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View Full Version : MX516 and ST7-ME Side to side


Jaime Alemany
February 3rd 04, 08:07 PM
Hi all,

I've been lucky enough to buy one of the ST7-ME (parallel version) sbig has
sold recently. First thing I've done, has been test it versus my older
starlight-xpress MX516 (btw, I've always been very happy with this camera).

My idea was to take similar shoots and compare the results. For funny
reasons I've been unable to make exactly this, but anyhow I've shoot several
times with each of both cameras at the same target (horsehead nebula).

Then, and after much thinking, I have used the following method to compare
both images:

- visually: st7 images look cleaner, but this camera can't take more than 1
minute long exposures due to the non ABG chip.
- noise measurement: for this, and after several tests, I've decided to take
two images for each camera, substracted each pair to have, as a result, only
the variations (noise), then calculate the standard desviation of pixel
value in a rectangle of the image. This is the most amazing result. The ST-7
sports an incredible 15.5 value (std. desv.), while the MX5 187.79, even
selecting a much smaller rectangle. In both cases no dark were substracted
(taking into account the higher dark noise from the st7, the result is even
more surprising).
Even more, being shots taken with both cameras self-guided (built in tc211
in st7 and star2000 for the mx5), one could expect better guiding from the
mx5, as the pixel size of the tc211 is bigger than the size of the st7 main
chip's pixels).

Now I will measure the signal of both cameras to have the SN ratio.

Should anyone want to take a look at the results, images, or whatever, just
drop me a line. Opinions on the measuring method or ideas for other test
very welcome, too.

Cheers,

jaime.