Oh, another Perseid question

Paul Ciszek:
Huh. I wonder why digital cameras even offer "BULB" and "TIME" mode
if they can't handle long exposures.

Chris L Peterson:
Most DLSRs start showing significant dynamic range loss from dark
current at around 10 minute exposures. So they can certainly handle
long exposures (even longer if the ambient temperature is low)...

...And in the case of meteor
imaging, there's normally no reason to stack. You just want to go
through lots of fairly short exposures and catch the ones with
meteors.

Mr. Ciszek should understand that "long" is a relative term. 10 minutes
is not a long exposure for a cooled CCD camera under decent skies, but
it is too long for any DSLR I have seen or heard of. If you look at the
very best astrophotos from DSLRs they are usually made from
sub-exposures of not greater than five minutes. In the context of a
DSLR camera manufacturer a "long" bulb exposure usually means one or
two minutes, at most.

Meteor trails are, as you note, best done with short exposures, perhaps
30 to 60 seconds. If one wants star trailing, one may, of course,
increase the exposure time accordingly, sky conditions permitting. For
longer exposures it will probably be necessary in post-processing to
remove an ugly orange-yellow-green tinge from around the horizons.
Making a series of short exposures for hours on end is very tedious.
The software that is included with Canon EOS cameras can automate the
process; no doubt other camera makers have equivalent software.

I think my camera can be set
to take multiple 30 second exposures, but I don't have a good way of
"stacking" them--I can't open my raw files in LightBox or Photoshop
Elements. :-(

There's something to be said for learning how to use the features that
your camera has well in advance of an important event that you want to
photograph. So sad to see mommy and daddy getting unrecognizable photos
of little Worthingfroth-Smythe's first steps because they didn't take
five minutes to learn how to operate their camera. And at some point
you need to decide how serious you are about photography of all kinds
and either stay where you are or move up to better hardware and
software. You don't have to pay the $5k and upward that pro's pay for
their cameras to make pro-level photos, but you do need a camera that
has some of the basic features that their cameras have. The most
important of those features are available in cameras that are
relatively inexpensive. Interchangeable lenses, the option to control
exposures manually, and a camera RAW format are at the top of the list
of features that a serious photographer needs. Camera RAW enables you
to do things with raw photos that would have seemed almost magical a
few years back.

Recent versions of Elements can open RAW files. At $80 from Adobe or
the App Store, Elements is reasonably priced.

A good way of pre-processing RAW files is to use software such as
Aperture (Mac, $79) or Lightroom (Mac/Windows, $149). Both programs are
available in the App Store on Mac OS. Either program will allow you to
do amazing non-destructive editing of your RAW files (in addition to
the programs' sophisticated cataloging functions). In many instances
photos that I pre-process in Aperture require no additional processing
in Photoshop--though that is less likely to be the case for
astrophotos.

Elements can read and save 16-bit TIFFs but it has limited capabilities
for editing 16-bit TIFFs--for $80, Adobe is not going to give you all
of the features of Photoshop CS6 ($700 basic, $1k Extended Version).
For publishing, 16-bit is a big deal, but 8-bit is fine for viewing on
a display, including on web pages. Aperture and Lightroom can export
8-bit TIFFs for post-processing in Elements.

--
I agree with almost everything that you have said and almost everything that
you will say in your entire life.

usenet *at* davidillig dawt cawm

On Aug 10, 7:50*pm, "Androcles" wrote:

Position and direction are different animals.
As Bud said, "up" is as good a direction to aim as any other.

It is difficult to discuss something like this without veering into
being critical or condescending yet more than anything you
statement,intentional or not,differentiates between astronomers from
antiquity up to the time of Galileo and the magnification guys who
think in terms of 'up' rather than looking out into the celestial
arena.I notice it more than anything else when trying to discuss
astronomical cause and terrestrial effect as few really develop a
level of understanding that matches the older astronomers - it is
almost a lost art.

"For if whatsoever space, and whatever thing exists away from the
center of Earth, is the ‘above,’ then no part of Earth is ‘below,’ but
Earth herself and the things upon Earth; and, in a word, everybody
standing around or investing the center, become the ‘above;’ whilst
‘below’ is one sole thing, that incorporeal point, which has the duty
of counterbalancing the whole constitution of the world; if, indeed,
the ‘below’ is by its nature opposed to the ‘above.’ And this is not
the only absurdity in the argument, but it also does away with the
cause through which all ponderous bodies gravitate in this direction,
and tend downwards: for there is no mark below towards which they
move: for the incorporeal point is not likely (nor do they pretend it
is) to exert so much force as to draw down all objects to itself, and
keep them together around itself. But yet, it is proved unreasonable,
and repugnant to facts, to suppose the ‘above’ of the world to be a
whole, but the ‘below’ an incorporeal and indefinite limit: whereas
that course is consistent with reason, to say, as we do, that the
space is large and possessed of width, and is defined by the ‘above’
and the ‘below’ of locality."

http://thriceholy.net/Texts/Moon.html

In all things under discussion,perhaps this inability to look with the
same eyes as astronomers once did is the most pronounced and
telescopes and clocks tend to obscure the natural tendencies which
break through the mechanical clockwork solar system of empiricists and
the theoretical junk they insist in dumping into the celestial arena
under the name of astronomy.The rare astronomer today who can look out
at the planets and the Sun will cease to think in terms of what is
'up' or direction and position in the homcentric sense beloved of Ra/
Dec observers.When Wormley posts the weekly 'Sky and Telescope'
bulletin,all you will see is a celestial carousel of a rotating
celestial sphere where planets,stars,moons and everything else move in
unison by people who look up and never look out from a moving Earth.

On Aug 10, 2:13*pm, Davoud wrote:
Interchangeable lenses, the option to control
exposures manually, and a camera RAW format are at the top of the list
of features that a serious photographer needs. Camera RAW enables you
to do things with raw photos that would have seemed almost magical a
few years back.


Do the RAW formats available for DSLRs allow you to obtain the actual
data numbers for the sensor pixels?

--

FF

On Fri, 10 Aug 2012 15:31:22 -0700 (PDT), Fred the Red Shirt
wrote:

Do the RAW formats available for DSLRs allow you to obtain the actual
data numbers for the sensor pixels?

Not entirely, and the actual meaning of the numbers depends on the
type of camera. All of them do some internal processing on the image
first, such as corrections for fixed pixel defects (in essence,
applying something like dark and flat corrections). Some (e.g. Canon)
come closer than others (e.g. Nikon) to giving you something like raw
ADU values.