First post: how to post-process a globular cluster?

[kokanee]

Hi all,

I'm currently using PI to post-process an image of M13 taken with my Canon DSLR (ISO 1600) through a Hutech IDAS LPR filter.  The image is therefore very noisy,  has an uneven field illumination, and has a bluish colour cast due to the filter.  I've been trying to find a tutorial which uses a globular cluster as an example and found this relatively old one:

http://pixinsight.com/forum/index.php?topic=695.msg3157#msg3157

Unfortunately the location of the image thumbnails is invalid.

Could somebody please direct me to a tutorial that is relevant to a large starfield, and specifically shows how to generate a starmask that captures all sizes of stars, and change colour cast of the overall image?


Thanks,


Anuraag

[Alejandro Tombolini]

Hi Anuraag, welcome to the forum!.

See this globular cluster as an example: http://proxima-sur-fotos.blogspot.com.ar/2011/07/ngc-5139-details-of-processing.html

If your M 13 is noisier or more complicate than the example, please post the picture in the Image Processing Challenges forum and we will try it.

Regards,
Alejandro.

[zvrastil]

Hi Anuraag,

next time you'll be taking picture of star cluster (especially globular), try to use low ISO (like 200 or even 100). Stars (even faint ones) are quite bright objects when compared to nebulae or galaxies. With DSLR and high ISO settings, most stars will be saturated and their colors washed away. With low ISO, you'll get much better preservation of star profiles, low noise level and virtually no information loss. High ISO is kind of tradeof - if you want to capture faint object like nebula, you sacrifice part of your dynamic range for stars in favor of nebula. But for star clusters, it makes little sense. Just try it, you'll be surprised (I definitely was).

best regards, Zbynek

[kokanee]

Hi Alejandro,

thanks, that's exactly what I was looking for!  And congratulations on an excellent photo.

I'll use your tutorial to process subs for my next target: Perseus Double Cluster (NGC 884 and 869).


Cheers,

Anuraag

Hi Anuraag, welcome to the forum!.

See this globular cluster as an example: http://proxima-sur-fotos.blogspot.com.ar/2011/07/ngc-5139-details-of-processing.html

If your M 13 is noisier or more complicate than the example, please post the picture in the Image Processing Challenges forum and we will try it.

Regards,
Alejandro.

[kokanee]

Hi Zbynek,

thank you for the advise.  I noticed that Alejandro used very short exposures (30s) at ISO 800 using his Canon 5D MkII.  If I was to shoot using ISO 200, what exposure time would you recommend to get similar results?  I'd guess 2 min since sensitivity goes down to about a quarter from ISO 800, so multiply the exposure time by 4.

BTW, here's my the results of post-processing after viewing the Harry's Astro Shed newnie videos (see below).

I used seven subs at 5 min each, but at ISO 1600.  Comparing my photo to Alejandro's, there's no star colours besides white so it could be that I overexposed my subs.  I'm amazed that PixInsight was able to clean out noise so well though!  And masking using Luminance is a lot easier than I originally thought.  A very amazing product.


Cheers,

Anuraag

Hi Anuraag,

next time you'll be taking picture of star cluster (especially globular), try to use low ISO (like 200 or even 100). Stars (even faint ones) are quite bright objects when compared to nebulae or galaxies. With DSLR and high ISO settings, most stars will be saturated and their colors washed away. With low ISO, you'll get much better preservation of star profiles, low noise level and virtually no information loss. High ISO is kind of tradeof - if you want to capture faint object like nebula, you sacrifice part of your dynamic range for stars in favor of nebula. But for star clusters, it makes little sense. Just try it, you'll be surprised (I definitely was).

best regards, Zbynek