Star Colours

[Scooot]

Hi everyone
The link is an image I've taken with my Canon 450 & 135mm lens of the Hyades. Its about 50 30 secs and 20 1 minute exposures at ISO1600.

The colour of Aldebaran should be much more Orange but I dont seem to be able to bring out the colour. My initial thought is that the core is over exposed and I also needed some shorter exposures. Is this the case?

If not I'd really appreciate some help with the colour processing.
I did DBE, BN, Colour Calibration before a slight histogram stretch, followed by a masked stretch with a star mask, plus auto histogram to equalise the colour channels.

https://www.dropbox.com/s/956et25jqz2eapv/Hyades%20135mm%20ISO1600%2030secs%20%261%20min.xisf?dl=0

The colour of Aldeberan in the unprocessed linear stack is a dark red so it does seem to have picked up colour. I also used an Astronomic CLS clip filter, so I also wonder whether this has affected it?

Richard

[bulrichl]

Hi Richard,

The colour of Aldebaran should be much more Orange but I dont seem to be able to bring out the colour. My initial thought is that the core is over exposed and I also needed some shorter exposures. Is this the case?

Funny, I don't see Aldebaran but a bird box and some insects.

Bernd

[Scooot]

Whoops sorry!!

Thanks for pointing it out Berndt

Try this 

https://www.dropbox.com/s/956et25jqz2eapv/Hyades%20135mm%20ISO1600%2030secs%20%261%20min.xisf?dl=0

[bulrichl]

Hi Richard,

this is a heavily processed image, can't do anything with it. If you want to check whether your exposure time was correct, you will have to take a look at the unprocessed subframes. The file name suggests that you took subframes with 30 s and 60 s, right? Perhaps you can upload one of each exposure time.

Some additional information (e. g. which camera was used) would also be helpful.

Bernd

[dld]

Hello Richard,

If your lens is a Samyang/Rokinon and you are working wide open at f/2, I think you will be able to recover the color of Aldebaran, at least from the 30s subs. On my 550D and at f/2, right now I have a nice blue Rigel from 1 min & ISO 800 subs.

Maybe you should use MaskedStretch without the star mask. I've had strange results myself after trying that trick!

[Scooot]

Hello Richard,

If your lens is a Samyang/Rokinon and you are working wide open at f/2, I think you will be able to recover the color of Aldebaran, at least from the 30s subs. On my 550D and at f/2, right now I have a nice blue Rigel from 1 min & ISO 800 subs.

Maybe you should use MaskedStretch without the star mask. I've had strange results myself after trying that trick!

Hi dld

I did try all sorts before I used a mask whilst stretching. Thinking about it I think it was range mask not star mask. A masked stretch on its own just turned the bright stars pink.

[Scooot]

Hi Richard,

this is a heavily processed image, can't do anything with it. If you want to check whether your exposure time was correct, you will have to take a look at the unprocessed subframes. The file name suggests that you took subframes with 30 s and 60 s, right? Perhaps you can upload one of each exposure time.

Some additional information (e. g. which camera was used) would also be helpful.

Bernd

Thanks again Bernd

The first is a raw 30 seconds sub at ISO 1600, the second is a raw 1 minute at ISO 1600 taken at f2.5 with an Astronomik CLS clip filter.
Camera is Canon 450D with a Pentax Takumar 135mm f2.5. Camera mounted on a Star Adventurer.

https://www.dropbox.com/s/97u463ej37z3ayp/IMG_3876%20RAW.xisf?dl=0
https://www.dropbox.com/s/rkjs8bppfq11nl5/IMG_4030%20RAW.xisf?dl=0

and the CR2 files

https://www.dropbox.com/s/d9ra4edqa1zqmwq/IMG_3876.CR2?dl=0
https://www.dropbox.com/s/65mtdhrb8w66hcl/IMG_4030.CR2?dl=0

and the unprocessed stack

https://www.dropbox.com/s/gl8mb5w5b2qb0io/drizzle_integration.xisf?dl=0

[bulrichl]

Richard,

there is no way to recover the colour of Aldebaran because even the subframe which was exposed for 30 s is heavily overexposed in that region of the image. I took a look at the 30 s exposure (CR2 file). In the case of Aldebaran, the region with saturated intensity is 23 pixels in diameter, see attachment.

Generally I would set a lower ISO setting. Then decrease the exposure time (in an exposure series) in order to determine the adequate exposure time so that saturation of the stars does not occur.

Bernd

[dld]

Richard,

You have a lot of stars with halos and a few very dim stars in your raw files. This looks very strange. Maybe something else is causing this? Did you had this problem before with this lens/filter combination?

[Scooot]

Richard,

there is no way to recover the colour of Aldebaran because even the subframe which was exposed for 30 s is heavily overexposed in that region of the image. I took a look at the 30 s exposure (CR2 file). In the case of Aldebaran, the region with saturated intensity is 23 pixels in diameter, see attachment.

Generally I would set a lower ISO setting. Then decrease the exposure time (in an exposure series) in order to determine the adequate exposure time so that saturation of the stars does not occur.

Bernd

That’s great thanks for looking into it.

My plan is to take 2 or 3 different exposures next time and try to use the HDRComposition tool to combine them. All good learning 

[Scooot]

Richard,

You have a lot of stars with halos and a few very dim stars in your raw files. This looks very strange. Maybe something else is causing this? Did you had this problem before with this lens/filter combination?

It’s the first time I’ve used the lens.
I wonder if my focus is slightly out?

Edit
I've just found this thread that makes interesting reading about red halos
https://www.cloudynights.com/topic/407300-red-halos-from-around-stars/page-2

[Scooot]

The red rings aren't the filter so I presume its CA from the lens.

I just took this single image of Vega without a filter, f4.8 15 secs, ISO400. I did get critical focus with a bahtinov mask, but didn't polar align properly.

The red ring is very visible. Is there a tool in Pixinsight to remove or improve it?