ASI 1600MM-C Bias and Darks @ -30c

[Magnus_e]

Hi

With high clouds and a lot of moon I figured I will start a dark library tonight for my new camera.

I will start by saying that either there is no noise from this camera @ -30c or I'm doing something wrong.

I stacked the biases and darks as explained in this blog http://trappedphotons.com/blog/?p=693

I have used that method on my dslr and I have got normal looking masters. However on this attempt there is no noise except some hot pixels!?

All the masters have been stretched with the screen transfer tool in PI. The st tools process has been dropped to the Histogram transform tool and that process has been dropped on the image two times before saving as png.

Maser bias 146 frames

Master dark 50x30sec

Master dark 35x60sec

Master dark 25x120sec

/Edit images removed due to incorrect settings.

 

I'm using INDI to image, and at the moment it is the default settings, only temp and exposiure time that is changed.

You must probably open the full size version to see the hot pixels.

[sharkmelley]

The entire frame (except a few hot pixels) is clipped to black - why is this?  So I'm afraid this tells us nothing useful whatsoever.  Try stretching to the point where the background noise and any amp glow become visible. 

Mark

 

 

 

 

[Magnus_e]

I tried stretching it to the max, but there is nothing else there.

After posting this last night I sat the camera to take 180s, 300s and 600s darks, but now PI wont stack them because of this error: pix Error: file.fits: Zero or insignificant signal detected (empty image?)

I will have to read up on the gain settings, as I just used the default values. Only one issue. When I read about settings for this camera there is Gain, Unity Gain and Offset. In INDI thee controls are Gain, Gamma, Brightness.

Do you have a tip on setting these values to something that would be usable when imaging?

 

[Magnus_e]

I should probably read what the default settings are before using them. As Gain was set to 0.....

Still wondering on the difference between gain, unity gain and offset vs gain, gamma brightness.

The values that can be set are Gain [0-300], Gamma [0-100], Brightness [0-60]

[Magnus_e]

Took some exposures with Gain 139, Gamma 50, and Brightness 21 and they looked a lot more like darks should.

I might have to revise these settings, but I don't have my scope here so I cannot test any lights to see if things look normal.

I figured Gain = Gain, The Gamma was set to 50 in a rage 0-100 so I'm guessing 50 might be a neutral setting, possibly same as Unity Gain = 0. Brightness is a range from 0-60 witch seams to be the same as the offset setting so I sat that to 21.

Gama 139, Unity 0, Offset 21 is settings I have seen on Astrobin for this camera, so it's a starting point.

Camera is now outdoors cooled to -30 and shooting quite a few 30, 60, 180, 300 and 600 sec darks and 100 bias. I will post back when I have some new masters that can be more useful

[Gina]

The gain of the camera goes up to 600 which is what I use for dim DSOs with 60s or 120s exposure and several hundred subs.  I plan to go over to INDI etc. but if that only allows a gain of 300 I'll have to abandon that idea and stick with Windows (groan).  I use KStars/Ekos/INDI for my all sky cam using an ASI178MM camera.  For astro-photography I would leave the gamma at 1.0 which is 50 on the scale.  Not sure about brightness - I left that at default.

[Magnus_e]

3 minutes ago, Gina said:

The gain of the camera goes up to 600 which is what I use for dim DSOs with 60s or 120s exposure and several hundred subs.  I plan to go over to INDI etc. but if that only allows a gain of 300 I'll have to abandon that idea and stick with Windows (groan).  I use KStars/Ekos/INDI for my all sky cam using an ASI178MM camera.  For astro-photography I would leave the gamma at 1.0 which is 50 on the scale.  Not sure about brightness - I left that at default.

I will double check that 300 is max gain, and if it is open a topic on the indi forum. If the camera can go to 600, then there is no reason why this should not be possible in indi.

The nice thing with indi is that it's in constant development. When I started using it there where no hibernation for the celestron avx, so I would not be able to use it in a remote observatory. By starting a topic and being available for testing the avx now hibenates.

Jasem (knro) on the forum is the maintainer of indi, ekos and kstars and is a really capable programmer, and he really takes the time to fix tings if you find something that is not working.

[Gina]

Thanks Magnus - yes, I've been in the INDI forum and seen all the good works

[Magnus_e]

So now I have redone the darks and biases.

Hopefully these are more useful.

All are Gain 139, Gamma 50 and Brightness 21. Only exsposure times that differ. All are @ -30c

 

Single bias

Master bias (x200)

super bias (from master)

 

 

Single dark 30sec

Master dark x40

Single dark 120 sec

Master dark x30

Single dark 180 sec

Master dark x20

single dark 300 sec

Master dark x15

Single dark 600 sec

Master dark x6

// Edit: removed some more darks with wrong settings in PI. Do not use winsored sigma clipping for darks.

 

So there different than the first I did, but still not sure if I'm doing things the right way. (they look nothing like darks from my dslr).

Let me know if I'm going the right way

[Magnus_e]

Link to linear files unstretched https://drive.google.com/drive/folders/0Bx0H87uxM0zZR1M1M2FCdUdhLVk?usp=sharing

[Magnus_e]

6 hours ago, Gina said:

The gain of the camera goes up to 600 which is what I use for dim DSOs with 60s or 120s exposure and several hundred subs.  I plan to go over to INDI etc. but if that only allows a gain of 300 I'll have to abandon that idea and stick with Windows (groan).  I use KStars/Ekos/INDI for my all sky cam using an ASI178MM camera.  For astro-photography I would leave the gamma at 1.0 which is 50 on the scale.  Not sure about brightness - I left that at default.

Hi Gina. I did not look closely enough at the max gain. It is indeed 600

[Gina]

34 minutes ago, Magnus_e said:

Hi Gina. I did not look closely enough at the max gain. It is indeed 600

Phew!  Thank you Magnus

[sharkmelley]

12 hours ago, Magnus_e said:

Link to linear files unstretched https://drive.google.com/drive/folders/0Bx0H87uxM0zZR1M1M2FCdUdhLVk?usp=sharing

I took a look at your 200 frame master bias (master-bias-x200-min30-g139-g50-b21.xisf) in PixInsight (I didn't have time to look at any others).  Something strikes me as very odd indeed.  An average of 200 frames should contain a continuum of floating point values.  However, that master bias has a small set of discrete values.  I can't think of any good reason why that should be the case.  You can visually see the effect when you apply an STF Autostretch - it gives the appearance of some kind of weird posterisation instead of the typical random noise background.  Unfortunately I don't know what may have caused this.

Mark

[Magnus_e]

10 hours ago, sharkmelley said:

I took a look at your 200 frame master bias (master-bias-x200-min30-g139-g50-b21.xisf) in PixInsight (I didn't have time to look at any others).  Something strikes me as very odd indeed.  An average of 200 frames should contain a continuum of floating point values.  However, that master bias has a small set of discrete values.  I can't think of any good reason why that should be the case.  You can visually see the effect when you apply an STF Autostretch - it gives the appearance of some kind of weird posterisation instead of the typical random noise background.  Unfortunately I don't know what may have caused this.

Mark

I will revice my stacking and see if I did something wrong. 

I notised the tutorial I used (for pi) showed a sigma hig and sigma low of 7. Other tutorials use 3. Not sure it it's related?

[Magnus_e]

I re stacked with the instructions fro pi site, and got the same result. http://www.pixinsight.com/tutorials/master-frames/index.html

This time I stretched the rejection low a lot, and it looks like a lot of rejection.

Any tips?

[Gina]

That's it then - rejection level set too high - you're rejecting the data you want.

[Magnus_e]

So, I sat the rejection low to 0.75 and it looked like it worked for the biases but the dark did not look too different (I only tried on the 30sec darks)

Are this master and super bias more what I'm looking for?

master x200

superbias

Not sure why the biases has the dark spot?

 

The new stacking did almost nothing for the dark, even when there was almost no rejection

 

Master dark 40x 30sec

(or is it closer?)

[Gina]

I think it was Harry who told me the superbias isn't worth it - far better to capture a few hundred real bias frames which takes very little time.  There's certainly something wrong with your superbias.  Mine have a variation over the frame but nothing like that.  Your master dark looks reasonable though mine show amp glow at the bottom which doesn't appear on yours.

[Magnus_e]

Now I figured out the settings for stacking darks. Apparently low sigma high|low clipping values rejects more, so back to 7 on that.

Also I thought more than 10 subs benefited from winsored sigma clipping. Not so. It did work well on the 200 biases but not on 15 > 40 darks, so back to sigma clipping.

 

The 40x 30sec again.

 

And the 15x 300sec (I guess this is the amp glow showing up)

 

Not sure why it has a line in the middle, but i guess that is how the dark current is on this camera ?

At least it looks like I can keep my subs.

[sharkmelley]

1 hour ago, Magnus_e said:

And the 15x 300sec (I guess this is the amp glow showing up)

Not sure why it has a line in the middle, but i guess that is how the dark current is on this camera ?

At least it looks like I can keep my subs.

It looks very much like a light leak to me.  I've never seen amp glow like that.

Mark

[Gina]

Nor me!

[Magnus_e]

16 hours ago, sharkmelley said:

It looks very much like a light leak to me.  I've never seen amp glow like that.

Mark

 

15 hours ago, Gina said:

Nor me!

I'll have an attempt in doing the darks at night time or covered when it stops raining.

I did do them with the fw screwed securely on, and with the rubber cower and pointing in to the box it came in.

So if it's light leaking in, it's trough the camera bothy, witch is not great...

[sharkmelley]

It is definitely worth taking a systematic approach to finding any potential light leak because light leaks will cause you no end of problems.  Does the camera have "live view" or some kind of continuous feed option?  You can then shine a focused bright light at different parts of the rig until something shows up.

Mark

[Magnus_e]

7 minutes ago, sharkmelley said:

It is definitely worth taking a systematic approach to finding any potential light leak because light leaks will cause you no end of problems.  Does the camera have "live view" or some kind of continuous feed option?  You can then shine a focused bright light at different parts of the rig until something shows up.

Mark

Will do.

By looking at it (and the manual) I see that the (old) version could be screwed open to replace desacent tabs, but the new one is completely closed (it has a screw that opens and takes a nippel with tabs). So no light should be able to get in.

However I'm looking at the usb port for the fw as a possible opening. Will test your method when I have time. Sat to Mon to Thu is forecasted 100 sky free with little wind.

Must plan install of new camera and add a powersupply to my dustcap, and plan a target to image. So many things to do, and so little time Better to be busy than bored!

(I also packed down the camera for the 6th time to take it to remote location. Why do I use tape every time?)