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. Cos
4 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 cos
4 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.
[quote="NoelC"]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.[/quote]
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. Cos[sup]4[/sup] 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 cos[sup]4[/sup] intensity falloff, and is not primarily intended to produce images of high scientific value.
[quote]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.[/quote]
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.
[quote]The design documentation for that camera would be an interesting read, I'm sure.[/quote]
Some basic information can be found [url=http://starbrite.jpl.nasa.gov/pds/viewInstrumentProfile.jsp?INSTRUMENT_ID=NAVCAM&INSTRUMENT_HOST_ID=MER1]here[/url].