Telescopium Telescope simulator with list of targets for the day.
I wanted to figure out how many pixels the ISS or a planet would cover at full zoom. I found some good formulae on this site but I had trouble relating to it. I pinned up a scale size of the ISS at the end of our hallway to try out reality(that’s 1/3 cm at 13 m by the way – almost invisible). Then I put up an 8 1/2 X 11 sheet in the same spot and measured how much of i i could get in at full zoom. Turns out that 25cm fills the 4608 px at 13.5 meters. That calculator told me that’s 3814″(arcseconds) – roughly 1 degree. So on 4608 px that’s .83 arcsec/pixel or 1.2 px/arcsecond. That translates into 60 px for a close ISS pass and 45 px for jupiter at 47″.
Update: While doing my Saturn moon shots, I measured 650 pixels between two stars in Sagittarius that Stellarium says are 17.2′(arc-minutes) apart. That’s 1.6″(arc-seconds) per pixel.
In a second mathstravaganza I determined that the entrance pupil of the P900 is 1.5mm at wide angle and 55mm at full zoom. For comparison the T3i has a pupil of 5mm at wide angle and 25mm at a zoom where the P900 is about 8mm. So the T3i with kit lens has about 3X the pupil diameter admitting 9X the light. The t3i has a larger sensor with about the same number of pixels but i don’t think that matters for this purpose – it’s admitting much more light per pixel. **That’s assuming that any of this matters** I’m not sure it does when the exit pupil is larger than the sensor size.