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Bad seeing?


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Normally when imaging I have the guide cam set to exposures of 1 second but tonight when doing that it's all over the place. Now what I normally do is assume the problem is my polar alignment and I drop the exposure to 0.5secs but tonight this made it worse so..... I upped it to 5 seconds and it seems a lot better. Weird huh?

Do you experienced imagers reckon this is down to bad seeing?

Here is a 1sec guide and 5 secs guide image to compare.



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Lengthening the guide exposure makes a lot of sense when the seeing is poor. The rapid scintillations are averaged out making the centroid a more reliable indicator of the true star position than when using a 1 second exposure. I never use 1 second exposures these days, 3-5 seconds is plenty short enough for most reasonable mounts

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I agree with Martin, if the seeing is bad i tend to have to go from 1 second to 2 or 3 seconds.

I like to stick with 1 second, but sometimes it is not possible.

If i get this situation, I check the lense and clip filter to ensure not misted over or frosted, and if they are clear, then more than 1 second on PHD via the guide scope is a definite indication to me that it is misty /foggy and so bad seeing compared to normal.

Sometimes it looks clear on a zero moon night, but you can't see the mist or thin cloud layers. PHD will see it via the short exposures as the average is much less. Having to up the rate means it needs more data and all things being equal means the starlight must be blocked by something.

Edited by Catanonia
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