Rosette - LRGB question

[Bolts_Tweed]

OK ive jumped intot he world of LRGB (AstroDons arrived) and this isnt ready for posting but i've hit a snag and include it anyway.

If I focus the Televue on a star with the RGB or even Ha filters I get say a HFD of 4 (for example) with the same exposure. I then achieve best focus with the Lum filter and get a HFD of say 8 (same exposure) - at the lowest possible value it is always nearly twice the size of the coloured filters - am I missing something here? I'll admit ignorance but any advice would be greatly appreciated.

This image is bodgied up with some Ha and Red to form a Luminance of 10 x 6 min and RGB of 5 x 6 minutes each so 60, 30, 30, 30. Hopefully I can improve it with some exposure to reduce noise and soting out this Luminance problem. The colour also needs a bit of attention ;) but will do some Ha blending and full colour balance processing when I work out whats going on. It shows enough promise to pursue.

Televue np101is, ST8300, Astrodon E series filters

[AlexN]

Mark, Nice looking image...

I have the same issue, my RGB exposures seem to focus up a lot tighter than my L exposures.. I'm using Astrodon I series. I think this is because each colour filter cuts out a great deal of the light bandwidth where as the LUM filter allows in everything except UV/IR.

If you run some deconvolution over your Luminance frames you will see them sharpen up nicely.

As for your exposure times, I think 6min subs are a bit short for the rosette.... for colour its fine, but for the lum data I'd be looking at 10 min subs...

Colour data is generally unimportant... as long as its calibrated well, its pretty forgiving... In one of my recent images, a 5 min bin 2x2 sub didn't even show the target, I only took 3x5min per colour channel and the colour balance ended up fine... Luminance is life.. get as much Lum as you can...

[Bolts_Tweed]

Thx Alex

Yeah - I think the wider spectrum allowed by the Lum obviously is burning in stars - in that the star fringe in narrow banded filter images becomes a full burnt in round star. Interesting problem.

I just checked my 30 sec framing images and they are even biger than the RGB images. I suppose thats why (or one of the reasons) we see a lot of Ha blend stuff going on.

I used 10 min Ha on that image, but the stars get even bigger at 10 min lums - I agree re fainter detail in longer exposures - i'll experiment in belnding methods and see how I go.

Ive searched the web and cant find much on hte problem - probably looking in the wrong place.

Just another problem to overcome - will keep playing

M

[Bolts_Tweed]

Sry mate I forgot to add - the Astro Physics turned up late last week. Fantastic bit of kit. Nothing to report yet - will finish mounting it properly and maybe put a motor focuser on it for next moon and see how it goes.

M

[AlexN]

That right there is a great way to make me cry like a little sissy girl Mark... :) I wanna see pics of it and through it! :D haha

MMMM AP130EDT.. :) droooolllss!

Agreed - Ha / Lum blending of emission nebs will be the way to go, teeny-weeny stars and more contrasty details.. The only problem is that Ha filters will cut out dusty areas which is a real shame, and can be VERY hard to overcome.

[Bolts_Tweed]

WIll post something under the general equipment section just to annoy you ;)

[Bolts_Tweed]

Alex - OK just before it goes to trash I had a little play with blending what limited data I had (ie 1 x 10 min Ha and 10 x 6 min red) and did a (Ha+R), (Ha+R). G,B image. It shows I will be using the Ha filter for a while for Lum shots until I sort out this luminosity filter.

Now for some data and I may finally get something out of this.

Thx fgor the comments

M

[Bolts_Tweed]

forgot the image

[AlexN]

Looking the goods mate! :) Don't go too silly wasting good time capturing epic amounts of RGB data.. get "enough" and make the lum (or Ha in this case) do all the work...

So far the longest RGB data I've captured for any target with the ST8300 is 4x5min.. for the majority I've stuck with 3x5min.. I get them out of the way when the target is about 45° above the horizon, once I've got the 45 mins of colour, I focus it up as good as possible through lum and let it run 5 min subs untill the meridian, do a flip and do 5 min subs all the way down to 45° in the west...

Lum/Ha is life.. colour is pretty, thats about it.. :)

[troypiggo]

Looking great so far! If that's the "quick and nasty", I can't wait for the complete!

[Bassnut]

Some very nice detail on the 2nd image Mark.

Yes, the wider the bandwidth, the bigger the stars get due to broadband skyglow, street lighting etc. Ha will often do as lum on its own, and you can do Ha at anytime, save it for when the moons up.

6 mins is too short for Ha, go 15 or 20mins even, stars shouldnt saturate with Ha.

You can squash RGB stars in PS so they are the same size as the Ha stars, to aviod fringing.

[Bolts_Tweed]

Thanks fred

It seems strange but makes sense when you think about it. To get faint detail I expose lobnger without going too far which ends up with larger stars. To get smaller stars I expose less and miss faint detail.

There could be some serious pinching going on here soon.

I am going out to the obersvatory tonight to give the AP a work out over the weekend so I will experiment with exposure times in 6nm Ha (10 minutes plus) on somthinbg like the horsehead (not again !!!!!!!!!!!!!!!!!!!) but it seems like a good target at the moment - a little further from the moon than the Rosette plus it will frame better in the f8.

Seems strange me trying to minise exposures - I was taking 30 minutes with in camera darks with the 350D not too long ago to get faint dust under the horsehead. Time to push it bit

Thanks Fred

Mark

[multiweb]

Nice! Although it's very noisy I just love the colors :thumbsup: