Last one from 21 March - widefield M3

[Helen]

The last of my tourist shots M3 - 60subs at 30s with SXVFH9 on ZS66, unguided. Stacked in DSS and processed in elements. I'm a bit dissapointed with the detail in the core - should I go shorter or longer subs to get more resolution? (I've got some 5s subs too I could add...) or should I just use the C8 next time

Helen

[barkis]

Oh that's a very nice M3 Helen. The globular has a tight core anyway, so although I'm no expert, it requires some rather deft processing to bring it out, but don't ask me how .

Ron.

[robindurant]

Very nice Helen, a much neglected Glob and not an easy one.

Must try it myself.

Robin

[Tim]

It's not a bad pic at all Helen. With globs, the most important thing I find is getting round stars, and you have done that. Sub length will vary a bit depending on conditions, but you dont want to be saturating the stars. As you suspect, the C8 should do a much better job of resolving the stars.

How do the originals look in the core? Most of the effort is in the processing of them if all other factors are equal.

Cheers

TJ

[jgs001]

Very nice Helen

[Beyond_Vision]

Very nice image Helen. The tracking and focus are spot on.

Regards

Kevin

[Psychobilly]

Very nice image Helen. I would have thought that Tracking and focus are critical for these "globs" and you have nailed them..

A mix of shorter and longer subs should help with some layer processiing alomng the same lines as you would do for balancing the trap region of M42 witht he fainter outer stuff....

Billy...

[CELESCOPE]

Its agood image Helen. but i would go up a scale . with the C8.try different exposures , 30s to 1 min. but i have found with globs that its a bit of practice in the processing .

Rog

[MartinB]

Looks good to me Helen. As for the core you can try mixing different sub lengths but this only makes sense if the unstretched core is saturated. Easier to add together 2 images which have had a different amount of stretch. Does elements let you use layers??

The optimum exposure time for individual subs, for the vast majority of targets is determined by measuring back ground sky brightness. I don't know what capture software you are using but in Maxim you just run the cursor over a dark bit of background and you get a read out of the brightness level in ADUs. As a rough guide this should be around 2000 ADUs. The correct figure depends on the readout noise which SXV say is typically 7 but less than 12. The optimum background brightness for a readout noise of 7 is around 1100 ADUs, whereas for 12 it is 3000.

With the H9, once the sky brightness has risen above this value the Read noise is no longer an issue and you won't benefit from taking longer subs (you will start to loose dim stuff in the skyglow)

[steppenwolf]

Helen, globulars are not simple to capture and although the core isn't perfect, this is a very pleasing image - great star shapes too.

[Helen]

Thanks for the advice everyone. Hopefully there'll be lots of time to perfect my technique in the coming months.

Helen

[RobH]

I'l agree with the others Helen.

Very good round stars and nice framing.

Martins tip about using layers and stacking different stretches is an approach I've used before and it works fine.

Have a look at your unstretched subs. If you have resolved stars right to the centre without saturating them, you will be able to do this, and it's a lot less hassle than shooting different length exposures.

Cheers

Rob