Question: 3nm Narrowband filters vs 7nm Narrowband filters

[symmetal]

16 hours ago, MonsterMagnet said:

I tried upping my exposure time as suggested and tested both 5 minutes and 10 minutes and both worked very well with excellent Ha exposures.  The 10 minute one is better but hard to tell how much more information is then until I have a proper chance to stack some frames.  My only concern with 10 minute exposures is the increased chance of bad frames and also less frames at the end to stack meaning some noise removal from dithering and trails might be harder to remove in the stacking process.

Good to see you're getting good results with the longer exposures. To have enough frames for dithering and trail removal to work satisfactorily when stacking, I try to use a factor of at least 8 frames. To remove a satellite trail then a minimum of 8 frames should be stacked. If you dither every frame then again 8 frames is the minimum. If you dither every 2 frames then 16 frames is the minimum and so on. You can probably get away with less frames in most cases but it's a good starting figure.

Looking at your image it seems you have significant image tilt left to right, and top to bottom indicates your spacing is incorrect too if that concerns you. 😉

Alan

[MonsterMagnet]

7 hours ago, symmetal said:

Good to see you're getting good results with the longer exposures. To have enough frames for dithering and trail removal to work satisfactorily when stacking, I try to use a factor of at least 8 frames. To remove a satellite trail then a minimum of 8 frames should be stacked. If you dither every frame then again 8 frames is the minimum. If you dither every 2 frames then 16 frames is the minimum and so on. You can probably get away with less frames in most cases but it's a good starting figure.

Looking at your image it seems you have significant image tilt left to right, and top to bottom indicates your spacing is incorrect too if that concerns you. 😉

Alan

Thanks Alan.  It's a lot of data to collect at the moment because the nights are non-existent but I think I'll go for something like 7 minutes over the longer term.

Yeah, there is a spacing issue which is clearly visible in the corners.  I've just looked at a few diagrams and I think I'm actually supposed to put the tilt plate back on the ASI2600MM and then use a smaller spacer - will look into it today given it's supposed to be clear tonight.

MM

[licho52]

On 17/07/2024 at 10:21, Clarkey said:

I don't think it is really as simple as this. You need to consider other things such as pixel scale, QE, light pollution etc, etc. I have never used more than 5 minute subs, even at f8. Using longer subs just means more chances for a poor sub and more data loss. If you live in B1 or B2 you might need to use longer subs just to swamp the read noise. However, the OP lives in B9 so short subs is probably more sensible.

But it is simple, you don't get signal in dark areas of the sensor at slow f ratios and you get a lot of sensor noise that's not swamped.  It's something I've dealt with and it's rather logical.  You must have tons of LP to swamp sensor at f/8 in dark areas with 3nm filters.

[Clarkey]

8 hours ago, licho52 said:

But it is simple, you don't get signal in dark areas of the sensor at slow f ratios and you get a lot of sensor noise that's not swamped.  It's something I've dealt with and it's rather logical.  You must have tons of LP to swamp sensor at f/8 in dark areas with 3nm filters.

A simple concept, yes. But you cannot say at certain f ratio's you need a certain amount of time - it will depend on too many things in the imaging train. I use 3nm Antlia filters and do not image for more than 5 minutes, even with an f8 RC scope and an older 1600MM pro. Certainly no issues with read noise in B6.