Jump to content

Banner.jpg.b83b14cd4142fe10848741bb2a14c66b.jpg

Helix Nebula - NGC 7293

Petergoodhew

By Petergoodhew
in Imaging - Deep Sky

Recommended Posts

Petergoodhew

Petergoodhew

Posted
Posted

This has been a tricky one.  I've hit OTA flexure problems that mean I've had to discard all subs that are more than 5 mins exposure.  So I've had to do Ha and OIII at bin 2x2.  I'm not happy with the star colours, and need much more data to pull out the outer shells.  I will re-image at bin 1x1 once I've got the flexure issue resolved. meanwhile this is the best I can achieve.  HaOIIIRGB a total of 7 hours of data imaged from Spain.

NGC7293 RGB.jpg

Link to comment
Share on other sites
Barry-Wilson

Barry-Wilson

Posted
Posted

Excellent image Peter - very impressive detail.

The background needs a little work - some green gradients on the left of the frame (and below the Helix, maybe to its right too) with a blueish cast otherwise.

Touch up these areas and you will have a real winning image.  Top drawer!

Link to comment
Share on other sites
Petergoodhew

Petergoodhew

Posted
  • Author
Posted
2 minutes ago, Barry-Wilson said:

Very well done Sir!

OTA flexure?  Can you expand . . .

Yes Barry.  I decided to ship my Star71 + SX814 down to Spain and stuck it on top of my TMB OTA.  Ever since then I've been plagued with star-trailing on long NB exposures (like 1200s, so not very long).  They were so bad that I couldn't even get some subs to register. I have had occasional eggy-stars, but this was dramatically worse. I've got everything on the optical train screw-threaded together so there should be no flexure there. At first I blamed the 10Micron - and so used the Star71 as an over-spec guide scope and started imaging with PHD2 guiding.  PHD2 worked fine, but the trailing didn't improve one iota, so the conclusion was that the extra weight of the wide-field rig must be causing flexure on the TMB OTA .  Later in the week I should get an OAG installed on the TMB.  If it works (and I'm pretty sure it will) then I will know for sure that the problem was OTA flexure caused by adding the wide field rig (and I will be able to do 30-min NB subs again).  

Link to comment
Share on other sites
ollypenrice

ollypenrice

Posted
Posted

No one image ever defines an object - fortunately. This has the etherial quality of the Helix at the eyepiece, though I doubt that anyone ever saw so much detail or colour visually. I'd regard version 2 as an entirely valid statement about the object. You can go on making different statements as you continue to collect data. I admire your call on noise reduction, which is to keep it minimal (if you used it at all.)

Olly

Link to comment
Share on other sites
Petergoodhew

Petergoodhew

Posted
  • Author
Posted
10 minutes ago, ollypenrice said:

No one image ever defines an object - fortunately. This has the etherial quality of the Helix at the eyepiece, though I doubt that anyone ever saw so much detail or colour visually. I'd regard version 2 as an entirely valid statement about the object. You can go on making different statements as you continue to collect data. I admire your call on noise reduction, which is to keep it minimal (if you used it at all.)

Olly

Thanks Olly.  I used a curves-based technique for noise reduction promoted by a gentleman called Penrice.  The beauty of it is that you can't see when it's been done!

Link to comment
Share on other sites
gorann

gorann

Posted
Posted
13 hours ago, ollypenrice said:

No one image ever defines an object - fortunately. This has the etherial quality of the Helix at the eyepiece, though I doubt that anyone ever saw so much detail or colour visually. I'd regard version 2 as an entirely valid statement about the object. You can go on making different statements as you continue to collect data. I admire your call on noise reduction, which is to keep it minimal (if you used it at all.)

Olly

 

13 hours ago, Petergoodhew said:

Thanks Olly.  I used a curves-based technique for noise reduction promoted by a gentleman called Penrice.  The beauty of it is that you can't see when it's been done!

Beautiful Helix, especially version 2.0!

Can any of you gentlemen point me at a thread or site describing Olly's curve based noise reduction?

Link to comment
Share on other sites
Petergoodhew

Petergoodhew

Posted
  • Author
Posted
1 minute ago, StargeezerTim said:

That's stunning Peter. I looked at it on my phone and thought 'that's nice' but on my computer screen the detail is terrific.

Thanks Tim.  I think its a gorgeous target.  It's a great narrowband target alone as the OIII is strong and totally different to the Ha.

You can see why they call it "The Eye of God"!

Link to comment
Share on other sites
Petergoodhew

Petergoodhew

Posted
  • Author
Posted
1 hour ago, gorann said:

 

Beautiful Helix, especially version 2.0!

Can any of you gentlemen point me at a thread or site describing Olly's curve based noise reduction?

Olly has posted it a couple of times, once recently, but I can't recall where. No doubt he will point you in the right direction.  It's beauty is its simplicity and subtlety.

Link to comment
Share on other sites
wimvb

wimvb

Posted
Posted
7 hours ago, gorann said:

 

Beautiful Helix, especially version 2.0!

Can any of you gentlemen point me at a thread or site describing Olly's curve based noise reduction?

If I recall correctly; very crude description:

In curves stretch, put a marker on the curve (straight line, still) just left of the histogram peak that represents background. On the right hand side of the same peak, pull the curve/line down to almost the same level. This will narrow the histogram, and iron out any noise, but also any detail. Use with caution and don't overdo it.

Link to comment
Share on other sites
ollypenrice

ollypenrice

Posted
Posted
3 minutes ago, wimvb said:

If I recall correctly; very crude description:

In curves stretch, put a marker on the curve (straight line, still) just left of the histogram peak that represents background. On the right hand side of the same peak, pull the curve/line down to almost the same level. This will narrow the histogram, and iron out any noise, but also any detail. Use with caution and don't overdo it.

That's not quite it, though I did do that recently on one image. I normally pin the curve at a value at the upper end of those found in the background sky. Personally I try to get the brighter background pixels to 23 so the pin goes in at 23 in that case. Next I put in some fixing points above that and then lift the curve below 23 to drive the darker background pixels up in value. I like this because it is unlike normal NR which is a blurring process in which neighbouring pixel values interact with each other. In the Curves method the pixels don't interact at all so they retain their original grain, though it is reduced in contrast.

Olly

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.