Smart Histogram Brain taking long time to measure brightness with L-eNhance filter

[cydonia]

Hi,

I have SharpCap 4 and a Redcat 51, Optolong L-eNhance filter and ASI193MC Pro camera which has had sensor analysis run on it.

Last night I went to perform the measurement in the Brain and had the max exposure set to 3 minutes which I believe should have been fine for the target at the time however the measurement just went on and on to the point it was trying 17 minute+ exposures which seemed odd. I couldn't wait for it to finish these massively long exposures and so I ended up just manually setting what I thought would work (2 minutes) but I would love to know why it did this.

I had measure brightness of "Green" channel set then also tried "Darkest" but both still caused very long test exposures. Maybe it is something I have set wrong or the -L-eNhance filter but this behaviour seemed odd and I have used the filter with the Brain before without an issue. Well I say that but I have seen this on occasion previously on a few times and never known why it's done it. I do need longer exposures using the L-eNhance filter rather than just my IR blocker but only a max of 2-3 minutes usually.

It was told to calculate the best settings using Unity Gain.

Any help or advice is appreciated.

Thanks

James

[admin]

Hi James,

it would be helpful if you can find the SharpCap log from the problem measurement and post it here - a fair bit of information gets logged during the sky brightness measurement and it would help understand what is going on.

The Optolong is a fairly narrow band filter (maybe 30-40nm of transmission bandwidth at a guess, so 10%), which means that you can expect longer exposures to be necessary. This can also be made worse if you have any vignetting of the corners of the image, as SharpCap will try to measure the darkest part (the vignetted corner). If this is the case, enable the 'avoid sides/corners' option.

I do like the idea of limiting the measure procedure to the max exposure listed in the setup area - not sure why I never thought of that before. I'd still like to check the log though to make sure it's not something unexpected that I haven't thought of.

cheers,

Robin

[cydonia]

Hi Robin,

Here is the log from the session last night.

I believe the part you are looking for will be from here onwards in the log:

Info 19:52:26.705905 #1 Smart Histogram Brain shown

I think these past 2 nights are the first time I have tried to use the Smart Histogram Brain in SharpCap 4.0 with this filter. I am sure I have used it in 3.2 OK and whilst it would take a bit longer due to exposure times increasing with the filter it never went as far as 17+ minutes.

Thanks,

James

[abmscopes]

On a related topic- do you find that the L-enhance filter basically just makes all emission nebula red? Or do I maybe have a defective filter? I know that the l-extreme will bring out more greens, but I never see any green/blue at all with the L-enhance.
On topic (ish)- I've not really used the smart histogram sky measurements much.. I'm almost afraid to move away from my default selections of 300 or 180 sec, gain 50 and brightness zero !
I take it a measurement is meant to be carried out for each target/different bit of sky? Or do folk usually just use the same measurement results for multiple sessions?

[admin]

Hi,

from the log it looks like you had set either 'darkest' or 'blue' channel as the one to be measured. The blue channel tends to be the dimmest, and your filter cuts out almost all of it anyway, so this leads to the need for much longer exposures to try to find out how much blue there is.

Code: Select all

Info   	19:56:41.328220	#32	Frame darkest area median Blue channel ADU : 0, Real ADU : 0, electrons : 0	

Now, the question is, is that the only problem? I can understand that there is very little overlap between the filter pass frequencies and the blue channel, but seeing values of exactly 0 ADU is a bit odd. Could you see an image on screen of some sort while the measuring was taking place, or was it all black?

Try changing to the green or red channel and see how that goes. SC3.2 always measured green, but since that is often the brightest channel, it could lead to insufficient exposure lengths to optimized the other channels, hence the extra flexibility in SC 4.0

cheers,

Robin

[cydonia]

On a related topic- do you find that the L-enhance filter basically just makes all emission nebula red? Or do I maybe have a defective filter? I know that the l-extreme will bring out more greens, but I never see any green/blue at all with the L-enhance.
On topic (ish)- I've not really used the smart histogram sky measurements much.. I'm almost afraid to move away from my default selections of 300 or 180 sec, gain 50 and brightness zero !
I take it a measurement is meant to be carried out for each target/different bit of sky? Or do folk usually just use the same measurement results for multiple sessions?

I think the issue is the Ha emissions often eclipse the other wavelengths. I still need to try some false colour images from the data as I have seen videos of people doing that and it allows you to see the other wavelengths. It's basically a case of boosting the other channels up to something close to the Red channel and then mapping them to the Hubble palette. I'm no expert on it though as I haven't done it like that yet.

I used to use the measurement on whatever target I was going to shoot that night. It does mean a dark library isn't as handy as the Brain can shift exposures around depending on conditions but found it pretty reliable in the past. I know a lot of others that stick to just sets of settings and so have dark libraries but I haven't bothered yet.

[cydonia]

Hi,

from the log it looks like you had set either 'darkest' or 'blue' channel as the one to be measured. The blue channel tends to be the dimmest, and your filter cuts out almost all of it anyway, so this leads to the need for much longer exposures to try to find out how much blue there is.

Code: Select all

Info   	19:56:41.328220	#32	Frame darkest area median Blue channel ADU : 0, Real ADU : 0, electrons : 0	

Now, the question is, is that the only problem? I can understand that there is very little overlap between the filter pass frequencies and the blue channel, but seeing values of exactly 0 ADU is a bit odd. Could you see an image on screen of some sort while the measuring was taking place, or was it all black?

Try changing to the green or red channel and see how that goes. SC3.2 always measured green, but since that is often the brightest channel, it could lead to insufficient exposure lengths to optimized the other channels, hence the extra flexibility in SC 4.0

cheers,

Robin

I noticed that when looking at the log and thought it was a bit strange. From what I can remember I saw something resembling an image on the screen but it was flashing up only for a moment before the next exposure.

I did previously try "Darkest" for the channel and "Green". I'll have another experiment next time I get a clear sky (god knows when that will be now though) and see what happens. It does feel like it was just trying longer and longer exposures and not detecting anything which I guess is why it kept on going and going.

Thanks,

James