View Full Version here: : What 5 Hours of 3nm NII Gives
08-07-2012, 12:42 PM
This image is 37 frames of 8 minutes each 7MB
It just shows that even with a 'fast' optic the really dim stuff still needs a lot of time to get the signal to noise to acceptable levels.
I meant to put this in Deep Space my connexion is very slow with IIS. ?
08-07-2012, 02:17 PM
Just looking at the data and my observations Bert.
You have star elongation over the entire frame. Indicative of flexure from guide to camera. The image is very noisey overall. Are you dark subtracting? That many frames ought to produce very strong signal and have little if any noise. What temp are you running the subs at?
08-07-2012, 02:25 PM
Great pic still.
I think though that the scope is no longer "fast" when shooting narrow band.
One question though, how do you know when you have enough total imaging time? Doesn't longer time mean the image can be pushed harder to bring out faint details ad infinitum?
08-07-2012, 02:56 PM
All is explained here Paul. It is image train flexure.
Can you show me an image that has the same if not better detail in the very dim bits.
08-07-2012, 03:00 PM
The filter passes better than 90% of NII so for that wavelength it is still fast.
The Moon was up so I decided to take forty 8 min frames while I slept to get an idea of what would pop out.
Once I have the image train stabilizer I will see what a bunch of 16 min or even 32 min frames gets me.
All that matters is more photons more images. I want to see the really dim stuff!
Below is a quickie in NII and HA of the SMC. NII to red and HA to green. No flats with near full moon.
08-07-2012, 05:36 PM
Yes I have followed that thread. Am I to assume that you are using the stablising rig and did so for this image? If so I would have thought the whole train would be stiff so that only leaves one option to narrow down the flexure. It must be coming from the guide scope or the connections of both scopes to each other or both.
However, to make things clear I would suggest you do the same area again but at 15 minutes. If the stars grow more elongated then you can be assured that the flex is related to either the connection of the scopes or the actual guide scope. I know you have been using a micrometer but try this to satisfy your own curiosity. After all we only want to see you succeed and produce great images.
For a deep image of one of these targets I point you toward martin Pugh's image of NGC6357 (http://www.martinpughastrophotography.id.a u/images/NGC6357-Narrowband.jpg) That is a deep image showing dim detail and with no noise.
I suggest you should be imaging at -45 or -45C with that camera, doing that with longer subs on these sort of targets and dark subtracting will produce little if any noise. I would think that subs of 20 minutes should produce the sort of results you are trying to achieve. My recent image was done with 10 minute subs and lacks sufficient signal to stretch the image too far. The bottom line is to over come the background noise with the strength of signal. With your bandwidth perhaps even 40 minutes would be better. You would only need 16 subs though in that instance.
Anyway good luck with that. Without narrowing down the causes of flexure in your system it is all moot anyway. I have been through all this and know how frustrating it is to control this issue. Perhaps this camera is just too big for this optical assembly?
08-07-2012, 05:55 PM
Paul I was not using the new stabiliser. It is being finished as we speak.
08-07-2012, 06:04 PM
I love those faint bits Bert. :)
Quite a striking image. Love the nebulosity coming out between both objects.
08-07-2012, 08:25 PM
Yes they are interesting. What most people fail to realise is that 3nm NII is about half of the intensity of a 5nm HA filter which passes both HA and NII.
As they say in the classic movies 'you ain't seen nothing yet!'.
vBulletin® v3.8.7, Copyright ©2000-2013, vBulletin Solutions, Inc.