40D vs D3/D300 Astrophotography


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theveed

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Apr 20, 2007
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#1
http://www.astrosurf.com/buil/nikon_test/test.htm

The readout noise of the Nikon and Canon CMOS detectors is very similar. The high ISO sensitivity displayed by Nikon is for the marketing: Nikon D3 CMOS (and also the CMOS D300 CMOS - Sony origin) is a very high quality sensor, but in the end, Nikon just rises now the level of Canon technology.

The behaviour of Nikon DSLR are radically different from the Canon ones for long exposure:
- For Nikon, the hot pixels are eliminated by a sophisticated digital processing external to the sensor. During this digital processing, the signal of the neighboring pixels is also affected. The damage of such processing is well-known in astronomy: the weak stars are also eliminated and the image loose photometric qualities on stellar like objects.

- For Canon, the thermal signal is reduced for each pixel by a differential reading method. The thermal signal level measured at the output of the sensor is very low. The residual can efficiently be removed during the image processing (a simple substraction of a reference dark signal map).

It is tragic to see that Nikon solved the problem of thermal signal by a digital processing of the RAW files (i.e. NEF files do not contain true raw data). This processing can surely meet the daytime users and the high performance for main application is evident. But by repeating the same mistake made on the D70 and the D200 (equipped with a CCD) on the news Digital SLR Nikon probably divorces once more with the astronomical community.

Today the Canon and Pentax cameras seem to be the only ones useable digital SLR for efficient and advanced astronomy.
 

gooseberry

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Mar 11, 2004
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#2
Yeah, the issue is that the Nikon cameras run a "median filter" on the images on expsoures greater than 1 sec to remove hot pixels (but this also may remove faint stars as well). However, this can be overcome (although a little troublesome as you have to turn the camera off and on between exposures.

Have a look here where this guy believes that the Nikon D50 was the best cam for astrophotogrpahy at the time (June 2006)

"Compared to the D70/S/200, the D50 has lower noise, especially amplifier glow and a higher dynamic range. Compared to the Canon 350XT/20D/30D the D50 exhibits lower noise, less amp glow (somewhat temperature dependent, however), has higher quantum efficiency, and a deeper full well at ISO200 and higher, for greater dynamic range, during long exposures.

To sum up, the D50 compared to the 350XT/20D/30D:

20-25% greater quantum efficiency (actually, I mean total ability to convert photons to electrons, per pixel).

higher dynamic range at ISO 200 or greater, during long exposures

lower noise, especially dark current

10% larger sensor (12.5% larger than the 350XT)


The D50 is superior to any other, half frame sensor size, DSLR for astro work, with the exception of it's suitability for automated imaging. Compared to full frame (FF) DSLRs the D50 also appears to have an edge( possibly) in sensitivity and (probably) noise reduction, and this must be balanced off as to whether the larger field of a FF DSLR is worth the extra cost. The D50 like the D70/S requires an IR remote signal to stop and start exposures longer than 30 seconds. I, typically, use the Nikon IR remote, ML-13, for this purpose, although I understand that a typical multi-function IR remote, can be programmed for the same function. A computer can also be programmed to issue the IR remote signal via standard serial or parallel cable that is linked to a IR transmitter. A computer, so equipped, can then act as an intervalometer (image sequence timer) to take a predetermined number of images of any duration, up the the firmware limitation, of 30 minutes."

http://www.sfu.ca/~dmunro/DSLRnotes.html
 

Rashkae

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Nov 28, 2005
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#4
There a re a lot of people very happy with the A700 astrophotography performance...
 

Photo Nuts

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Aug 27, 2007
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#5
That article about the D50 being useful for astrophotography is completely rubbish. The author obviously has no idea on how to use programs like DCRaw to extract MEANINGFUL data that is not tainted in any way.

A properly conducted test shows that Sony designed APS-C CCD/CMOS sensors have horrible read noise (the noise that dominates in low light conditions) in comparison to Canon CMOS sensors. Before the advent of D3, Nikons have read noises of anywhere from about 28 to 60 12-bit ADUs at ISO 1600; Canons range from 4.6 to 7.2 ADUs (from 400D to 1Ds MkII). Only the recent Nikon designed FX CMOS sensor rises to the same level of performance as Canon CMOS sensors.

The Nikon D2X has about as much read noise at ISO 100 as the 1Dmk3 has at ISO 1600. It has higher read noise at all ISOs than a Panasonic FZ50. But, in the right hands, it is capable of capturing excellent images at low ISOs with good optics and exposure.
 

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