Comet subtraction from Staraligned Frames.

Niki Haselwanter

I finally made it to get some shots of Comet A3.

So i went through almost the whole process with the comet acadamy videos running on the 2nd monitor. 

Wverything is fine until it comes to the subtraction of the comte only from the staraligned frames. 

The tail is subtracted quite good, where the nucleus makes strange things, but see in the pictures.

I have the Comet master, the staraligned master and a cometsubtracted light.

Ideas about that? 

cheers, Niki

BlockHead

Subtraction is tricky!

You need to pay attention to two parts:

1. You need need to make sure you understand the reference!! It does not appear you have done this in your picture. Please review the section that I explain... The starless comet (operand) needs to have the same alignment as your reference frame in your list of staraligned images. Does it?

2. Then you worry about whether you should use the Linear FIt or not. For  A3..I would think Linear Fit would work since it is bright.

The issue I think is #1. 

-the Blockhead

Niki Haselwanter

Hey!

I understand. 

Did id from the beginning on and chose in wbpp the reference frame manually. 

AND in Comet-Alignment i decided to mark EVERY picture because i believe that the dithering i had running when taking pictures is interferring the whole thing. 

My comet path was kinda zigzag... 

But now it worked. 

I have another set of pictures i will have a try on now.

This is my final pic from set 1. 

Its not a very colorful one compared to Neowise lately, but its only 60X10 seconds, so not so much time for this one

Thanks so far!

Niki

BlockHead

Yeah..I really should make it clear. If you have dithered data... and you want to not double interpolate you will need to click on the comet in each frame. OR... you can run CometALignment on the StarALigned frames and take advantage of linear motion... But you will be registering the comet data twice (StarALignment and CometALignment). 

Most people pick the latter anyway and do not think about it... 

But... there you have it.

-the Blockhead

Niki Haselwanter

Great!

So that was the "fault" 

It would have been easyer to just not guide the whole set.

I learned for the future.

But thanks for the confirmation.

What comes to mind in this case ist. Wouldn´t it be easyer to just take the comet aligned frames that where allready made before the StarXterminator Process, and use these for comet subtraction, and staralign them afterwards? 

Niki

BlockHead

I am not certain I understand. When you do comet subtraction you are using a comet aligned *masterlight* frame to subtract from individual staraligned frames. You would not want to subtract a single sub from a staraligned frame... it would not work (too noisy). Is this what you are asking?

-the Blockhead

Niki Haselwanter

Sorry, had a knod in my head.

Everything is clear now, i just go and mark the comet in every pic, and next time i just don´t dither when it comes to comet pictures.

Thanks!

Niki