A luminance question

[swag72]

Following on from a thread I posted about using a LP filter, Rob mentioned that he is routinely able to get 10-15 minute exposures in the luminance channel. My issue is that I manage 5 minute subs and still manage to end up with many saturated stars.

I have posted a couple of images (Same as the other thread ..... sorry!) to show you a screen grab showing my fully saturated star and a screen greab of the entire image, with just DDP processing in order to present on the forum.

This was taken I *think* with my reduced 120ED, so at about f6.5 - Not that fast really, and the Atik 314L+.

I would welcome some thoughts you may have on this. I am wanting to do more than 5 minute subs, but these saturated stars would suggest that much more will be more detrimental than good.

[swag72]

Anyone care to share some specific luminance thoughts on exposure times etc?

[Martin-Devon]

Sara - I hope folks respond to your query - there's a lot of LRGB imaging done, and it's an important question to get feedback on whether saturation occurs (especially if there are some bright stars in the field) within the duration of the exposure or not; if it does then it seems plausible that it will compromise the quality of the resulting image. I routinely use 5 minute unguided subs unbinned in Lum to check the accuracy of my polar alignment since I have a portable set-up and want to be sure that I have a good starting point each night - even with 5 mins Lum on some fields the stars look pretty saturated so it's possibly a real concern if you were going on thereafter to do a full night of LRGB.

[ollypenrice]

I tend to remove the L layer from stars anyway, so it doesn't matter if they are saturated. There are cases (when the stars are against nebulosity) when this is tricky but it is usually possible. I think I first heard of this idea from Rob some years ago, in fact.

Olly

[swag72]

I tend to remove the L layer from stars anyway, so it doesn't matter if they are saturated. There are cases (when the stars are against nebulosity) when this is tricky but it is usually possible. I think I first heard of this idea from Rob some years ago, in fact.

Olly

Is this easy to do Olly?

[ollypenrice]

Is this easy to do Olly?

No, Sara, it requires skill, daring, low cunning, an almost fanatical devotion to the Pope and a visit to somwhere that does imaging courses.

In the absence of any or all of the above you could paste the LRGB onto the RGB only, get the background of the RGB lower layer similar to that of the top LRGB, use Noel to select brighter stars, expand and feather the selection (using low cunning, an almost fanatical etc etc...) and then erase the stellar cores from the top layer. That will be £1.99 if you please.

Olly

PS I can only make it work one time in three but sshhhh.....

[swag72]

Thanks Olly, you do make me chuckle!! Only £1.99? Add it to the bill please!