DeepSkyStacker out performs AIP4Win
I have and been using DeepSkyStacker far longer than I have been playing with AIP4Win. So, I just wanted to see how well AIP4Win performed when stacking the very same collection of Tiff format images extracted from the X3F files by X3F.exe.
My bottom line conclusion -
DeepSkyStacker is great, both Free and it works !!!
AIP4Win costs $100US, it comes with a book, and it may have it's place, but to stack images, it sucks !!!
Here is my proof:
Look at the DeepSkyStacker results
Here ( Just a few posts earlier to this thread )
and compare to what AIP4Win yielded:
View attachment 1741
A note of distinction between the DeepSkyStacker image posted previously and AIP4Win the image, both needed processing in Photoshop to allow them to be presented here. Since the Milky Way passes through Cassiopeia, I toned down the Milky Way's glow to better bring out the stars in the DeepSkyStacker image. I did not feel going to such efforts would have improved the AIP4Win image.
And here are the stars I had to manually identify for every frame to AIP4Win:
View attachment 1740
A lot of good that did :z04_head_wall:
You can see why I immediately concluded that I must have done something wrong. This is the first time that I used AIP4Win's stacking function. Only in the areas surrounding the alignment stars do the stacked stars achieve alignment. The further away from the alignment stars, the worse the distortion. Compounding this, look at the orientation of the distorted stars - the distortion varies and is inconsistent.
Now, for a final nail in the AIP4Win coffin, I contacted AIP4Win support and received a timely reply:
From: Jim Burnell
To: Steaphany Waelder
Subject: Re: Stacking alignment in AIP4Win
Hello Steaphany,
What you are experiencing is the wide-field astrophotographers lament.
At low elevations,. atmospheric refraction distorts your image, such that
all areas of the image are not seen at the same scale. This is not a simple
correction that can be implemented by shifting and scaling the image.
Another problem occurs when using widefield photographic lenses.
These lenses have pincushion distortion. When images are stacked that
have been shifted relative to each other, the scale of a particular region
is not constant from image to image, as the sky moves across the field.
Again, this is a complex distortion that is not easily corrected during
processing. This is not much of an issue with a well-aligned tracking mount,
but is a real problem shooting off a static tripod.
Jim
This really put me in a bad mood, and I'm not about to reply back. Instead, I'll disect their issues here for everyone to see.
At low elevations,. atmospheric refraction distorts your image
Hmmm, I shot these images on November 19, 2008 between the times of 10:02 PM and 10:22 PM Central Standard Time, November 20th 4:02 to 422 Universal Time, when Cassiopeia was on the meridian. The location of my camera was at 98º 28' 35"W 33º 13' 32" N 386m. Calling this up in SkyMap Pro, Cassiopeia is about 60º above the horizon. ( A low elevation ?
) Looking towards the lower left of the image, the stars of Cepheus show that the lowest altitude in the image is between 50º and 55º. ( Again, A low elevation ?
)
when using widefield photographic lenses.
Hmmm, I clearly state that I shot these images with a Sigma SD14 dSLR, a camera which uses an imager smaller than a standard 35mm film frame. In fact, the Sigma SD14 User's Manual, page 121 titled "Specifications" describe the "Picture Angle" as "Equivalent to 1.7x the focal length of a lens when used on a 35mm SLR camera". I also clearly state the focal length of the lens used as being 28mm, yielding 47.6mm on a 35mm SLR. ( Wide angle ?
) I even calculated the combined SD14 & 28mm lens field of view at Horizontal 40.57°, Vertical 27.69°, and Diagonal 47.91° ( Again, Wide angle ?
) The stars captured in the image are proof - Cephus can be seen in the lower left and Perseus to the upper right.
These lenses have pincushion distortion
Like Sigma, known across many camera brands for quality lenses, would allow even an out of spec or defective lens to suffer from a problem as indicated by the AIP4Win stacked image. The image looks like it was shot through a lens made of melting ice. The lens used was a Sigma 28mm f/1.8 EX DG Aspherical Macro which I purchased on October 6, 2008 from B&H Photo for $299.00. Please note that this is a DG lens, not a DC lens. I specifically selected this lens for it's ability to accurately operate over a full 35mm film frame, simply to ensure that I'd have an accurate, distortion free, image on the smaller Foveon imager area. This is not a "kit" lens and my SD14 purchase was the individual camera body with lenses purchased separately. I rather spend the money for quality components and instruments rather than getting stuck buying junk that gets sold as a "kit".
this is a complex distortion that is not easily corrected during processing.
mmm, b-u-t DeepSkyStacker took the very same collection of images, accurately identified from 84 to 146 stars in each of the 24 images, 19 of which were used in the stacking after receiving a quality level of 877.67 to 1024.83 and accurately aligned each, completely over the full field of view all on it's own. And remember, these frames where manually shot, leaving the frame to frame time variable, with my SD14 sitting on a static Velbon tripod. ( I couldn't make it more challenging by tieing one hand of my SD14 behind it's back since it doesn't have hands. I could have waited for the Moon to rise, but it was just too cold
)
and finally:
This is not much of an issue with a well-aligned tracking mount
Hmmm, so a well polar aligned tracking mount would some how compensate for and keep the stars in the sky from dropping below the low, distortion prone, altitude of, I don't know, 60º
I think I've done enough ranting for the time being. Keep this in mind it you're considering a purchase of AIP4Win
