I'd like this lens, but I forgot to first check if it'll work with my D90. And I of course can't find it online. Do you know if your lens and the D90 are compatible?
WayneT,
I'm very sorry hear it.
I'd like to lock this sale down. I've PMd you with particulars.
I'm interested, is this still available? Do you take Paypal? Does price include shipping? And finally, why are you letting it go?
bbrown5154,
I'm interested, is this still available? Do you take Paypal? Does price include shipping? And finally, why are you letting it go?
Correct, but a rectangle sensor/film will image a rectangle of that circular lens image. The lens of a typical camera also does not provide a rectangular image; you only get that part of the image that is projected onto the sensor element/film.
Some astronomical sensors are square (same number of pixels on X and Y axes), and so better approximate the coverage of the full round image a lens produces.
On a side note, an astronomical camera, called a Schmidt Camera (https://en.wikipedia.org/wiki/Schmidt_camera), puts the unexposed negative on a curved surface at the telescope's prime focus point/surface. Because of the fast focal ratios used, the focal plane is significantly curved, hence the negative being placed on a curved surface.
This telescope setup allows for fast focal ratios (translated: short exposure times), wide view, and tight focus edge-to-edge (a must for pinpoint, high-contrast subjects like stars) for stellar pictures (pun intended).
Its primary use is for sky surveys where a significant portion of the sky is being looked at or studied.