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Tiny Small

NGC 6888 Ha. First narrow band image.

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This is 63 x 300s with a 7nm Ha Altair filter, so a total of 5 hours and 15 minutes. It needs much more and perhaps some longer subs too before I start collecting the O3 data to go with it.

 

 

 

Crescent-Ha-5-hours-15-minutes-small.jpg

Edited by Tiny Small
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Nice--what scope did you use?  You won't see much of a difference in the crescent with longer subs--but the background is another story.  

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I used the 130 PDS. It's still very noisy so I think I need to double my subs. I had a play with 5 minute O3 subs and I don't think that they're going to work. I think at least 10 minutes in O3.

I was thinking longer specifically for the background as there is a lot of nebulosity there that is showing up when I really push the stretch.

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1 hour ago, Tiny Small said:

I used the 130 PDS. It's still very noisy so I think I need to double my subs. I had a play with 5 minute O3 subs and I don't think that they're going to work. I think at least 10 minutes in O3.

I was thinking longer specifically for the background as there is a lot of nebulosity there that is showing up when I really push the stretch.

The longer the better.  I used to take 20 min NB subs and I switched to 30 min (for all NB filters).  It really helps keep noise down, and it reaches deep.

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I'd be inclined, now, to hit it with the OIII. This is an unusual, but not unique, target in which the OIII records a totally different aspect of the object - an outer shell which looks like a cling film wrapper. Once you have both you can decide how far to finesse each layer.

Your Ha looks good to me.

Olly

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3 hours ago, ollypenrice said:

I'd be inclined, now, to hit it with the OIII. This is an unusual, but not unique, target in which the OIII records a totally different aspect of the object - an outer shell which looks like a cling film wrapper. Once you have both you can decide how far to finesse each layer.

Your Ha looks good to me.

Olly

Thanks Olly. I was going to do that tonight as the forecast is clear... Which turns out to mean wall to wall cloud. At least it gives me the opportunity to build more of a darks library while I get some sleep  :/ 

 

Edited by Tiny Small

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8 hours ago, swag72 said:

This is looking good :) As Olly says, some OIII is worth the effort. Here's an interesting comparison I did between Ha and OIII so you can see how worthwhile the OIII is :)

27723897463_b6174beebd_c.jpg

A comparison between Ha and OIII data in the Crescent nebula by Sara Wager, on Flickr

It's forecast to be clear all night tonight so I'll hit it with some longish O3 subs if it clears up.

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excellent start, be wary though as the moon is still quite bright and i find OIII to be susceptible

to moonlight 
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Last night I ran a few hours of 600s subs in O3. Thankfully the moon was about 180 degrees away so gradients are not huge. However, given how much detail was picked up in 300s Ha subs, I'm very surprised by how little comparative detail is picked up in O3 at double the exposure. I'm only just starting to see the faintest hints of the bubble at the front of the nebula (though a fair amount everywhere else). That's fine, I'll just increase the exposure time until I get the detail I'm looking for... but this presents a couple of problems; firstly, I'm only about 50 miles west of Heathrow and as such, the longer I expose, the more chance there is of a significant amount of time being wasted by passing aeroplanes. Secondly (and more importantly)... star bloating. I can't do anything about aircraft but how do I go about tackling the issue of vastly different star sizes in each channel? Do I reduce them in each prior to combining? And if so, is there a simple way to ensure that each channel has stars of a similar size without tens of iterations to check?

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I've now added some O3 data. I used 600s subs but I think I need to go to 900s to get the bubble to show. Is the processing going down the right line with this? Never done one of these before so it's a learning curve, that's for sure. The darker bit on the left... I can't tell if it's a gradient or just a lack of nebulosity or a bit of both?

 

 

crescent small.jpg

Edited by Tiny Small

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