4 hours of unstackable data (first time using mono camera)

[Magnus_e]

Hi all

Yesterday I had the rare event of a clear night. I managed to platesolve, calibrate guiding and focus (or so I tought), just after the California neb passed the meridian.

So something I learned was that I must set the camera to high gain when focusing. I was using the settings I would do 5min exposures with (Gain 139, Offset 21). When I was taking 5sec subs for focusing, there was not a lot of stars to use for focusing, but eventually the autofocus completed, and I was happy.

What was kind of a unknown was that the linear data of 5min subs looked black, except one bright star (that looked perfectly focused). So I had to stretch the data to see what I was getting, and thought it was the stretching that made the stars look a little big. It looked like I got a lot of the nebula in Ha and S2, so I was happy about the session.

I've tried stacking in PI and it finds no stars. Deep Sky Stacker finds around 35 - 128 stars in the different subs (with a 2% register setting), but the result looks like a mini startrail image.

 

It's forecasted clear skies tonight too, and I want to hear what I have to fix to get  usable data? (Is it actually the focus that is off, or other issues?) Also if there is a way I could manage to stack what I have, it could be fun to play around with. PixInsight would actually not even stack my biases and darks claiming non or insufficient data.

Any help appreciated!

 

Link to the fits straight of the camera https://drive.google.com/drive/folders/0Bx0H87uxM0zZQkdfWVJSLWpJdVU?usp=sharing

A couple screen transferred subs.

[Uranium235]

Looks like a focus issue to me, you need to nail that first before any software can get a decent grip on the image data.

[Gina]

Those stars are out of focus.

My experiments with the ASI1600MM-Cool have shown better results with high gain and short exposures and lots of them.  I suggest using a gain of at least 400 (I use 600 for weak DSOs and NB).  I use a maximum exposure of 120s and that's only for the faintest DSOs.  Mostly I use 60s exposures and several hundred subs for each filter. 

You should be able to see something of the DSO in individual subs.  You can check single subs to see that the brightest parts are not saturating the white (zoom in until you see the pixels).  You should aim to set the exposure and gain to get the brightest part of your sub just below saturation.  That will give you the best signal to noise ratio in your image.

[Davey-T]

Looks out of focus, are you using any software help for focusing ie: to show FWHM doing it by eye isn't very accurate.

Dave

[Gina]

As for the Offset - if too high this will cut out your fainter details in the image and in the worst case - all of it.  You will need to do a pretty extreme histogram stretch to see the darkest parts of the image - you should be able to see the noise as a good portion of this will be eliminated by calibration and integration.  You don't want to throw away any deep detail.

[vlaiv]

I see two issues that might be problem - first one, and that certainly is part of the problem - you are way off in focus.

Second issue I see (but that just might be me, and my software) - fits you posted are 8 bit.

You really want 16 bit data captured, for all frames (dark, bias, flat, and light), ASI1600 is 12 bit camera, but software usually records in either 8 or 16 bit - use 16 bit not to loose precision. All processing should be done at 32 bit for these cameras, especially if you take a lot of frames, and you should (at least for bias, darks and flats, regardless if you are using narrow band filters and long exposure, or short exposure for lights).

For focus - take care about temperature and temperature changes, especially in winter when its cold and there are big drops in temperature. Your scope should be well cooled before you do focusing. Also for every 1-2C drop while you are shooting - you should adjust focus.

When working with cmos sensors, and high speed cameras, I usually use software for planetary recording to do my focus - it allows for "movie" mode, or rapid download of frames. I find very bright star, set exposure so it does not saturate, and manually do focus. When I'm happy with focus (smallest FWHM) I lock focuser in that position, and then slew to target. Depending on your shooting routine, you can incorporate focus check. Good place to do that is for example when doing meridian flip - instead of just flipping and slewing to target, and aligning - slew to bright star first, check focus, adjust if necessary, and then complete flip - align your target again.

 

[Gina]

For focussing I use SharpCap and zoom in to at least 200% so that I can see individual pixels then finely adjust focus remotely for which I have designed and built my own remote focussing system hardware and software.  I can see the difference in a couple of focus steps and reckon to get the stars down to a couple of pixels wide using very short exposures (3 - 5 secs).  I haven't yet produced an automatic focussing system.

[RayD]

14 minutes ago, Davey-T said:

Looks out of focus

Thank god for that, I've been cleaning my glasses for 20 minutes 

Yes another +1 for nailing the focus first and you'll then have a ton more good data to work with.  Worth spending even a whole night just working on and practicing your focusing routine as without good focus your whole session is fruitless.

[Gina]

You need very accurate focussing for this camera with it's tiny pixels.  Smaller pixels are great for high resolution without spending a fortune on filters but you need a good optical system and precise focussing.  Find a bright star in the vicinity of where you want to image in the sky and put it in the middle of the frame.  Doing that means you should find it easier to find when zoomed in by moving SharpCap's sliders to the centre of their range, also you may find it helps to keep the gain/exposure fairly high until making the final adjustment and then reduce to avoid saturation.

Check focus either on other stars or slew to move you star to other parts of the frame.  If you get a variation across the frame indicating that your image isn't flat, you will do better to focus on a star a third of the way from the centre to the edge though I suggest a centre frame to start with to get near best focus.  By focussing on a star one third out you will get optimum focus across the frame.

[ollypenrice]

Autofocus is fine when it works. If you focus yourself it always works!

Olly

[Petergoodhew]

10 minutes ago, ollypenrice said:

Autofocus is fine when it works. If you focus yourself it always works!

Olly

Yes Olly, but we don't all have a bed next to the scope!

[Davey-T]

10 minutes ago, ollypenrice said:

Autofocus is fine when it works. If you focus yourself it always works!

Olly

Depends how good your eyesight is 

Dave

[ollypenrice]

Just now, Petergoodhew said:

Yes Olly, but we don't all have a bed next to the scope!

Well you should have!! You can't call yourself a man with a shed unless you sleep in it.

Olly

[ollypenrice]

Just now, Davey-T said:

Depends how good your eyesight is 

Dave

No, you just read the FWHM values!

Olly

[Gina]

Quite!   Or zoom right in till you see the pixels...

[Davey-T]

Just now, ollypenrice said:

No, you just read the FWHM values!

Olly

You need your fat fingers and eyes to get somewhere near to start with and then FWHM never stabilises just keeps jumping about, best left to autofocus 

Dave

[Davey-T]

Just now, Gina said:

Quite!   Or zoom right in till you see the pixels...

There you go with the seeing again 

Dave

[ollypenrice]

1 minute ago, Davey-T said:

You need your fat fingers and eyes to get somewhere near to start with and then FWHM never stabilises just keeps jumping about, best left to autofocus 

Dave

Indeed, we found this with the ODK14. FWHM was useless for the reason you say. But FWHM always works on the refractors. On the ODK we just used a B mask.

Olly

[Magnus_e]

Thanks for all the replies

I will spend the necessary time getting focus spot on tonight. I guess I was a little inpatient when getting started. I fought for several hours getting the new camera to connect to my odroid indiserver.

As for the bed next to the scope.... I have around 50cm of clearance between the scope and the wall where I can sit on a stepping stool to service the electronics in a double wall (If I point the scope to Polaris, and after climbing over the wall, avoiding falling over the fence of the balcony).

The hole setup should be well adjusted to outside temp as there is not any heating, and a lot of ventilation in the obsy.

 

It's getting darker and not a cloud in sight, so Ill have a good chance to try.

1. Set Gain much higher when focusing ~3-400

2. Set offset lower so dso (and noise) is visible on single sub, and not clipped to black.

3. Focus on a bright star, not the dso. And test focus across fov + several bright stars

4. Make sure Ekos is set to re-focus on filter change.

5. Set Ekos to re-focus if Half Flux Radius (HFR) has increased with 0.5 since last focus, or so.

 

I must also investigate why I get a error message when setting 16bit in the driver. It's complaining about no RGBG bayermatrix supported. (Or similar).

 

I will attempt California nebula, but I noticed yesterday that there were no visible nebula on the 03 subs, so I'm considering HaS2. Or perhaps I will get something on 03 with focus and proper offset / gain.

[Gina]

Get things working with Ha first then, when you have satisfactory Ha images, move on to OIII.  The amount of SII anywhere in the sky is small compared with Ha and even OIII.  There is far more hydrogen in the universe than any other gas.  Oxygen is next.

Don't consider anything else until you're satisfied with your Ha images.  That is the golden rule

[Magnus_e]

Just now, Gina said:

Get things working with Ha first then, when you have satisfactory Ha images, move on to OIII.  The amount of SII anywhere in the sky is small compared with Ha and even OIII.  There is far more hydrogen in the universe than any other gas.  Oxygen is next.

Don't consider anything else until you're satisfied with your Ha images.  That is the golden rule

Sounds like a top tip. Makes things a little more manageable.

[paraman]

Its also worth knowing that although the OIII filter is a narrow band it is not by any means as Moon proof as the Ha, so if you can do your OIII on the moonless nights and Ha when the devils light bulb is out.  Even the Ha filter will suffer  though if the moon is bright and you are imaging near it.

[Thalestris24]

1 minute ago, paraman said:

 the devils light bulb

Ha ha - indeed!

Louise

[Magnus_e]

A huge thanks for all the tips. I do believe I have taken the first sub I'm truly happy with

 

I tried setting the driver to 16bit and noticed it was not a error message, it was a message saying it was not supported by the ser recorder (so I could not shoot video).

I sat gain to 300 and offset to 50 when platesolving and focusing, and I could clearly see the nebula for framing with 10 sec exposures.

Focus ended up with a HFR of 0.692, witch looks good to me.

I have also sorted the biggest problem I had with my dslr, witch was the field flattener. No I'm at exactly 54.5mm from the sensor, witch helpes. (I was aiming for 55, but there you go...)

 

So this is 5min sub focused @gain 139 and offset 21, and the most beautiful thing I have ever made but I'm sure there are improvements to make. (I will experiment with shorter exposures at some point, but I have seen a lot of nice images on astrobin with the settings I used here).

There should also be WCS data in there, but I'm not sure how to display it.

 

 

[Gina]

That's very much better   Nice flat field too