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350D and 400D/1000D sensitivity comparison


michaelmorris

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I'm now getting close to a final decision about whether to buy a secondhand 350D + a load of other astro stuff or a 1000D for widefield astrophotography. My one remaining question relates to sensitivity. I understand that the larger the pixel size > the more sensitive the pixels > shorter exposures needed. Therefore the more sensitive the pixels, the lower the likelihood of star trailing/tracking errors in subs because subs can be shorter. The 350D has bigger pixels than the 1000D (same chip as 400D I think).

So here are the questions.

- What is the difference in sensivitity between the two cameras?

- What is the difference in the sub length before one gets star trails on an unguided picture?

- If the 350D is more sensitive than the 1000D, are these differences offset by other features (except live view) on the 1000D?

Thanks

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- What is the difference in the sub length before one gets star trails on an unguided picture?

Not an easy question to answer - it depends on the focal length, accuracy of your alignment and the periodic error. It also depends on how much trailing you're prepared to accept; long unguided exposures and genuine point stars require high-end mounts, whereas a degree of trailing can be hidden by resampling a DSLR image.

For a typical 'scope you'll be sampling in the 1-3 arcsecond/pixel range and until you get to the high-end mounts periodic error is typically significantly higher than this, my HEQ5 is somewhere over 20" peak-to-peak and my old LX200 was double that. So a degree of trailing is likely to show up quite rapidly, indeed my LX200 had regions of PE of greater than 1" per second, which would show trailing for virtually any useful DSO exposure length. My gut feeling is that sensitivity isn't particularly relevant here, because it seems unlikely to me that the 350D is sufficiently more sensitive to allow you to use significantly shorter exposures for the same S/N.

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I'd also suspect that the noise handling of the 1000d would be much better than the 350d. I know from experience with the 450d, that I've pushed up to ISO1600 on my Konus (ST80) on my NexStar SLT and whilst the exposure time has been limited due to AltAz mounting, and trailing creeping in, it's made big differences to the image data itself. (I was using the higher sensitivity to allow for effectively longer exposures without increasing the actual exposure time). With the above rig up, I've managed to go to 2 minute exposues, I lost 50% of subs to trailing but I figured that was worth it. I don't think that using a 350d would have made any difference to the trailing though.

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Noise wise the 1000D is way better than the 350D - I have both... the 350D suffers from ampglow... although mine seemd better than most but I had taken some steps which may have helped it slightly...

Batterry life is a lot better on the 1000D and liveview and single cable remote operation makes it really useful... and it can capture video as well using the russian software that Geroge found recently...

Billy...

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