Stack or Edit First?

[Domer]

Let me start by stating that I'm fairly new to astrophotography.  I have a Canon 6D Mark II with an EF 24-105 F4L IS USM lens and a Rokinon 14mm F2.8 lens, a Manfrotta tripod and an iOptron star tracker.  I've done a ton of research and tried to plan thoroughly for a recent Milky Way shoot in the Anza-Borrego desert last weekend.  I took about 20 shots with the Rokinon lens at ISO 1000, f2.8, 120 second exposures.  I had to toss 8 of them because of planes flying through, but that still left me with 12 decent images.  I shot 7 dark frames and 10 offset frames.  I tried to capture flat frames using the white T-shirt method but I could clearly see uneven lighting through the material so I figured they were going to do more harm than good and skipped that.

The star tracker was aligned very well - reviewing the raw images in Lightroom 6 and PaintShop Pro showed no visible migration of stars from one image to another, even when zoomed way in at the corners.

I used DSS to stack the photos and made sure that the “embed changes but do not apply them” box was checked before saving the final image.  When I imported that into Lightroom 6, the image was very dark.  The stars and Milky Way appeared only after boosting the exposure - a lot.  But the final image was nearly colorless, save for a strong yellow tint.  I tried everything I could in Lightroom to draw out the colors, but the results never came close to the original images in terms of color accuracy. 

Making matters worse, while I had no problem applying the Rokinon lens corrections to the original raw images in Lightroom (it appears in the list under the "Custom" setup option), it would not offer me the Rokinon profile when editing the TIFF file - the list only includes the default lenses.  So I cannot eliminate the slight fish eye effect or the blurring of stars in the corners.  That would seem to be a non-starter for me.

So I decided to try it another way.  I edited all 12 of the raw images in Lightroom first, exported them to TIFF files, and then let DSS do the stacking (no dark or offset frames used).  The results were much better.  The colors were intact and the air glow was substantially reduced.

This leads me to my questions:

1) Does anyone know how to apply lens corrections to TIFF files using Lightroom 6 if they aren't in the Default list?

2) Every work flow I've read on line has the stacking done first and then the final editing in Lightroom or PhotoShop.  But in my case, that just didn't work very well so I'm wondering if I'm doing something wrong or if reversing the order is more commonly done than it would seem?

I've attached some files to show you what I'm seeing:

 

IMG_0499.JPG: This is a sample of an original, unedited Light frame.

IMG_0499.-1JPG: This is the same shot, editing in Lightroom with the lens corrections, tone curve adjustments, and a little sharpening (nothing else).

DSS Output.JPG: This is what the DSS stacked output looks like once imported into Lightroom (screen shot)

DSS Output (exp+3).JPG: This is what the DSS stacked output looks like once I crank up the exposure by +3 (screen shot).  Notice the absence of all color except for a strong yellow tint.

DSS Output (TC and WB).JPG: This is what the DSS stacked output looks like once I make soem slight adjustments to the tone curve and dial down the temperature (-18).  The yellows are weakened but not completely gone, and half of the stars are now blue in color, which is clearly unrealistic.

Milky Way (PSP).JPG: This is what the final image looks like if I edit the raw files in Lightroom first, then stack using DSS.  Although some stars are still too blue in this image than I would like, the colors of the Milky Way are more accurately reproduced than when I stack first. 

 

But there isn't that much difference between the 2nd image (single edited RAW sample) and the final image (stack of edited samples.  So I'm not sure I'm even achieving the desired result here.

I've read countless posts by other people who are losing color in the DSS tacking process.  I've tried many of the suggestions for adjusting various settings, but nothing seems to work.

[wxsatuser]

If you stack RAW files in DSS the output will be dark and lack colour, that's the nature of RAW files.

RAW files are linear, dark, lack contrast and colour, this applies to AP and normal terrestrial photography.

Most photographers don't see the linear as software and the camera will add tone curves to process the image.

BTW I would'nt use inbetween ISOs, go for 800, 1600 or even 3200 with a 6dmk2.
Use daylight white balance for correct colours.

Think you could have exposed longer, rule of thumb is to get the camera histogram peak to at least 25%.
This should separate the histogram from the left hand side.

Here is a linear image of North America nebula followed by the software tone curved one.
The tone curved one is what will also be seen on the camera screen.

Edited July 23, 2019 by wxsatuser

[Demonperformer]

Hi, Domer, and welcome to SGL.

As you have discovered, AP has a steep learning-curve, but it is worth sticking with it. I would be quite happy with your MW shots.

Enjoy the journey.

[Domer]

wxsatuser,

Thanks for the advice.  I'm planning another shoot in a couple weeks and will try your suggestions.  BTW - I started out using ISO 1600 but the resulting images looked a little blown out so I backed it off to 1000.

But I'm still struggling with the loss of color issue (or more accurately, the yellowing of the stacked image) as well as the inability to apply lens corrections to TIFF files in Lightroom.  Those are the problems I need to fix here.

[wxsatuser]

Do you have Photoshop?

As to the yellow, the colour balance is out or there was another light source.

Assume you used daylight white balance.

 

[Domer]

Also, I noticed that the stars are not very crisp in the corners of the images.  This is the case for both the originals and the stacked version No lens corrections applied).  In the upper-left corner the stars have a strange diamond-like shape and in the lower-right corner they are more like star trails (see attached images).  Is this due to the sper wide angle lens or a slight misalignment of the star tracker - or both?

If it's a star tracker alignment issue, that may be a good reason not to do longer exposures.

[Domer]

Blue Straggler,

No, I don't have PhotoShop - I have Lightroom 6 and PaintShop Pro 2019.

I believe my white balance was set to Auto when I took those shots.

[wxsatuser]

Unfortunately there are not many lenses that don't have aberrations like these.

Chromatic aberration and mono chromatic aberrations.
You have chromatic aberration on those diamond stars and the other image could be coma.

Use daylight white balance for true colour, can you change it in Lightroom?

[Xplode]

6 minutes ago, Domer said:

Also, I noticed that the stars are not very crisp in the corners of the images.  This is the case for both the originals and the stacked version No lens corrections applied).  In the upper-left corner the stars have a strange diamond-like shape and in the lower-right corner they are more like star trails (see attached images).  Is this due to the sper wide angle lens or a slight misalignment of the star tracker - or both?

If it's a star tracker alignment issue, that may be a good reason not to do longer exposures.

This is probably caused by sensor tilt or by the lens not being perfectly adjusted/collimated.
If it was an abberation from the lens design it would show up the same in all corners, if it was too long exposure it would show up all over the image (except when pointed at the pole)

[Domer]

Yes, I can adjust the white balance in Lightroom.  But when I tweak it so the Milky Way looks more normal, many of the stars turn blue.  And while that looks nice, it's not realistic.  There was a lot of yellow light pollution on the horizon when I took these shots...

I'll set the WB to daylight on my next shoot and see if that helps.

Thanks for all the advice.

[wxsatuser]

2 minutes ago, Domer said:

Yes, I can adjust the white balance in Lightroom.  But when I tweak it so the Milky Way looks more normal, many of the stars turn blue.  And while that looks nice, it's not realistic.  There was a lot of yellow light pollution on the horizon when I took these shots...

I'll set the WB to daylight on my next shoot and see if that helps.

Thanks for all the advice.

That's it the LP.

It should be possible to subtract the LP with curves.

Take a look at this.

https://clarkvision.com/articles/astrophotography.image.processing2/

[Domer]

Great article - I've read some of his other articles on that site, but hadn't seen this one yet.  It looks like you have to have PhotoShop to do those adjustments to the histogram.  I was hoping to avoid that but apparently subscribing to the PS monthly fees in inevitable.

But does PS allow you to apply lens corrections to a stacked TIFF file if the lens isn't in the default list?  Because Lightroom doesn't offer that option - the Rokinon lens only appears when you are editing the raw image.

Edited July 23, 2019 by Domer

[wxsatuser]

Does Paintshop have curves?

I doubt you can apply corrections to stacked images but I'm open to correction.

The normal way is to correct RAW but again if anyone knows better.

[Domer]

PaintShop Pro does have curves, and it also has layers so it can stack aligned images.  But I don't know how the stacking compares to DSS.

So if you cannot apply lens corrections to a stacked TIFF file, then what should be my work flow?  Apply lens corrections in LR or PS, export to TIFF, stack in DSS, then edit in LR or PS?