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XTi/XT controlled low lighting...new dcraw results

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Thanks Rick.

I'm not sure if I understood much about the last two paragraphs you wrote about quantatizations, gamma stretch and dark subtractions. Goes waaaay beoynd what I can comprehend this time of the hour. LOL ..but I was able to shoot the picture with out NR and remapping of hot pixels.

Ta-daa.. zero noise reduction. 168,5 sec / f7.1 / ISO 800
I left a litte more light into the room this time.



I'll do little more experimenting tomorrow.

-T

I was shooting in RAW and converting in PictureProject.
RicksAstro said:
I didn't try to quantify the light, so it's impossible to compare
results apples to apples. The f/32 really cut the light getting to
the sensor.

Are you shooting in RAW mode? How are you converting? The noise
depends more on how much light is available rather than ISO
setting. Like I've said, I use the ISO setting to adjust the
dynamic range depending on conditions. If there are no blown
highlights in ISO800 (as in your image), it's often better to shoot
at ISO1600 to minimize quantization noise at the low end (seen
sometimes as posterization of flat, dark areas). If ISO1600 is
blowing out highlights, drop it to ISO800 or ISO400...the results
will be similar if both are stretched based on their histogram.

My bright images had a fairly normal daytime looking histogram, so
they aren't very noisy. My dim images were very, very dark
unstretched. Setting a low value for a whitepoint and doing a
gamma stretch on the RAW data (presumably still 12 bit A/D on the
XTi) made them look more normal, but still very, very noisy on both
as expected. I mean, visually I could just barely see the color of
the little nascar car and with the lens at f/32, it's remarkable
what these cameras captured really.

For shooting stars, your do NOT want any noise reduction. First,
it makes calibration (dark subtraction) much, much less effective,
and second it wipes out much of the detail in the basement of the
histogram, which is where most of the data I want is. That's why I
do exposure and calibration in B&W Bayer RAW.

Rick
Click to expand...
--

 
RicksAstro said:
But for now, I'm convinced that the XTi is not a step down from the
XT. It seems similarly noisy (maybe a bit better) and is similarly
sensitive (worse blue, better red)
Click to expand...
I also had this very impression, when seeing the Japanese images I linked to previously today, and now seeing yours, that 400D definitely has a warmer white balance than the 350D does.

Overall I like better the more neutral tone of 350D, but, it shouldn't be too hard to fix the reddish shift when shooting RAW with the 400D.

The sensitivity thoughts you have, coincide completely with the conclusion I came to today: that it's really the metering system in the 400D to mostly cause the apparent darker images. There may be, and probably is, also a tiny difference in the sensitivity of sensors, but like you, I think that it's so small, it is, in practical life, negligible.

On the noise side, I have to remark that based on what I see here, when the lighting conditions are still decent, the 350D and the 400D seem to perform comparably, while when the lighting is really poor, the 400D comes out like a clear winner.
 
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