Re: Hale-Bopp

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

>Date: Thu, 15 May 1997
> John Ohrt writes:
>...........
>As I understand it, you would select the time interval such that the
>background stars would register as "infinity" and the movement of the
>comet relative to the stars would provide the stero effect.

***** Are you saying that the comet didn't move relative to the background
as much as it moves relative to us? I thought it made pretty steady headway
across the sky.

Of course you are trying for the stars at infinity. That doesn't happen
naturally due to the movement of the comet over the time it takes to reach a
significant change in baseline. I saw a stereo image composed of images from
a base of several hours, proclaimed as the ideal baseline. It had slight if
any stereo of the comet and the stars were twisted in their locations due to
earth's rotation relative to a fixed camera. 

If one waited longer to take another picture, the comet would have moved too
far to get the background stars to be coincident in the same frame. For
example, images taken a day or so apart and with the sky of equal
brightness. I don't know just how far it moved each day but it's more than
over a couple hours. It's distance of travel at some point affords a
reasonable change in perspective for a possibly satisfactory stereo image.

There are two problems with this process. A comet is not a stationery object
nor static of form. In a computer I can separate the comet from the
surroundings and place it relative to it's paired image over an identical
copy of the background stars. If the comet remains similar enough in
appearance over 1 to 3 days, perhaps due to the distance from which we are
viewing it, the change in perspective could provide a more satisfactory
stereo experience than what I've seen so far. The results of the process
would be composited, but as close to reality as is possible by using the
existing data. I would like to composit a series of pairs from increasing
numbers of days separation from some common starting point. They would have
to be taken essentially with the same telescope/camera/optical
configuration. In the reslult you would be able to freeview several pairs,
with an increasing baseline. They could be strung together in an AVI file as
a repeating loop.

One set of stars + several perspective instances of the comet = 2d
background and 3d comet. It would be interesting to see how far into such a
sequence the image develops optimum stereo and at what point in number of
days it stops working at all.

Did no one take pictures on consecutive nights?

>
>I think the problem with HB was that this interval is relatively long
>and unless you are truly fortunate, you will have difficulty matching
>the "sky" levels between the two shots without loosing the fine detail
>in the tail structure.

********  If one brackets with several photos over a range of sky light
levels, there are bound to be close matches of relative brightness between
consecutive nights. At least close enough to be able to make computer
adjustments to fine tune a match for stereo.

>
>Up here, the required observing conditions were rarely if at all
>available.  I belong to an astroclub, and all the images I have seen,
>some of them of awesome quality, differed in this area.
>

******  That's understandable. In N. California there were several clear
nights which would have afforded a series of at least several days. I
suspect some places in big sky country had more of those clear days.

If I don't find real stereo images I may synthesize one from a good
original... Anyone know of a good physical 3D description for the tail
structures?

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


------------------------------