Ngc 5128 - iso 400

[jsmoraes (Jorge)]

And another try, now with ISO 400 and more total time.

GSO 305 mm - Canon Rebel XT - ISO 400 - 1 hour 15 min - 15 x 300 sec - OAG - DSI1 - Cor. Coma

large scale:
http://cdn.astrobin.com/images/29ce3...8c733c67e7.jpg

Detail in large scale:

http://cdn.astrobin.com/images/1f8b6...8ccd6df91e.jpg

To get stars with more color I think that Iso 100 ou 200 will be best with my Canon. More than those cause some saturation of the stars to white.

[rmuhlack (Richard)]

The detail in the dust lane is very nice indeed and tracking is excellent too - well done.

Regarding the choice of ISO setting, I have been experimenting with with different ISO settings as well, also in an attempt to get more star colour. However what I found was that whilst star colour is improved at low ISO, the signal to noise ratio is much worse. Your camera is similar to mine, and so this is likely to be the case for you as well. I did an experiment earlier in the week to try and determine what the optimal exposure time would be - see here for details.

[rmuhlack (Richard)]

Also, a trick I use to improve star colour in processing is to use a star mask (so that only the stars are revealed). Then you can make a large boost to saturation to bring out the star colour without affecting the background.

[alpal]

Hi Jorge,
The data in your pics is excellent.
Yes - you do need star masks - most stars were clipped -
but there was still plenty of color left in those stars for me to boost it.
I hope you don't mind? -
I reprocessed the full frame to get these examples.

[jsmoraes (Jorge)]

Thanks, Rmulak and Alpal.

Yes, all you are right. The star mask is very important to isolate the stars and process them. I already did some work, using the star mask from DSS.
To process an image is multi-task . Some times I forget the star by working with noise. Other, I forget histogram, by working with stars.
I need a method to deal with it. Step by step. Each task must be done in a coherent way.
Up to now this was not important because my shots were with short exposure. Therefore, with lack of data. But now, it is different.
I will improve my procedures !

And I can't forget of Flats. Darks and Bias are more easy to produce. Flats... they are more complicated.

Thanks Alpal by the examples. I will try to reproduce them.

[jsmoraes (Jorge)]

Rmuhlack, Your study about noise and ISO is new information to me. My tests show ISO 1600 is the worse case: a popcorn machine. But I am not absolutely sure. I am now experimenting long exposure.
I copied your graphics, and thank you for information. I will better analyse each case.

[Ross G]

Very nice photos Jorge.

You have some great detail in the dust lanes.

The longer exposures you are getting have really improved your photos.

I also have a modded Canon 350D and I have also found 1600asa to be the best setting when you are doing long exposures, 5 minutes and 10 minutes.

Ross.