Moon Speed

[pathways]

Does anyone have empirical data of the shutter speed at which the moon

begins to lose its roundness and begins to become elongated? John

[erol_a.]

I have no specific times for you, but an experience that may prove relevant~ this past winter I was treated to a dramatic moonrise over Mangrove Bay in Bermuda. Having only Velvia left for colour film, I attempted exposures between 25 and 35 seconds for different effects. The eerily backlit clouds I knew would lose some definition in long(ish)exposures, but figured the moon wouldn't be moving quickly enough to be rendered soft.

For one reason or another, the moon is fuzzy. Exposure priority wasn't given strictly to the moon, so it is somewhat blown out, and the Velvia colour cast from the long exposure certainly is a bit unnatural... however by this point of the night (I was in wraps from a rather nasty accident) I wasn't too intent on doing anything but sitting down;) I mounted my 300/4 Nikkor on a Bogen 3021 and head and fired by cable release on a relatively windless night and I know not of what to attribute the fuzziness of the moon (but not background) to other than the moon's movement... crazy? Well- I have a mediocre quality scan of the image, but can't seem to figure out how to upload it w/ the message. Hmm.

[jim_doty]

LONGEST SHUTTER SPEED WITHOUT BLURRING THE MOON: This is a brief summary and oversimplification from Michael Covington's ASTROPHOTOGRAPHY FOR THE AMATEUR (worth looking up in your library, or buying if you do a lot of this kind of thing). With a 100 mm lens: 2 seconds for critical work, 8 seconds with some blur. With a 300 mm lens: 1 second for critical work, 4 seconds with some blur. With a 500 mm lens: 1/2 second for critical work, 2 seconds with some blur. As you can see, the longer the lens, the faster the shutter speed to avoid obvious blur. My own experience agrees with Covington's. I don't worry too much unless getting near 1 second with a long lens. Depending on the aperture in use, you risk overexposing the moon at shutter speeds this long. For a full moon well above the horizon with no clouds, I prefer Basic Daylight Exposure plus one or two stops, but I like a light toned (not washed out) full moon. An overexposed fingernail moon shot with a wide angle lens is less objectionable to me than a burned-out (clear film base) full moon at 300 mm. Experiment!

[erol_a.]

correction to previous post, the moon photos were far less than 30 seconds; that was the time for shots simply going across the harbor... I believe the shots of the moon were closer to the 8 second range.

[robert_segal1]

So ya know:<br>

Full moon (or sun's) diametre = 1/2 degree.<br>

Time for Earth to rotate 1/2 degree (and so move the moon 1 diametre) = 4 minutes.<br><br>

 

At that speed, 30 seconds lets the moon move 1/8 diametre. Quite blurry!

[david_evans]

The rule I remember for a stationary camera and stars is: longest exposure for no appreciable track is 600/lens focal length. Probably very close for moon shots of short duration.

[john_macpherson]

Found *something* that may help, from an old photo magazine. This is

from a table for photography of star trails rather than the moon, and

I am sure the astrofizzy photogs will correct any errors here if this

does not have a reasonably similar application for moons - we still

move at the same speed!

<P>

In order to photograph a twilight lansdcape with stars visible, but

NOT record the stars streaked (due to earth rotation) use this

formula:

<P>

600 divided by focal length of lens.

<P>

eg maximum exposure for 50mm lens is 12 seconds; for a 35mm lens it is

17 seconds; for a 20mm it is 30 seconds; and for a really wide 17 or

18 figure around about 35 seconds. In practice a few seconds either

way is fine. Obviously, doing the maths for longer lenses gives really

short times eg 200mm lens is only 3 seconds before the blurring effect

becomes noticeable.

<P>

I have not personally tried all of these settings so dont take this as

gospel, but at least it is a starting point for you to go try it out.

[pathways]

Thanks to all those who wrote about the moon shot. I was really concerned only with moon speed, not the exposure, and the problem referred not to photographing the moon up in the sky but at moonrise. On a day in which I had been shooting a setting sun with 210mm +1.4 with Velvia at 1/30 f/4.5, then about 40 minutes later a blood red moon arose. Obviously the 1/ISO, f/16 doesn't work here. That's when I went into the 30 sec, 15, 8,4,2,1 sec, 1/2, etc. bracketfest. For the record, out of about 40 snaps, about 30 were usable, several excellent with all maria clear and defined - some of the shots were slightly distorted somewhat like a 16th century map of the New World. Thanks again, John.

[pathways]

One last item to the moon shots, (normally I shoot everyting on manual) the best photos I got were the ones I shot at program dual, matrix metering - since I wasn't sure of how to shoot this one, I thought I would let Nikon try their thing - and those were the best shots. John.

[ross_geredien]

At 420mm, I got eliptical elongations at about 3- 4 sec.

 

Multiply by four for 100mm?

 

Ross

[pathways]

Final? response to this - for archives, perhaps. I contacted a research astronomer who said:

"i get a slightly different result than one of the responses, who

said a 30 sec

exposure lets the moon move 1/8 diameter. i got that the moon

moves 1/4 diameter

in 30 secs. The moon moves approx. 15arcsec per sec of time. At

this rate, the

moon will travel about 15"/1800" = 1/120 diameter in just one

second. This means

1/4 diameter in 30 seconds. (assuming the moon's diameter is

1800" = 0.5 degree)"

 

From this, with my emperical data, I conclude that the moon shows no apparent motion at speeds up to one second, two and four seconds will show some motion, but only if you look hard for it. Eight seconds will be noticable, and at 15, an unsuspecting viewer will notice it. However, if shooting a moonrise, since the moon's image will appear flatened due to atmospheric distortion, the rising effect of the earth transport motion will tend to lessen the noticibility of the moon's motion, and will result in just a "larger" moon; therefore, both eight and fifteen seconds for a rising moon are viable options. 30 seconds is totally hopeless. John.

[wildpicture]

Last week I took some pictures of the moon too. It was a nice clear and cold night. Since I mainly wanted to test the stability of my new tripod, I took several pictures with combinations of my FD 500/4.5L lens and the 1.4x and 2x converters. So I used:

<p>

500mm<br>

500mm with 1.4x = 700mm<br>

500mm with 2x = 1000mm<br>

500mm with 1.4x and 2x = 1400mm<br>

500mm with 2x and 2x = 2000mm<br>

500mm with 1.4x, 2x, 2x = 2800mm<br>

<p>

I tried all of these combinations with lens fully opened and closed down at F8. If anyone is interested I could put pictures of the series on my site. Up until 500mm with 1.4x and 2x the results were okay.

<p>

I have put one example on my site at: <a href="http://www.wildpicture.com/special/moon.htm">Full Moon.</a> It's a full scan at 1024x768 of the slide. No cropping or anything. I only adjusted the lower tones slightly because my slide scanner (HP Photosmart) isn't very good at scanning all black parts.

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Greetings,

Hans

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