M1 - Crab, help

[zakkhogan]

Hi all, i wounder if someone could shed some light on what ive dont wrong here.

This is a 40min exposure,  ISO1600 of M1,

Equipment:

Imaging Scope: CPC800 @F/10

Imaging Camera EOS 500D 

Guide 60mm Scope + ASI120m

Lights and darks only.

 

STacked in DSS processed in CS2, 

 

The histrogram is on the left, hardly anything on the right side?

 

any advice is greatly appreciated

 

My processed image 

 

 

 

 

[zakkhogan]

Heres a overly processed version to bring out as much as possible, this is a 44m exposure , any idea on why there's so little data captured ?

[vlaiv]

Could you post 32bit version of stacked data for inspection?

Also, how many light and dark subs did you use? Did you dither?

You are sampling at 0.48"/px - which is very high sampling rate, you are oversampling quite a bit. This will bring signal down, and SNR per exposure will be low.

Can't tell what sort of conditions this was shot in, but could be low transparency that contributed.

Could be that this is due to processing, but I think you are out of focus a bit:

 

[StargeezerTim]

Strange!  I'm not sure why you wanted such a long exposure, 9 X 5 min exposures would make more sense. 

Clutching at straws, but was it dewey? Tim. 

[zakkhogan]

Lights

26  x 90 seconds

2 x 120 seconds 

 

Darks

10 x 90 seconds

 

Visibility wasnt amazing,  wasnt a moist atmosphere also i had a dew heater and inside an observatory

 

Thanks for the replies  

m1 x3.TIF

[vlaiv]

I think something went wrong with calibration of this data.

Maybe try to stack just lights without any darks. Stack only 26x90s without two additional longer subs. Save result as 32bit format rather than 16 bit format just to make sure.

Blue channel and green channel look ok / similar:

Same vignetting / same dust shadows, blue being more noisy because camera is less sensitive in blue and also there is twice as many green pixels so more data there.

But look at red:

It is almost flat. It does have some signature of central region being vignetted but corners are flat - as if something clipped histogram - or maybe sensitivity in red is by far lowest of the three.

To reiterate:

Stack without darks and stack only subs of 90 seconds so you don't mix them. Use super pixel debayering mode, use regular average stacking method (nothing fancy) - don't use background calibration - we want the simplest stacking method / options to see if data is poor or something went wrong in the settings. Don't remember to save it as 32bit image rather than 16bit.

[zakkhogan]

Thank you , i willdo this now

[zakkhogan]

Heres the 32 bit file

m1 32.TIF

[StargeezerTim]

Have a look at the subs as well... if you some filament detail on the individual exposures, then you know it is the stacking causing the problems.

[vlaiv]

Ok, data is poor. Now it is a bit better, but still lacking quite a bit.

Here are green and red channels of this new stack.

Hot pixels are now visible due to fact that no sigma clip was used. Red also shows some vignetting now.  There is evident structure in M1 unlike in previous stack.

I think there could have been dew on scope and you should be able to see it if you compare different subs. Subs from the beginning of the session won't have it, but later subs will show reduction in brightness.

Because of this difference between subs caused by buildup of dew - sigma clip algorithm (for which I believe you used quite aggressive settings) threw away quite a bit of data - believing that regular data are outliers due to differences between subs caused by dew.

I'm not 100% sure that above happened, but you can test it by looking at the subs themselves - if they get progressively worse towards the end of session - its likely dew issue.

HTH

[zakkhogan]

Thank you so much, Im starting to tease some data out now..

 

Thanks you so much 

 

Craig

[zakkhogan]

Thank you for all your help, this is what ive managed to achieve,

Im relatively new to DSO and this was more of a practice for  guiding (which still need tweaking),

Im well chuffed with how its finally turned out, i know its not amazing but its definitely a start.

Thank you so much for you help

 

ALl the best

 

Craig

 

[zakkhogan]

This will be my last comment, but here is my final edit. Thanks again

 

Edited March 30, 2020 by zakkhogan
attached wrong image

[StargeezerTim]

Good result! 😊

[knobby]

Good to see you posting again Craig, been a long time ! I think you've done well there, it's not easy guiding a C8.