Brain and unity gain or max dynamic range

[Desbarry]

Hi there, I have a Hypercam 183 fan cooled. I ran the brain function last week with my IDAS D2 filter attached and it came up with 84 sec exposures 21 of them at unity gain. I only had 30min integration time on M31, probably not enough to stretch.

My question is. For galaxies eg M31 is it better to increase integration time to say 90 min keep the same exposure and change the other setting to MAX DYNAMIC RANGE? My M31 was lets say rather weak, it was visible but I couldnt really strech much in the outer cores. Thanking you.

Derek

[admin]

Hi,

I must admit to not being particularly convinced that there's any benefit in running cameras at unity gain – the amount of noise that is inherent in the pixel measurements both from the random variation in the number of electrons captured in each pixel and from the read noise and the camera is always much more than 1 ADU, so the fact that 1 ADU is equivalent to one electron seems superfluous. I would personally usually go for the maximum dynamic range option, but the differences are likely to be relatively small when viewed in the final stacked.

The amount of detail visible in the fainter regions of your image should only depend on the total amount of time that you have imaged for (providing you meet or exceed the exposure times recommended by the brain window) – longer total exposure time will definitely bring out more detail. Remember that you can always use longer exposures than the brain recommends – providing that they don't cause problems due to tracking/guiding issues or oversaturation.

Finally, it would be interesting to know how much the light pollution filter reduces the measured sky background brightness – the transmission graph for the filter makes it look as though it cuts out about half the visible spectrum, which is quite a lot for a general-purpose light pollution filter. Hopefully it's reducing the sky background by significantly more than that factor of two, it would need to to prove effective.

Cheers, Robin

[Desbarry]

Thanks for replying Robin. I have ditched the D2 I think its too extreme for my bortle 5 skies. Can I ask you my licence is about to expire next month on my Altair camera, I have also just got a new ZWo533 that I wish to use with Sharpcap sensor brain etc. If I apply for a new licence do I get a months credit??? No problem if not but I need Sharpcap brain to now work with all my cameras.
Thanks Derek

[admin]

Hi Derek,

yes, you will get an extra two months added to your renewal license if you renew before your current licence expires (even if your current licence is on Altair license). Just make sure you use the same email address and that you don't try to renew before you have received the first reminder email that comes about 30 days before your licence expires.

Cheers, Robin

[KEJ]

Derek/Robin

May I ask, I have literally just bought and received my ASI533MC Pro.

And I think I am asking a similar question(plus not that experienced).

Have you had chance to have a play with your camera yet and any initial findings ?

1) Unity Gain
Should I be sticking around Unity Gain and going for many exposures.

If I calculated correctly:

For Gain 100. (1.5 log2 = 2.8)
20 X 2.8 x 2.8 /3.28 = 48 secs/exp

For Gain 350. (1.2 log2 = 2.3)
20 X 2.3 x 2.3 /3.28 = 32 secs/exp


2) General Guide
I have only taken pretty much two pictures over the last few nights, due to the cloud and I stuck with a Gain of 100, M31 being pretty bright and thats probably fine at a Gain of 100, but for Nebula and what you both discussed above, is it a case of either sticking with:

a) Stick with Gain of 100 and take 200 x 48 sec exp

Or

b) Gain 100, but for fainter objects Gain 100 X 5 min exposures

Or

c) Gain 350........100 X 3min exposures.


I am just trying to find/understand some basically rule of thumb !

Hopefully Thanks

M33(screen print)
22 X 3min exposures, 101 gain, -10 degrees.
Bortle 6.

M33.jpg (426.02 KiB) Viewed 1781 times

M31(screen print)
Gain 101, 37 X 2 min Exp, -10 degrees.
Bortle 6 sky.

M31.jpg (541.89 KiB) Viewed 1781 times

I have just asked a similar question:
viewtopic.php?f=29&t=3244

[KEJ]

My Gut feeling is to stick a Gain of 100 and potentially just alter the duration of the exposures, depending on the target.

Ie:

Bright targets stick with 48 secs and many exposures.

Faint targets stick with 3 to 5 min exposures, many exposures.

But then its back to the optimum duration..........

[Desbarry]

Hi Kej, sorry I havent yet got a psu for the camera, thats coming next week. I strongly suggest you perform a sensor analysis and use the smart histogram in Sharpcap Pro. As your bortle 6 then may I suggest you using say an Optolong L Pro broadband filter with the camera. I think the IDAS D2 with LED suppression is too extreme for me in bortle 5. I would say that if you run the 533 at -5 cooling you shouldnt need to use a lot of gain as the sensor is pretty clean Im told, even if you did push the gain past unity (sensor analysis should give you your value in Sharpcap Pro) then I doubt the noise would be excessive. I would tend to try it at unity and alter your exposure time and overall integration time and see what results you get. In a few weeks or so having had a chance to test the 533 I sould be in a better position to give you some better thoughts on it.
Cheers Derek

[Desbarry]

Hi Derek,

yes, you will get an extra two months added to your renewal license if you renew before your current licence expires (even if your current licence is on Altair license). Just make sure you use the same email address and that you don't try to renew before you have received the first reminder email that comes about 30 days before your licence expires.

Cheers, Robin

Thanks Robin, will wait till I get an email then will upgrade .Derek

[KEJ]

Hi Kej, sorry I havent yet got a psu for the camera, thats coming next week. I strongly suggest you perform a sensor analysis and use the smart histogram in Sharpcap Pro. As your bortle 6 then may I suggest you using say an Optolong L Pro broadband filter with the camera. I think the IDAS D2 with LED suppression is too extreme for me in bortle 5. I would say that if you run the 533 at -5 cooling you shouldnt need to use a lot of gain as the sensor is pretty clean Im told, even if you did push the gain past unity (sensor analysis should give you your value in Sharpcap Pro) then I doubt the noise would be excessive. I would tend to try it at unity and alter your exposure time and overall integration time and see what results you get. In a few weeks or so having had a chance to test the 533 I sould be in a better position to give you some better thoughts on it.
Cheers Derek

Derek hi

Sorry, I forgot to mention I was running at -10 degrees on the cooling.
Ok, I never actually used or tried the sensor analysis tool on SharpCap - I'll have a read.

Filters I may invest in later, if I spend anymore money I will be waking up with a Horses Head in the bed and the GodFather music playing!

Thanks