I have just finished taking the three minute test exposures to use with the sub calc tool. After entering the data in the calculator I got some very long sub exposures.
Tak fs60c with an AP 0.75 focal reducer giving f4.2. ST 2000 with 2010 chip. Maxim DL so 100 removed from background.
Hutech LPR filter fitted for all exposures.
Lum non IR blocked original adu 658 sky eflux 129 sub exp 11.5 min
Red non IR blocked original adu 126 sky eflux 25 sub exp 60 min
Green non IR blocked original ADU 315 sky flux 62 sub exp 24 min.
Blue non IR blocked original adu 233 sky flux 46 sub exp 32.4 min

I calculated my gain and read out noise to numbers not far off those given as standard in the calculator. The gain is very close to that detailed in the fits header for the camera:
Gain 0.587.
RON 12.31
All exposures taken at -30 deg C.
Test light frames in best sky location for light pollution and at zenith.

Do these look right or have I missed something? When using the calculator I left the "Temperature of dark signal" set at Zero. other negative numbers used in that setting made no difference to the sub calcs.

Many thanks Dave Osborne.

These numbers make sense to me for the following reasons:

1. The Hutech LPR requires that you take exposures almost double what you would normally take. It blocks quite a bit of light.

2. The ST2000 has very low QE in red and high in Blue. So that would explain the differences in filters.

When you add the low QE of the ST2000 plus a LPS filter, you will need to exposuse much longer to overcome read noise.

rb

Ok thanks Richard.
I did know that the Hutech cuts out a lot of light and that the st2000 qe is low. On a practical note taking sub exposure in excess of 12 min exposures for the luminance seems OK. However, much longer than 12 to 15 minutes tends to give saturated stars for the other filters. Not withstanding the other problems associated with very long subs such as guiding and intermittent cloud here in the UK are these long subs really practical? I would assume that from a practical perspective it would be better to take shorter exposures of around 15 min for the red and 12 min or so for the blue / green (ball park figures) and more of them using dithering and sigma combine methods.
What do you think?

I used to image with an ST2000 with many scopes.

I used to bin the RGB 2x2 which in essence would reduce your RGB exposure times by 1/4.

If you are using the stock SBIG filters then I agree that you should take different legnth exposures for the different filters.

I used to take the following:

Red (binned): 500 Seconds
Green (binned): 300 Seconds
Blue (binned): 450 Seconds

This would allow me to combine with a 1:1:1 ratio and get good balance.

I would also take more Red abd Blue exposures than green. This helped Signal to Noise in the weaker Red and Green channels.

For instance:

10 Red @ 500 Seconds
5 Green @ 300 Seconeds
8 Blue @ 450 Seconds

Remember, you must average the exposures and not Sum them for this approach to work.

rb

Many thanks Richard. I will give things a try and see what I get.