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Posted by: Fox Nov 27 2021, 06:40 PM

I understand that Pioneer 10 & 11's imaging photopolarimeters were different from cameras on later spacecraft. But I'm wondering what the "focal length" equivalent might have been. In other words, were the photopolarimeters "zoomed in" like a telescope, or did they behave like something closer to a 50mm "normal" lens on a modern camera? I realize this is probably comparing apples to oranges, but I was wondering how they worked in this respect.

Posted by: JRehling Nov 27 2021, 09:24 PM

Here are some interesting tech specs:

https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1972-012A-07

It may indeed be hard to compare those details to a more conventional telescope, but one way or another there was some effective limit to the resolution, which would correspond to that spec for such a telescope. By the back of my envelope, the resolution was about as good as or worse than that of a typical handheld camera of the pre-cell-phone era.

Posted by: mcaplinger Nov 27 2021, 11:11 PM

The IPP had a stated IFOV (instantaneous field of view, the angular resolution of one pixel) of 0.5 mrad, which is actually a little higher-resolution than Junocam's 0.673 mrad. In reality, I suspect there was a significant loss of resolution from the detector and electronics, blur from spin, imperfect geometric registration, and other sources.

The IFOV of any camera is its detector's pixel pitch divided by the focal length of its optics.

Posted by: JRehling Nov 28 2021, 05:27 PM

At those specs, at closest approach, the resolution per line pair would have been 132 km, although that's not taking into account that the subspacecraft point would have been considerably closer to Pioneer than the center of Jupiter was. The spec doc claims "about 200 km at best" resolution. So it would seem that the factors that Mike listed indeed reduced resolution by perhaps 2x.

The images look as good as they do because Jupiter is very large and Pioneer 10 was very close to it.