i want to take a shot of the moon tonight

North and South. You have inverted the moon's image as seen with the naked eye or a camera.

I have inverted nothing. My camera was level with the horizon. I was not standing on my head shooting.

One of you lives in the northern hemisphere and one of you lives in the southern hemisphere. Doh.

Tom W wrote:
I have inverted nothing. My camera was level with the horizon. I was not standing on my head shooting.

The Mare Crisium (the stand-alone dark round patch close by the right edge) should be in the northern hemisphere but the pictures show it in the southern.

Ken

kfong wrote:

Tom W wrote:
I have inverted nothing. My camera was level with the horizon. I was not standing on my head shooting.

The Mare Crisium (the stand-alone dark round patch close by the right edge) should be in the northern hemisphere but the pictures show it in the southern.

Ken

OK, so either Tom is seriously mistaken about what he did, or Ken's grasp of celestial geometry isn't quite what it could be. Ockham's Razor suggests the latter, but I don't know either of these guys , so let's keep an open mind and do some science.

Tom's from Chattanooga, which is at latitude 35°4' North, longitude 85°15' West. The Exif data on the photo says it was taken at 05:33 on August 10th. According to my Planetary, Lunar and Stellar Visibility calculator, sunrise at Chattanooga would have been at 06:57 and moonset at 08:09 - so at 05:33 we'd expect the sky to be dark but the moon to be low in the western sky.

A detailed look at PLSV - see attached image, below - shows that at 05:32 the moon's equator would have been inclined at 19.5° relative to the celestial equator. But the inclination of the celestial equator to the horizon is the complement of the geographical latitude, i.e. 55° in the case of Chattanooga. So the moon's equator would have been inclined at 74.5° relative to the horizon when Tom took the shot.

My second attachment is a copy of Tom's shot, rotated by 74.5° anti-clockwise. This means that the north pole of the moon should be at the top, and the moon's equator should run horizontally across the middle of the image. It seems to me that Mare Crisium is definitely north of the moon's equator.

Sorry Ken. Looks like Tom wasn't as confused as you thought he was.

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Here's anothwer way of doing it. This is a screenshot from Your Sky showing the sky from the vicinity of Chattanooga at 05:55 local time on August 10th. Although it's only a few pixels across, the orientation of the Moon is clearly consistent with Tom's photo.

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Wow! Thanks for the additional explanations. I'd not really looked for a north and south pole on the moon before. I just line it up and shoot (especially when I'm only shooting for demonstrative purposes).

Good information, StewartR.

Thanks StewartR for such a concise explanation. I wonder how many of us realises that the moon takes on a different aspect dependant on one's location on Earth? Even though I'm interested in astronomy, and have even lived in the northern hemisphere, on the equator, and in the southern hemisphere, it has taken this post to make me aware of the fact. I have learned something today.

Glad to be of service. Isn't the Internet a wonderful thing?

Back to the camera settings, can someone explain to me why you'd choose ISO 400 with shutter speeds so fast? Wouldn't it be better to use ISO 100? Especially when you are using a tripod, mirror lock-up and a remote release?

Good point. It's not necessary to be that fast, to freeze the moon's apparent motion. Let's do some more science.

The OP has a 300mm lens, and attached to a 350D that has a field of view of about 4.2 x 2.8 degrees. The moon subtends an angle of about 0.5 degrees, so it will be about 410 pixels across on his photo. Now the rotation of the earth means that the moon moves across the sky at a rate equivalent to moving its diameter every 2 minutes. So it will move by 410 pixels in 120 seconds, which is about 3.5 pixels per second. Ergo, a shutter speed as slow as 1/10th ought to be fine.

Thanks Stewart. Science always intrigues, fascinates and impresses me. And I like knowing that my ISO choice is good too. Now i just need to wait a few days longer to get those crater shadows.

Good point, but in practice, 1/10 second will not give the crisp sharp image that a faster shutter can produce. It's not just a matter of the moon's movement (relative to earth) being equal to or less than a pixel's width in order to bring about a crisp image. It would seem to me, and is borne out in practice, that the shutter speed needs to be considerably faster than that. Why? - because any detail that moves a reasonable portion of a pixel during the exposure time will possibly have an effect on at least two pixels, and this results in some softening of detail. Ordinarily, this might not be important, but in an image that needs to be viewed at 100% on the screen, it will show as a gentle softening of detail.

Still, 1/400 or faster would probably be overkill for dealing with the moon's movement. What it does help with is camera movement. I'm not sure that ISO 400 is necessary if one can deal with the other effects of a slower shutter, though it appears to be plenty clean enough on the 30D to use without much of a noise issue.

All this babbling of mine really means that you can probably go with ISO 200 and 1/200-1/320 shutter speeds without having anything to fear of the moon's movement at 300 mm on a good mount. Handheld, I'd grab all the shutter speed I could get, with respect to the noise limit.

My experience has taken me to higher ISO settings out of necessity. I regularly shoot the moon at 1/80 to 1/200 second on my 5D at ISO 400, but I'm using stacked teleconverters and a much smaller actual f/stop (typically f/11-f/18 ). It's a constant battle between diffraction, noise, and movement when you put a lens/teleconverter combination to the edge of its performance limit. I haven't really had a chance to test the 30D at the limit, but I suspect that it should perform fairly well.

Interesting points, Tom. I must admit my calculations were purely theoretical - the longest lens I have (for now!) is 200mm, which just isn't long enough to get decent shots of the moon. So I'm happy to defer to your practical experience.

One factor that might be relevant is motion of the atmosphere. After all, that's why stars twinkle and that's why observatories tend to be built on mountain tops. I don't know enough about atmospheric phenomena to calculate what difference it makes, but I could quite easily imagine it has an effect at 1/10th of a second but not at 1/100th of a second.

I've had the experience where even a steady tripod can be shakey when the image is viewed very large. For normal shots where the entire frame may end up as an 11 X 14 inch print, it's not as critical. It's just that short of a very long lens, these shots invariably get viewed at 100% on the screen, or cropped to the point that the full moon image fills a good center on an 8X10 print.

I've had some pretty bad nights trying to shoot the moon, when it seems that the atmosphere is what my astronomical friends like to call the air "turbulent". Some nights, I just can't get a crisp image of the moon, so I'm certain that turbulence has a significant effect.