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Would you take longer exposures?

swag72

By swag72
in Imaging - Discussion

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swag72

swag72

Posted
Posted

Over the last few nights I have been imaging M66. I am using a modded 1000D, with an Astronomik CLS clip filter. SO far I have 6 hours of data, but looking at the histogram I am wondering whether I should be taking longer subs. I know I should have considered this on day 1, not 6 hours worth later!!!

So, the subs are at 420 secs, if they need to be longer, then that's fine by me. What do you think? There's a picture of the histogram and the actual image. All screen grabs, so excuse the quality.

If you think the subs need to be longer, then where should I be looking at getting the histogram for the best exposure?

post-18339-133877558147_thumb.jpg

post-18339-133877558158_thumb.jpg

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AlexB

AlexB

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I may be wrong as I'm not an expert, but it looks like you've got some elongation in the stars (ever so slight.) This will hinder obtaining a 'crisp' view no matter how much processing you do.

Also, I know you've got a modded Canon, however, it looks a tad on the red side.

But as Shibby stated, you've got a good image there. :icon_eek:

Hope that helps.

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3ggman

3ggman

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I now try and do 10mins subs @ ISo400, I had originaly started with five minutes but the double exposure captures so much more light.

The red is pretty normal for a modded 1000D and just needs to be processed out. (This can be done with PixInsight, photoshop or when stacking)

I think that you have a lot of detail there and with a little processing will have a very nice image.

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dph1nm

dph1nm

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If you are well above the read noise then there is no advantage to taking longer subs (as opposed to more shorter subs adding up to same total exposure). Looking at your histograms I would suspect you are (difficult to tell without actually numbers), although you might want to check the individual colour channels separately.

NigelM

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RobH

RobH

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That looks fine Sara.....get plenty of them at that length and you'll be able to stretch away to your heart's content with that data.

Like Steve says....get some flats too.

Rob

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swag72

swag72

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Nooooooo, not flats!!!! I can't do flats!!!!

I know that there is a little star elongation in this sub. I am awaiting a new focuser as I hope that will solve some issues I have had with elongated stars. Or do you think it's a guiding issue?

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swag72

swag72

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The flats I have tried, I used the PC screen as the white. I put the camera to AV and took the pictures, so that the histogram was exposed correctly - All I saw was lines across the screen, nothing that resembled anything like a flat!

I don't know if it is best to over expose by 1-2 stops, or what.

What is it about flats that seem just so damn impossible!!

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Photosbykev

Photosbykev

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it sounds like you refocused on the screen? flats should be taken straight after or before the subs so that the optical path is the same. Any evenly lit surface or sky will do and colour isn't important.

I use an EL panel and use Av +1 stop or manual to get the histogram peak 2/3-3/4 of the way to the right. The exposure isn't the important bit, reading the histogram is.

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swag72

swag72

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OK, 15 flats done. Looking a lovely shade of turquoise due to my filter!! So, I just add these in with the DSS run? Do I add them in with tonights data or on their own so that they count against all the data so far?

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swag72

swag72

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For them to be used for each session how do I best add them to DSS. I will be adding each nights imaging session into a seperate tab, including sepertae darks for each session. How do I add the same light to each tab?

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RobH

RobH

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Not taking flats for each session unless you leave the scope/imaging train untouched is a TERRIBLE IDEA :icon_eek:

You will end up adding dust donuts, not removing others, and in short, ruining your lights.

The only thing you'll deal with is vignetting.

Flats are easy to do and an essential part of imaging, even though they're boring as hell....get used to doing them.

Rob

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ollypenrice

ollypenrice

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I avoid taking the camera off like the plague. Before EL panels I would take the camera-scope inside and use the white bathroom wall as the flat source with T shirt over the lens.

Grab yourself a Gerd Neumann panel and be done!

As for sub length, difficult. For me at a dark site with Ha it can be 20 mins before I am safely above the noise. I'm doing that as I write on M106.

Olly

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martin_h

martin_h

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OK, 15 flats done. Looking a lovely shade of turquoise due to my filter!! So, I just add these in with the DSS run? Do I add them in with tonights data or on their own so that they count against all the data so far?

If you must use them for all of the data put them in the Main Group tab, they will then be used for all of the data in all of the tabs.

If you take flats each night you add them in the tab for that nights data

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swag72

swag72

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Perfect, thanks - SO I have now got flats sorted!! :icon_eek: Shame everything was a little out of focus last night for some reason and it's all been binned!!!

Alignment issue?.................................. Meaning?

I am really hoping that this is a result of that damn focuser - I wish the order would come in to FLO, It's been a month now waiting for my moonlite.

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