Comets and Nebula

Shawn Thompson

Hi,

I'm working through the comet academy of Comet C2021 S3 Panstarrs that I should in the Cygnus region. I'm not seeing anywhere how I can subtract the nebulosity from the comet only image, or if I missed something earlier in the workflow. 

Thanks,

Shawn

BlockHead

No. There isn't a method to get rid of nebulosity in the comet only image.

But there is a fundamental idea. Everywhere that there is nebulosity in your comet only image- there is nebulosity in your comet subtracted image. Right?

In the comet-only image the nebulosity is smeared and does not "add" up like the comet does when stacking since you are aligned on the comet. This means the nebulosity in the comet only image is much dimmer than the real nebulosity in the comet-subtracted data.

Which means that the way you blend the comet only image with the comet subtracted image is the key. You would agree with me that if you just use LIGHTEN... and blend these two images together that the stacked comet bit is obviously brighter than the comet-subtracted layer. And the comet-subtracted nebula is brighter than the smeared stuff in the comet-only mage. In practical terms, it becomes important to maintain this difference in brightness when stretching the images before blending them.

I hope you can see this can be a way forward. I do not have this example...because I did not example data to work with. But everything I said above is based on principles I outline in my content and I suspect leads to an approach that could be helpful.

-the Blockhead

Shawn Thompson

I understand. I'll mess around with it and see what I can get.

On a side note, if you want some example data Id be more than happy to provide some. 

Thanks,

Shawn

Shawn Thompson

I understand, but I can't seem to get this to work. 

My problem(I think) is that the nebulosity in the comet only image doesn't seem dimmer than the comet subtracted data. I can't figure out how to get the comet to stand out with the nebulosity doing the same. 

I get a little better result trying to blend in Photoshop, but can't get the comet to stick out.

Thanks,

Shawn

BlockHead

How many frames are in your comet only image? I suspect the comet isn't moving very much... this is probably the issue. However, mathematically... it really *has* be to dimmer if there is any smear. 

You can create screenshots of the readout preview showing values between the two images.

-the Blockhead

Shawn Thompson

There are 31 frames in the image.

I've attached the comet alignment with the first and last image to show the movement, which I don't think is much. And a couple of screenshots of the readout preview, hopefully I did it correctly.

Thanks,

Shawn

BlockHead

Yes, I have been thinking about this... the issue is when you subtract .. you really don't want all of the nebulosity to subtract from the star-aligned frames. That is what is making life difficult I think.

I tried to take some data of this comet myself last night.

Maybe I can come up with something.

-the Blockhead

Shawn Thompson

I was trying to think if there's a way to only select the comet during integration, or at some other time.

I shot it twice, first with 3min exposures and then 5min exposures, with the 5min being what I'm using

Thanks

Shawn

BlockHead

I think I have another idea... 

BlockHead

I hope you saw I did publish my workflow on this topic Shawn. 

-the Blockhead

Shawn Thompson

I did not but I'll be looking for it soon. 

Thank you very much!

Shawn

Shawn Thompson

I'm not trying to be too picky or anything, but I believe video #2 should be batch sxt and not bxt. It threw me off for a second.

Shawn

BlockHead

lol

Thanks!

-the Blockhead

Shawn Thompson

I really struggled trying to clean up the comet, but I'm content with what I came out with at this point.

Thank you for all of the help.

Shawn