From: Greg Harp (gregharp_at_antispamdomain.not)
Date: Wed Nov 26 2003 - 01:47:28 EST
Forrest,
That's a very nice M42!
You did a great job combining exposures to render the majority of
the detail within the dynamic range of the display. I don't know
the actual photometric values, but in "real life" this object seems
to go beyond the nine or ten stop latitude of the Canon cameras, so
most people tend to lose one end of the dynamic range or the other.
Since you're shooting at f/6.3 you might try some longer exposures
to catch the dimmest parts of the nebulosity. I am thinking that
four to five minutes at f/6.3 should do it.
Or you might be able to add that up using your ten 2-minute
exposures. In fact, I would try that before re-shooting. If you
take pairs of these images (after calibration and alignment, of
course) and do simple addition you should get (effectively) five 4-
minute exposures. That should be enough to work with.
At least I know that I have managed to capture pretty much all of it
at ISO 800 in one minute with f/2.8, and that's about a 5X times
faster aperture. (2 ^ 2.333333...)
As for focusing, even using the zoom in playback mode (after an
exposure) on the LCD doesn't seem to help me much. It's just not
enough.
I have found that DSLRfocus is indespensible, which pretty much
means you have to have a laptop. As it progresses to v2, a lot more
capability to analyze focus is being added. However, even v1 helps
a lot by simply allowing you to magnify a star by some large amount
(certainly more than 100% -- individual pixels are easy to see in
the zoom view)
I am noticing that a lot of M42s shot with Canon DSLRs are a lot
more magenta and gray than the reddish film images we've all seen in
the past. Those that aren't have had the red bumped up in
processing, usually. Are we seeing the H-alpha sensitivity of the
Canon sensor again? Or is that just color shift on the film due to
reciprocity failure?
Unfortunately, I've never managed to locate a source of information
showing what the actual spectography of certain objects is, so I
don't know what it's *supposed* to look like. Photos of this object
in particular vary quite a lot.
--Greg
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