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What's wrong with my data? M31...

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#1 jag32

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Posted 14 November 2017 - 07:02 PM

This is my first attempt with my new Pentax K1 of M31 with data consisting of the below details.  The issue i'm having is that when I stretch the stacked image, the entire left side "above" where M31 is pointing seems to blowout, like the entire black sky background also turns light (it looks like M31 is throwing up), I can't figure out why:

 

-Pentax K1 at ISO 800

-5 subs at 600 seconds (10 minutes) each

-50 minutes total integration time 

-Stacked in DSS with flats, bias, and darks.

-Takahashi FC-76DCU refractor (76mm aperture)

-MGEN II autoguider

-Orange skies (not sure if this is light pollution??)

 

I do think my first attempt with my unmodified K1 came out pretty decent, especially with no flattener and just 50 mins total integration, but I have no idea what's going on with the skies to the left of M31?  Here is the link to the raw stacked data:  

 

https://www.dropbox....ration.TIF?dl=0

 

And the next 2 posts will have screenshots of the difference... below is a screenshot of the image before stretching:

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  • Screen Shot 2017-11-14 at 6.58.22 PM.png


#2 jag32

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Posted 14 November 2017 - 07:06 PM

Stretched in Photoshop CS5, no other processing:

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  • Screen Shot 2017-11-14 at 7.05.31 PM.png


#3 jag32

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Posted 14 November 2017 - 07:06 PM

Wow, the upload on here really reduced the quality.  The raw data at the dropbox will give a much better idea.



#4 StarryHill

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Posted 14 November 2017 - 07:41 PM

Perhaps some source of stray light hitting the opening of your OTA either directly or bouncing off some reflective surface (i.e. a parked car) nearby? Other than this, pretty awesome image! I had to stretch your image pretty far in PI before it showed so the light source probably was pretty dim.


Edited by StarryHill, 14 November 2017 - 07:44 PM.


#5 jag32

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Posted 14 November 2017 - 07:52 PM

I actually had about 2.5 hrs worth of integration time which would have yielded an incredible image as opposed to this one with just 50 mins of integration time, but unfortunately I kicked the mount and didn't realize it so all the remaining subs had trails in them.  Either way, this was really just a test session for my Pentax K1!  I do think that stray light makes sense as i'm definitely not at a dark site and I acquired this from a balcony in my neighborhood, though there were no direct flood/street lights the occasional car drives by and the lights will sometimes shine on the balcony.  I guess that would do it?



#6 StarryHill

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Posted 14 November 2017 - 08:00 PM

It would be interesting to stretch each sub individually. If you find that there's only one sub that has the stray light, you could omit it and then produce an awesome image. But if you find that the stray light is in every sub, then it obviously wouldn't be from a passing car but, more likely, from some very dim light source nearby.



#7 mistateo

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Posted 14 November 2017 - 08:05 PM

I like to do a preview stretch in DSS and blink through my frames real fast to look for stray light from my nosy neighbor's flashlight :)



#8 bobzeq25

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Posted 14 November 2017 - 08:11 PM

I find this sort of gradient quite common in M31 images, also this particular example is unusually strong.

 

Do you do any gradient reduction in processing?



#9 jag32

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Posted 14 November 2017 - 08:13 PM

It would be interesting to stretch each sub individually. If you find that there's only one sub that has the stray light, you could omit it and then produce an awesome image. But if you find that the stray light is in every sub, then it obviously wouldn't be from a passing car but, more likely, from some very dim light source nearby.

Just did this and found the culprit, thanks so much for that idea!  

 

BTW, for anyone curious, here is just one single sub that was stretched.  I'm pretty happy with my Pentax K1.... what I used to get with 3 hours of integration time in my Canon 500D T1i, I now get with just a single sub in my Pentax K1!

Attached Thumbnails

  • Screen Shot 2017-11-14 at 8.11.34 PM.png

Edited by jag32, 14 November 2017 - 08:13 PM.


#10 jag32

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Posted 14 November 2017 - 08:14 PM

I find this sort of gradient quite common in M31 images, also this particular example is unusually strong.

 

Do you do any gradient reduction in processing?

Bob,

Typically I don't do any gradient reduction, although this is my first time imaging with my new Pentax K1.

Is there anything specific you recommend I do with regard to processing (I have Photoshop CS5) and is there anything I can do on the camera to reduce gradient at time of acquisition?



#11 ImNewHere

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Posted 14 November 2017 - 10:33 PM

http://www.prodigita...vancedUsage.htm use this, try the free trial, and I pretty well gaurantee you will love it.



#12 jag32

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Posted 14 November 2017 - 10:48 PM

Does this replace the need to have to always take flats with the camera, I just use that instead? Thanks!

#13 ImNewHere

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Posted 14 November 2017 - 11:52 PM

No,you still definitely need to do flats, but this will kill gradients much better than GX, and at a cheaper price too. I also use Astronomy Tools by the same guy too.

#14 bobzeq25

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Posted 15 November 2017 - 03:08 AM

 

I find this sort of gradient quite common in M31 images, also this particular example is unusually strong.

 

Do you do any gradient reduction in processing?

Bob,

Typically I don't do any gradient reduction, although this is my first time imaging with my new Pentax K1.

Is there anything specific you recommend I do with regard to processing (I have Photoshop CS5) and is there anything I can do on the camera to reduce gradient at time of acquisition?

 

Reducing gradients is all about processing, it's really impossible to reduce them in acquisition (other than by avoiding stray light, not generally the problem).

 

For Photoshop, far and away the best tool is the well regarded third party Gradient xTerminator.  Later on, you'll find one advantage of the dedicated astrophotography processing programs is excellent gradient reduction tools.  For now...

 

http://www.rc-astro....entXTerminator/

 

Bias, flats, and darks are a must.  Trying to extract the camera noise information from your lights is substantially inferior.  You're far better off measuring camera noise directly.  Flats do more than fix vignetting and dust spots.

 

A lot of really smart people have been doing this for a long time.  Honestly, especially when starting out, it's best to stick with the tried and true.  "Magic" solutions abound in the marketplace, and they're usually not magic.


Edited by bobzeq25, 15 November 2017 - 03:09 AM.



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