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Camera Reference and Field of View Calculator

Astrometric Position Calculator   Convert RA degrees-HMS   Astropy WCS conversions response

Clarkvision Page On Astrophotography.

Messier Objects with size and surface brightness

Light Pollution & laser Maps

ioptron skytracker specs


notes on surface brightness

Telescopium  Telescope simulator with list of targets for the day.

Clear Sky Forecast Forecast for an observatory near me

angular distances between stars


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.