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L-Extreme first light - does this look right?


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Last night I took my Optolong L-Extreme filter out for a spin for the first time, with a ZWO ASI 294MC-Pro.  I managed to get 26 x 5 mins of the Flaming Star Nebula and I've just finished calibrating and stacking (and applied a quick ABE). 

My first impressions where being a bit disapointed at the amount of noise, and also suprised at the amount of green in the image.  Once I split the master light channels I get:

 

image.thumb.png.05108466361a792473dc140e560ee5ee.png

 

I'd like to ask other L-Extreme users... Does this look about right?  

masterlight.xisf

Edited by scitmon
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Okay, clearly there is an issue with my calibration process somewhere which I'll have to investiage further.  Here is the result of stacking uncalibrated frames:

image.thumb.png.98ab3b599b856f6fc2fd292e602caed5.png

 

a slight difference!

 

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What gain & offset settings are yo using?

Some using the ASI294MC Pro (me included) have had issues with the flat calibration frames causing the red & green gradients in the combined image in your second post, this only seems to happen when a duel band filter, like the L-eXtreme, is used.

To make the flats calibrate correctly with this filter, the answer seems to be setting the gain at 200 and the offset at 30, see the thread below:

I've now used these gain & offset settings over four sessions and haven't had any issues and the flats have calibrated correctly, including the Flaming Star, which I did this weekend. ;)

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8 hours ago, Budgie1 said:

What gain & offset settings are yo using?

Some using the ASI294MC Pro (me included) have had issues with the flat calibration frames causing the red & green gradients in the combined image in your second post, this only seems to happen when a duel band filter, like the L-eXtreme, is used.

To make the flats calibrate correctly with this filter, the answer seems to be setting the gain at 200 and the offset at 30, see the thread below:

I've now used these gain & offset settings over four sessions and haven't had any issues and the flats have calibrated correctly, including the Flaming Star, which I did this weekend. ;)

 

I used the standard 120 gain 30 offset.  I wished I'd seen the attached thread before, but at least I know that I have the issue too.  I will give 200 gain a try next time.  May I ask length of subs you use with 200 gain?

 

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6 hours ago, scitmon said:

 

May I ask length of subs you use with 200 gain?

 

I've been using a 240s exposures since trying this but I also used 300s last night. I'm not sure there's an idea exposure time, it's more about getting the gain above the threshold so the Flats work. ;)

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I've just debayered and stretched one of the flats I took at gain 120, it looks a lot different to the flat I saw in the thread you linked:

 

 

 

dbflat.jpg

Edited by scitmon
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Ok, putting the flats aside for now because they are clearly not the issue in calibration.  There seems to be an issue with my darks but I can't work out what.  I've cabilrated a single frame with my master dark and it looks horrible:

 

image.thumb.png.5ef20ef5187955828ec1a6a7e5f2f274.png

top left: after calibration, top right: before calibration, bottom is my masterdark.

The image statistics for both the light frame and the master dark give a mean K value of around 0.03, beyond that I don't know what to do?

 

Can anyone help?

 

EDIT: attached my masterdark and a light frame

masterdark.xisf 2022-03-05_20-09-54_2_-14.80_300.00s_0002.fits

Edited by scitmon
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I've repeated the above process for one of my RGB frames, the only setting difference being the exposure (60s) and it looks fine.  Does dark subtraction require a difference process for Dual Band Filters?

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OK, I think (hope) I might have a possible explanation.  It was curious to see a small partial outline of a circle in the centre of my masterdark (see above), which suggests there was some light leakage when taking my darks.  I'm going to retake them with the camera off the scope and the cap on and in the dark.  Hopefully that fixes the problem.  Fingers crossed!

 

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Hello,

I use this filter but with a 2600 sensor, and find that you need dark flats to calibrate your flats with, and darks of course, but no bias, as the bias signal is in the darks and the flat darks.

I only use 120 second subs, and they calibrate perfectly, but the flats have to be at least a few seconds long, if they are too short they can cause issues, so I go for 25000 ADU at 4 seconds, my light panel adjusts brightness automatically to achieve this.

And as you say light leak can also cause problems, so worth checking that out too…👍🏼

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I've been meaning to make a separate thread about this, but I found that the use of ALL calibration files was required with my ASI533 and L-extreme filter. This means using darks, flats and dark flats. If I missed out certain calibration files (regular darks, if memory serves) then I ended up with an ugly colour cast over my master light which is quite bizarre. 

For the flats, I found issues in corner(s) over correcting when I created flats at 50% of histogram (about 30,000 ADU). With testing, I found that aiming for an average of 22,000 to 23,000 ADU prevented the corners from being over corrected and I also needed a better light source than my tablet screen. 

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It does sound like it warrants a separate thread.  Might be useful to survey as many people as possible about camera/light source/settings used to find what works best.  I myself am using a tracing light board with layers of paper, I doubt its ideal but I don't have the time to experiment different methods.

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  • 2 weeks later...
On 07/03/2022 at 01:00, Budgie1 said:

What gain & offset settings are yo using?

Some using the ASI294MC Pro (me included) have had issues with the flat calibration frames causing the red & green gradients in the combined image in your second post, this only seems to happen when a duel band filter, like the L-eXtreme, is used.

To make the flats calibrate correctly with this filter, the answer seems to be setting the gain at 200 and the offset at 30, see the thread below:

I've now used these gain & offset settings over four sessions and haven't had any issues and the flats have calibrated correctly, including the Flaming Star, which I did this weekend. ;)

I tried gain 200 offset 30 last night and made the flats today, with worse results unfortunatly.  Left is my gain 120, right is my gain 200

image.thumb.png.8eb58676a17bb4079408c3dc7659d95b.png

May I ask whats your method of taking flats are?

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1 hour ago, scitmon said:

May I ask whats your method of taking flats are?

The last flats I took with Askar Duo-Band filter were done with 4 or 5 layers of a white T-shirt over the end of the scope. I then put my Samsung Tab on top using an App called LightBox, which gives a uniform white screen with adjustable brightness.

Using APT's Auto Flats tool, I set it to use 26000 ADU as a target, which gave an exposure of 1.28125s and I took 20 Flats & 20 Flat-Darks. These were stacked in PI to create the Master Flat & Master Flat-Dark.

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The image on your right looked exactly like my calibrated light with l-extreme filter when I aimed for 30,000 ADU (mean) with my ASI533! By dropping it to about 22,500 ADU the correction is much better as I no longer see green corners and that one dark corner which you see. 

Before I used NINA, I was figuring out what exposure time I needed using the ASI Air app to get the desired mean ADU value. Now that I use NINA, I use the integrated Flat Wizard and ask it for 35% of my histogram, which is about 23,000 ADU. I found out this target ADU for my camera via trial and error. 

My flats are taken with a couple of layers of a plain white t-shirt and I use a Video LED panel as my light source. This is a great item as it has a built in rechargeable battery which I haven't had to recharge for a good couple of months. I set the brightness to 1% and colour temperature to white (the highest is 5,600K on this device). Exposure time is about 0.1s for UV-IR filter or about 0.45s with my l-extreme. 

Some cameras aren't linear when taking flats, and require a couple of seconds of exposure to get a clean flat frame instead of hundreds of milliseconds. The ASI533 doesn't appear to be affected with the exposure times I use for my flats so it would be worth checking which camp your ASI294MC sits in as this will determine the brightness of your light source. 

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  • 2 weeks later...
On 19/03/2022 at 20:37, scitmon said:

I tried gain 200 offset 30 last night and made the flats today, with worse results unfortunatly.  Left is my gain 120, right is my gain 200

image.thumb.png.8eb58676a17bb4079408c3dc7659d95b.png

May I ask whats your method of taking flats are?

Did you make new darks also? Remember everything has to be set to gain 200, flats, darks, lights and dark flats. 

Adam

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10 minutes ago, Adam J said:

Did you make new darks also? Remember everything has to be set to gain 200, flats, darks, lights and dark flats. 

Adam

Yes I did.  I've been trying various things since that post, I think pushing the exposure as far as possible seems to improve things but I still cant calibrate out those top left and bottom right corners. 

I read in other threads that 25k-30k ADU for flats is desired, but I cant get anywhere near that with NINA's flat wizard.  I set the mean histogram target to 90% and it still only reports to be 14k ADU.  Not sure what to make of that?

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4 minutes ago, scitmon said:

Yes I did.  I've been trying various things since that post, I think pushing the exposure as far as possible seems to improve things but I still cant calibrate out those top left and bottom right corners. 

I read in other threads that 25k-30k ADU for flats is desired, but I cant get anywhere near that with NINA's flat wizard.  I set the mean histogram target to 90% and it still only reports to be 14k ADU.  Not sure what to make of that?

That suggests to me you may have had the gain set incorrectly. 

@PadrePeace may be able to suggest something. 

 

Adam

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On 19/03/2022 at 20:37, scitmon said:

I tried gain 200 offset 30 last night and made the flats today, with worse results unfortunatly.  Left is my gain 120, right is my gain 200

image.thumb.png.8eb58676a17bb4079408c3dc7659d95b.png

May I ask whats your method of taking flats are?

Did you reduce your exposure time when you upped the gain to 200? 

I tend to use higher gain on my ASI 071 Pro camera, but tend to only go up to 2 mins when using a narrowband filter (usually the one I use is the L-enhance).

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42 minutes ago, iantaylor2uk said:

Did you reduce your exposure time when you upped the gain to 200? 

I tend to use higher gain on my ASI 071 Pro camera, but tend to only go up to 2 mins when using a narrowband filter (usually the one I use is the L-enhance).

 

No, but should that matter as long as I don't saturate pixels?  It should still calibrate out should it not?

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