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Canon Digital Rebel Questions



 
 
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  #11  
Old December 29th 04, 08:54 PM
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I wrote:

4x4


Excuse me: 2x2.

  #13  
Old December 29th 04, 09:51 PM
Chris L Peterson
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On 29 Dec 2004 11:35:22 -0800, wrote:

Do you have any evidence for this claim?


I shot a whole series of gradients from ISO 100 to ISO 3200, at 1/1000 sec,
1/100 sec, 1/10 sec, 1 sec, 10 sec, 100 sec, 1000 sec. I did this at 20°C
ambient and 0°C ambient. I measured the absolute dynamic range looking at the
gradients, and the S/N averaged over several areas of the sensor. I found that
the noise was constant up to 10 seconds, which suggests that readout noise is
dominant for shorter exposures (as you would expect). At 100 and 1000 seconds
(and a few intermediate speeds where I did some spot checking) the noise
increased proportionally to the square root of the exposure time, just as would
be expected for dark current noise. At all exposure times, the black level
remains at zero (no added pedestal) which shows that the dark current signal is
being subtracted off (I could see this in the raw data, so it is happening
before the RAW import stage). Both the calculated dark current signal (the
square of the noise) and the reduced saturation level of the gradients with long
exposure times worked out to a decrease in dynamic range of 6dB/300 sec at 20°C,
6dB/600 sec at 0°C. The S/N is always better at lower ISO settings, so given the
option, stacking more images at low ISO is better than fewer images at high ISO.
The best dynamic range I got was a 1 second exposure at ISO 100, 68dB (11.3
bits), which is very good indeed.


I have a 4921 second exposure taken with a Canon 10D: looks basically
fine to me (it's of course not the best one can get). Your 'logic'
says this is flatly impossible: 90/5 = 18 bits, which exceeds the
cameras DR by 6 bits.


Your bicycle image? Sure, it looks good. But you only need 4-5 bits of dynamic
range to look good. What is the S/N in that image? Also, I have no idea what the
actual variation is between cameras and sensors. Perhaps your camera does
better. If it lost a bit of range for every 15 minutes (about twice what I saw
with my camera), you'd still have about 6 bits of range, which would be visually
excellent with that particular image.

My point (made in another thread) is that preservation of linear dynamic range
is absolutely critical to stacking astronomical images. IMO, based on the tests
I've made, a 5-10 minute maximum exposure is consistent with this goal.
Empirically, I also note that the vast majority of good 10D/300D astroimages are
being made with 5-10 minute subexposures.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
  #14  
Old December 29th 04, 10:32 PM
RichA
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On Wed, 29 Dec 2004 20:31:10 +0000, Tim Auton
wrote:

wrote:
[snip]
I would recommend the 20D for a new camera buy. More expensive, but
better electronics -- particularly the AF system -- and features
(firmware glitches notwithstanding). In fact, it looks like the 20D
has the same internals as the 1D MkII, just re-arranged and down-sized
(reduced pipeline size, etc).


For general use I agree (I have one), but if it was purely for astro
I'd have gone for the 300D (Digital Rebel). Better AF, instant
turn-on, bigger buffers and many of the other improvements in the 20D
mean nothing for astro work. IIRC the 20D has lower readout noise too,
but it's not a massive difference.

It'll be a long time before I rip the IR filter from my 20D,


Why can't you buy an IR filter that screws onto the lens?
-Rich
  #15  
Old December 29th 04, 11:04 PM
Tim Auton
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RichA wrote:
On Wed, 29 Dec 2004 20:31:10 +0000, Tim Auton
wrote:

[snip]
Why can't you buy an IR filter that screws onto the lens?


They don't quite match the original filter, which throws the
white-balance out. You can correct for it, but you do lose some
flexibility (all the presets will be wrong and I don't know if auto
would work either). More importantly, I don't fancy tearing the guts
out of a new, £1000 camera!


Tim
--
This is not my signature.
  #16  
Old December 30th 04, 02:49 AM
RichA
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On Wed, 29 Dec 2004 22:04:29 +0000, Tim Auton
wrote:

RichA wrote:
On Wed, 29 Dec 2004 20:31:10 +0000, Tim Auton
wrote:

[snip]
Why can't you buy an IR filter that screws onto the lens?


They don't quite match the original filter, which throws the
white-balance out. You can correct for it, but you do lose some
flexibility (all the presets will be wrong and I don't know if auto
would work either). More importantly, I don't fancy tearing the guts
out of a new, £1000 camera!


Tim


No, especially since (unfortunately) it requires tearing it completely
apart to get the filter out. I read the site that had the process on
it.
-Rich
  #17  
Old January 7th 05, 08:47 PM
W. Watson
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laura halliday wrote:

I bought my Digital Rebel at my favourite local professional camera
store (Leo's Cameras, Vancouver): the usual kit with the body and 18-55
lens, plus a 512 MB compact flash card. I know I could have gotten it a
bit cheaper from Anacortes or B&H, but there is something to be said
for local support and backup.

....snip
I'm about to purchase one myself, and just talked to a highly respected tech guru
from SFran about the possibility of the price dropping. He suggested that I put off
any purchase at least until tomorrow. He thinks the MacWorld show currently running
in LV might have an announcement that has to do with Canon. I mentioned the CES, but
he thought MacWorld might be the more likely of the two shows to have anything to say
about it. We had to end are call abruptly, but that's the story.

--
Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

Web Page: home.earthlink.net/~mtnviews
  #18  
Old January 7th 05, 08:53 PM
Tim Killian
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Macworld starts next week. The show currently in LV is CES.

W. Watson wrote:

laura halliday wrote:

I bought my Digital Rebel at my favourite local professional camera
store (Leo's Cameras, Vancouver): the usual kit with the body and 18-55
lens, plus a 512 MB compact flash card. I know I could have gotten it a
bit cheaper from Anacortes or B&H, but there is something to be said
for local support and backup.

...snip
I'm about to purchase one myself, and just talked to a highly respected
tech guru from SFran about the possibility of the price dropping. He
suggested that I put off any purchase at least until tomorrow. He thinks
the MacWorld show currently running in LV might have an announcement
that has to do with Canon. I mentioned the CES, but he thought MacWorld
might be the more likely of the two shows to have anything to say about
it. We had to end are call abruptly, but that's the story.


  #19  
Old January 8th 05, 05:21 PM
W. Watson
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Tim Killian wrote:
Macworld starts next week. The show currently in LV is CES.

W. Watson wrote:

laura halliday wrote:

I bought my Digital Rebel at my favourite local professional camera
store (Leo's Cameras, Vancouver): the usual kit with the body and 18-55
lens, plus a 512 MB compact flash card. I know I could have gotten it a
bit cheaper from Anacortes or B&H, but there is something to be said
for local support and backup.

...snip
I'm about to purchase one myself, and just talked to a highly
respected tech guru from SFran about the possibility of the price
dropping. He suggested that I put off any purchase at least until
tomorrow. He thinks the MacWorld show currently running in LV might
have an announcement that has to do with Canon. I mentioned the CES,
but he thought MacWorld might be the more likely of the two shows to
have anything to say about it. We had to end are call abruptly, but
that's the story.


Strange. The guy said wait until tomorrow, which is today. Maybe he misspoke. I asked
if it wasn't more likely CES, and I'm pretty sure he said MacWorld in reply. He might
have been in a hurry. I was lucky to get to him and we got interrupted by another
call. When I asked him about the camera, he immediately enthused he had one and
called it a "kick-ass" camera.

--
Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

Web Page: home.earthlink.net/~mtnviews
  #20  
Old January 9th 05, 04:04 AM
W. Watson
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W. Watson wrote:

Tim Killian wrote:

Macworld starts next week. The show currently in LV is CES.

W. Watson wrote:

laura halliday wrote:

I bought my Digital Rebel at my favourite local professional camera
store (Leo's Cameras, Vancouver): the usual kit with the body and 18-55
lens, plus a 512 MB compact flash card. I know I could have gotten it a
bit cheaper from Anacortes or B&H, but there is something to be said
for local support and backup.

...snip
I'm about to purchase one myself, and just talked to a highly
respected tech guru from SFran about the possibility of the price
dropping. He suggested that I put off any purchase at least until
tomorrow. He thinks the MacWorld show currently running in LV might
have an announcement that has to do with Canon. I mentioned the CES,
but he thought MacWorld might be the more likely of the two shows to
have anything to say about it. We had to end are call abruptly, but
that's the story.


Strange. The guy said wait until tomorrow, which is today. Maybe he
misspoke. I asked if it wasn't more likely CES, and I'm pretty sure he
said MacWorld in reply. He might have been in a hurry. I was lucky to
get to him and we got interrupted by another call. When I asked him
about the camera, he immediately enthused he had one and called it a
"kick-ass" camera.

Well, it was CES, and here's their announcement.
http://www.macobserver.com/article/2005/01/05.20.shtml.

--
Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

Web Page: home.earthlink.net/~mtnviews
 




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