Best ISO for 1000D ?

[michael8554]

What would you say is the best ISO setting for an EOS 1000D?

Unmodified, 1200mm F6.3 OTA, multiple 3 to 5 minute exposures of DSO's.

RAW Lights and Darks into DeepSkyStacker.

Michael

[Demonperformer]

This has been asked on another thread recently, and it was suggested that anything over 400 (might have been 800) does not increase the signal, but only adds gain. Basically, you would just be adding noise.  Which was rather annoying as I have always used 1600 thinking that was best.  We live and learn.

[silios]

ISO 400 or 800 are quite good for a 1000D.

If you are on a really dark site i'd hazard a value of 1600 as well with this particular canon model as its quite capable.

[Spikey]

I always found 400 to be sufficient with those exposure times. Tried 800 and it was showing a bit more noise for the amount of subs I was managing to get, 200 didn't really cut it for me either.

By all means try 800 if you can get a lot of subs as it will really help but for average UK skies I was only managing a few hours per target.

[dph1nm]

This has been asked on another thread recently, and it was suggested that anything over 400 (might have been 800) does not increase the signal, but only adds gain. Basically, you would just be adding noise.

ISO1600 is probably actually the best in term of S/N on the 1000D. Certainly the read-noise is lowest there.  I also once read that different circuitry is used at ISO1600 from all other ISOs (on the 1000D), and mine has much less structure in the bias at ISO1600 than at lower ISO.

All ISO ever does is change the gain - the number of photons detected is always the same. So apart from the read-noise issue, the signal-to-noise ratio should be the same at any ISO. Higher ISOs do not add noise at the expense of signal.

NigelM