Thoughts on which imaging rigs to concentrate on

[Gina]

Thanks Ken   I seem to be finding that a gain of 500 (actually 501 as that's as near as I can get to 500 in APT, which I'm using for capture).  That with 60s subs seems fine for most of the DSOs I've captured so far with 30s for brighter ones.  This ties in with getting the histogram close to the white end and getting as much data depth as possible.  Higher gains and shorter exposures seem to go with greater numbers of subs.

[Gina]

Integrated image for 600 bias subs with gain of 440.

Edited November 21, 2016 by Gina

[Filroden]

That's a lot of gin!

[Gina]

Integrated image for 80 darks 30s gain 440 -30C.

[Gina]

Integrated image for 80 darks 60s gain 440 -30C.

[russellhq]

Gina, looking at your bias frames, do you think it's possible you're getting a thermal gradient across the sensor? I mean it might be possible if you are running the camera constantly for hundreds of frames at a time? I only say this because the pattern doesn't look like bias noise but more like dark noise. And if that is the case, it will not correct your light frames but make them worse! 

 

Might be worth adding a couple seconds pause in your imaging sequence between captures? 

[Gina]

Thanks Russel - I'll try that    Yes, I am running the camera for hundreds of frames with only a 1s pause between each - I'll try increasing that , still won't take long to capture several hundred bias frames.

[Gina]

Don't think there's much difference if any.  First image is 300 bias frames with 5s pause and second is 600 with 1s pause.  I think if anything, the first shows a little more noise than the second which indicates to me that the pause has made no difference but that maybe 600 give a bit better result.  I'll do a process of 300 of the 600 frames for true comparison.

[Gina]

OK - let's separate this out.  Firstly, 300 bias frames with 1s and 5s pause between frames.

[Filroden]

What exposure are you using?

[Gina]

Now the difference between the integration of 300 and 600 bias frame with gain of 440 and 1s pause between frames.  These are screenshots of the PI images.  The real "proof of the pudding" will be to run two lots of processing to compare the results.

[Gina]

7 minutes ago, Filroden said:

What exposure are you using?

32 microseconds = 0.000032s exposure time - the minimum for the camera.

[Filroden]

I wonder if that's too short even though technically it's within the specification of the camera? Your darks show what appears to be fixed vertical patterns which I'd expect to be calibrated out with the bias but that same pattern is not visible in the bias.

[Gina]

Just tried increasing it to 100 microseconds and collected 100 frames.  Here is the auto-stretched result.  I can't see much difference.

[Filroden]

Yes, no discernible difference. I wonder if it's just a combination of you having it scaled on screen at 1:6 then converted and reduced in resolution for the forum making it look like a flat grey background when in fact there might be fixed pattern noise there, but just not visible to me. Anyway, all you can do is use them in the integration process and see the results!

[Gina]

I've now increased the exposure to 1ms and the result is quite different.  I can also increase the size of the image window as you think that may make a difference.

[Gina]

Here's the image stretched in GIMP and saved as PNG.

[Gina]

Couldn't seem to stretch it enough in GIMP so here's a bit bigger image in the screenshot using PI's auto-stretch.

Edited November 22, 2016 by Gina

[russellhq]

Gina, did the camera come with it's own capture software and have you tried taking bias frames with that? In my experience, using 3rd party software can sometimes lead to capture issues.

That said, the 1ms bias looks more like what would be expected. What temperature was this captured at?

[Gina]

It might have come with SharpCap - not sure now.  I do use SharpCap for focussing and framing but APT seems more suitable for image sequencing.

I agree that the 1ms exposure seems much better and that's what I shall be using.  The extra concentration of lighter pixels at the bottom in the master bias with 32 microseconds corresponds with the errors I was getting in my integrated lights.

I have just completed integration of 300 bias frames taken with a 1ms exposure for gains of 440 and 500.  These look just like the 1ms stacks already posted.

Edited November 23, 2016 by Gina

[Gina]

I think that's the master bias business sorted out   I might want a lower gain one for (L)RGB but that depends on which imaging optics I use.  The current 135mm lens is too widefield for even the Andromeda Galaxy (M31) though I did take some RGB lights of it a while back.  My plan is to image M31 a bit later on when it's in a more convenient position.  I think I'll be using a 200mm f4 lens for that.  The smaller aperture will mean longer exposures or higher gain than I used before.

[Gina]

With the master biases ready I'm now onto the darks which the book says uses the exact same settings as the bias integration.  With nothing new lately due to the weather I'm going back to the earlier collections. viz.

On 08/11/2016 at 15:19, Gina said:

Have gone through a few dates in my data and correlated that with information from pages 26-27 in this thread.

Date             Object    Filter           Exp   Gain   Temp
2016-10-10    C-Loop    Ha & OIII    60s    440    -30
2016-10-11    C-Loop    OIII            60s    440    -30
2016-10-11    C-Loop    SII            120s    440    -30
2016-10-13    Flats       OIII              1s      ?     -27
2016-10-13    NAN       Ha               30s    440    -30
2016-10-13    NAN       OIII             60s    440    -30

So for these I want 30, 60 and 120 second dark frame exposures with a gain of 440 and temperature of -30C.  I think I have captured these and processed them so will check what I've got.

 

[Gina]

Already have 80 dark frames of 30s g440 and -30C so I'm integrating these in PI as I can't be sure which "integration.xisf" file is which.  Once this is finished I can save the resultant image in my Masters folder as a final good master.

Edited November 23, 2016 by Gina
screenshot added

[Filroden]

I'm giving -30C and 400 gain / 10 offset a try tonight to add to my NGC1333 project. If all else fails I can go back to -20C and 300/0. I'm assuming I only need new darks and not bias for any changes I make given how short the bias exposures are?

[Gina]

Yes, that's how I see it   Glad you have the weather