Hi Mike,
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No, when using the ST4 cable and checking "use dec compensation" in PHD2 settings you only have to calibrate once in the beginning of the evening. At the moment i calibrate at about 90 AZ and 38 ALT, works well.
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If you don't connect to the mount in PHD2 you will be promoted to enter the dec (az) before calibration and before starting to guide, if you connect to a mount driver PHD2 will automatically know where the scope is pointing in the sky.
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if you check "Auto-restore calibration" in PHD2 settings you will not have to calibrate upon each new session either.
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However my take is, that since the scope due to say humidity or some other factor may move mor easily one night than another pherhaps it's best to calibrate before each session so that PHD2 understands how the scope behaves that night, and you will also see that if the measured guidespeed is a lot less than the previous session pherhaps the bearings are not clean ore something like that which you could adress before imaging.
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But my guess is you could probably get away with calibrating once then just imaging night after night.
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Actually i avoid objects below 40 degrees so i often begin right around there so it has not been an issue getting 2-3 hours on an object provided i do som planing in Stellarium.
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To be really effective and minimize the effects of field rotation you can do 30-60 minutes on several objects during a night and continue adding time on them several nights at the same position they where the previous nights, so after many nights you would have many objects with much time where the frames will not have been rotated that much compared to tracking a single object one night for 3 hours.
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I also had massive backlash and did Gary's procedure however backlash comp does not work with autoguiding for some reason, the stars look like the scope has been hit by a wind gust, it's even written in PHD2 documentation to not use any backlash compensation outside the software.
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So i set the backlash comp to 0 in both alt and az in ServoCAT Sky and thought it would be a disaster, but no problem at all. As long as you slew UP untill the scope moves before doing PHD2 calibration no problem, and when autoguiding it has not been a problem at all either, pherhaps the motors never change directions only speed.
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I am a bit confused, because in PHD2 my scope shows less backlash than the dedicated AP rig i had (when changing from north step to south step). With the Virtual handpad in NINA backlash is more evident and with the physical handpad my backlash in alt is massive.
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My guidescope only has a focal length of only 180mm so no problem!?
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/Gabriel
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Gabriel Wiklund