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--- field_rotation [2024/06/23 14:48] – tailspin
+++ field_rotation [2025/02/23 16:55] (current) – tailspin
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 ====== Field Rotation ======
+{{:field_rotation1.jpeg?nolink&200 |}}{{ :fiked_rotation_2.jpeg?nolink&200|}}
 Field rotation smears stars in long-exposure photos, thanks to the Earth's rotation. Alt-az mounts like the Seestar’s don’t compensate for this rotation so stars at the edges of your image may appear as streaks instead of points.
-Note that field rotation is most pronounced when an object is near your meridian((An imaginary line you are on that extends from the North Pole to the South Pole)), as the object's altitude changes rapidly, leading to longer streaks. And it’s gets worse the closer you are to the equator.
+Note that field rotation is most pronounced when an object is near your meridian((An imaginary line you are on that extends from the North Pole to the South Pole)), as the object's altitude changes rapidly, leading to longer streaks. And it’s gets worse the closer you live to the equator. ((There's an [[https://kelly.flanagan.io/astronomy/astrophotography/field-rotation-and-alt-azimuth-mounted-telescopes/|excellent post]] by Kelly Flanagan the spells out the details with some excellent illustrations.))
-To minimize field rotation you can use a couple of strategies. Short exposure times helps, but the best solution is to limit your data collection ((Astrophotography uses a telescope as a funnel to direct light into a camera sensor that detects photons, converts their intensity into a number, which is stored as data for later processing)) to times when your target isn’t close to the meridian.
+To minimize field rotation you can use a couple of strategies. Short exposure times helps, but the best solution is to limit your data collection ((Astrophotography uses a telescope as a funnel to direct light into a camera sensor that detects photons, and converts their intensity into a number, which is stored as data for later processing)) to times when your target isn’t close to the meridian.
-Visibility plots can help you predict how an object's path changes throughout the night, offering a slick way to estimate field rotation. By drawing imaginary tangent lines on the visibility curve, you see how much field rotation will occur. The tangent line for a  target at 2000 (8PM) and 2400 (midnight) basically overlap, so there will be very little problem.
+Visibility plots can help you predict how an object's path changes throughout the night, offering a slick way to estimate field rotation. By drawing imaginary tangent lines on the visibility curve, you see how much field rotation will occur. The tangent line for a target at 2000 (8PM) and 0000 (midnight) basically overlap, so there will be very little problem.
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 {{ :img_4614.png.jpeg?nolink&400 |}}This tangent line technique also makes it clear why capturing images during a meridian crossing will create the greatest field rotation.
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 So plan your sessions for when the target isn't near the meridian and is closer to the horizon where field rotation is less severe. But keep in mind that the atmosphere is very distorted near the horizon, so don’t go too low.
-{{ :screenshot_2024-05-31_at_10.03.25 am.png?nolink&400|}}As a rule of thumb try to capture targets that are close to east (90º) and west (270º), not north (0º) or south (180º), above 30º from the horizon and below 70º.  Obviously, that’s not a firm rule. In other words, YMMV.
+{{ :screenshot_2024-05-31_at_10.03.25 am.png?nolink&400|}}As a rule of thumb try to capture targets that are close to east (90º) and west (270º), not north (0º) or south (180º), above 30º from the horizon and below 80º.  Obviously, that’s not a firm rule. In other words, YMMV.
+{{:480232120_9395784527127098_7672157940864184496_n.jpg?nolink&350 |}}An excellent web tool that lets you calculate the safe exposure times //for your latitude// is at [[https://apximhd.github.io/field-rotation/field_rotation.html]].
 By the way, many post-processing software packages can help correct field rotation, but it's not always a perfect solution. Just sayin’.
-If you get tired of the field rotation issue you can buy an equatorial mount, telescope, camera, guide scope and camera, ASIair, filter holder, and filters. The cost will be 4x - 6x what you paid for the Seestar.
+A bit off topic, but if you get tired of the field rotation issue you can buy an equatorial mount, telescope, camera, guide scope and camera, ASIair, filter holder, and filters. The cost will be 4x - 6x what you paid for the Seestar.
-If that’s out of the question, you can buy a good Dobsonian for about the price of the Seestar. But all it will do is sit there just taking up a lot of space unless you learn how to find things in the night sky. And even then it won’t let you see really dim objects like the Seestar’s sensitive camera will.
+If that’s out of the question, you can buy a good Dobsonian for about the price of the Seestar. But all it will do is sit there just taking up a lot of space unless you learn how to find things in the night sky. And even then it won’t let you see really dim objects like the Seestar’s sensitive camera captures.
 Like cameras, the best telescope to own is the one you use a lot. Seestar gets my vote.

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