SD14 in Astrophotography

jasonh

Well-Known Member
Jason,

I do recommend that you use a hand held GPS receiver. Knowing Latitude, Longitude, and Elevation are essential to set your location on the Heavens Above web site and in Stellarium. Plus, the time displayed on a GPS receiver comes from the atomic clocks carried on the GPS satellites which can be very useful when you need to know the exact time for your observations and photography.
Boy I'm glad I bought that GPS for my wife for Christmas, lol :)


I might have to see if I can get some shots of the moon tonight if it doesn't start snowing again and it stays clear. The last time I tried to shoot the moon I stupidly tried on a (almost) full moon using my late Fuji S5200. This is what I came up with by using 22 images to make an HDR:

 

jasonh

Well-Known Member
I think my first attempt at astrophotography will turn out to be an ultimate fail.

I had focusing issues (apparently the infinity mark on my lens is past infinity, which I did not know), and issues with the wind blowing my tripod around causing squiggly stars. Dcraw completely destroyed the images on conversion to tiff, so I'll have to wait till I get home to find out what I got. Lots of noise in the embedded jpg's. I don't think I will have much usable from last night...
 

Steaphany

Well-Known Member
Jason,

The focus guide imprinted on photographic lenses is rarely ever truly calibrated to the lens' optics. It is best to look through the view finder and focus manually by eye.

Since stars are usually too faint to properly focus on, try to locate a street light at least a mile or more away which you can use as a focus target. Aim the camera at the distant street light and focus. Then leave the focus setting alone while you aim your SD14 to the sky. Initially shoot 15 second images to get single frames with everything visible on the SD14's LCD to see how the framing needs adjustment. Once that is done, set the exposure to shoot with the exposure you want.

Another point that you need to keep in mind with long exposures is that they still need to be short enough to keep the stars as points, unless you are after a star trail image. With a Sigma 28mm DG EX lens, I have calculated the time for a focused star to move from one photosite to another at roughly 4 Seconds when the stars are located along the plane defined by the Earth's equator going across the sky. This is not much of a problem when stacking, since the short exposure also keeps noise down.

-=-=-

To everyone here interested in astrophotography, today, April 4th, you can watch the Live 24 Hour web cast of
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. Any missed segments are available to watch or you can watch, at least for today, the live broadcast.

We are also in the middle of 100 Hours of Astronomy, which started on April 2nd and runs through to April 6th. Both are events which are part of the
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is a global effort initiated by the International Astronomical Union (IAU) and UNESCO to help the citizens of the world rediscover their place in the Universe through the day- and night-time sky, and thereby engage a personal sense of wonder and discovery.
 

jasonh

Well-Known Member
I had thought about trying to focus on something far away, but I was doing my photos from a park in the center of my community so I was surrounded by houses and couldn't see much.

I didn't really have a problem with my stars arcing as most of my exposures were around 4sec or so. My main issue was the wind was blowing my camera around on the tripod, so I have a lot of squiggly stars. My tripod is just a cheap lightweight aluminum thing, pretty much worthless for long exposures in any condition but a vacuum. Lot of good mirror lockup and remote release did, lol.

I will go through the photos this weekend and see if anything is really usable. I think I have a few decent shots of Ursa Minor that I can stack.
 

Steaphany

Well-Known Member
Some Constellations

On the evening of April 4th, a friend and I went out to do some astronomy and photography. I had two goals for the evening, shooting of photo of the International Space Station as it flew close by Saiph, a star in the constellation Orion, and shooting a pair of Iridium flares an hour later occurring about one minute apart.

I have my telescope and SD14 all set up

IMG_0507s.jpg

But, when the ISS flew by, the sky was still too bright to even see Saiph. :(

I then set up the SD14 with my Sigma 28mm DG EX lens to shoot the Iridium flares. By this time, the night was as dark as it was going to get, with a more than 50% lit Moon, it was still too bright to even see the Iridium satellites move across the sky and I saw one of the two flares. :(

Here is a view of my house with a 30 second exposure at f1.8 from the location where we set up the telescopes showing just how bright the night was:

SDIM1540s.jpg

It wasn't a complete waste since I was able to shoot some nice constellation photos:

Canis Major:

SDIM1513s.jpg

Perseus:

SDIM1536s.jpg

and the Big Dipper (Ursa Major):

SDIM1517s.jpg

All the constellations were shot with a Sigma 28mm f1.8 DG EX Lens with a 30 Second shutter, f1.8, ISO 100, Sunlight White Balance, single images processed in SPP.

I just need to plan for the Next good pass of the ISS and Iridium flares with better Moonless evenings.
 

Steaphany

Well-Known Member
CEZEO's X3F.exe to the rescue

Using X3F.exe, I was able to get my hands on the most basic Raw data from the 24 images that I originally shot way back on November 19, 2008. Everything that I did previously ended up doing too much leaving the astronomical processing flawed from somewhat processed Raw source data.

The Answer:

First, I used X3F.exe to extract the RAW image section of several images to sample and review the data with
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which allowed me to see that the peak histogram non-zero data values were roughly 23. :rolleyes: So much for concluding that the exposure saturated the imager's photosites. I also found that a Tiff file where the data is contained within the range of 0 to 24 of a dynamic range going up to 65,535 is hard to work with.

The Fix:

I extracted the RAW image sections of all 24 images with the following scaling matrix:

Code:
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This brought the histograms peak non-zero value to roughly 750, enough to work with without severely amplifying too much noise. I'm also well aware that this is far from a quality photo transformation matrix, but then, I'm just dealing with photos consisting of focused points of dim light. ;) I will have to derive a better transformation matrix when I go to processing deep sky objects like galaxies and nebula.

I used
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to align and stack the images. I left the default quality selection to stack 80% of the highest image quality frames, which turned out to be 19, equalling a total exposure time of about 5 minutes.

The Tiff file produced by Deep Sky Stacker had 96 bits per pixel and I used Photoshop to enhance and reduce the image to a presentable form:

Autosave.jpg

:z04_smilieparty: Yay !!! The Sky is dark, free from noise. ALL the stars are points of light, not shadowed by illuminant triangular ghosts, the strange noise in the upper right of the image is gone.

The only compromise that I made to the image presented here was to not have the glow from the Milky Way being too prominent. Very subtle changes to my Photoshop adjustments control the expression of the Milky Way, indicating that this image actually contains a lot of quality data.

:)
 

Steaphany

Well-Known Member
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
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( Just a few posts earlier to this thread )

and compare to what AIP4Win yielded:

tSDIM_stack-2009-06-13.jpg

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:

annotated_tSDIM_stack-2009-06-13.jpg

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 ? :mad: ) 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 ? :mad: )

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 ? :mad: ) 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 ? :mad:) 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 :rolleyes: )

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
 

tc95

Well-Known Member
Steaphany, sounds like there software is for the novice user...the tech was trying to scare you off...with technical mumbo-jumbo....:z04_975:


I would reply to his email....and see if they will refund your $100.00...from what you have said in your post...I would not want to spend the money for that product....it seems like a waste of money....

Thank you again for giving us your knowledge on this....I am getting my equatorial next week...and hopefully take a crack at this next...

Tony C.
 

Steaphany

Well-Known Member
It's bad enough that I've already gave them something to fix.

The latest version of AIP4Win, 2.3.0, is supposed to support natively reading Sigma X3F files, it doesn't work. When I reported this problem, I learned that they never had any X3F files to work with prior to the ones I provided to them. (the files that I provided are the same ones that AIP4Win couldn't stack :rolleyes: )

It would have been fine if they off loaded the raw file reading to dcraw, which is how Qimage, DeepSkyStacker, and Tawbaware's products handle it.

I've also received feed back on an astronomy forum that AIP4Win is great when stacking narrow fields of view with out any rotational skew between frames. I do admit that it has value, but there are severe limitations too.
 
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