Starship Asterisk*

by **Rare White Ape** » Wed Sep 14, 2011 11:08 am

A modern take on the classic premise:

Click to play embedded YouTube video.

by **neufer** » Tue Sep 13, 2011 4:40 pm

DavidLeodis wrote:
The item brought up through the "tilted" link was funny as also were those that I saw that were available through the link.
I must admit that I do not recall hearing of Ernie Kovacs before.

Click to play embedded YouTube video.

by **NoelC** » Tue Sep 13, 2011 4:03 pm

Chris Peterson wrote:
NoelC wrote:I'm curious as to your opinion on my suggestion that there isn't as much vignetting in the Mars image as the composition makes it appear.

It seems possible, at least to some extent, but the corrections I had to dial in to flatten the image (per the above animated image) were pretty extreme. I can honestly say I can't recall ever having had to adjust an image from a dSLR anywhere near that much. I stand by what I have been saying about the rover's camera exhibiting a greater amount of vignetting than in a typical terrestrial dSLR. Vignetting seems a sufficient term for discussing the effect.

Now, regarding YOUR 28-135 and 40D, and what may be wrong with it...

Here is a shot I just did of the sky with my 40D and Canon 28-135 at f/13, 30mm. NO vignetting correction has been done (the profile-based lens correction feature was disabled for these raw conversions). This is a color and grayscale representation of the same image. I really don't perceive any vignetting or light falloff at the corners - not at all like what you showed, Chris. This is so different than the result you showed, I'm actually wondering whether there may have been two different designs for that lens. I bought mine back in 2000.

: Canon EOS-40D, 28-135 @ f/13, 30mm; NoVignettingVisible.jpg (42.6 KiB) Viewed 7865 times

: Grayscale conversion of same; NoVignettingVisibleBW.jpg (38.5 KiB) Viewed 7865 times

Here's the raw file for the above shot, if you'd like to open it and look for yourself:

http://Noel.ProDigitalSoftware.com/Foru ... G_6098.zip

-Noel

by **DavidLeodis** » Tue Sep 13, 2011 11:20 am

Opportunity continues to amaze me that it is still operating. Spirit does seem to have definitely ended but it was also an amazing achievement. I know I should not anthropomorphize them but I will feel sad when both Opportunity and Spirit rovers have ended.

PS. The item brought up through the "tilted" link was funny as also were those that I saw that were available through the link. I must admit that I do not recall hearing of Ernie Kovacs before.

by **Chris Peterson** » Tue Sep 13, 2011 1:14 am

NoelC wrote:I can find no way to get an f/12 aperture setting with that combination (I have the same camera and lens). F/11 or f/13 is as close as I can get. You did not save EXIF info in your image, so I can't see what focal length you used, but I will assume 28mm. Nor have you listed how you developed that image.

I put the camera on f/11 at 28mm, and then increased the focal length until the display showed f/12. The header (it was RAW, so no EXIF) shows 31mm. I didn't do any real processing at all- just brought the raw into PS CS5, resized to 400 pixels wide, converted to B&W, and saved as a JPEG. Of course, we don't know what processing was done (mainly what transfer curve was used) with the APOD image.

If you're seeing that much vignetting, I believe there is something wrong with your setup... What have you got screwed onto the front of your lens?

Nothing- not even a UV filter. And this is typical of what I see with other lenses and cameras if I'm stopped way down (which virtually guarantees this isn't vignetting, but just cos⁴ intensity falloff).

I'm curious as to your opinion on my suggestion that there isn't as much vignetting in the Mars image as the composition makes it appear.

by **NoelC** » Tue Sep 13, 2011 12:54 am

I can find no way to get an f/12 aperture setting with that combination (I have the same camera and lens). F/11 or f/13 is as close as I can get. You did not save EXIF info in your image, so I can't see what focal length you used, but I will assume 28mm. Nor have you listed how you developed that image.

Okay, if you're seeing that much vignetting, I understand why you made the statement you did.

However...

If you're seeing that much vignetting, I believe there is something wrong with your setup... What have you got screwed onto the front of your lens?

For now, here is a 28mm f/13 defocused shot of an even white surface (my monitor) with the same lens and camera you used, developed from the raw .CR2 file in Photoshop using default parameters that make a natural looking image normally (but with NO vignetting correction), then converted to grayscale. As you can see, there is nowhere near as much vignetting as in the image you showed.

: 28mm f/13 with 28-135 zoom on Canon EOS-40D; EvenlyIlluminated_28mm_f13.jpg (20.29 KiB) Viewed 7993 times

It's night here, but I'll be happy to shoot a similar image of the sky tomorrow for a better comparison.

-Noel

by **Chris Peterson** » Tue Sep 13, 2011 12:15 am

NoelC wrote:From my (considerable) photographic experience I can say that the level of vignetting (or whatever you want to call it) in this image is FAR greater than that seen in a common dSLR (or SLR) with all the lenses I've ever used. Note that it almost goes to black in the upper-right corner! To say otherwise, as though it's an unquestionable fact, is rather insulting.

You might want to consider trying to write a bit less "matter of factly". There are some things even you don't know.

I have no idea why you find my comments insulting, but I apologize if I said anything that was.

Here is a picture of the sky I took just a couple of minutes ago, with a Canon EF 28-135 IS lens on a Canon 40D (at f/12, the same as the Rover lens). In my opinion, the intensity falloff here is more severe than what is seen in the Mars image. As I said before, I think there is actually only a minor degree of falloff in the Martian image, and that there is an optical illusion caused by all the bright material in the center of the field which makes the image look much more vignetted than it actually is.

: vig.jpg (4.19 KiB) Viewed 8009 times

by **saturn2** » Tue Sep 13, 2011 12:09 am

This rock has many zinc.
It doesn´t look like a rock of impact.
It does look like a rock of sediment, it erode for some liquid ( water? )

by **NoelC** » Mon Sep 12, 2011 11:57 pm

Chris Peterson wrote:It has nothing to do with the camera or sensor. It is purely a function of the lens, and plenty of consumer lenses paired with DSLRs show this amount of illumination falloff

I'm REALLY not interested in getting into an argument over semantics with you, so I will just say I'm not in agreement with the above statement.

From my (considerable) photographic experience I can say that the level of vignetting (or whatever you want to call it) in this image is FAR greater than that seen in a common dSLR (or SLR) with all the lenses I've ever used. Note that it almost goes to black in the upper-right corner! To say otherwise, as though it's an unquestionable fact, is rather insulting.

You might want to consider trying to write a bit less "matter of factly". There are some things even you don't know.

-Noel

by **dlw** » Mon Sep 12, 2011 9:45 pm

Actually it's the remains of an alien spacecraft that crashed landed millions of years ago. Don't lift it up! There may be eggs under there waiting for nourishment!!

by **Chris Peterson** » Mon Sep 12, 2011 7:37 pm

NoelC wrote:But even our consumer grade dSLRs - even those going back a few years - don't exhibit the level of brightness fall-off shown here. I don't know if maybe it's because the imager chip is optimized for different things than my trusty Canon with its little microlenses, but I still would have expected the imager design / lens combination on the rover to have delivered a flatter field than what we're seeing.

It has nothing to do with the camera or sensor. It is purely a function of the lens, and plenty of consumer lenses paired with DSLRs show this amount of illumination falloff. Cos⁴ illumination falloff is found in all optics, including the highest quality photographic lenses and telescopes.

Keep in mind that this image was not made with one of the science cameras, but with the navigational camera, which has a very wide field of view (and consequently will show more prominent cos⁴ intensity falloff, and is not primarily intended to produce images of high scientific value.

If nothing else, the amount of falloff shown is enough that the pixels for objects around the edge would seem to lose at least a bit of accuracy.

It depends what you mean by "accuracy". As with all images, the reduced illumination at the edges means that the S/N is reduced there. This S/N reduction is present whether or not the image is flat field calibrated. And the optical aberrations will increase away from the center, which introduces mechanical distortions.

The design documentation for that camera would be an interesting read, I'm sure.

Some basic information can be found here.

by **PeteG** » Mon Sep 12, 2011 7:20 pm

The zinc table is interesting, but the first thing that caught my eye was the rusted-out old Martian tractor just behind it, with only the rear wheel still on it. Or maybe it's just another rock.

by **NoelC** » Mon Sep 12, 2011 7:08 pm

Yes, it makes sense that the calibration processing would be done at the receiving end, as I said.

But even our consumer grade dSLRs - even those going back a few years - don't exhibit the level of brightness fall-off shown here. I don't know if maybe it's because the imager chip is optimized for different things than my trusty Canon with its little microlenses, but I still would have expected the imager design / lens combination on the rover to have delivered a flatter field than what we're seeing. If nothing else, the amount of falloff shown is enough that the pixels for objects around the edge would seem to lose at least a bit of accuracy. The design documentation for that camera would be an interesting read, I'm sure.

FYI, for anyone who might be wondering about what we're talking about, I took a moment to flatten the luminance (strictly by eye, not using anything more than just subjective judgment) in this image, which is animated to show the difference.

: Removed Vignetting; RoverImageVignettingCorrected.gif (143.82 KiB) Viewed 8100 times

-Noel

by **Chris Peterson** » Mon Sep 12, 2011 6:38 pm

rstevenson wrote:If the rover's camera uses center-weighted auto-exposure, then it's not surprising the darkening is more noticable in this image, as there's something very light and bright right in the center.

The camera doesn't use any sort of autoexposure. The exposure time is commanded from the ground as part of the target selection.

While setting the exposure for a large bright object will obviously darken remaining parts of the image, it isn't obvious to me that this will enhance the visibility of the illumination falloff. I can believe, however, that having a bright white object at the center can create an optical illusion which makes the image appear vignetted- and all the more so if some actual vignetting or illumination falloff is present.

by **rstevenson** » Mon Sep 12, 2011 6:13 pm

If the rover's camera uses center-weighted auto-exposure, then it's not surprising the darkening is more noticable in this image, as there's something very light and bright right in the center.

Rob

by **Chris Peterson** » Mon Sep 12, 2011 5:16 pm

NoelC wrote:Wow, this being a research vehicle I might have expected the need for image calibration to have been minimized to levels lower than what we're seeing here, but maybe that's just something where the processing would have required more power and they assumed it would/should be done here on Earth.

AFAIK, there are no spaceborne cameras, or cameras on other planets, which perform any sort of internal calibration. There is no reason to devote the processing power, electrical power, time, and other resources to that job when it can be done better at the receiving end. Calibration images change with time, as well, so you wouldn't want anything preloaded in the instrument.

If you look back over images published by APOD, there is a range of calibration, from noisy raw images to perfectly clean post processing. A lot depends on why the image was released in the first place. Not all types of calibration are performed on all images... it depends on the science goal as well as any intent for the release of "pretty" pictures to the public.

(That said, different people respond to artifacts in different ways. I didn't notice the intensity falloff at all. Of course, I see it once it's pointed out, but I have to think about it. This particular artifact doesn't bother me.)

by **NoelC** » Mon Sep 12, 2011 5:05 pm

Wow, this being a research vehicle I might have expected the need for image calibration to have been minimized to levels lower than what we're seeing here, but maybe that's just something where the processing would have required more power and they assumed it would/should be done here on Earth.

If this is indeed the issue, then I think someone has fallen down on the job, as it would have made a much more real-looking photo if the darkening had been corrected.

-Noel

by **Chris Peterson** » Mon Sep 12, 2011 2:45 pm

NoelC wrote:Does the camera used to take this image have a vignetting issue, or did someone process this image artistically to bring viewers' attention to the "table"? The lighting definitely does not look like a Martian "sunny day" - it looks more like it was lit from overhead by a flood lamp, and I don't recall there being one of those on the rover...

I doubt the camera has any vignetting issues, but pretty much all optical systems show cos⁴ artifacts- a dropoff in intensity towards the edges that visually mimics vignetting. I expect that's what we see here- an image that hasn't been corrected by flat fielding.

by **NoelC** » Mon Sep 12, 2011 2:32 pm

Does the camera used to take this image have a vignetting issue, or did someone process this image artistically to bring viewers' attention to the "table"? The lighting definitely does not look like a Martian "sunny day" - it looks more like it was lit from overhead by a flood lamp, and I don't recall there being one of those on the rover...

-Noel

by **orin stepanek** » Mon Sep 12, 2011 12:29 pm

Ann wrote:
If only rocks could talk!

Ann

in some ways rocks can talk

I found this in the links
http://www.youtube.com/watch?v=UZhmePA5r24

http://www.youtube.com/watch?v=5wrdMaoy ... re=related

by **Ann** » Mon Sep 12, 2011 11:57 am

starstruck wrote:I know we've moved on now, but is there time to just say, as probably the newest member of the 'Ann fan-club', her post on yesterday's APOD was a breath of fresh air. My thanks Ann, you put it back into perspective, perfectly.

Thanks for that lovely compliment, and I'm so glad I could put something in perspective for you!!

And today's APOD is pretty neat. Rocks are people too, or at least they have their individual personalities and their fascinating histories, which can tell us a whole lot of stuff about what has been going on in the Solar system and our own history.

If only rocks could talk!

Ann

by **starstruck** » Mon Sep 12, 2011 7:34 am

I know we've moved on now, but is there time to just say, as probably the newest member of the 'Ann fan-club', her post on yesterday's APOD was a breath of fresh air. My thanks Ann, you put it back into perspective, perfectly.

by **neufer** » Mon Sep 12, 2011 5:56 am

: [url=http://photojournal.jpl.nasa.gov/catalog/PIA14747]Elevated Zinc[/url] and Bromine in Rock on Endeavour Rim

http://volcano.oregonstate.edu/education/minerals/base.html wrote:
<<Zinc-Copper volcanogenic massive sulfide (VMS) deposits have been observed as they form at mid-ocean ridges. Chimneys formed at the ridges have as much as 29 weight % zinc and 6 weight % copper in sulfide minerals (pyrrhotite, pyrite, sphalerite, and chalcopyrite). The minerals are dissolved in fluids at temperatures as high as 380 C flowing at 1-5 m/sec. The minerals precipitate as the hot solution comes in contact with cold sea water. Lead, zinc, and cooper are found in VMS deposits. The deposits form in deep ocean water by the precipitation of sulfide minerals released by submarine volcanoes.>>

http://asterisk.apod.com/viewtopic.php? ... 53#p155953

by **Beyond** » Mon Sep 12, 2011 4:40 am

No fears, owlice. It's just a chart. Not one of the 'more' interesting links we sometimes get.

by **owlice** » Mon Sep 12, 2011 4:30 am

I was almost afraid to click on the link for "strangely high."

Starship Asterisk*

APOD: Tisdale 2 Rock Formation on Mars (2011 Sep 12)

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