[AZ-Observing] Re: APOD picture of the duh Peaks
- From: ketelsen@xxxxxxxxxxxxxx
- To: az-observing@xxxxxxxxxxxxx
- Date: Wed, 16 Apr 2008 18:38:25 -0700 (MST)
Hi Brian-
I was just going to argue that it could be done, but then I looked at the
full-rez version - if you look at the interface between mountain and sky,
the graininess doesn't quite match up, so I now agree with you, the
mountain was cut and pasted against the sky image...
There are tricks you can play - first, point north where the stars appear
to move more slowly. Then you can split the image motion - I recall Frank
Zullo's Rule of Thumb for exposure in seconds (without star trailing) was
650/focal length. This shot looks pretty wide, say 24mm, so Frank's ROT
would be about 30 seconds. But if you put it on a tracked mount for the
first 30 seconds, then let it trail for 30 more, supposedly the exposures
would be short enough not to show motion either in the stars or land and
still get a full minute of exposure. Your mileage may vary...
-Dean
> It's just occurred to me that the Duriscoe shot of the Peaks
> _must_ be a composite. The reason simply is that Earth still spins:
> you can't get a sky shot that deep without having the foreground
> smeared out from trailing at least a little bit. So there might
> be just two shots taken back-to-back---maybe the slight trace of
> illumination on the cloud-cap isn't from the east side of Flagstaff,
> but instead from a bit of morning twilight.
>
>
> \Brian
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