Quote:
Originally Posted by Shiraz
The basis for the procedure is summarised very well on the Starizona website, but the underlying idea is that you can minimise the read noise contribution to the total noise by making subs as long as possible (to minimise the number of read events). The accepted rule of thumb is that subs are “long enough” when the read noise contribution is below ~ 5% of the total noise.
I ran your 102 system through my spreadsheet – purely on the basis of signal to noise ratio, you will do best with subs of about 20 minutes for the native focal length and a bit under 10 minutes with the focal reducer. You can use shorter subs if you increase the total imaging time. I have a QHY8 which has the same chip as your camera and with my f4 scope it works best with at least 5 minute subs - this is based on practice as well as theory.
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Thanks for the info Ray.
didn't pay much attention to these aspects before. it was more winging it.
it makes sense now cause the other day, I tried a 5 min sub of M83 on my 8inch F4 with the qhy8 and then a 10min sub. There was hardly any difference, but it was less grainy on the 10min sub, I'm guessing because there was slightly more signal. I've noticed that with 2 and 5 min subs. the mild graininess disappears with the 5 min sub.
would you have a link to the SS?
Else I'll the online calc at starizona.
I have a qhy8 and an 8inch F4 and a 10inch F4.
whilst determining exposure time, shouldn't it be based on the sky background measurement as well as explained in the site?
so the optimum exposure length would vary based on seeing conditions as well?
the specs on the qhy8 are
Spectral Response:
QE max at 540um ~60%
Read Noise:
less than 11 -e RMS (typically less than 9 -e)
Full-well capacity:
Greater than 25K -e un-binned
so does this mean the dynamic range is between 11e- and 25Ke-?
Cheers