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Astronomy Calculations:
Max Exposure time on tripod


With this tool you can calculate how many pixels a star moves on your sensor along RA axis during one exposure when having the camera on a tripod. For a wide angle lens it will be very different movement along the DEC axis, it calculate movement at center, top and bottom of sensor along DEC axis.

This is new to me to create pages that do calculation. I think you must have a HTML5 compatible web browser to use it.

It start to calculate as soon you change or write new figures in the dark red boxes. Do not exceed the maximum number of characters, delete characters if necessary.

Galaxy M33
pixel pitch in my
(1 to 9.99 my)

focal length in mm
(1 to 1000 mm, distorted lenses as fisheye will not be correct)

= Calculated results arc sec / pixel (pixel scale)


number of pixels along DEC axis
(1 to 9999 pixels, it depends if the camera is oriented in portrait or landscape mode relative DEC axis)

center of image point at DEC?
(-90.0 ... 0 ... +90.0 degrees)

= Calculated results degrees (sensor upper point at DEC)


= Calculated results degrees (sensor bottom point at DEC)


exposure time seconds)
(0.01 to 999.99 seconds)

Below you find how much a star will move on the senor during one exposure at different DECs.

= Calculated results arc sec move per exposure along RA axis.


= Calculated results number of pixels move per exposure upper part of sensor against north/south pole.


= Calculated results number of pixels move per exposure center part of sensor.


= Calculated results number of pixels move per exposure bottom part of sensor.


How much can we tolerate that a star move and get an elongated ugly look?

It's a bit personal, but with a sharp lens, in center 2 or 3 pixels, at the edges where the lens is softer maybe a bit more.

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