell on our own misunderstandings, here's some bad astronomy straight from Harvard: http://www.youtube.com/watch?v=p0wk4qG2mIg
    None of the interviewed folks appear to have been from the southern hemisphere.
     
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  21. tkamiya

    tkamiya Member

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    I think I am contradicting myself here, too. If I said earth's rotation is going to be more of a factor, that would mean 360/24 = 15 degrees. The moon certainly doesn't occupy 15 degrees of arc.

    Please ignore everything I said. I'm going back to my cave and punish myself.
     
  22. Vaughn

    Vaughn Subscriber

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    Ah, thanks...I did not think about trying to photograph a "stationary" moon (using some sort of tracking mount for the camera) against a moving background of stars -- that sounds interesting!

    One would need very slow film, very small aperture, in order not to blow out the moon.
     
  23. michael_r

    michael_r Subscriber

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    True, but printing Moonrise required a lot of work, particularly to bring the sky down. My situation would indeed involve an unavoidably overexposed moon, falling on Zone X, but plenty of detail would be recorded and I can bring it down with development and printing controls. I've had to deal with significantly higher contrast scenarios so this is not a very difficult luminance range to handle. It's really only the movement of the moon that troubles me.

    As Diapositivo suggested above, perhaps a "manual" double exposure, keeping the shutter open for hours and blocking the lens etc. But my shutter is not mechanical. Another variation on this occured to me. I could do a double exposure using the multiple exposure lever on the camera, and if I do the moon exposure low enough, say zone V-VI, everything else in the scene will receive essentially zero exposure, so even if the film moves slightly out of register between exposures it won't matter. This wouldn't work if there are clouds around though. Anyhow, always challenging out there.
     
  24. DWThomas

    DWThomas Subscriber

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    I shot a series of the lunar eclipse last winter using a fixed tripod. Once it got into total shadow and I was trying to bring up the red appearance, shots through a 210 mm lens at twenty seconds showed substantial motion, stuff in the 2 to 3 second range wasn't bad (relative to all the other things that were dubious! :D )
     
  25. JBrunner

    JBrunner Moderator Staff Member Moderator

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    600 divided by focal length = max shutter speed on stationary mount to avoid apparent celestial movement. So in your case 600/85 gives you about a seven second exposure before things start to smear. Sharpness is, of course, subjective, but this is a good rule of thumb that yields satisfactory results by most persons standards, the aforementioned 250 divided by focal length being about twice as conservative. IMO the wider you are the sharper things look. Print size and viewing distance are of course factors as well. The 600/fl formula was taught to me by Wally Pacholka (one helluva nice guy), and he knows his shinola. You will notice he tends to shoot wide to give himself more exposure time, and also time to "paint" terrestrial objects in his compositions with a light. You can see his stuff here:http://astropics.com/ What will be satisfactory to you will depend mostly your own subjectivity.

    Moon and stars in the same exposure would be very difficult. Compared to stars the moon is very very bright.

    The mount to follow celestial movement is called an equatorial mount. It wouldn't help you shoot the moon against moving stars, however, because the moon's apparent movement is in sync with the stars. It is you that is moving, relative to the moon and stars. Of course it, and they, and everything else are moving too, but the mechanics lend the POV movement of the observer as the perceptible factor for rude observation, such as ours.

    The only time I have made an observation that yielded a movement of the moon against the stars was when the moon occulted a star, and I was out with my scope looking for it to happen. It took a long time, relatively speaking, but things like that blow my skirt up.
     
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  26. 2F/2F

    2F/2F Member

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    I'd do two exposures and stack the negs. Try different lenses for the moon shot, so you can pick the one that is the size you want when you go to print. If there are any other lights that show up on the neg when you take the moon shots, you can bleach them out and refix to eliminate them.