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On Saturday, May 10, 2003, at 05:40 PM, Brian Skiff wrote:
> Is there really a photometrically-reliable shutter that will work
> at this exposure? I bet not! Probably the minimum exposure where the
> finite shutter time will not be a significant fraction of of the
> exposure
> itself is perhaps 4-5 sec. This is something you can test, of course,
> using a suitable star to see how the instrumental magnitude changes as
> one goes to progressively shorter exposures.
Yes. I know such short -mechanical- shutter is not reliable.
Exact exposure time is different and varies each time.
I combined 50 images thus I expected that these variation were averaged.
I also know there is uniformity across image may (must?) not be
guaranteed in such short shutter.
Exposure time may be different among edge and center.
Next, I made aperture stop (hole on paper board) and fixed it in
front of telescope.
Using small aperture, I could take objects (delta Sco etc.) with
several second exposure time.
But exposure time that variable star was not saturated is short for
comparison.
So, I also combined images (also, 50 or so) and saved in 32-bit Fits
format.
It was very time consuming step.
I needed to take several hundred images to compare several images (50
images combined, each) and to estimate error.
Even though, I could not get any reliable result yet.
Variation between images are very lager than I expected.
Now I check what is most contributed in error.
Seiichiro Kiyota
I will continue this experiment until next galactic supernova :-)
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