[X] My Assistant

[elakdawalla]

Biggest Doug'n'Jim show ever...
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Enjoy!

Emily

[mcaplinger]

I have to take exception to one thing that Jim said, about the Pancam field of view. It isn't necessarily as simple as taking the IFOV and multiplying it by the number of pixels, because most optical systems with fields of view more than a few degrees have optical distortions that cause the IFOV to vary slightly from the center to the edge of the field. I'm not sure if the Pancams have appreciable distortion, but the Navcams certainly do.

[djellison]

I have to take exception to one thing that Jim said, about the Pancam field of view. It isn't necessarily as simple as taking the IFOV and multiplying it by the number of pixels, because most optical systems with fields of view more than a few degrees have optical distortions that cause the IFOV to vary slightly from the center to the edge of the field. I'm not sure if the Pancams have appreciable distortion, but the Navcams certainly do.

From JB

In case anyone wants to know them, the similar IFOV numbers for the Navcam is 0.82 mrad/pixel, and for the Hazcam is 2.1 mrad/pixel.
This is ultimately the origin of statements like "Pancam has 3 times the resolution of the Navcams", etc. For reference, the MI gives 0.42 mrad/pixel, MPF IMP had 0.99 mrad/pixel and the Sojourner rover had 3.1 mrad/pixel, and the Viking Lander cameras had two modes that gave 0.70 and 2.1 mrad/pixel. These numbers are referenced and derived for the MER engineering cameras in a paper Justin Maki et al. wrote in JGR, vol 108, No. E12, pages 12-1 to 12-24, 2003.

Determining the total size of the field of view for these other cameras is not as simple as it is for Pancam, however. That's because most wider-field camera systems have appreciable geometric distortion. So you can't just take Navcam's 0.82 mrad and multiply by 1024 and convert to degrees. That will get you close, but not spot on, and the calculation is even worse for the Hazcams, which have an enormous amount of distortion. The details of those cameras' fields of view can be found in Justin's paper--which I hope is posted online somewhere for folks to access, but I am not sure. The reason that the simple "multiply 0.273 by 1024" equation works for Pancam is simply because there is *no* geometric distortion in the optical system. We tried hard to measure it so we could characterize and correct for it, if needed, but as we wrote in our 2003 JGR paper we couldn't detect *any* distortion down to a residual of 0.01% or so across the field--even in the corners. The Cooke triplet lenses, designed by optics guru Greg Smith (see Chapter 31 of Greg's book at http://www.zemax.com/kb/articles/103/1/The...r-Camera-Lenses
, http://www.mwoa.org/Ch31.pdf , and
http://bookstore.spie.org/index.cfm?fuseac...roductid=660181
for details), are just absolutely spectacular--as you can tell.

Doug

[centsworth_II]

"The reason that the simple "multiply 0.273 by 1024" equation works for Pancam is simply because there is *no* geometric distortion in the optical system." -- Jim Bell, quoted by DE

I'm impressed. As an innocent bystander to the various technical threads on imaging it has all seemed so complicated to me. Can it be? Finally... a simple truth?

[mcaplinger]

"The reason that the simple "multiply 0.273 by 1024" equation works for Pancam is simply because there is *no* geometric distortion in the optical system." -- Jim Bell, quoted by DE

Well, Jim certainly knows more about Pancam than I do, but it's a little surprising to me. Maybe it's because the lenses are so optically slow. The radial distortion parameters in the CAHVOR model for Pancam are certainly not zero, but that may be an artifact of the way the CAHVOR pinhole model works.