A few rebuttles:
Your original complaint had something to do with wanting something done to
the histogram.
Presumably to ensure you aren't taking more than the bare minimum of
exposures required to do the job.
Astro-photography often averages lots of images. If you bracket
dozens of shots, it's even *MORE* data to deal with.
My suggestion was to learn correct exposure instead.
I've never said anything against bracketing, it's a pretty useful tool.
In order to bracket effectively, you need to have a fairly good idea of what
the correct for you exposure.
In a very high dynamic range situation, that can be difficult to
determine.
In the situation you described, to me, it would have made more sense to
bracket a few exposures and see which one looked best, it's not costing
anything except time, and probably will take less time that pulling up the
histogram and examining it.
I'll disagree here. Again, going back to the moonshot. It's not
really possible to get a good idea of what "what looks best" from the tiny
LCD screen on the camera while peering at it in the dark (while trying to
maintain some semblance of night vision). Also, due to the JPEG
compression/expansion on the LCDs' screen, you are never sure that
WYSIWYG. The only way to truly evaluate the shot is to pull it up on a
computer and look... that can't be done at shoot time without some
inconvenient heroics.
Now, my histogram argument gives one an *objective* way to ensure
not only that the exposure is correct, but also that it "exposes to the
right" for maximum signal/noise. Consider the ASCII art "histograms"
a: b: c:
| | |
| | |
|_________ |_________ |_________
a: Taken 1 stop less than "perfect"
b: Taken at "perfect" exposure for the moon
c: Taken 1 stop more than "perfect"
That's right... there is no difference between the three. Say 20%
of the area of the frame is taken up by the moon. Also say that the
moon brightness is distributed over 2 stops of dynamic range. There
aren't enough pixels at a *single* intensity to even register a single
vertical dot on the histogram, even though a large percentage of the frame
is *MUCH* brighter than the black. In the best case (when it's actually
registered), you might get:
a: b: c:
| | |
| | |
|...______ |.....____ |.......__
Again... very difficult to see. Semilog histogram will compress
the vertical axis to bring out the contrast and make it quickly and easily
seen from the LCD at shoot-time.
You'll learn more about making exposures doing it that way.
You'll make fewer exposure errors in the future, having learned more about
exposure.
You'll learn more about how histograms translate into pictures.
I'm an engineer... the more bells, whistles, dials, gauges, and
indicators I've got to choose from, the better I can tailor my learning
curve.... :)
What you are suggesting is that I am suggesting something I am not
suggesting.
Then might I suggest suggesting suggestions applicable to enthusiasts as
well as avid professionals.... :) (*everyone* is learning to some degree)
Was that better?
William Robb
Yes, I'll suggest it was. :)
-Cory
*************************************************************************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
*************************************************************************
