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Hi Martin,
This is an extract from the PHD1 user manual so I assume PHD2 will be the same.
The guide rate should be selected such that typical guiding commands are in the range of 10 to 300 milliseconds. The image scale of the guide system will affect this choice.
In most cases the image scale will be 2 to 5 arc-seconds per pixel and a guide rate of 50% is recommended. If the image scale is greater than 5 (such as when using a very short guide scope) a higher guide rate is probably appropriate – as much as 100%.
If the image scale is less than 2 you might want to go down to 25%. This would often be the case when using an off-axis guider through a long 'scope such as an SCT. In any of these cases, the characteristics of the mount might also influence the choice of guide rate.
A very well behaved mount should use a slower rate to get the best precision in pulse timing, but one that moves erratically might need a faster guide rate to keep the pulses reasonably short.
As for me I have always used 0.5 with no problems.
Cheers
Bill
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