Why cant I see the Ha detail? - Forums

Topic starter

Jan 21, 2023

Hello,

I can't for the life of me figure out what's wrong. Can anyone help?
Here is an example of Sh2-240.
As you can see, there is no detail in the Ha sub.
I am using a Chroma 3nm, QHY260M, Esprit 80ED. SQM reading last night was 20.20
Are my coordinates off, LOL?

Any help here would be highly appreciated.

Monty Chandler

Jan 21, 2023

300 more and it'll appear.. CS!

Marcelof

Jan 21, 2023

As mentioned, you need more frames, a lot more. If you are new to narrow band try something bright like orion, the same 300s will show a lot of detail.

Stjepan Prugovečki

Jan 21, 2023

This is veeery faint object, and the centre of your image is in the centre of nebula , where it is not the brightest part of it. I assume you ned at least an hour or so of total integration to see something meaningful. Patience is the key word with this object

Roger Renberg

Topic starter

Jan 21, 2023

Thanks, guys.

I just thought it was weird and I have seen others get some signal, at least with 5min subs. Maybe I'm wrong here.
I did a test and did a 2min sub and bin2 at the rosette nebula, and I didn't get any signal there either. That's why I thought something might be wrong. This is certainly no contest from me, Esprit 120 with QSI and Astrodon. This setup gives me ample signal in Ha with these exposure times (I never tried Sh2-240 with this setup)

Here are a few inverted images, NGC6888 and Sh2-240. Both 5 min subs. You can see faint detail in NGC6888, but that's about it.

Can someone confirm that they also have subs looking like this with 5min subs on an f4 system?

Monty Chandler

Jan 21, 2023

I also shoot with an es120ed. Of course this target is far too wide for it but its brightness is very similar to the Medulla Nebula and the Phantom of the Opera Nebula. Both of those required >30hrs and there was nothing visible in the subs until I debayered and stretched in blink. Then I saw the first hint of nebulosity. I had stopped after 8 subs because there was nothing in my subs. Resumed after that confirmation. Cheers

Bob Lockwood

Jan 21, 2023 · Edited: Jan 21, 2023

Just to give you an idea, this is a single 900sec sub using a TEC110 @ f5.7 630mm and a FLI 16803 with Astrodon 3nm, the FOV is 3.2 x 3.2 degrees.

Roger Renberg

Topic starter

Jan 21, 2023

I see,

Thanks for the info. I hope it's just the exposure time that's the problem. And the fact that I am surrounded by snow which makes for a much brighter SQM reading. I'll try to do a 20min sub to see if I get anything.

Appreciate the help guys

Clear skies!

Victor Van Puyenbroeck

Jan 21, 2023

Thanks, guys.

I just thought it was weird and I have seen others get some signal, at least with 5min subs. Maybe I'm wrong here.
I did a test and did a 2min sub and bin2 at the rosette nebula, and I didn't get any signal there either. That's why I thought something might be wrong. This is certainly no contest from me, Esprit 120 with QSI and Astrodon. This setup gives me ample signal in Ha with these exposure times (I never tried Sh2-240 with this setup)

Here are a few inverted images, NGC6888 and Sh2-240. Both 5 min subs. You can see faint detail in NGC6888, but that's about it.

Can someone confirm that they also have subs looking like this with 5min subs on an f4 system?

I think something is off with your setup. NGC6888 should be very easy to see on a 5 min Ha sub. The Rosette nebula is also very bright and should be easy to see even in a single 2 min sub.

Well Written Concise

Roger Nichol

Jan 21, 2023

Here is a 20min sub red channel (using an Antlia ALP-T 5nm dual filter). This is from a bortle 5 location with a 14% moon. I doubt I will every finish this one, part of a 6-panel mosaic - its going to need 100s of hours and its low on the horizon for me.

Arun H

Frequent contributor

Jan 21, 2023

I would agree with Victor. I've imaged the Crescent with an 80mm f/6 refractor and you should be able to easily pick up detail in a 5 minute exposure and certainly with a high quality 3nm Ha filter. Have you offline plate solved your images and verified the coordinates?

Well Written Concise

Torben van Hees

Jan 21, 2023

I agree, there should be something visible. I’m suggesting now the „easy“ solutions - sorry if you checked them already:
The images are stretched, aren‘t they?
Make really sure you put the filters in the correct order. If you swapped S2 and Ha, it might explain the lack of signal, although the Rosette should show up there, too.
One way to test the filter is with a known good Ha-filter: If you shine white light through both, it should not be much fainter than through one only.
If you bought the filters used, there is a chance you didn‘t get what you paid for.

Helpful

Victor Van Puyenbroeck

Jan 21, 2023

Hello,

I can't for the life of me figure out what's wrong. Can anyone help?
Here is an example of Sh2-240.
As you can see, there is no detail in the Ha sub.
I am using a Chroma 3nm, QHY260M, Esprit 80ED. SQM reading last night was 20.20
Are my coordinates off, LOL?

Any help here would be highly appreciated.

Can you confirm which driver mode, gain and offset were used? The signal level with a 3nm filter is very small and offset zero will very likely clip your shadows.

Also I think you asked a question about gain on CN: https://www.cloudynights.com/topic/830943-qhy268m-settings/ where gain 56 / offset 25 was recommended for narrowband. This is for driver Readout Mode #1 (High Gain Mode).

Well Written Helpful Insightful Concise

Roger Renberg

Topic starter

Jan 22, 2023

Torben van Hees:
I agree, there should be something visible. I’m suggesting now the „easy“ solutions - sorry if you checked them already:
The images are stretched, aren‘t they?
Make really sure you put the filters in the correct order. If you swapped S2 and Ha, it might explain the lack of signal, although the Rosette should show up there, too.
One way to test the filter is with a known good Ha-filter: If you shine white light through both, it should not be much fainter than through one only.
If you bought the filters used, there is a chance you didn‘t get what you paid for.

*** Hello Torben,

Yes, they are stretched in SGP. I'll head home and see what happens in Pixinsight. Someone mentioned that it might be as simple as a filter swap. And I bought them new, so the markings should be visible here. Finger crossed its that simple

***

Roger Renberg

Topic starter

Jan 22, 2023

Victor Van Puyenbroeck:
Hello,

I can't for the life of me figure out what's wrong. Can anyone help?
Here is an example of Sh2-240.
As you can see, there is no detail in the Ha sub.
I am using a Chroma 3nm, QHY260M, Esprit 80ED. SQM reading last night was 20.20
Are my coordinates off, LOL?

Any help here would be highly appreciated.

Can you confirm which driver mode, gain and offset were used? The signal level with a 3nm filter is very small and offset zero will very likely clip your shadows.

Also I think you asked a question about gain on CN: https://www.cloudynights.com/topic/830943-qhy268m-settings/ where gain 56 / offset 25 was recommended for narrowband. This is for driver Readout Mode #1 (High Gain Mode).

*** Hello, my gain is 56 and the offset is 24. I do have the high-gain readout mode too. ***

Brian Puhl

IOTD Staff

Jan 22, 2023

Victor Van Puyenbroeck:
Hello,

I can't for the life of me figure out what's wrong. Can anyone help?
Here is an example of Sh2-240.
As you can see, there is no detail in the Ha sub.
I am using a Chroma 3nm, QHY260M, Esprit 80ED. SQM reading last night was 20.20
Are my coordinates off, LOL?

Any help here would be highly appreciated.

Can you confirm which driver mode, gain and offset were used? The signal level with a 3nm filter is very small and offset zero will very likely clip your shadows.

Also I think you asked a question about gain on CN: https://www.cloudynights.com/topic/830943-qhy268m-settings/ where gain 56 / offset 25 was recommended for narrowband. This is for driver Readout Mode #1 (High Gain Mode).

*** Hello, my gain is 56 and the offset is 24. I do have the high-gain readout mode too. ***

In your file name you have gain 54, that doesn't lie unfortunately. You missed the 56 mark. Try longer subs if your mount can handle it. I do 10 and 20 minute subs standard, the 268M will be right at home with that exposure time.

Concise

Roger Renberg

Topic starter

Jan 22, 2023

Victor Van Puyenbroeck:
Hello,

I can't for the life of me figure out what's wrong. Can anyone help?
Here is an example of Sh2-240.
As you can see, there is no detail in the Ha sub.
I am using a Chroma 3nm, QHY260M, Esprit 80ED. SQM reading last night was 20.20
Are my coordinates off, LOL?

Any help here would be highly appreciated.

Can you confirm which driver mode, gain and offset were used? The signal level with a 3nm filter is very small and offset zero will very likely clip your shadows.

Also I think you asked a question about gain on CN: https://www.cloudynights.com/topic/830943-qhy268m-settings/ where gain 56 / offset 25 was recommended for narrowband. This is for driver Readout Mode #1 (High Gain Mode).

*** Hello, my gain is 56 and the offset is 24. I do have the high-gain readout mode too. ***

In your file name you have gain 54, that doesn't lie unfortunately. You missed the 56 mark. Try longer subs if your mount can handle it. I do 10 and 20 minute subs standard, the 268M will be right at home with that exposure time.

*** Indeed, it's 54 because this was the number I got after doing a test in SharpCap. Someone mentioned that I might have swapped SII and Ha. I need to check this first. How easy would that be (and embarrassing) ***

Mike Hamende

Jan 23, 2023

Very strange, I just looked back at my subs from this target last year with an f/4.5 system. I could see signal in Ha and Sii with 300s subs using Antlia 3nm filters.

Roger Renberg

Topic starter

Jan 23, 2023

It's very strange, and I contacted the dealer of the Chroma filter. They told me that it could be that this particular filter is off band, but if that were the case it's the first time they have heard of this happening with Chroma filters.

Well Written

Arun H

Frequent contributor

Jan 23, 2023

It's very strange, and I contacted the dealer of the Chroma filter.

You can also contact Chroma directly. My experience with them is that they stand behind their product and will replace a defective filter, if that's the problem here, without question. In my case, my OIII filter had halos. They replaced it promptly after I showed them the issue - and this was two years after I purchased it. Your Chroma filter should also have come with a transmission curve specific to your filter which you can check.

Well Written Helpful Concise

Torben van Hees

Jan 23, 2023

Yes, Chroma is very good and quick to work with. I‘m sure they can sort you out (and also maybe suggest some other test you can make yourself to test it).

Well Written