High-frequency star motion

[Tom van Peer]

I have a question about the High-frequency Star Motion number in the Guiding Assistant. Since PHD2 cannot correct for this kind of motion, should you consider this number to be the (lower) limit of what guiding could achieve? So if for instance the number is 0.55" arc-sec Total RMS, my guiding can never be better than this number?

[Brian Valente]

I would treat high frequency RMS as more of a guideline - this is an approximate measurement of your seeing conditions *at that time and and that sky position*.  Also remember there are other factors such as mount error, exposure time, and others that also affect that value.

Your guiding RMS can certainly be lower, but don't be surprised if it hovers around that number. 

If you want more specific feedback, please upload your guidelogs 

On Thu, Feb 26, 2026 at 11:12 AM Tom van Peer <tvan...@gmail.com> wrote:

I have a question about the High-frequency Star Motion number in the Guiding Assistant. Since PHD2 cannot correct for this kind of motion, should you consider this number to be the (lower) limit of what guiding could achieve? So if for instance the number is 0.55" arc-sec Total RMS, my guiding can never be better than this number?

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Brian Valente

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