If there already was a discussion about, then I would gladly ask: where is it? Otherwise does someone know something about the object size in the pics, getting from Pancam and Navcam, in comparison with "seen by human eyes"? For example, probably the object sizes getting from Navcam are smaller as we would see it with our own eyes at the same position, but how much approximately? And how about Pancam?

Primarily I would like to know the "real" size of sun by the sunset seen from Spirit on sol 489 (Pancam): http://www.unmannedspaceflight.com/index.p...indpost&p=10917

Pancam is just about the resolution of 20:20 human vision. There are some images on the Athena site that show a mosaic from inside one of the clean rooms and you can see subsamples of the same imagery at full res. A briefcase, a label, a cranes etc - things we're used to seing so that they give a sense of performance.

Navcam is about 1/9th of that resolution iirc

Doug

Thanks Doug, I've found it here (below on the site): http://athena1.cornell.edu/the_mission/ins_pancam.html and also this: "...equivalent to the view that would be seen on the Martian surface by a person with 20/20 vision".

Does that mean Pancam magnify the objects 20 times and Navcam 2,2222.... times So we would have a view about 20 or 2,22 times smaller on Mars when we look at the same object?

I think the best analogy is the eye-sight test that you can do..

If Pancam were to do this test..

http://www.goacupuncture.com/Product-picture/F-006.JPG

then it would score about as well as a human with good eyesight

As for the 'view' - well - the typical f.o.v. of human eyesight at its very limits is almost 200 x 120 degrees, when Pancam is only 16.6 x 16.6 degrees. But it is only about the central third of that is really 'usefull' and even less, a tiny central area, which can be used to really 'look at' things. i.e. look at the X in the corner of a window in windows - and you cant actually read the text IN that window - you have to look at the text to do that.

I think it's safe to say that perhaps two navcam frames side by side is about as much of mars as you'd see when looking around normally ( 90 x 45 deg ) and a single pancam frame is as much of mars as you'd see properly to 'look at' and identify things.

Doug

Good comparison, I think too it could be the right scale.

But, sorry if I am a liitle "slow on the uptake" (or sorry due to my imprecise English). Hasn't this "20:20 vision" to do with magnification? Wouldn't a Pancam picture show the characters 20 times magnified (on your eye-sight test ) than an human eye at the same remote position? In other words, isn't the Pancam optics like a field glasses with magnification of ?? times on Mars?

No - 20:20 is the 'score' your eyes get. 20:20 Human vision = perfect healthy human vision. You can have 18:17 - which is a little bit off perfect, and the lower the numbers the worse the quality of the persons eyesight, it's not a factor of zoom. 20:20 human vision just means 'good' human vision - wthout any 'aids'

Doug

Actually, 18:17 would be eyesight a bit better than "normal." The 20:20 ratio is referring to distance in feet to a standard eyechart. If you have have "normal" vision you see the same resolution at 20 feet as everyone else with the same "normal" vison. If your vision is 20:40, your view at 20 feet is the same resolution as a person with 20:20 vision standing 40 feet from the chart. Lower numbers indicate better than "normal" vision. It's not terribly uncommon for people to have 20:10 resolution.

Paul

Ahh - I thought it was more complicated that that

Doug

It is a little more complicated than that.

I hate to disagree with the explanation above, but the way *I* always heard it was this:

The first factor in the ratio is, indeed, distance from an eyechart. The *second* factor is point size of type.

Someone with 20:20 vision can't resolve type smaller than 20-point from 20 feet away. Someone with 20:40 vision can't resolve type smaller than 40-point from 20 feet away. If you have 20:200 vision, you can't resolve type smaller than 200 point from 20 feet away.

There are some people with 20:15 and even 20:12 vision. This is extraordinarily good vision -- it means they can resolve 15-point or even 12-point type from 20 feet away.

As you can see, this allows the ratio to actually measure visual acuity. If it were simply a comparison between better and worse vision, as suggested above, it would have no absolute value and therefore would be a rather meaningless measure.

The "20:20" thing doesn't have anything to do with apparent size of objects, anyway. That's governed by the degree of curvature of the camera lens. I know that in regular photographic equipment, objects appear in fairly normal perspective (i.e., as large and small, by distance, as they would to a human eye) when you use a 50-mm lens. A wide-angle or "fisheye" lens, of 35-mm or less, makes objects appear farther away than they are (smaller at a greater rate with distance than we see with the eye). A narrow-angle, 75-mm up to 500-mm or more, makes distant objects appear much closer than they are (smaller with distance at a lesser rate than seen by the eye).

-the other Doug

Wikipedia to the rescue!
Though it's still confusing to me, but maybe because I am reading this forum from 20 feet away.

There are also a couple of advantages that the Pancam has over our own vision.

First, the Pancam doesn't have a blind spot. Where the optic nerve and blood vessels enter the retina, we don't have any vision receptors. Although we aren't normally aware of it, when we look straight ahead, there are actually areas within our field of vision that we can't see! To see this illustrated for yourself, check out Blind Spot (anatomy).

Also, our retinas don't have uniform sensitivity to light. In the fovea, the exact center of the optical axis, the color receptors (cones) are very tightly packed, and there are very few rods. The cones perceive color, but they are less sensitive to light than are rods. Astronomers are well aware of this -- we use "averted vision" when looking at the sky or through a scope. You can see dimmer objects if you don't stare directly at them.

Thank you for your explanations - again something learned for educational background.

Due to my primary concern (Doug (the other) has it discussed): By the stiching software PTGui is both to set in "Lens Settings" -> "horizon field of view" and "focal lenght". Exactly, when I set one of the two, then there is automatically the other setting provided from the software itself.
Now for a Pancam panorama I only always apply the "horizon field of view" with 16,6 degrees and the software provide 123.386 mm "focal lenght" (for a Navcam pan 45 degrees and get 43.4558 mm).

Has someone the knowledge what that means in "plus" and/or "minus" magnification when we look at the Pancam and Navcam raw pictures from Mars - as per description "for human eyes at the same position like the camera".

Or, How about the real focal lenghts for both cameras, Pancam and Navcam by the MERs?

We sometimes called it "Averted Imagination" in our astro club. I always enjoyed telling newbies that they could see an object better if they didn't look at it.

The limitations of the human visual system are even more far-ranging than you indicate, and the quirks of performance vs. retinal eccentricity (angular distance from the fovea) are bizarre and nonlinear. Most especially, *acuity* is enormously degraded away from the fovea. Lock your vision on one location on a page of text and see how much text you can read in your peripheral vision, and you'll see that acuity is terrible away from that one spot. Of course, we move our eyes quite rapidly (~ 0.25 seconds, when needed) and are unaware of the limitation because we scan visual areas much larger than the fovea and "eventually" see much of it at high acuity.
The areas outside the fovea are more sensitive to dim light (as you say: peak is about 4 degrees off-fovea) because there are the most rods there (it is not possible to pack the fovea with maximum numbers of rods *and* cones -- only so much real estate), and also to motion. The whole point is that the periphery will alert you to foveate objects of interest.
For an example of other nonlinearities, the time to respond to stimuli varies with retinal eccentricity, the effects of retinal eccentricity are not concentric (generally, better performance is had X degrees to the ear-side of the fovea than X degrees above or below it), and the sensitivity to color on the blue-yellow axis of chromaticity falls off more gradually than does sensitivity on the green-red axis (because blue-sensitive cones increase in relative distribution away from the fovea)! Then there's the Purkinje effect, in which a pair of printed color patches might change their order in perceived brightness depending upon lumination levels. Some of these weirdnesses have their origin in the retina; others, in visual cortex.
The homogeneity of camera systems across their visual field is in the most profound contrast to the variation across the human visual field, and it remains an open research project (and a peculiarly difficult one to even devise a comprehensive experimentation program) even to finish an initial characterization of the parameters of normal human vision. There are some optical illusions that remain unexplained!
I once worked at NASA Ames trying to model and summarize some of the combined knowledge of human vision -- I know of at least one researcher at U. Michigan interested in the same thing, and equally flabbergasted by the impossibility of it. Engineers who marvel at the complexity of human-designed gizmos can rest assured that they have nothing on the human eye!

Hi Tman, I do not fully understand your first question, but on the last one you can find lot of informations; try:
http://athena.cornell.edu/the_mission/ins_pancam.html

About focal lenght, real value is 14.67mm on NavCam and 5.58mm with PanCam; these numbers are almost 9 times smaller than those mentioned by Doug because sensor size (the CCD) is smaller than classic picture film; this is exactly the same issue you encounter when reading specification of a digital camera lens, where "equivalent" focal lenght is larger than real focal lenght written on the lens!
I hope is more clear now...

Yes, thanks, it's clearer, though, are you sure about these (focal lenght) values for Navcam and Pancam? Isn't it inverted?

Have you a guess about the proportion between Pancam and human eye for object sizes on Mars? What do you think about this sunset from sol 489? Would sun be smaller if we would be there at the same position and look with one's own eyes westward this sunset - how many times?

Without getting into the optics discussion, I can give a comparison. The Sun would have appeared 70% of the diameter it would seem to have in watching the same sunset on Earth. To give myself a feel for how it might seem, I printed out the full pan 23 cm across, and held it 30 cm in front of my face -- that should have the apparent sizes about right. (The pan was 2.5 pancam frames wide with overlap, so that's +-20 deg from center to edges.)

Please ignore this post - it's in the wrong thread!

Oops, you're almost right Tman... in fact, NavCanm value is correct while PanCam focal lenght is 43mm!!! (the smaller number was referred to hazcam ). Very sorry!
Anyway, if you have a 15inch monitor and use a 1024x768 resolution, you should stay about 1m away in order to have the correct view of the sunset image; in fact, consider that scale is 0.28mrad/pixel for PanCam, so distance from monitor must be about 3500 times the pixel size!